Feeding Rainbowfish Fry

Rainbowfish fry require a varied diet to reach maturity and should be fed several times a day. This is not always possibly as we all have other things in our life to do each day. However, there are several kinds of live foods that can be fed to young fry that will remain alive in the aquarium until consumed. This often means that you will have to culture or collect them. Live foods such as paramecia, phytoplankton, freshwater rotifers, or other microorganisms (infusoria) all fall into this category. As the fry grow they can be fed other live foods such as brineshrimp nauplii, microworms and vinegar eelworms, which will remain alive in the aquarium for 4 to 8 hours, providing food until you can feed them again.

High mortality rates can often occur, especially during the early feeding stages. Having such tiny mouths, the size of the food is crucial to their surviving the most difficult period in their lives. However, I would like to outline a relatively simple way for feeding baby rainbowfishes while ensuring maximal survival.

Begin feeding with small amounts of live paramecia or other microorganisms starting at day 2 or 3 because the yolk sac is mostly depleted by then. Feed 5-10 mil (for 20-50 fry) of paramecia suspension three or four times per day. You can tell if they are feeding well as the baby fish should have nice 'swollen stomachs' after feeding. They will also benefit from the addition of small amounts of phytoplankton (green water). Another live food that is gaining increasing attention for rearing larval rainbowfishes is rotifers. Rotifers are an excellent supplementary live food in addition to paramecia. Several characteristics, including their nutritional quality, size, and relatively slow mobility contributes to their usefulness as an excellent live food for larval rainbowfishes.

Around day 7 to 14, when its obvious that they are feeding well, you can begin feeding brine shrimp nauplii, microworm or vinegar eelworms. Brine shrimp and microworm will accelerate growth so it is important to commence feeding as soon as possible. The smallest will eat the paramecia and the bigger ones brine shrimp nauplii or microworm. The intermediate baby fish will eat all three. Gradually increase the proportion of brine shrimp nauplii or microworm and phase out the paramecia - this should be around day 14 to 21. When weaning fish to a new food, introduce 10% of the new food daily while reducing the same percentage of the initial food until 100% of the new food is accepted.

Continue feeding the baby fish with brine shrimp nauplii and microworm three times a day. Do not overfeed, a good rule of thumb when feeding brine shrimp nauplii is that they should be mostly eaten after about 20 minutes, at which point the babies will have nice red stomachs. In addition to microworm or brine shrimp nauplii feed them once each day with a sprinkle of powdered spirulina. Spirulina is an algae derived food rich in protein, carbohydrates, amino acids, vitamins and minerals, and essential fatty acids. (Spirulina powder is available from most health food stores).

A nursery tank can be used through the baby fish stage until they are large enough (about 10-12 weeks) to be moved into regular tanks, still feeding them the above foods until they are weaned onto crumbled flake food. Feed adult foods as soon as the babies are big enough to eat it. Adjust the fish density in the nursery tank as necessary to prevent overcrowding. Monitoring water quality levels is a good way to help determine when dividing is necessary. For maximal growth keep the number of fish per aquarium low and feed them often (at least twice daily).

It should be noted that the hatching of larvae might vary, resulting in the presence of fry at different stages of development. If you wish to raise an entire spawning, you may have to sort the growing fry by size, as the larger ones will eat their smaller siblings or repress their growth rate. If you have a batch that differs greatly in size, you will often find that the smaller ones are females.

Size grading separates the faster and slower growing fry. When these separated fry are transferred to another tank, growth of the smaller fry is no longer negatively impacted by the faster growing individuals. Smaller fry should increase their growth rates to compensate for the initial retarded growth rates that developed during the nursery phase. The continued growth and development of the baby fish will vary from one hobbyist to another and is largely conditional upon captive environmental conditions such as temperature, water quality, and feeding regime.

Feeding Fry Prepared Food
If you don't want to culture or feed live foods to your baby rainbowfishes, you can still get reasonable results rearing baby rainbowfishes entirely on a fine powder-based diet manufactured by a number of commercial suppliers. However, rainbowfish fry fed only a dry or liquid formulated diet often show poor growth and survival when compared to those fed with live food. Non-living feeds do not yet have an advantage over live food organisms.

The major reasons why are:

1. Deterioration of water quality due to decomposition of prepared diets, which are usually fed in excess in order to achieve satisfactory growth and survival;
2. High mortality rates, due to insufficient, excessive or unbalanced diet from the inability of the fry to absorb dietary components.

Prepared diets should be nutritionally complete, palatable, be less than 100 microns (µm) in size, and remain floating or suspended in the water column. I have found OSI Micro-Food an excellent first food for rainbowfish larvae. OSI Micro-Food is a microencapsulated diet rich in protein, fatty acids, and vitamins. Micro-Food or A.P.R., as it is known in the aquaculture industry, was designed for feeding prawn larvae, but it works well on baby rainbowfishes too. Just use it dry and sprinkle it over the surface of the water. Microencapsulating involves covering a small particle of feed with a thin layer of a special coating that is water insoluble but breakdown in the digestive system of the larvae. These feeds are very water stable and vitamins and minerals are well retained. Don't be afraid to try some of the marine fish diets such as Kent Marine ZooPlex or Kent Marine Zoe. Kent Marine ZooPlex is a suspension of whole bio-engineered marine zooplankton. Animal size is approximately 800 microns. Look around the different aquarium stores and see what is available.

Sera Micron and Tetra Fry Food for Egg-layers are also effective. As the fry grow you can change them over to Sera Micropan or Microgran until they are large enough to take regular flake and pellet feeds. Dry prepared diets can be fed by an automatic feeder and can be programmed to feed continually through the daylight hours. However, care should be taken not to overfeed as prepared diets tend to easily decompose and pollute the water if overfed. Just a small tip here, keep all your fish foods in the refrigerator, they last longer.

You can use one of the liquid preparations, but I find that liquid foods sinks rather quickly and baby rainbowfishes need their food on the surface or just below. All the same, a few drops wouldn't hurt and it gives them something different in their diet. Another simple, less expensive but very efficient method to feed newly hatched baby fish is hard-boiled egg yolk. Just wrap the yolk in a clean cloth and twist it down into a section of the cloth. Then all you have to do is swish it around in the water. The egg yolk will keep in a refrigerator for a few days. An even easier option is to purchase some powdered egg yolk from your local baker. Powdered yolk can be stored in the refrigerator for several months. When you want to feed the yolk just dissolve a small quantity in a few drops of water and add to the aquarium or sprinkle it dry on the water surface.

Feeding Fry Frozen Food
Instead of hatching fresh brine shrimp nauplii for your baby and juvenile rainbowfishes every day, you might consider making frozen brine shrimp blocks and feeding these instead. First, hatch a large batch of brine shrimp. After hatching, collect the shrimp in the normal way and rinse with fresh water. Place the normal ration of brine shrimp for a tank into the well of an ice cube tray (plastic ones that make small cubes are best). Add fresh conditioned water to fill the trays and freeze. When it is time to feed the fish, just pop out a block and add to the tank. The ice will slowly melt and release the brine shrimp, feeding your fish. You can do the same thing with other types of live food.

Frozen food can usually be fed approximately 14 to 21 days' post hatching. A suitable homemade food can be made up using fish, shrimp, and/or squid flesh; chicken eggs, beef liver, and cod liver oil. The fry should be eating brine shrimp nauplii before feeding this food.

The recommended procedure for preparation is as follows: Thaw shrimp, squid or fish (if frozen), heat on high setting in microwave for 5 to 10 minutes per kilogram weight. Blanch liver in boiling water for at least 10 minutes. Homogenise with fish, shrimp, or squid in a food processor until well-blended (smooth texture with no chunks). Mix chicken eggs, cod liver oil, and then add to food processor. Add a binding ingredient (gelatine or agar) gradually, and continue mixing slowly until a paste is formed. Take the paste and place in a plastic ice cube trays and store frozen.

The frozen food can be finely grated with a cheese grater. This procedure will result in a mixture of particle sizes. However, depending on the size of the fry, you may require a certain particle size. To obtain a specific particle size, take a frozen cube out of the freezer, thaw and blend with water in an electric blender and manually pass the material through a sieve having a specified size. Drain the sieved diet thoroughly to remove dissolved particles that can foul the water and contribute to bacterial growth within the nursery tank.

© Copyright Adrian R. Tappin
Updated July, 2005.