The key factors to keeping the fry alive and healthy are keeping the water and environment clean, protecting the fry from adult fish, and providing proper nutrition. Most fish owners already know how to take care of the first two, but feeding fry is often the stumbling block that new breeders run into. Newborn fish cannot eat the same foods as the parents, so the challenge is providing the proper food until the fry grow large enough to eat standard foods.
Keep in mind that young fish will eat different foods at different stages of their development. Likewise, different species of fish have somewhat different needs. For instance, newly hatched Discus fry feed off their parents' slime coat for the first few days of life and therefore do not need to be fed until they have grown past that stage. It is wise to study the species of fish you are breeding to determine if the fry have special feeding requirements.
Taking a broader view, there are two general types of fry, those that are hatched from eggs and those that are born live. Fry that are born live are larger and have developed more fully than those hatched from eggs. Consequently, these live-born fry have a larger mouth than the typical fry hatched from an egg, and can, therefore, eat larger foods from the start. It is quite common for live-born fry to eat a finely ground version of the same foods as parent fish.
Fry from egglaying fish are smaller when they hatch and often are not free swimming for the first few days. In these cases they remain at the site where the egg was attached, feeding off their yolk-sac until they begin to swim free on their own.
Fry that are freshly hatched have very tiny bodies, and can only eat the smallest of foods. However, they are growing rapidly, and have demanding nutritional needs. This stage is particularly critical, as newly hatched fry can starve to death quickly. Some of the best foods at this stage are infusoria, freshly hatched brine shrimp, and green water. These foods must be available immediately when the fry hatch, as they cannot wait even one day for foods to be prepared. If the previously described foods are not available at the time the fry hatch, egg yolk preparations, and commercially prepared fry foods are good alternatives that don't require a lot of time to prepare.
Once the fry have passed the first week or two of life, they are generally large enough to eat similar foods as the parents, just in smaller portions. Virtually all purchased foods, either flake, pelleted, or freeze-dried, can be ground to a fine size that fry can eat. This article describes simple steps for creating your fry foods, using simple tools that you probably have on hand. As the fry grow larger, you can make the food particles larger until they can eat the same size food as the parent fish. Keep in mind that although the fry may now be eating the same foods as the parents, they need to be fed more often due to the small size of their stomachs.
There are several basic high-quality foods that most fry will do well on. As previously mentioned, these foods must be on hand at the time the fry hatch, and the supply must be continuous until they can eat traditional foods. So prepare ahead of time to ensure you have what you need. Aquarium clubs come in handy when rearing fry, as there are often members who can help you in a pinch. If you want to breed and raise fish, consider finding a local club for support.
- Infusoria: Infusoria grows naturally in most tanks, particularly those with live plants. However, there may not be sufficient quantities to sustain the full hatching of fry. Therefore, it is helpful to culture your own infusoria to ensure having an adequate amount. This infusoria article from your Guide gives plenty of tips for growing your own culture.
- Brine shrimp: Few things can rival the nutritional value of freshly hatched brine shrimp or the appeal it has to virtually all fish. If you choose to raise it yourself, you will have to start the culture before the fry hatch and keep it going for a while to ensure the fry have sufficient quantities. Another option that owners use is a commercially prepared live brine shrimp preparation, or frozen baby brine shrimp.
- Green water: Green water is exactly what it sounds like, water with microscopic algae growth that turns it green. It makes excellent first food for young fry and is easy to grow. Simply take a gallon jar and fill it with aquarium water, scrape some algae out of your tank and add to the jar (if you have no algae, a bit of grass will suffice). Add a few drops of plant fertilizer, then leave the jar in full sun. Within a matter of days, the water should be green and teeming with microscopic nutrients that are ideal for your fry. Take a few ounces out of the jar for each fry feeding, and replace it with treated freshwater.
- Egg yolk: Egg yolk is a power-packed food that is easy to make into preparation for newly hatched fry. Hard boil an egg, take the yolk and wrap in a small piece of gauze, compressing it so small portions protrude through the cloth. Hang it in the tank and the fry will feed off it. Remove and replace daily for the first several days.
- DIY fry food: Live born fry, or fry that are a week or more old can usually eat finely ground foods, that you can prepare yourself.
- Purchased fry food: Commercially prepared fry foods.