A terrapin is used to describe different species of aquatic turtles, but there is a species of turtle called the diamondback terrapin. Because these turtles are aquatic, they coexist with fish in the wild and sometimes in captivity.
Water that terrapins live in has to be kept clean with frequent water changes that filter waste. The addition of fish means that the water will have to be cleaned more often.
Terrapins and fish can coexist at any age as members of the food chain, but hatchling and juvenile terrapins eat a mainly carnivorous diet and may eat or attempt to eat the fish. Adult terrapins eat a mainly vegetarian diet and are less likely to stress or eat the fish and more likely to happily coexist with them. If the fish are being eaten, the turtle should still be supplemented with commercial turtle food to ensure it receives all of the necessary nutrients.
Small, speedy fish like zebra danios, platies, minnows or tetras may coexist well with turtles because they can avoid being eaten. Slower fish, like goldfish, are not recommended because they will quickly be eaten. Goldfish are also known to produce more waste than other types of fish.