I can't answer the question of whether fish sleep or not.All fish conserve energy,in a state of relaxation,whether that qualifies as sleep or not is another question.
different species do it in different ways.Catfish can sit on the bottom of a lake or pond for weeks and never move.Sharks,of course,the age old scenario that they can never stop swimming or they die,is true;for the most part.Larger sharks,like the great white,hammerhead,and others,can't ever stop moving.Other smaller species can stop,and even sit on the bottom for long periods. Of course,you have the plecostamus (type of catfish) that sits on the bottom.
For the most part,where the fish dwells in the water usually determines what kind of "sleep" habits they have.
1)Bottom dwellers-sit back,relax,napping away sitting on the bottom.
2)middle dwellers-can usually hover in place,drifting silently,reflecting on it's day
3)top dwellers-are fairly constantly in motion,sitting around isn't their style,they have too much to do and not enough time to do it.
4)fish that go all over.top,middle,bottom are pretty much the same as #3 species,with the added option,they can relax for short periods,catch their breath before taking on everything again.
There's a lot more scientific explanations for it,but that's the general break-down. Do they sleep like we do,knocked out catching some ZZ's and dreaming about fish,well;I will leave that up to you. Every living organism,has to "re-charge" so to speak,but some are adept at doing it while on the run.
Me,I was born a tadpole,and was transformed into my existing state by my unsatiable desire to rule the world. King Neptune wouldn't let me stay in the ocean to cause trouble,so he sent me to the humans to take over this world.MUAHAHAHAHAHAHAHA
