The frequency and quantity with which you should feed tropical fish is dependant on the amont, species and size of the tropical fish you are keeping. Small fish such as tetras and guppies should be fed more often that the larger fish, two to three times per day, with small mouth sized food is best for these fish. Feeding them too much or too often will lead to more food passing straight through, ending up as feases and increasing the detrius as well as the eventually the amonia within your system placing strain on your filtration system.
The larger fish within your aquarium will fall into 2 generalised categories, predatory and non predatory fish. Large predatory fish like Pike barbs and piranas, should be fed in a manner that will replicate their behaviour in the wild whereby they would eat few larger meals. For such fish once a day or even more infrequently with frozen or dried foods is best. For the largest specialist predatory fish live foods should always be fed such as frozen fish as dried food will not contain the correct micronutrients. Non predatory fish shoul be fed a couple of times a day with frozen or dried foods.
Temperature also affects the amount of food fish will eat with their metabolic rate increasing with temperature. The warmer the aquarium temperature teh more food will be required, althogh the problem with this is that the more they eat the more oxygen will be required and thus efficiant oxygenation must be created for fish which require higher temperatures.
When transporting fish they should not be fed for a dayor two beforehand as doing so will increase amonia in the transport housing due to feaces within the water.