|MadSci Network: Zoology|
Sea horses very well may eat krill - they eat
benthic plankton, What the sea horse eats depends on where the sea horse is - some of them are littoral, that is, they swim just offshore; many of them are reef dwellers, living on or closely around a reef. A few of them have even been found in fresh water, although this is not usually the case. Plankton is abundant in both of these areas. Seahorses don't have any teeth - not too surprising when you consider that their mouth is comprised of a tiny little tube snout! This tube snout, though, while not particularly useful for chewing, functions as a great vacuum cleaner. The sea horse can get up next to its intended prey and just suck it in, very rapidly (assuming it's small enough!). Sea horses have no economic value: they are not sought by fisheries for any purpose. They wouldn't be worth the effort to eat; they're tiny and covered by bony plates on top of it. They are sold as aquarium fish, though, because they are interesting to watch: they can use their tail in a prehensile fashion, and the male carries the eggs and very young in a pouch, so they are neat to watch. Sea horses are in the fish order Syngnathiformes ("syn" = together; "gnath" = jaws), but are the only ones in the group with the characteristic look of the sea horse; the rest of the members of this group are more eel-shaped.
If you had sea horses in an aquarium, I expect they would eat regular fish food - flakes might be a little difficult, and pellets (depending on the size) might also be tough. But there are varieties of pelleted food that are smaller than peppercorns that they could eat, as well as freeze-dried krill, which i bet they would also eat. If you are contemplating one/some as a pet, the person who assists you in the fish store will be better able to assist you with their diet than I.
Good luck, and thanks for asking!
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