I’ve always thought that when fish jump out of the water they do so because of lack of oxygen in the air. I thought I read this in a Straight Dope article or MB, but a search proved futile, using “fish +jump.” A Google search had several hundred thousand candidates. I read one wherein the author believed that fish jumped due to lack of water quality, which I had always believed. I also read that elsewhere.
However, I was talking to some one this morning, noting the number of mullets jumping out of a stream that I saw yesterday, and jumping quite high. He said they were jumping to catch food, probably mosquito larvae. If they wanted oxygen, he said, they’d just breathe at the water-air surface where the absorbed oxygen is greatest and wouldn’t expend ATP jumping in the air. That would be counter-productive.
That makes sense to me. Moreover, if fish can breathe the oxygen that is in the air through their gills, as they do water, why can’t they live in the air?
So, it appears that I’ve been under a misapprehension and the fish jump to catch food. Can some one point to an authoritative source or otherwise confirm this? One always is reluctant to discard long-held beliefs.
Sometimes fish jump in order to catch flying insects over the water. (But not mosquito larvae which are aquatic and of course winglees.) Often, however, they jump in order to avoid larger predatory fish under the water that are trying to catch them - a good example is flying fish. Fish that are trying to get more oxygen mostly just gulp air at the surface - there’s little point ot jumping.
Fish can breathe in air, they just can’t do it for very long before their gills dry out and collapse, preventing oxygen from being absorbed. Certain fish, like mudskippers, have special mechanisms for keeping their gills wet and can survive prolonged exposure out of the water.
When I was a kid growing up in Florida, we always said the mullet were jumping to avoid the sharks. Never knew if this were actually true or not. I would jump to avoid a shark, I suppose. But I at least half believed we said this just to scare each other. We never did go swimming when the mullet were jumping, though.
By authoritative source I don’t know if you mean just some dude’s webpage or something more… I can give you a fish biologist’s short answer. In short, no, fish don’t jump to get more oxygen. They can’t breath out of water because their gill filaments collapse due to no support from the water - like having a mop in a full bath tub… under water the strings all spread out, take the mop out and they all clump together. Add to that that in air they have no way to draw more oxygen over their gill filaments. Under water they can either pump water over the gills with their operculums or force water over them using ram ventilation (swimming with the mouth open). Those mechanisms won’t work in air, and even if they did the gill filaments would be all clumped together and wouldn’t take up much O2 anyways. Sometimes if the water quality is real bad, the fish will go all squirely and dart about, sometimes breaking the surface - but that’s a panic reaction (I once put a small trout into my stagnant backyard pond and it did this - very poor water quality compared to what it was used to). When fish are in low O2 environments, they’ll lethargically gulp water right at the surface. Some fish are more adept at extracting O2 from water than others, while some can actually breath atmospheric oxygen from a modified swim bladder. When they do jump it’s usually to get food, or to avoid becoming food. You see schools of small fish come shooting out of the water on lakes or the ocean when something’s chasing them from below. Big fish will sometimes follow them out, though usually not. There are all kinds of bugs and aquatic things that sit on or near the surface, and big fish will jump at them to catch them. Some fish will even jump into low tree branches or spit water at bugs to get them. There are other imes when fish will jump for reasons we’re not quite sure of - like chum salmon jumping around near the mouths of rivers during their spawning run; it might be to loosen eggs from the sceines, might not. Alright, I said short answer, so that will do for now.
I can’t remember where I heard this, but I thought that dolphins sometimes jump to conserve energy. There is less drag in the air than in the water, so making long low jumps out of the water is actually easier than staying sumberged. Whether this is also true for some kinds of fish, I don’t know.
I’m not sure about the dolphin energy conservation thing, but the difference in density between air and water is how flying fish get enough steam up to fly (glide). Some species have a larger bottom lobe on the tail and race towards the surface on an angle, breaking it with most of their bodies. They leave most of the tail in the water and power away with the large surface area of the bottom half of the tail against the dense water while their bodies are up and out in the thin air, giving them much less resistance so they can gain enough speed for flight (light a high-speed power boat). Tuna will swim in a sine wave pattern at high speed to conserve energy, but they stay underwater while doing it. They power up the rising part of the curve, and then hold in their fins, stop flexing, and glide through the downhill part (being very streamlined) until it’s time to power up again. Thus they move say 100m, but only actively swim 50m of it.