Fish fry need tiny, nutrient-rich foods that match their mouth size, starting with microscopic organisms and gradually moving to larger live foods over the first few weeks of life. What you feed and when you introduce it depends on the species, but the progression is similar for most freshwater fry: infusoria or liquid fry food first, then microworms or baby brine shrimp, then crushed flake or pellet food as they grow.
The First 24 to 72 Hours: The Yolk Sac Stage
Newly hatched fry don’t need food right away. They’re born with a yolk sac attached to their belly, a built-in nutrient supply that sustains them for the first one to three days depending on species and water temperature. During this stage, fry typically stay near the bottom or cling to surfaces and aren’t actively swimming. You’ll know the yolk sac phase is ending when fry become free-swimming and start darting around the tank looking for food. At that point, their body water content rises to around 80% as the yolk is absorbed, and they need external nutrition within hours.
Missing this window is one of the most common reasons fry die. Once the yolk sac is gone, fry that don’t find food quickly lose energy and starve. Having your first food source ready before the eggs even hatch gives you a much better survival rate.
Infusoria: The Smallest First Food
For very small fry (bettas, gouramis, tetras, rasboras, and many egg-laying species), infusoria is the ideal starter food. Infusoria is a catch-all term for a mix of microscopic aquatic organisms including paramecium, euglena, rotifers, amoebas, and tiny algae like volvox. These organisms are small enough for fry that can’t yet eat anything visible to the naked eye.
You can culture infusoria at home with minimal effort. Fill a jar or small bucket with one to two quarts of aquarium water, which already contains some of these organisms naturally. Add a nutrient source to fuel their growth: blanched lettuce is the most common choice, but banana peel, boiled rice, raw potato, dried grass, or even a few drops of milk all work. Place the container in a sunny spot and wait three to five days. The water will turn cloudy as the infusoria population explodes. In some cases, you can actually see the tiny organisms moving if you hold the jar up to light.
To feed, use an eyedropper or turkey baster to draw water from the cloudiest part of the culture (usually near the surface, away from the decaying nutrient material at the bottom) and add small amounts directly to the fry tank. The culture will smell unpleasant, which is normal. Keep multiple jars going in rotation so you always have a fresh supply, since each culture tends to peak and then crash after a week or so.
Microworms: A Step Up in Size
After three to seven days on infusoria, most fry are large enough to eat microworms. These tiny nematodes (about 1 to 2 millimeters long) are one of the most practical live foods for home breeders. They’re especially useful for species whose fry are too small to eat baby brine shrimp right away.
Nutritionally, microworms hold up well. Their dry matter is roughly 40% protein and 20% fat, and research from Texas A&M’s fisheries extension program has shown that fry growth and survival rates on microworms are not significantly different from those fed brine shrimp. One practical advantage is that microworms stay alive in freshwater for 12 hours or more, giving fry plenty of time to find and eat them rather than fouling the water immediately.
To culture microworms, you need a shallow plastic container with a lid, a bed of oatmeal or baby cereal mixed with water to a paste-like consistency, and a starter culture (available cheaply online from aquarium hobbyists). Spread a thin layer of yeast on top, add the starter worms, and close the lid with a few small air holes. Within a few days, microworms will crawl up the sides of the container where you can swipe them off with a finger or small brush and rinse them into the fry tank.
Baby Brine Shrimp: The Gold Standard
Newly hatched brine shrimp nauplii are considered the best live food for fry once they’re large enough to eat them, typically around one to two weeks old depending on species. Their jerky swimming motion triggers a strong feeding response, and their bright orange color makes it easy to tell whether fry are actually eating (you’ll see orange bellies).
Hatching brine shrimp is straightforward. Add brine shrimp eggs to a container of salt water (roughly two tablespoons of aquarium salt or non-iodized salt per liter), keep it aerated with an air stone, and maintain a temperature around 80°F. Nauplii hatch in 18 to 36 hours. Shine a light at the bottom of the container to attract the shrimp away from unhatched shells, then siphon them out and rinse briefly in fresh water before feeding.
One limitation of brine shrimp is that they die quickly in freshwater, so feed small amounts several times a day rather than dumping a large batch in at once. Uneaten dead shrimp decay fast and spike ammonia levels in a fry tank.
Vinegar Eels and Other Options
Vinegar eels are another tiny nematode popular among breeders. They’re slightly smaller than microworms, which makes them useful for especially small fry. Their main advantage is that they swim in the water column rather than sinking to the bottom, keeping them accessible to fry that feed in mid-water. Cultures are also nearly maintenance-free and can last for months without much attention. The downside is that they’re less nutrient-dense than microworms or brine shrimp, so they work best as a supplement or bridge food rather than a sole diet.
Egg yolk is a common emergency food when you don’t have live cultures ready. Hard-boil an egg, take a tiny pinch of the yolk, and squeeze it through a fine cloth or mesh into the water to create a cloud of particles. Use extremely small amounts because egg yolk fouls water rapidly. It’s a viable short-term solution but not a substitute for live food over more than a day or two.
Commercial Fry Foods
Several commercial products are designed for fry feeding. Liquid fry foods (like Liquifry) contain suspended particles small enough for newly free-swimming fry and can substitute for infusoria in a pinch. Powdered fry foods are essentially ultra-fine ground flakes or pellets suited for fry that have graduated past the microscopic food stage but aren’t yet big enough for crushed regular flakes.
Commercial foods are convenient, but most experienced breeders use them as supplements rather than primary nutrition. Live foods consistently produce better growth rates and survival, likely because the movement stimulates feeding behavior and the nutritional profile of live organisms is more complete than processed alternatives.
How Often to Feed Fry
Fry have tiny stomachs and fast metabolisms, so they need to eat frequently. Research on catfish fry found that feeding five times per day produced significantly better growth than fewer feedings. For most freshwater species, four to six small feedings spread throughout the day is ideal during the first two weeks. As fry grow into fingerlings (roughly four to six weeks old), you can reduce to three feedings per day without sacrificing growth.
The key is small, frequent meals rather than large ones. Overfeeding doesn’t just waste food. It drops dissolved oxygen levels and raises ammonia, which stresses fry and increases disease susceptibility. After each feeding, watch for uneaten food settling on the bottom. If food is accumulating, you’re giving too much per session. A turkey baster is useful for spot-cleaning debris between water changes.
Transitioning to Regular Food
Most fry can start accepting finely crushed flake food or micro pellets by three to four weeks of age, though this varies by species. The transition works best when you overlap foods: continue offering baby brine shrimp or microworms while introducing tiny amounts of dry food. Over a week or two, gradually increase the proportion of dry food as fry learn to accept it.
Crush flakes between your fingers until they’re almost powder-fine, or use a mortar and pestle. Pieces that are too large will be ignored or, worse, can choke small fry. Some breeders soak crushed flakes briefly before adding them to the tank so they sink slowly through the water column rather than floating on the surface where bottom-dwelling fry can’t reach them. By six to eight weeks, most species are eating the same foods as adults, just in smaller portions.