Identifying normal behaviors in Polypterides and the purposes behind them...

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Cohazard

Arapaima
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In this post I will list many of the interesting and somewhat unique behaviors in fish of the Polypteridae family.

I will provide a brief explanation of the purposes and benefits these behaviors have to Polypterides in their natural habitat, and also how some of those same behaviors can actually work against the fish in captivity.


Fish of the Polypteridae family, boast relatively low diversity compared to other common aquarium fish such as cichlids and catfish. Their superb adaptation to their environment appears to have created an evolutionary 'if-it-aint-broke-don't-fix-it' pattern. More information can be found here regarding their fossil record, natural history, and anatomy.

Because of this low diverisity, the Polypterides share many common behaviors between the two genus: Polypterus (which will be referred to henceforth as 'bichirs') and Erpetoichthy's (which will be henceforth referred to as 'ropefish' or 'ropes' or grouped with 'bichirs'). Below is the list of common and very normal behaviors:

Defensive behaviors:

Floating:

After staring at a tank full of small active bichirs or ropefish in an aquarium at your local fish store, you finally decide to bring one home.

After introducing it into your aquarium, many first time keepers are disturbed when their active baby bichir or rope is suddenly inactive, and remains floating at the waters surface in the aquarium. Rest assured you are observing normal and healthy behavior, which instinctively helps these fish survive in the wild.

In nature:
To understand how this behavior helps young polypterus survive, it helps to know about their natural habitat. Bichirs come from lakes and river systems in Africa, some with quick moving water and all with plenty of vegetation along the banks.

This vegetation acts as a nursery for young bichirs, who remain where the water is calm, and hide amongst the leaves. Because bichirs need to breathe atmospheric air, baby bichirs and ropes cannot afford to venture too deep, and must remain relatively close to the surface. By floating, they have easy access to breathe air, easy prey such as insects and their larvae, and remain relatively sheltered from predators.


In the aquarium:
As previously mentioned, young polypterus instinctively prefer to spend most of their time floating amongst floating plants, which is why I always suggest floating plants for bichir grow-out tanks.

Newly introduced adult bichirs and ropes may also float to help them feel secure at first, before they settle into a tank. It is less common in adults, and seems to be mainly done by upper-jaw species and ropes.

Unnatural floating:
Sometimes, you may observer your bichirs struggling to swim towards the bottom of the tank, with their tail-end floating towards the surface. Most times this is only temporary, and cause by the fish eating floating type pellet food before it's had enough chance to absorb water.

If the fish becomes bloated, or symptoms last longer than a couple days, refer to The Polypterid health information sticky.

Burst of speed/ Freak-out:


This behavior is a defensive reaction by the fish when they feel threatened. The fish may seem passive and at rest, and will suddenly burst into motion at high speed due to a sudden disturbance.

In nature:

Because bichirs mostly come from river systems, they need to be powerful swimmers to escape a perceived threat. Their physiology is clearly adapted for this, evident in their muscular bodies, and capability for short bursts of great speed.

In the aquarium:
In the home aquarium, most stimuli which will disturb the fish will be external to the aquarium. A sudden thud against the tank, or the opening and shutting of the doors on the aquarium stand, even stomping on the floor around the aquarium can send them into this defensive freak-out behavior.

This natural behavior which helps protect them in the wild, can cause the fish to harm themselves for obvious reasons. When in 'flight' mode, they do not care what obstacles are in their path, and will crash into the aquarium walls and decor repeatedly for several seconds until they calm or feel they have escaped the threat.

Keeping their setup in a low-traffic area, as well as furnishing their setup with ledges made of driftwood or other common aquaria decor for them to hide under, will help with keeping them calm, and reduce the likelihood of a freak-out, as well as making sure their aquarium is large, long and wide rather than tall.


Feeding behaviors:

Perching/Tail balancing:

One of the more curious and unique behaviors of the Polypterides, I like to call 'perching'. When the bichirs or ropes perch, they will balance themselves on their tails, and hold as still as they can until unsuspecting prey wanders too close....

In nature:
Not enough field work has been done to closely study the natural diet, but based off observations in the aquarium, they are certainly adept fish catchers.

A study into the natural diet of polypterus senegalus, found that the bulk of their stomach contents were made up of insects and crabs. It may still be that other species prefer fish, however at this time, there are no scientific papers to support this, only observations by hobbyists.


In the aquarium:
I have personally observed my polypterus use the perching behavior near a group of fish, and hold still until the fish come withing striking range, at which point the bichir would make a sudden burst of speed to catch the fish.


Stomach packing:

This behavior is seen after the fish appears to have eaten its fill. When the fish's belly begins to show fullness, you may observe it bend it's body from side to side once or twice, using it's muscular body to adjust the food in it's stomach to allow for more space, the same way you would over-pack a suitcase.

In nature:
Being opportunistic predators in their natural habitat, bichirs need to eat all they can when they can. Because they use a lot of muscle to swim, they have a high energy cost to move around and hunt.

If the fish happens upon a large meal, either a fish carcass or some other chance opportunity for a large meal, the bichirs make the best of it by stuffing in as much food as they can.

In the aquarium:
Only the bichirs that are well settled into the aquarium environment, with voracious appetites will display this behavior. Because they don't need to work as hard to get their food, they may become obese if the aquarist does not control how much they are fed daily

The Death Roll:

Strikingly similar to the behavior observed in crocodilians, bichirs use this behavior for the exact same reason, albeit less often.

In nature:
Polypterides have a strong sense of smell, which is their primary means for locating prey. Being opportunistic means that they will feed upon a smelly fish carcass of if the chance presents itself.

They will bite into the carcass, and their teeth which are mainly meant for holding on, will secure them a bite sized piece of flesh. Then they will spin their bodies rapidly to tear off a piece of meat.

In the aquarium:
This behavior is rarely observed in the aquarium because we try to feed our fish bite sized pieces of food to avoid choking and accidental death. You may try offering a large piece of fish, or a large shrimp, something that the bichir cannot fit into their mouth and must bite and tear to eat.

Spawning behaviors:


Breaching:

Aside from the normal surfacing for air, breaching the surface is part of the intricate breeding behavior in polypterus.

Anal fin cupping (males only):

The muscular anal fin of the males plays a role in spawning. When becoming sexually mature, males will cup their anal fins instinctively to signal they are ready to spawn. The cupped shape of the anal fin allows them to catch eggs released by the female, and fertilize them, then release them.

Nudging/following:

Another part of the spawning ritual, the male will repeatedly nudge the female and follow her around the aquarium, and swim along side of her bump her with his body and cupped anal fin.

Miscellaneous curious behaviors:

Scratching:

Sometimes you may see your bichirs use their pectoral fins to 'scratch' their sides. They may even bend their bodies to reach further down the length of their sides. This is a very unique behavior of bichirs and may or may not signal the presence of external parasites.

In nature:
Polypterides are targeted by nasty external parasites, and for the most part are protected by their ganoid scales, but not fully. To help, they evolved this behavior of scratching themselves to help remove parasites, which uses less energy than a full body 'flash' which is more dramatic and costly energy wise.

In the aquarium:
I have observed wild caught polypterus do this behavior in quarantine, but I have also observed fish in my main setup, who are parasite free, display this as well. This leads me to believe there may be some other mild discomfort either from particulate matter being stirred up by the sudden activity of a fish which may have landed on or near their sensitive lateral line.

Yawning:

Most fish with jaws that retract a bit, will display this behavior. I believe it helps them keep their jaw healthy by 'exercising' their ability to extend their outer jaw with a yawn.

After a meal, yawning may help them adjust their jaw back to the correct position.


Piling/Grouping (bichir pile):

Because Polypterides prefer low-light setups, and to be hidden, often in setups with lots of open space and little decor, you may observe bichirs piled together in a corner. This is simply an attempt to hide, and and they feel secure lying side by side because they can't see much past their neighbor.
 

Cohazard

Arapaima
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Defensive/Feeding behavior:

Head Burying:

This behavior is curious in that it hasn't been observed in all species as most other behaviors have, mainly Polypterus endlicheri, delhezi, and weeksii. It is a behavior which is used for hunting prey, as well as in situations when the fish feel threatened. They will point their head towards the substrate, and shake their body quickly, burying most of their head with just the eyes showing.

In nature:
Anne has personally observed this behavior being used as a hunting technique in polypterus delhezi and weeksii. Their striped patterns on their backs were great camouflage for hiding in the shadow of a grassy type plant.

It makes perfect sense to infer that this is beneficial to them in nature as an ambush hunting technique, when perching may fail.

In the aquarium:
Because of the brute strength they use to bury their heads, it is important to make sure you have appropriate substrate for your bichirs, with sand being the best, or small smooth pebbles.

This behavior may be used to escape a perceived threat instead of the burst of speed/freak-out behavior, and may be more common in bichirs being kept alone.
 

Cohazard

Arapaima
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Great pics Kenta! Thank you for sharing! I am working on trying to get video of some of these behaviors such as 'stomach packing'.

The lapradei is displaying what I call 'perching/tail balancing' behavior. It is a hunting behavior, but rather than hunting for free floating fish, looks like your lap is hunting bottom dwelling critters such as crab or sinking pellets lol


lukesha, you can sex a polypterus by looking at the anal fin which is just below the tail. It is thick and wide as you can see in Kentas lapradei. Female will have thinner (slightly more opaque) and narrower anal fin.

What size are these fish?
 

Cohazard

Arapaima
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Wow now that is rare! I've only seen pics like that one other time of a delhezi which was similarly almost completely buried.

Salamat pare for sharing the pics!
 
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King-eL

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Cohazard;2891778; said:
Wow now that is rare! I've only seen pics like that one other time of a delhezi which was similarly almost completely buried.

Salamat pare for sharing the pics!
They are actually digging for weather loaches that's trying to went under the substrates. That's why you see two of them were digging. The gar was just waiting for the weather loaches to popped out and take it chance to grabbed it. The bichirs were doing the hard work and the gar was getting all the benefits. It's not very common to see a bichirs hunts as most live food that most hobbyist that they offer their bichir are fast moving all around fish.
 

Cohazard

Arapaima
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King-eL;2891788; said:
They are actually digging for weather loaches that's trying to went under the substrates. That's why you see two of them were digging. The gar was just waiting for the weather loaches to popped out and take it chance to grabbed it. The bichirs were doing the hard work and the gar was getting all the benefits. It's not very common to see a bichirs hunts as most live food that most hobbyist that they offer their bichir are fast moving all around fish.

Wow, that is cool! You're right, we usually advise against live food, and if I did, I would prefer to use something closer to the bichir natural diet such as african aquatic frogs, insect larvae, etc...

Still, this is fascinating to learn about this hunting behavior, it is definitely a more active approach to hunting by digging, than what I discussed with Anne.

She has observed ambush hunting by head burying, especially in the shadows of grass type aquatic plants, likely to camouflage the fish's stripes.
 

vaine111

Fire Eel
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hey cohazard just an update. i didnt notice this when i last posted this but my ornate is getting huge. now that he has started gobbling up the shrimp it seems like he has grown an inch in like a week. or maybe he's just getting fatter.

but i traded in my pair of dempsey's last week for a paraya that i was for sure was big enough for my tank, the ornate had alot more confidence when i added him, swimming all over the place when he is usually very docile. he went into my fake plants that i have at one end of the tank and just layed there pressed against the glass with his head sticking straight up. and no lie my pbass which was harassing the paraya for a bout 10 minutes straight scared the paraya over to the ornate no less then 30 seconds after he went into the plants and he gobbled him up. i swear it was like they set it up that way.

ever since then the ornate is very active. and thats when i noticed that he keeps his belly full of shrimp instead of wondering if he was eating at all. maybe it was a confidence boost for him. but either way i hope that is the last fish he will eat. i hate feeders.
 

Cohazard

Arapaima
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Well sorry to hear for the loss man but what a fascinating observation you've made!

Probably not confidence lol but having his belly full must have jolted it's metabolism or gastrointestinal system into needing more energy to maintain itself lol

I had a senegalus that never really had a large appetite, but grew well and had great shape.

I sold it to a friend who probably fed it more than I did, and when I got it back, the darn thing returned with a serious serious appetite!

Your experience gives me insight into what may have happened in that case, thank you!
 

Cohazard

Arapaima
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Got a pic of my delhezi displaying the 'perching/tail balancing' behavior:

 
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