Feeder fish

A silver guppy fish
Guppies are a common example of feeder fish

Feeder fish is the common name for certain types of small, inexpensive fish commonly fed as live food to other captive animals such as predatory fishes (e.g. aquarium sharks, farmed salmon and tuna) or carnivorous aquarium fish (e.g. oscars, gar, grouper and rays), turtles, crocodilians and other piscivores that naturally hunt in fresh, brackish or salt water ecosystems (zoo animals such as grizzlies, water snakes, cetaceans, pinnipeds and penguins).