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Many problems can be encountered when feeding rainbowfishes in an aquarium. First, delivery of feed to fish in a water medium requires particular physical properties of feed together with special feeding techniques. It is not possible in the literal sense to feed rainbowfishes on an "ad libitum" basis. The nearest alternative is to feed to "near satiety" with a pre-determined number of feedings per day; however, this can be very difficult and subjective. Rainbowfishes will, however, easily adapt to a feeding schedule. In their natural environment, rainbowfishes will adjust their food consumption to satisfy their requirements. If the amount of food available decreases they will increase their food intake during feeding. In captivity, however, rainbowfishes have to rely entirely on the aquarist on the amount, as well as when and how often, they feed. This means that a dominant fish may be able to consume more feed than other less-dominant or smaller fish, which are held in the same aquarium. Being attentive to changes in appetite of fish is, nevertheless, a very important skill that aquarists must acquire.
Feeding frequency and timing is another factor that has been suggested as affecting feed intake and utilisation by rainbowfishes. On a weekly basis, studies have suggested that feeding the equivalent of six days a week resulted in growth performance similar to feeding seven days a week. Feeding five days a week resulted, however, in significantly less growth. There is no dependable evidence that daily feeding frequency and timing affect feed utilisation. The most important factor is to insure frequent and spaced meals to insure that the fish can consume enough feed to meet their growth potential. This generally means more frequent feeding for fish of smaller size.
It is obvious that food availability and abundance have important effects on reproduction. However, it is not always the case that more food is better. Therefore determining exactly how much food and how often to feed the fish in order to maximise reproductive capacity is important for optimising reproductive output. Feeding too little will result in decreased reproduction, while feeding excessively will increase the probability of having poor water quality problems, which can compromise fish health and create significant problems.
Rainbowfish feeding research (Badger, 2004) found that Melanotaenia splendida coped much better with lowered rations on a daily basis then infrequent feeding. From this study it may be deduced that it is not as important in this species to feed to 100% satiation every feeding as it is to feed every day. Although a 100% ration on a daily basis would still provide the best reproductive performance. These findings are important as it is necessary to know how often and how much to feed the fish in captivity.
Knowing how much to feed rainbowfishes without overfeeding them is a problem for most aquarists. A rule-of-thumb is to feed the fish all it can consume in 5 to 10 minutes. Unfortunately, this method can easily lead to overfeeding. Rainbowfishes always seem to be hungry; you can feed them, and five minutes later they will look at you as if they are starving. This is because the fish have learnt to associate you with food and get excited whenever they see you. It is necessary to understand about conditions in the wild to appreciate why rainbowfishes have this behaviour. Food is a limiting resource in nature and it is rarely available in excess quantities. The individuals that survive are those best able to acquire this limited resource. Rainbowfishes are opportunistic and feed whenever they can find food. It is neither necessary nor advantageous in the wild to control their appetite.
Water temperature also directly influences the desire of rainbowfishes to feed. Being poikilothermic animals, the metabolic rate, growth, energy expenditure, and feed intake are highly influenced by water temperature. In tropical waters, which have prevailing high temperatures, rainbowfish generally grow faster, mature younger, and have a shorter life span than rainbowfishes in temperate waters. It is, therefore, important to understand how water temperature affects these parameters. When temperatures drop below 20°C, rainbowfishes will consume less food so reduce the feeding rate accordingly. During cold weather conditions, it is best to feed late in the afternoon when the water temperatures have had a chance to elevate during the day.
Most rainbowfishes require a feeding ratio of about 5~10% of their body weight daily and ideally, should be fed this amount in four or five smaller feeding's during the day. However, knowing the weight of your fish is not practical, so feed sparingly, and supply enough to give three to five minutes of continuous feeding per meal. The amount of food required depends on the type of food, aquarium conditions, and individual fish. Juvenile rainbowfishes consume a higher percent of their body weight per day than do adult fish. Newly hatched larvae need to feed continuously. Research has shown that juvenile rainbowfishes will grow faster if fed three or four times a day. Feeding several times a day can also reduce problems of feeding dominance among juveniles of different sizes. Multiple feeding's also spread the waste load on the biofilter.
Feeding is also the best opportunity for you to observe the overall vitality of your fish. Poor feeding response is a signal that something has gone wrong in the aquarium. Check all aspects of the system particularly water quality, and look for signs of disease or stress.
Literature
Badger, A. C. (2004) The effects of nutrition on reproduction in the Eastern Rainbowfish, Melanotaenia splendida splendida. Masters (Research) thesis, James Cook University.
© Copyright Adrian R. Tappin
Created July, 2005.
Updated December, 2008.
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