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.
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.