Feeding Program
The essential requirement for successfully raising rainbowfishes is the implementation of a suitable feeding regimen for the larvae. Using the following feeding program, the survival of rainbowfish larvae can be as high as 80–95%. Begin feeding with small amounts of infusoria. The term infusoria is a collective name for many micro-organisms and can include paramecium, unicellular algae, ciliates, bacteria, protozoans, desmids, rotifers, and a host of other small organisms. Rainbowfish larvae will also benefit from the addition of small amounts of phytoplankton (greenwater).
It is well known that phytoplankton (microalgae) contain an array of essential nutrients that help the growth of rainbowfish larvae. Providing natural greenwater with infusoria as food for the newly hatched rainbowfishes has several advantages. The larvae are easily able to switch to different sized prey, a feature not present in monocultures of organisms such as rotifers or brine shrimp. Greenwater also enables the “infusoria” to feed on resident algae and bacteria, thus retaining their nutritional value for greater periods of time. Feed 5−10 ml (per 20−50 fry) of infusoria suspension three or four times per day. You can tell if they are feeding well as the larvae should have nice “swollen stomachs” after feeding.
Starting on day 7, depending on size, you can begin introducing small amounts of newly-hatched brine shrimp nauplii and/or microworm. The feeding of rainbowfish larvae on the brine shrimp nauplii will be very inefficient at first; so add just enough such that the fry will encounter a small “cloud” of nauplii for a few minutes in the water column. Do this each time you feed brine shrimp nauplii to older fish. Observe fish closely after feeding. Once you can see that the fish have been successfully taking the brine shrimp (their bellies will be orange), add more with each feeding. Never add so much brine shrimp that more than 10–20% of it dies in the tank. Brine shrimp will accelerate growth so it is important to commence feeding as soon as possible. The smallest larvae will continue to eat the infusoria while the larger ones will start feeding on the brine shrimp nauplii or microworm.
Gradually increase the proportion of brine shrimp nauplii or microworm and phase out the infusoria - this should be around day 14 to 21. Continue feeding the juveniles 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. 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. Commence feeding adult foods as soon as the juveniles are big enough to eat it and feed them often (at least twice daily).
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. The powdered microalgae Chlorella and Dunaliella that are sold in most health food stores can also be used as aquarium food supplements.
The growth rate of the rainbowfish larvae is generally slow, with little variation until after 14 days. After that time growth rates increase. However, considerable variations in growth rate are frequently observed. Adequate food and suitable temperature generally results in higher growth rates. Lack of food during early development leads to appreciable variation in growth (length), if compared to larvae offered food ad libitum. Beside effects on growth, a decline in mortality between larvae receiving inadequate amounts of food and well-fed larvae has also been observed.
It should be noted that the hatching of eggs might vary, resulting in the presence of larvae at different stages of development. As the larvae increase in age, the variation in length between individuals also increases. To raise the entire spawning, you may have to sort the growing fish by size. Size grading separates the faster and slower growing fish and will allow the smaller fish to grow better due to the reduction of competition and social hierarchy. When these smaller fish are transferred to another tank, their growth rate is no longer negatively impacted by the faster growing individuals. They should increase their growth rates to compensate for the initial retarded growth rates that developed during the nursery phase.
It is best to maintain fish of similar size in the culture tanks to improve the utilisation of food. Size-grading at an early age results in better growth than at a later stage when social structures may have already developed. In addition, a high fish load can retard the growth of juveniles, probably due to release of growth-inhibiting substances. For maximal growth keep the number of fish per aquarium low and avoid overcrowding.
Uneven larvae growth can also lead to cannibalism. Uneven larvae growth rates means that some will quickly reach the size where they are capable of ingesting other, smaller larvae. Rapidly growing larvae have a high food intake requirement. If that need for food is not satisfied by supplemental feeding they might start looking for extra food sources such as their smaller siblings. It is believed that larger larvae are also more aggressive and successful at feeding when supplementary food is added. This then gives the larger larvae a further growth advantage. The main way to control cannibalism is with regular size grading. This is the single most effective method for reducing cannibalism. Also, if the fish are fed regularly and sufficiently, it reduces the number of fish that are hungry and may decrease the cannibalism on their siblings. If you have a batch that differs greatly in size, you will often find that the smaller ones are females.
General maintenance includes daily siphoning of the aquarium to remove any uneaten food and faeces, and 25−50% waterchange at least one a week. The continued growth and development of the fish will vary from one hobbyist to another and is largely conditional upon captive environmental conditions such as temperature, water quality, and feeding regime. Sexual differences begin to appear between 9 and 12 weeks after hatching with sexual mature at 6 to 12 months.