You may be surprised to know that
fish fart just like the rest of us (
some of us more than others). Fish create gas in their
intestines as a result of food
digestion. When fish
excrete their
feces, its usually surrounded by a gelatinous casing. The feces may then either float or sink (if they dont eat it first!), depending on the gas content. Some fish, upon taking in too much gas while eating flaky food from the top of an aquarium, will fart out the extra gas which would otherwise disturb their
buoyancy.
Most sharks (which are not fish) need to continuously swim in order to keep from sinking to the bottom of the water. They do not have the swim bladder than most fish use to maintain buoyancy. Sharks have high quantities of the lipid, squalene, which helps contribute to their buoyancy. One species, the Sand Shark, has found another solution. They will ingest air at the surface and then fart out the necessary amount of gas required to float!