Agree. Not pointing to or trying to argue with anyone in this thread, but in general, some people really get this wrong when they talk about pellets swelling up inside the fish or when some think a fish that lives in deep water can't afford to take in any air-- which is the other thing some people say.
Some people may see their pellets swell a bit in water and conclude it must be the air in the pellets, but imo/ime it's not so much how much air as how much starch. If you've ever cooked rice or oatmeal or pasta you can see this. So it's not so much about floating or sinking as it is the ingredients, meaning some pellets will swell very little or some more than others, whether floating or sinking. I've checked this and some (floating) pellets swell very little compared to others. Secondly, since when can't fish (or animals in general) handle their stomachs expanding to any degree? It's funny how I've seen the same people that will let their fish gorge themselves on brine shrimp or worms or frozen fish food or market shrimp, etc. think they have to soak their pellets, squeeze out the air, not feed any floating foods, etc.
As for deep water fish not being able to ingest air, what do you think happens when they eat other fish, including their swim bladders? Some of the same people who think it's a bad thing to let their fish feed at the surface, in case they gulp some air, think nothing of taking them out of the water to strip eggs or fry or measure them, etc.
I don't know about certain man made fish with odd shapes and unnaturally configured guts and intestines, maybe they need special care, but otherwise I've never seen where floating vs sinking foods makes a difference to fish digestion. It's more about what's in the food and not overfeeding than anything else ime. As far as flakes vs. pellets for larger fish, sure it's possible to feed them flakes, just takes a lot more of them for a large fish compared to small fish, so pellets are more efficient imo.
On the point of fish gulping air, yes they will consume some when eating another fish, but I would imagine its far less than what they would when consuming flakes or floating pellets, especially taking into consideration how much people tend to overfeed.
I have seen that but it's because the pellets were too big. I switched to smaller pellets and never had that problem again, and that was a messy oscar. Flakes are easy to feed because they are a one size fits all kind of food. If the right sized pellets are fed, there is no comparison between the two.
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+1 Also, when I had an oscar, he was just as messy with hikari cichlid gold as he was flake food. NLS on the other hand wasnt as messy since it was swallowed whole. Point being if pellet food is softer it can be very messy, like a flake, but not all pellets are like that.