Here is a direct quote from the sticky over in the poly section of this forum.
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.
i recently got a oscar that is around 2"-2.5" around there. he's in a 55 gallon with a small senegal bichir. the water temp is reading 80 degrees which shouldn't be the problem. and the bichir is doing good besides being lethargic sometimes at the top of the water. but the oscar is always hiding and darts back into hiding when i go around the aquarium and idk why. i want him to come out and eat but he just won't. the water is good with the bacteria needed and it's been cycled so my water is good.
