Fish are aquatic animals; their feeding roles depend on their diet and life stage. Small and large fish in the illustrative food web are generic groups chosen to distinguish two feeding positions, rather than a measured relationship between named species.
A fish species with surface and cave populations used in studies of eye development and degeneration.
A member of the fish family Cichlidae, with radiations informing studies of sensory evolution and speciation.
Gymnothorax javanicus, the moray in the cited interspecific hunting study.
A group of predatory fishes including the Red Sea fish studied in coordinated hunting with moray eels.
Gasterosteus aculeatus, used in experiments on personality, social feedback and collective decisions.
A freshwater fish used in live embryological studies; rapid external development makes cell tracking and experimental manipulation particularly useful.

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Fish by Ciro Santilli 40 Updated 2025-07-16
This paraphyletic subgroup is easy to form the "acquatic only" (fishes) vs "things that come out of water" (tetrapods). Though mudfishes make that distinction harder.
Which kind of makes sense, why would you want for limbs unless you are going to stay out of water!