You should feed the RTC everytime he becomes really active and displays "prowling" behavior (the instinctive behavior that kicks in when the fish is very hungry), young RTC's need a lot of regular meals.
RTC are facultitive piscivores, that is, while they have evolved to catch and eat small fish, they also eat a variety of other small animals as well. A good RTC diet should thus contain more than just feeder fish- you should try feeding your RTC crayfish/lobsters, crabs, prawns, earthworms, bloodworms, mussels, and other meaty foods. Many will also take frozen whitebait and lancefish as well.
One of the many keys to good health in RTC is to give them a varied diet

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The main disadvantage of using live fish as food is the risk of introducing parasites and bacteria into the aquarium. Cheap, mass produced fish, especially goldfish, are maintained in squalid conditions. Mortality, even when these fish are kept as pets, is high. While one goldfish might only pose a small risk to a predator, the risk is cumulative over time. So if you feed a predatory fish a goldfish once every two or three days, even after only a few months the chance of infecting your pet fish with something nasty is virtually a certainty.
A second disadvantage is nutritional imbalance. Goldfish in particular are fatty and are not a healthy staple diet for most piscivorous fish. In the wild, piscivorous fishes will take a wide range of species, some herbivorous, others smaller predators. This means that the piscivorous fish will be able to obtain a correspondingly wide range of nutrients. Simply feeding one species of feeder fish is both unnatural and very likely unhealthy. This problem can, to a degree, be mitigated by "gut loading" feeder fish (see Best Practise, below). By contrast, flake and pellet foods have been carefully formulated to provide a perfect diet for fish. While it might seem monotonous to us, these prepared foods are actually the best all-round diet for most fish.
A third disadvantage is that some feeder fish (notably goldfish and rosy-red minnows) contain large amounts of the enzyme thiaminase. This breaks down thiamin (vitamin B1) and over time this will lead to serious health problems.