Raising Fish Fry

How to raise fish fry: the rearing tank, staged feeding from infusoria to baby brine shrimp, and the water quality that drives growth.

Overview

Raising fry is the stage between hatching and a robust juvenile. Egg-layer fry emerge very small and need tiny first foods, while the larger fry of livebearers can take coarser food sooner. Success rests on matching food size to mouth size and on keeping water quality high during rapid growth. Because fry grow quickly and feed often, the two demands are linked: more food means more waste, and the diet has to advance in step with the fish.

The rearing tank

Fry are reared in a gently filtered tank, typically using a sponge filter or air stone so the current does not harm them. Lowering the water level after hatching reduces the energy fry spend swimming. A well-seasoned tank with biofilm and microfauna also supplies natural first food, and keeping the parents out once the spawn is laid prevents the adults from eating the eggs or newly free-swimming fry.

First foods

The smallest fry need very fine live foods. Common first foods are infusoria, vinegar eels, green water and paramecium, along with mulm from mature filter media. These are small enough for newly free-swimming fry that cannot yet take larger prey.

Moving up to brine shrimp

Once fry are large enough, generally around one to two and a half weeks old, they move on to baby brine shrimp. Newly hatched brine shrimp hatch at about 450 microns and carry a yolk sac rich in proteins and healthy fats, which maximises survival and significantly speeds up growth. They are widely regarded as one of the best fry foods.

Later stages

As the fry grow, the diet broadens to finely crushed flake food and other prepared foods sized to the fish. Feeding is frequent during this period, with three to five small feedings a day supporting steady growth without fouling the water. Each food should be small enough to fit the mouth, so the size of prepared food is increased gradually as the fish enlarge rather than switched all at once.

Water quality and grow-out

Heavy feeding produces heavy waste, so frequent water changes are essential. Daily or several weekly partial changes keep ammonia and nitrite low and support fast, even growth. Maintaining clean, stable water through the grow-out period is as important as the feeding itself.