Feeding Aquarium Fish Fry

How to feed fish fry: tiny first foods like infusoria, rotifers and newly hatched brine shrimp matched to the fry's mouth size, frequent small feedings, keeping water clean under heavy feeding, and how egg-layer and livebearer fry differ.

Fry are not just small fish - they have tiny mouths and fast metabolisms, so feeding them well is mostly about food size and feeding frequency. The size of the mouth is decisive in choosing a first food (FAO): a particle the fry cannot swallow does nothing, however nutritious it is.

First foods and matching mouth size

The smallest first-feeding fry start on microscopic foods and graduate to larger ones as they grow. Rotifers are used first for the tiniest larvae because they are small - roughly 90-350 microns, with the common Brachionus around 150-200 microns - while newly hatched brine shrimp nauplii are larger, about 450 microns (200-500 microns), and are introduced only once the fry can take them (UF/IFAS; FAO). Copepod nauplii span about 38-220 microns, and fine artificial fry foods are typically made in particles of about 0.1-0.3 mm.

• Infusoria or green water - for the very smallest first-feeding egg-layer fry.
• Rotifers (about 90-350 microns) - the first live food for tiny larvae too small for brine shrimp.
• Newly hatched brine shrimp / Artemia nauplii (about 450 microns) - once the fry's mouth is big enough.
• Powdered or liquid commercial fry foods (particles around 0.1-0.3 mm) - convenient and can be combined with live foods.
• Larger foods - microworm, then crushed flake and normal foods, as the fry grow.

Livebearer vs egg-layer fry

Livebearer fry - guppies, mollies, platies - are born relatively large and free-swimming, and can usually take finely powdered flake and newly hatched brine shrimp straight away. Many egg-layer fry are far smaller at first feeding and need infusoria or rotifers before their mouths are big enough for brine shrimp nauplii. Whichever you keep, feed small amounts several times a day rather than one large meal, because fry grow fast and empty their guts quickly.

Sources: ask.ifas.ufl.edu , www.fao.org , www.fao.org