Everything you need to know about bichirs.

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Hendre

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Everything you need to know about Bichirs.

Foreword
Polypterus is a genus of prehistoric fish found in Central and Northern Africa known for being one of the oldest groups of fish, having retained a similar structure for up to 100 million years. Since their scientific discovery in 1802 polypterids have been subject to intense research into their prehistoric origins, almost as a window into the past. Biologists have found that polypterus, common name “bichirs”, have many structures and features not seen in any other fishes alive today.

This group is also a popular choice for aquariums with their prehistoric features, often being likened to dinosaurs, and for good reason. They make for a great addition to many aquaria and are relatively easy to keep.

This article aims to compile scientific knowledge and many collective years of bichir keeping experience into one place, to highlight the scientific importance, biological features, and quality husbandry practices for this amazing group of fish. I trust that all who read this piece may learn something new and that prospective or beginner bichir keepers will find the care section useful in their aquatic endeavours.

Enjoy,
Hendre


Contents:

Section A: Polypterus biology
  • History and fossil record
    • Polypterus in the last 200 years
    • Prehistoric history and fossils
  • Taxonomy and recognised species
    • Position in taxonomy
    • Taxonomic classification
    • Currently recognised species
  • Anatomy
    • Gular plates
    • Spiracles
    • Lungs
    • Stomach muscles
    • Fins and dorsal spines
    • Armoured scales
    • External gills
    • Lateral line
    • Brain and sense of smell
    • Sexual dimorphism
    • View of the internal organs via dissection
  • Behaviour
    • Defensive behaviour
    • Feeding behaviours
    • Spawning behaviour
    • Other interesting behaviour
Section B: Bichirs in the home aquarium
  • Bichirs as pets
  • Setting up your tank
    • Tank size
    • Filters
    • Heaters
    • Substrate
    • Lighting
    • Décor
    • Tankmates
    • Escape proofing
  • Water chemistry
  • Buying your new fish
  • Prophylactic treatment
    • Salt bath
    • Chemical treatment
  • Importance of quarantine
  • Nutrition
    • Pelletized foods
    • Frozen foods
    • Live foods
  • My fish isn't eating! Help!
  • Common health issues
    • Bloat
    • Internal worms
    • Bichir worms
    • Anchor worms
    • Fin damage
  • Breeding
  • Conclusion
References
 

Hendre

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Section A: Polypterus biology

History and the fossil record

Polypterus in the last 200 years
One of the many lasting scientific effects of Napoleon Bonaparte’s expedition to Egypt in 1798 was the opening of Egypt to the scientific community of the West. One of the 167 scholars and artists chosen to accompany this great excursion was French naturalist Geoffroy Saint-Hilaire, the first scientist to interact with Polypterus! Along the banks of the Nile river, he observed a large green fish with hard scales and many fins on its back, naming it Polypterus (Many fins). He later gave out the scientific name Polypterus bichir at a scientific conference. The term “bichir” (pronounced bee-sheer) is derived from the name locals gave to the fish, thought to relate to the description of a whip. Saint Hilaire later stated this about his discovery in 1809: “If I had discovered only this species in Egypt, it would compensate me for the pains usually involved in a long journey”. He was made a professor of zoology in Paris in 1809 and worked extensively in anatomical study and worked closely with influential naturalist Baron Georges Cuvier for many years.

Classification of bichirs remained a hot topic for many years with great uncertainty about their placement in nature due to their combination of unique and unusual features. As a result, Thomas Henry Huxley created the order Crossopterygii in 181 to house extinct and extant animals, such as Polypterids, with lungs and fleshy pectoral fins. This was done purely from the study of preserved specimens; more work was required. Francis Balfour and students from Cambridge established in the 1870s that embryology was a key foundation of studying evolution, spurring a renewed interest in Polypterus and lungfish, which group gave rise to modern tetrapods? (such as humans)

Nothing was known about the life cycle of Polypterus at the time due to the remote, inhospitable nature of their habitats and recurring wars in the area. This is where the next major player in this history enters the stage; his name was John Samuel Budgett (1872-1904). Budgett was a zoologist from Britain who ultimately discovered much of what would be known about Polypterus for decades, he did so over four expeditions in 1898, 1900 and 1902 and 1903. His main goal was to study the breeding habits and embryo development of polypterus.

The first expedition, to The Gambia, produced fish with eggs but Budgett was unsuccessful in finding developing ova or achieving artificial insemination, this trip was cut short due to severe illness. He returned here in 1900, again failing to find fertilized ova. Expedition 3 in 1902 took Budgett around Uganda where he caught many bichirs laying or having laid their eggs but was unable to find any fry. Despite his history of poor health and the safety risks, Budgett took his final expedition to Sierra Leone towards the end of 1903. After two weeks of travel and another month of failed attempts he successfully captured some P. senegalus and artificially impregnated about 1000 eggs, success at last! Despite losing this first batch to fungus after a week he continued his research and within a month had preserved specimens of each developmental stage and a few larvae.

Back in Cambridge Budgett worked fervently to publish his work, finishing his drawings the day he was struck by a bout of blackwater fever, followed by a malarial attack a few days later. He died from these diseases on 19 January 1904, the day he was expected to report his work to the Zoological society. His friend John Graham Kerr was left with the task of publishing Budgett’s reports, which were done in memorial and published along with his original sketches.

Budgett’s work was a key factor in the decision to remove Polypterus from the Crossopterygian order and instead place the genus as a paleoniscid; the most primitive ray-finned fishes. This removed Polypterids as a candidate for study of the development of tetrapods. This has now been confirmed through genetic study. His publications remain as some of the most important studies ever done on Polypterus, a 1997 study confirmed Budgett’s work on the embryonic development of bichirs as well. Budgett’s frog was named in his honour.

Study of Polypterids is continuing today with a huge interest in their morphological features that are unique amongst animals alive today. Apart from the scientific interest, they have become popular prehistoric pets for aquaria where they have found a different appreciation.


Prehistoric history and fossils
The story of polypterids’ fossil record spans back a whopping 100 million years, and that’s just with the fossils we have found. Scales, dorsal spines and various other bones have been unearthed in South America (Bolivia and Brazil) while scales and spines have been found in Niger and Sudan. Most importantly two articulated fossils have been discovered in Morocco. The fossil distribution covers a larger area than the modern distribution of polypterids, there are no modern species alive in South America. South America and Africa detached from one another since roughly 180-200 MYA (Million years ago), implying that polypterids inhabited the earth before the division of the continents long ago.

Fossils of polypterus have been distinguished by their unique 3-layer ganoid scales containing isopedine in the middle. Those in South America have been dated to 53-65 MYA while the African record stretched back to 96 MYA. It is suspected that Polypterids developed in the area that was then divided into modern Northern Africa, where they persisted, and South America where they died out. This table shows the placement of fossils arranged by their appearance over history:


1588688502912.png


Throughout the fossil history, there have been two species that have stood out for different reasons: the well-preserved Polypterus farou and the hulking Bawitius. Bawitius is an extinct genus of polypterid from modern-day Egypt with only a single species; Bawitius bartheli. Known only from a few bones and ganoid scales, but from a comparison of the sizes, it was believed to be tremendous, measuring in at around 3 meters in length! Imagine this:

1588688616556.png


Credits to prehistoric wildlife, you can find their website here

Polypterus farou is a more recent member of the Polypterid lineage and has the most well-preserved fossil of any polypterid with a fully articulated, three-dimensional skeleton from Chad. The fossilized fish lived in the late Miocene era (5.3 MYA) and is the only verifiable fossil on record for Polypterus, closely resembling modern species P. bichir and P. endlicheri with a more primitive body type and opening of the lateral line on the scales in a similar fashion to P. bichir, P endlicheri and P. ansorgii.

1588688698553.png


There is still much to learn about the fossil record of polypterus, they are a valuable group in terms of evolutionary history.

Taxonomy and recognised species

Position in taxonomy

Polypterids are classified under the subclass Actinopterygii, also known as ray-finned fish, and are one of the oldest lineages of fish alive today. The bichir group has a distinct lineage from the rest of the ray-finned fish, as can be seen in the diagram below. This was determined from genetic and morphological data
1588688773462.png
Photo from BMC evolutionary biology

This is significant as they are therefore the most prehistoric lineage of ray-finned fish alive today, making them vital for studying evolution and getting a better understanding of the development of primitive features. Nowadays two extant genera survive: Polypterus and Erpetoichthys. The last of a group of fish predating many groups of fish living today.


Taxonomic classification
To date, most classification of bichirs are done through morphology (the study of form and structure) and comparison of proportions or counts of certain body parts (eg scale counts, numbers of finlets)

1588688886629.png

This diagram shows many of the measurements used to classify and compare Polypterus species in scientific studies. This is a standard in the field of Ichthyology.

Currently recognised species
The species distribution of polypterus has undergone revision many times, several subspecies or regional varieties are known to the hobby but are now considered invalid to the science. The latest and most thorough revision, “Revision of the extant Polypteridae (Actinopterygii: Cladistia)” has been done by European scientists Timo Moritz and Ralf Britz, published in July 2019. This was a morphological study done to classify the order on a species level. The original study can be found here

The study established the presence of 13 valid species of polypterus as well as the single species of ropefish, namely:
  • P. ansorgii
  • P. bichir
  • P. congicus
  • P. delhezi
  • P. endlicheri
  • P. mokelembembe
  • P. ornatipinnis
  • P. palmas
  • P. polli
  • P. retropinnis
  • P. senegalus
  • P. teugelsi
  • P. weeksii
  • E calabaricus
Several changes were made, due to the depth and complexity of the changes I will summarise them here:
  • P. lapradei and “katangae” are classified under P. bichir
  • P. palmas buettikoferi and P. retropinnis lowei are classified under P. palmas
  • P. senegalus meridionalis is synonymized with P. senegalus; it is a larger, regional variant of the latter
Work on the genetic relationships between polypterid species is ongoing and this list is subject to change, a proper phylogenetic analysis will give a more concrete framework to base the classification from when compared to pure morphological analysis. The last genetic review of the lineage was in 2010 and is currently under revision.

Anatomy
Polypterus have long bemused those who study the natural world; there is almost nothing on earth like them! In the early days of scientific exploration into the genus they left researchers perplexed, and for good reason. To name a few of the oddities about them is easy:
  • They have bony, ganoid scales made of bone salts
  • Polypterus larvae resemble tadpoles in shape, also having the same fluffy external gills
  • Fleshy, lobe-like fins. Were they ray-finned or lobe-finned?
  • Two highly vascularised lungs allowing them to breathe air
  • The only vertebrate to have lungs without a trachea
  • They had a row of finned spines instead of a true dorsal fin
  • They could live outside of water for extended periods
  • Presence of only 4 gill arches, 5 is the standard for most fish
  • Specialised male anal fin for reproduction
The discovery of bichirs created a flurry of excitement in the scientific community and now after over 200 years, we have a solid knowledge base; scientifically and for the general hobbyist. Now to look at some of the cool anatomical and morphological features that polypterus possess.

Gular plates
A rare feature in modern fish, the gular plates are a pair of bony plates that extends forward from under the gills and reach under the bottom jaws. The function of these plates is to help crush and compress foods, helping them. Bowfin (Amia calva) also have a single, thick gular plate. These plates are only seen in some bony fish species nowadays.

Spiracles
Rather than gulping down air to breathe, bichirs prefer using two small vents in the top of their skull known as “spiracles” to breathe, especially if they feel secure in their surroundings. Through a method called “recoil aspiration” bichirs can almost fill their lungs in a single aspiration cycle, it is thought many early tetrapods used a similar breathing mechanism.

As mentioned in the above paragraph, polypterus prefer to breathe through their spiracles when they are feeling secure. They do this by contracting their muscles, forcing air out of the lungs before relaxing, creating a negative pressure gradient. Air is drawn through the spiracular valves and is sucked into the lungs and buccopharyngeal chamber (essentially their jaw cavity) where dedicated muscles then close the valves and compress the remaining air to fill the lungs to full capacity. Any excess is released afterwards, usually seen as a bubble leaving the fishes heads. This is a stealthy and effortless method of obtaining extra oxygen.


Lungs
One of the most unusual features of polypteridae is their pair of fully functional lungs. They are quite large in comparison to their body. The right lung is almost double the length of its counterpart, as can be seen in the image below:
1588689008685.png


These lungs are fairly simple in structure compared to mammalian lungs as they do not have alveoli and instead have folded areas to increase surface area while also being highly vascularized, the high concentration of blood vessels allows for better diffusion of oxygen into the circulatory system. This system appears to be sufficient to allow them to live out of water indefinitely.

It is believed that the lungs were developed to help these fish survive in the sometimes-hypoxic environments in which they live; some stagnant bodies of water end up having little to no dissolved oxygen available. Another theory is that fish started gulping air to increase their buoyancy and developed air-breathing mechanisms as a result. There is evidence of both theories as air-breathing has developed independently 38-67 times over history. More information can be found
here

Stomach muscles
Another behaviour seen in bichirs is something named "stomach packing" by members of the community. Food can sometimes be hard to come by, so, to make the most of a sudden abundant food source such as a large fish that died, bichirs can use their abdominal muscles to compact the food in their stomachs to make space for more. This can result in abnormally fat-looking fish, but it helps them prepare for hardship in the wild. Take care not to overfeed the fish in your tank as this behaviour could contribute to obesity

Fins and Dorsal spines
Polypterus have unusual fins. Firstly, they have no true dorsal fin. Instead, they have a series of dorsal "finlets"; spines with small fins attached. These finlets can be controlled by the fish and are often erected in displays of dominance, aggression, or warnings to predators. No other fish possesses such a dorsal system. Secondly, despite being ray-finned, they have fleshy pectoral fin bases that are reminiscent of lobe-finned fish, a feature that confused many zoologists for years. It is now known that this is simply a curious prehistoric trait, they are firmly established as primitive ray-finned fish.

1588689066617.png

Armoured scales
Part of their prehistoric appeal, a bichir looks heavily armoured with a criss-cross of bony, tough scales. Known as ganoid scales, these tough plates protect ancient fish such as bichirs, gar and bowfin from harm. The name “ganoid” is derived from the inorganic salt ganoine which forms the outer layer of these scale plates. In Bichirs and bowfin (Amiidae) the scales follow this layering:
  • Ganoine forms the hard, outer layer
  • Dentine - A hard & bony tissue also found in our teeth
  • Isopedin – The underlying layer of the scale composed of connective tissue embedded with bone
Fish such as gar also have ganoid scales, just without the inner layer of dentine. This distinguishes their scales from the bichirs and bowfin.

Polypterus scales are rhomboid in shape and joined with "peg and socket" joints for maximum protection and strength in exchange for some flexibility. If you ever feel a bichir's scales it can be noted how hard the scales are compared to most other aquarium fish. These scales are another weapon to protect polypterus in the wild, imagine a fish with chainmail.


External gills
Something that distinguishes bichirs from any other fish is their unique development of large, external gills during the larval stage in a similar fashion to amphibians like Axolotls. These gills grow from the main set of gills to help supplement the young fish with oxygen while their lungs develop and mature. Makes sense due to their environments often being low in oxygen.

Bichirs hold onto these gills for varying durations, usually shedding them by the time they are 3-5 inches in length, but it can vary. Some fish retain “stubs” of the gill base for significantly longer, but this is nothing to worry about as it will detach eventually.

This feature confused earlier biologists, was it an amphibian or a fish, or a mixture of the two? Bichirs have been established as fish by now but this feature remains incredibly unique to them as non-amphibians.


Lateral line
The lateral line is a system of sensory organs found in most aquatic vertebrates, especially fish. Every species of fish has some form of lateral line or similar sensory organ. This lateral line network is found on the head (Head canal system) of some fish and in a line extending from the gill plates to the caudal fin base (trunk canal system) and is used to detect movement of other creatures or to avoid colliding with objects, all through the lateral lines ability to detect changes in water pressure and direction nearby the fish. Any changes are translated through the nervous system to the brain, allowing for split-second adjustments to avoid predators or catching prey. This is how blind or nocturnal fish can navigate and find prey without being able to see. Interestingly the lateral line can also detect low-frequency sounds of 100 Hz or less. Most fish have a modified lateral row of scales to accommodate the specialised structure of the lateral line organs.

Polypterus have a well-developed head canal system alongside a trunk canal system. This makes sense as they must be able to find food effectively at night or in murky conditions. This system is shown in an illustration posted by Anne ( beblondie beblondie ) previously:


1588689149102.png


Brain and a sense of smell
Apart from the lateral line, how do bichirs find food? The lateral line system is limited in range to the immediate area around the fish. The eyesight of polypterus tends to be poor in most cases, likely due to their often-murky habitats. To get past this fact bichirs have developed a potent sense of smell to locate prey or food sources and analysis of their brain regions confirms this.

1588689178824.png
Original article can be found here

In this diagram by Michael Coates (University of Chicago) the brain of Polypterus is compared to that of a sea trout. It can be noted that in comparison the polypterus has significantly larger olfactory bulbs (smell) and a reduced optic tectum, indicating a strong sense of smell, while the sea trout has a reduced olfactory bulb system and tremendous optic tectums, indicating vision-base hunting.

In aquaria, bichirs don’t always see food coming down but will often simultaneously spring to life when the smell hits the water column and home in to eat. Another interesting adaptation to their native environment


Sexual dimorphism
Sexing bichirs is a little different from most fish, where patterns, colours, body shape or size are used to easily distinguish between genders. Polypterus sexing is done almost exclusively through the differences in the anal fin; males have a thick, fleshy fin while females have a reduced, pointed fin. This diagram posted by Oddball Oddball shows the difference clearly:
1588689320809.png


This differentiation becomes apparent in juvenile fish and is about the only way to sex them at a young age. Mature females may be slightly larger than males, especially when swollen with eggs.

Another point of interest is the difference in maturation times; males will begin breeding at 2-3 years of age while most female bichirs mature after 5+ years. Female bichirs also seem to be more prominent than males. A poll on the forum gave a rough ratio of 30% males to 70% females, this was also observed by Budgett in his studies of polypterus. The exact reasoning behind this is unknown but may be to ensure that a greater amount of female fish survive to maturity.


View of the internal organs via dissection
Finnish biologist and author Maija Karala treated bichir enthusiasts with high-quality photos of a dissection she did of a female Senegal bichir. Her blog can be found here
1588689408260.png
1588689423413.png


Behaviour
As expected by now, polypterus also display many curious, sometimes unique, behaviours in the wild and in aquaria. Sometimes new keepers are worried about behaviours such as inactive floating in young bichirs for example, while it is just part of their survival strategy. This part of the article is adapted from Cohazard Cohazard along with new information. The original thread with photos can be found here

Defensive behaviour:

Floating

The worrying behaviour mentioned in the introduction, floating is a common behaviour in younger bichirs and is nothing to worry about.

In the wild young bichirs will often congregate in the still-water areas of marginal vegetation for a few reasons. Firstly, and most obviously, it provides shelter from predators as well as an abundant food source in the form of insects and their larvae. Secondly, by hiding amongst leaves and debris it allows the young fish to hide near the surface where they have easy access to atmospheric air while their lungs develop.

As a result of this young bichirs will often prefer to hide among surface plants in aquaria. Newly introduced fish may also exhibit this behaviour. This is less common with adult fish and is mostly done by upper jaw species and ropefish. It is rarer in lower jaw species. The implications of this will be discussed in the décor section further down in the article.



Bursts of speed
Fleeing from danger is a common survival tactic in most organisms, bichirs are no different and will often burst into rapid movement in response to sudden threats. In the wild, their muscular structure allows for explosive bursts of speed over short distances and allows them to escape predation but can be dangerous in aquaria.

At home bichirs can be frightened by external stimuli such as knocks to the tank or stand, shutting doors or other sudden forces which results on them turning into a scaly torpedo, crashing into anything in their path until they calm down. This could harm them in confined spaces. It is best to provide plants and décor for them to hide in to help them feel secure, as well as having a long, wide tank to give them more space to move in.


Flaring finlets
Something every bichir-keeper will witness is a behaviour known as “flaring” where a bichir will erect the dorsal spines and finlets in a formidable-looking display. This could serve several purposes for wild bichirs by making them harder to eat, look bigger, show aggression to other bichirs, and may form part of other interactions between conspecifics. The fish are often seen flaring when feeling threatened or aggressive, or just and random times. It is a versatile tool in the bichir behaviour toolbox

Feeding behaviours

“Perching”
Common in decorated tanks, polypterus will often be seen balancing on the rear part of their body, remaining perfectly still in wait for prey to move close enough to be ambushed. They will often do this off plants or structure such as wood. Not much is known about the prominence of fish in the diet of bichirs, but people have noticed this behaviour being employed to catch feeders in aquaria.

“Stomach packing”
As mentioned in the anatomy section, bichirs possess the ability to pack extra food into their stomach. Once a bichir has eaten its fill, it will adjust its body side to side, using its muscles to compact the food and open some more space. In nature, bichirs are opportunistic feeders so they will make the most of a large meal such as a fish carcass by stuffing as much as possible in a single meal.

Take care not to overfeed your bichirs to the point where they begin stomach packing, they do not exert much energy in an aquarium environment and subsequently could quickly become obese if they receive too much food.


Death roll
Steve Irwin would be proud of bichirs for they can death roll in a similar manner to crocodilians for the same reason: to tear off chunks of flesh from larger food items.

If a bichir locates a large food source (such as a large, dead fish) they will bite and grab hold before violently spinning to tear off a bite-sized chunk. This is rare in the aquarium as we usually feed smaller pieces of food to avoid choking but can be observed when feeding large chunks of food that they cannot fit in their mouths, there are many examples of this on YouTube.


Spawning behaviour

Breaching
Breaking the surface through jumping is something that bichirs will seemingly do at random but is also a part of their long display of courtship behaviour before mating.

Anal fin cupping (males)
Males are distinguished from females primarily by their larger, muscular anal fin which is utilized as an appendage for mating. They can often be seen bending the fin into a “cup” during courtship and reproduction, this cupped fin is used to catch eggs released by the female and fertilize them with milt before releasing the eggs, repeated several times over the course of a breeding session. Males will sometimes cup at random, even when no female fish are present.

1588689696674.png
Photo by Josh's Fish Josh's Fish

Nudging/following
The last part of courtship behaviour entails a male bichir following a female around and nudging her sides with his head while cupping his anal fin to coax her into mating. This will often go on till the male loses interest or the couple love to a suitable spawning area and mate.

Other interesting behaviours

Scratching

Occasionally bichirs will be observed scratching themselves with their pectoral fins, going as far as to bend their bodies to reach further down their sides. It is a unique behaviour developed to remove external parasites without having to expend large amounts of energy to "flash", throwing themselves at a structure to dislodge parasites. This is commonly observed in wild-caught fish in quarantine although parasite-free fish will also do this at times, perhaps to clear particulate matter from the surroundings of their sensitive lateral lines or for other reasons yet unknown.

Yawning
Bichirs, along with most other fish that possess retracted jaws, will sometimes extend their jaws into something keepers affectionately call “yawning”. They exhibit this behaviour at random times and it is often observed after eating, perhaps to readjust their jaw positions or exercising their outer jaw extension.

“Bichir piles”
When looking at sparsely decorated tanks with many bichirs, this behaviour of the fish forming piles can often be observed, especially in corners. Naturally, bichirs prefer dimly lit environments with places to hide, if no structure is available, they will clump together in an attempt to hide. Their neighbours obstruct most of their view of the surroundings, helping them feel secure.

Hierarchy/dominance displays
While not known as an aggressive genus of fish, bichirs will often form hierarchy structures in a relatively nonviolent manner. Common displays of dominance behaviour include:
  • Dorsal finlet flaring
  • Nipping at fins or body of other bichirs
  • Lying side by side, flaring and wobbling
This last behaviour was observed between two Senegal bichirs and would last anywhere from 10-20 seconds with dorsal spines erect and wobbling side to side on their pectoral fins until the dominant fish nipped at the other and they broke away from each other. This behaviour was most frequent in the months after introduction after which the fish rarely showed aggression towards one another.

Head burying
Another unique behaviour exhibited by a small number of species, namely P. delhezi, endlicheri and weeksii, is head burying where the fish can be observed digging their head into the substrate and rapidly shake their body till they are mostly buried. This may serve a dual purpose: it helps hide the bichir from predators and may provide another ambush mechanism if perching fails.

In aquaria, it is important to provide a fine substrate, such as sand, to allow the fish to easily bury themselves without injury. Other species may also rarely display this behaviour.
 
Last edited:

Hendre

Bawitius
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Section B: Bichirs in the aquarium

Bichirs as pets
Polypterus and ropefish are perhaps the most popular ancient fish in the hobby due to their prehistoric looks, ease of care and relatively calm demeanour. Combine this with the fact that they come in various sizes, are relatively common and start at a relatively low price point and it’s a no brainer that they make for an ideal introduction into the world of Ancient fish.

The following section will equip you with some of the knowledge you need to provide the proper care and husbandry to look after your polypterus. Or, if you don’t own any yet, help you prepare for the first of many you will end up owning. They are addictive, you have been warned.

This guide will take you through the following important topics:
  • Setting up your tank
  • Water chemistry
  • Buying your new fish
  • Prophylactic treatment
  • Importance of quarantine
  • Nutrition
  • Common health issues
  • Breeding
Setting up your tank

Tank size
Your glass or acrylic aquarium is the basis of keeping fish, but which type is best for bichirs? Well as it turns out, they are not too fussy! The only things to keep in mind are the footprint of the aquarium and the depth when talking about young bichirs which should have a lower water level for ease of access to air. Let’s break it down further.

The footprint of an aquarium determines the amount of floorspace real estate available, important for relatively bottom-dwelling bichirs, especially the more sedentary upper jaws. You still want space for your fish to move around comfortably, extra water volume never hurt anyone either. If making use of grow-out tanks then there is no hard-and-fast rule for size, just make sure to graduate the fish as they start outgrowing their tank. For the purposes of this guide, I will try and simplify it and place the bichirs into 3 different groups based on their adult size. This is a rough approximation; sizes are highly variable. Here is the list:

  • A) The smaller group – The fish that will max out at 12-15” - mostly upper jaw species such as P. senegalus, P. Delhezi etc
  • B) The medium group – Those fish that max out at 14-20" such as wild-caught upper jaw species, P. ornatipinnis or some P. endlicheri
  • C) The big boys – The larger lower jaw species that grow 20” or more
Now that we have divided the species into groups, we can have a closer look at what they require in terms of space as adults. Group A, the smaller group, should be housed in a tank with a minimum footprint of 36"x 18" (90x45cm), or even better 48x18" (120x45cm) for heavily active species such as the Senegal bichirs, it is best to adhere to a standard of 48 x 18". A standard 75 gallon would be perfect for this group.

When looking at the larger fishes in group B, the endli’s, ornates and wild-caught upper jaws a 75 gallon will not cut it for life. Depending on their size, an 18” wide tank may work for a few years, making a standard 125 gallon (72” x 18” x 23”) a good fit. For proper long term care a long, wide tank would be ideal – 72” x 24” is a good baseline for long term care. A Standard 180-gallon tank (72”x 24” x 24”) would be perfect.

Lastly, for the largest of bichirs placed in group C, you will need an equally large tank! A standard 180 would work for some time but many species can outgrow that width and as a result, these bichirs need monster tanks. The general standard is that a tank of 8’ x 3’ (96” x 36”) footprint is ideal for long term care of these hulking fish.

Filters
The filtration system is the backbone of an established tank; it is the machine that processes toxic ammonia and thereby keeps your fish alive. A good filter is vital for the long-term health of your aquarium. With so many models and varieties available, what works for polypterus? Let’s look at the requirements:

  • High media capacity – Polypterus are somewhat messy eaters and consume large amounts of food, large quantities of biological media for beneficial bacteria are needed to process the resulting ammonia produced by the fish.
  • Moderate turnover rate – A filter flow rate of 5-7 times your tanks volume per hour is a generally agreed-upon ideal for optimal movement of water through your filter for effective filtration. It’s also a sweet spot for not creating too much flow, polypterus live in relatively still waters in the wild.
  • Escape proof – Any parts of the filter attached to the tank must be escape-proof, I have had polypterus swim up a hang on back overflow and hop out while the filter's lid was off. This is not a lesson you want to learn the hard way. Keep it sealed, any long term bichir keeper would advise this. Cover your sump intakes or pipe outlets in your lids.
Knowing this, large hang on back filters (such as an Aquaclear 110) or canister filters work well for most keepers, they provide enough flow and hold large volumes of filtration media. For monster tanks where several hang-on-backs or canisters are not affordable or efficient, a sump is the best option to provide extra water volume and hold significantly more filter media than the other filters. Do not forget to filter or cover your intakes, bichirs like exploring.

Heaters
Warm water puts the tropical into tropical aquariums, heaters are used to achieve this. The wattage that your heater requires will vary based on your climate but 2-3 watts per gallon is a good baseline.

It will be important to position your heater upright so that your polypterus can not lie on it, or make a heater guard. This is important to prevent heater burn. Heater guards are easy to make with PVC pipe, drill large holes in a length of piping and slide that over your heater. If your tank is kitted with a sump then it’s best to place your heater in there.

Substrate
In some ways bichirs act a little like a chameleon or cuttlefish; they will adapt their colouration based on their moods or to fit their environment. Therefore, the substrate you choose will influence the colouration of your fish. Dark substrates tend to bring out deeper shades of pigment and sometimes more dark barring, lightly coloured substrates tend to wash the colours out a little. The same fish can look wildly different on different substrates!

Another thing to consider is ingestion of substrate; bichirs will often swallow bits of the substrate with their food, being messy bottom-feeding fish with a big mouth and all, so it is imperative to pick a substrate that's small in grain size. Small grains of sand will find their way through the digestive system easily while gravel may remain stuck, therefore I would always use fine sand if possible. Just make sure to wash out super fine particles that may get stirred up by the fish as these are harmful to filter impellers.

Some tried and tested substrates for bichirs include:
  • Black diamond blasting sand
  • Pool filter sand (Silica sand)
  • Garnet sands (Red, purple and brown are popular)
  • River sand
  • Tahiti moon sand
There are many other types of substrate available that are not mentioned here that are suitable to use, just refer to the above guidelines!

A bare bottom tank will work too. I used a bare bottom with the bottom painted black as a grow-out/quarantine tank previously. It’s a good way to keep the fish more comfortable while making the tank easy to clean.

Lighting
Less can be more, as is the case with bichirs. Low lighting is the ideal for these fish, old literature states an ideal range of 1-1.5 watts of fluorescent light per gallon of water, but many factors will influence the ideal lighting strength. Most standard lighting solutions will work well for bichirs, just avoid extremely bright or strong lights such as those designed for high-tech planted tanks. Lighting that replicates moonshine is also an option for watching more nocturnal species.

Décor
Apart from equipment and substrate, what else can you add to a bichir tank? Quite a lot. As mentioned elsewhere in the article, polypterus do enjoy having structure and places to hide. The addition of wood, plants and rocks is ideal for a bichir tank, just ensure that any sharp points are filed down to avoid injury if a bichir gets startled and swims into the décor.

Epiphytic plants (Anubias, java fern, moss), tall rooted plants (Echnidorus, cryptocoryne and Vallisneria) and floating plants often make good additions that can survive boisterous activity of bichirs. Floating plants such as water sprite are important for younger fish who like to perch among the roots. Many other species of plant will work, there are far too many to list in one place.

For some examples of other keepers aquaria, you can visit THIS THREAD LINKED

Tankmates
Listing all the potential tankmates for bichirs would be impossible, many fish will work. There are only a few considerations to consider:

  • Tankmates must be large enough not to be eaten (Bichirs are predators after all)
  • Overly aggressive fish must be avoided, bichirs rarely fight back with anything that won’t fit in their mouths
  • Slime sucking fish – There have been instances of fish such as plecos sucking the slime coat off of bichirs, keep an eye out for this behaviour.
If it won't eat the bichir, bother the bichir or get eaten by the bichir then the fish is fair game for a tank mate.

Escape proofing
Adventure is written in the DNA of bichirs, pretty much everyone who keeps them for extended periods knows that they will often take any chance to escape, even if their excursion can be fatal. It is in the best interest of your fish to make an aquarium version of Alcatraz to avoid any mishaps and seal off any escape routes. Some recommendations to do this are listed below:

  • Always use a well-fitting lid or close off the aquarium top with glass, egg crate or anything the fish can’t fit through. It is also advised to weigh this lid down if dealing with larger fish.
  • Seal off any places where pipes or cables leave the tank, the fish may slip out of any holes dedicated to equipment.
  • Protect your sump overflows with a strainer to bar the fish from taking a trip down to sump town.
  • Lastly, close any other gaps in the tank, eg keeping the lids on HOB filter lids (Learnt the hard way personally) and so on. You don’t want any gaps.
If a bichir does manage to jump ship, don’t panic! They have an almost unrivalled air-breathing ability so will last longer out of the water than many fish, at least a few hours. Scoop up your fish and place them in a net, sometimes the slime coat is just dried out and they will begin to move again in a few hours. If the fish has been out of water for too long then, unfortunately, there is not much that can be done, it is always worth seeing if the fish recovers though.

Water chemistry

Water chemistry is one of the founding pillars of keeping fish and is an important factor when stocking your tank. Luckily for bichirs that isn’t something you need to worry about; polypterus are quite flexible.

In their natural environments in Upper and Central Africa, bichirs occupy a wide range of slow-moving rivers, swamps and lakes. The ranges of vary quite a bit, take pH. They are found in waters with a pH between 6.4 and 9.0, although this may be at the very borders of rivers feeding into Lake Tanganyika. They don’t often venture into the lake itself, rather inhabiting the swamps leading into the lake.

For aquaria you can aim for conditions in these ranges:

  • pH: 6.0-8.0
  • Water hardness: 2dH – 20dH (36-356 ppm or 20-200mg/l
  • Temperature: 24-28°C / 75-84°F
  • Nitrates < 20 ppm
  • Ammonia and nitrites: 0
Polypterus are quite adaptable so most tap water sources will work. It is also important to do regular water changes to reduce nitrate (NO3) levels in the aquarium. While not immediately harmful, nitrates are known to contribute to weaker immune systems and the occurrence of opportunistic health issues. Long term exposure to high levels of nitrate could significantly reduce the lifespan of your fish. As with any other fish, it is imperative to keep Ammonia (NH3/NH4+) and Nitrite (NO2-) levels at 0, elevated levels of these metabolites can quickly become dangerous for fish.

Buying your new fish
When looking to buy a bichir at a shop it is a good idea to try and look for a healthy fish to take home to reduce the risk of death during the adjustment period. The most important things to look out for are:
  • Eyes are clear
  • All fins are present (Pectoral, pelvic, anal and dorsal finlets)
  • No visible fungus or parasites on the fish
  • Fish is active and not lethargic
  • No visible deformities of the nostrils or jaws
  • It should be eating in the shop, polypterus rarely avoid eating after the first day or two.
If the fish is wild-caught it may be worth placing the fish on hold for a week or two, the trapping techniques are stressful and unfortunately, some will not survive the first week or two of captivity. If they are going strong after that period, then the fish will be fine. Picking a healthy fish is important to improve the chances of successful acclimation.

Prophylactic treatment
Treating your fish for common issues is an important preventative step to prevent disease transmission between your new fish and established tankmates. It is vital to do for wild-caught fish as many, if not all, carry parasites that will be significantly more harmful in an aquarium. There are two main prophylactic treatments for bichirs that should be used:

Salt bath
This is the first step in treating new arrivals and targets external parasites. For the salt solution mix 5 teaspoons (20ml) of regular salt (NaCl) per gallon of water, or 5ml of salt per litre of water. Mix this into the transfer bucket and keep the fish in this solution for 20-30 minutes. Keep a close eye on the fish, if it becomes erratic, unresponsive or shows any other signs of acute stress then immediately move the fish into the quarantine tank and allow it to recover. This should cause most of the external parasites to drop from the fish, don’t forget to sterilize it afterwards.

It is important to use plain salt for this, products such as “Marine” salt will rapidly change the pH of the water which can contribute greatly to osmotic stress.

Chemical treatment
Once your fish is in the quarantine it is imperative to clear out any encysted or internal parasites that may remain in your bichir. Medications that target parasites, usually anti-helminthic (anti-nematode) are suited for the task, praziquantel is a key ingredient to treat a wide range of parasites. Products such as “Parasite guard” or “Parasite clear” by Jungle labs are some examples. Follow the recommended dosing regimen closely. This will clear your fish of any other parasites and protect your other bichirs outside of quarantine.

Importance of quarantine
Quarantine: a state, period, or place of isolation in which people or animals that have arrived from elsewhere or been exposed to infectious or contagious disease are placed. This process is vital for bringing new bichirs (especially wild species) into our tanks and is best done with a dedicated quarantine tank. If done properly it will save your collection from potential parasites or diseases as well as reducing the amounts of medication you may need.

The setup of a quarantine tank can be as simple as an aquarium with a filter, heater, plastic plants, and structure for the fish to hide in. It can be more complex, but everything should be simple to take apart and sterilize after the quarantine period. This same tank can be used as a hospital tank if needed.

The actual process of quarantining fish is easy: Set up the tank, acclimate the fish then observe it for a period. This lets you keep an eye out and treat any potential issues or diseases, perform prophylactic treatment, and can ensure that the fish is eating readily before addition to the main tank. A time span of two weeks should be the minimum considered, with 4-6 weeks being ideal as an observation period. If no problems are apparent, it is then safe to add the fish to your main tank.

Nutrition
Feeding bichirs is simple enough, they are adept at tracking food down and eat heartily, but what do you feed them? There are 3 main categories of food options you can give your fish: Pelletized, frozen and live foods. The types, benefits and caveats of each type will be discussed individually in the following paragraphs.

To summarize this at the beginning, it is important not to overfeed your bichirs due to their ability to pack on food. In a captive environment, they do not exert as much energy as a wild fish would, therefore making them susceptible to obesity and fatty liver disease, a common cause of death for many captive fish. It is best to feed them till they are visibly full; you get a feel for how much food they eat and can adjust according to the fishes’ size.

The best diet is a mixed diet, this is key for balanced nutrition.

Pelletized foods
A backbone of home aquaria, pellet foods are the simplest way to deliver quality nutrition to your pets. There is a bewildering array of pellet types aimed at different groups of fish made with different ingredients, there is nothing made specifically for bichirs though. Bichirs will often eat sticks or pellets such as shrimp, fish, seafood, worm, spirulina, brine shrimp or algae-based foods. Even cichlid pellets work.

To choose your foods it is best to look for the following in the nutritional information and ingredients:
  • The first 3 ingredients are animal or algae-based before moving to filler ingredients, eg Fish meal, shrimp meal and krill, “fillers and other ingredients”. These foods are more nutritious.
  • Protein content: 40-45%+ is ideal for carnivorous fish
  • Fat: 3-6% maximum
  • Fibre: 2-4% maximum
A good pellet should form the majority of your bichirs diet and can be supplemented with frozen or live foods.

Frozen foods
Aptly named for foods that are stored in your freezer, frozen foods make for a good supplement to a bichir diet. These products will often be available at your local fish shop or seafood section of a supermarket. The list includes:
  • Bloodworms
  • Krill
  • Brine shrimp
  • Mosquito larvae
  • Tubifex worms
  • Squid
  • Silversides
  • Other non-oily fish fillets
  • De-shelled market shrimp
These can be thawed and fed to your fish. For raw seafood, particularly thiaminase-containing foods such as market shrimp, should be pre-soaked in a vitamin product that contains vitamin B1 to combat deficiency caused by thiaminase. It doesn’t hurt to add vitamins to raw seafood in general. For a better list of seafoods containing thiaminase click here

Live foods
The final, and smallest, component of your bichirs diet can be live foods. This includes:
  • Small shrimp
  • Insects such as small freshly moulted cockroaches or mealworms
  • Crickets
  • Earthworms
  • Small fish
  • Insect larvae
  • Even frogs
These should only be given as occasional treats. Chitinous insects such as mealworms and cockroaches should only be fed after moulting as their otherwise hard exoskeleton can cause intestinal blockages.

Any feeder fish should ideally be bred at home or quarantined for extended periods due to the sub-standard conditions in which they are raised, and the high rates of disease and parasites. Goldfish should be avoided as they are oily, contain lots of thiaminase and are not nutritious compared to pellets or prepared frozen foods.

My fish isn’t eating! Help!
Despite their notoriously voracious appetite, it is not uncommon for bichirs to ignore food after acclimation or in response to changes in their environment, refuse prepared foods and sometimes they just avoid food for no apparent reason. Firstly, do not panic; bichirs can go long periods without food and will very rarely starve to death voluntarily. Secondly, there are a few things that can be done to get them eating again or get them eating what you want them to.

For newly added fish it is normal for them to refuse to eat while they are settling in; capture, transport and acclimation is a stressful process and as a result, they will not eat. Be patient, the fish will eventually give in. This can take anywhere from days to weeks but once they are settled, they will eat well.

Another commonly encountered issue is for a bichir to ignore pellets, especially from wild-caught fish or those used to eating live feeders. Non-moving foods may not appeal to them and are ignored. To rectify this the fish can be weaned off live food with frozen foods such as silversides, shrimp, or krill. Once they are eating dead foods readily then pellets can be added at feeding time, eventually, the fish should start eating some pellets and will begin to accept dry foods.

Eating strikes are a common response to stresses, sickness or will happen at random. If your tank is well maintained and any health issues are treated, then your bichirs will begin to eat again soon after. Strikes are not something to worry about and will rectify on their own in time.

Common health issues
Bichirs are susceptible to many of the same ailments as other fish but also have a few ailments that are more unique to their genus or are generally more susceptible to. For a more thorough article on health issues and answers then please click here

Bloat
The most common cause of bloat is a condition named “Dropsy”. This is characteristically a side effect of a decline in osmotic regulation with the kidneys, causing the fishes body cavity to swell with fluid. If caught early this can be treated with Metronidazole, the treatment regimen is detailed in the thread linked above. Common causes are poor nutrition and/or low water quality that allows opportunistic infections to reduce kidney function. The addition of a Calcium chloride-based salt (such as rift lake salt) in trace amounts is said to help maintain homeostasis in bichirs.

If your fish has a bloated stomach specifically it is often an indication of overfeeding or a build-up of gas, sometimes resulting in a floating fish. This will eventually find its way out. Offering algae or spirulina-based foods occasionally will help reduce the likelihood of this as plant proteins are important for gut health.

If bloat persists longer than a day, then it would be advised to start treatment for dropsy.

Internal worms
Flatworms, spiny headed worms, and tapeworms are often found in wild-caught fish. Most of these require an intermediate host (eg crustaceans) that are eaten to transmit the worms. If the fish is starving, the worms will be expelled. Praziquantel can be used to treat suspected worms, it is also standardly dosed in quarantine for this reason.

Bichir worms
Macogyrodactylus is a genus of flukes that will commonly be present on wild-caught bichirs. They resemble small white threads on the body of the fish. They spread easily, but only to other bichirs. Praziquantel is a tried and tested treatment for bichir worms.

Anchor worms
Another type of “worm”, these crustaceans (Lernaea haplocephala) attach themselves to the bodies of bichirs and again are mostly found on wild-caught fish and will spread to other bichirs. As with bichir worms they are treated with a round of praziquantel and it is best to do so in quarantine.

Fin damage
Split or damaged fins occur because of aggression from other fish, leaving them tattered. In most cases, this will heal given time and clean water. In rare cases fins can be split permanently, such is the case with this P. lapradei owned by Ledzepp6266 Ledzepp6266

1588690872545.png

It is unclear whether this was caused by a birth defect or deep damage before he was acquired by the current owner. This sort of injury or defect is rare but not unheard of.

If your bichir has damaged fins they will often recover without any permanent changes.

Breeding
Despite their widespread occupation in aquaria around the globe, breeding of polypterus at home is still relatively uncommon. Certain species such as senegals, delhezi, lapradei, endlicheri and some others are bred in commercial farms for the trade, most likely through artificial insemination, but their secrets are closely guarded.

In a hobby setting, it is rare for bichirs to breed, likely due to the extremely long maturation time of female fish. When bichirs are of breeding age they will reproduce frequently with eggs often turning up in filters or sumps.

To breed bichirs at home it is best to use a breeding mop, the fish lay eggs in between plants in nature so a green woollen mop will do the trick. Fish ready to spawn will display courtship behaviour for at least a day (read under behaviour) and will proceed to mate and release their eggs into the mop. The eggs can be removed and added to incubation containers. By most accounts they hatch within 3-4 days, living from their yolk sac for another week. Once the yolk sac is consumed they can be fed with freshly hatched brine shrimp (Artemia nauplii) or microworms. Regular breeder giseok jung giseok jung uses tubifex worms to raise them further.

Conclusion
Bichirs are truly amazing fish, if this article hasn’t convinced you of that then I don’t know what more could be cooler than a living relic, a window into the past. I have learnt a lot of new things writing this article and I trust it will be enriching to everyone who takes the time to go through it. Thanks for reading!
 

Hendre

Bawitius
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Jan 14, 2016
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Reference list

Here is the list of resources I have used for information or photos in this article. I highly recommend checking them out!

Researcher Michael Coates:

Phylogeny of ray-finned fish:

Revision of bichir species:

Bawitius:

John Samuel Budgett and Francis Balfour:

Polypterus farou:

Information from MFK:

Maija Karala's blog:

Spiracular breathing:

Brain structure:

Ray finned fish:
 
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