There is much debate as to the necessary frequency of feeding fish. It is important to know the reasons for this debate as there is no real consensus amongst fish keepers. (Note whilst this article talks about fish, most of it equally applied to other aquatic animals kept in aquariums.)
Overfeeding occurs when all of the food that is put into the tank is not consumed. The rule of thumb is that the food should be consumed within 1–2 minutes. The unconsumed food will sink to the bottom of the tank and begin to rot, adding ammonia to your tank. This condition can negatively affect the health of your fish by initiating a mini-cycle, stressing your fish. The sight of obese fish in peoples aquarium is very common.
Frequency of Feeding
Most aquarium owners feed their fish on a daily basis, or multiple times per day. This is generally considered an unnecessary amount of food, but there are exceptions which will be discussed below. One of the primary arguments for an every-other-day feeding regime is that a daily feeding is frequently more food then these fish would ever get in the wild.
An alternate method sometimes proposed as a compromise between the two schools of thought is to feed very small portions on a daily basis. This is thought accomplish the same goal, but will typically only work in a significantly understocked tank. This will not work on a over-stocked, or even a well stocked tank because a single (typically the dominant) fish will consume the majority. This could lead to starvation in some of your more timid fish.
Variation of Food
It is equally important to vary the type of food you feed your fish. No single food source can supply 100% of the amino acids, vitamins and protein. A good variety of food will ensure the animal has a healthy immune system and a long life. Studies with farm fish have shown that even feeding commercial fish food is not as good as live food . Many fish are opportunists and will eat dead fish flesh even herbivores. So perhaps consider adding a monthly treat of a piece of raw fish like Tilapia or Salmon flesh .
Fry almost always require hourly feedings of specialized food. Specific care instructions should be researched for every species of fry you are caring for. Some more uncommon fish do require daily sustenance, but these fish will not be typically found in your local pet store.
Many people considered feeding a fish every other day a healthier feeding regime because they feel it prevents a wide assortment of fish ailments. These claims are largely unsubstantiated as there is little to no evidence supporting or refuting the claim. It is however generally accepted that an every-other-day feeding regime is not harmful to fish.
- PFK publishes news article about how the use of low phosphorus diets is bad for fish, May 14, 2004, Matt Clarke
- PFK article on their Buyer's guide to health foods,30th June 2003, Matt Clarke
- PFK article on how Live foods produce better Koi, 1st April 2007, Matt Clarke. Paper - Jha P, Barat S and K Sarkar (2006) - Comparative effect of live food and manured treatments on water quality and production of ornamental carp, Cyprinus carpio var. koi L., during winter, summer, monsoon and post-monsoon growout experiments in concrete tanks. Journal of Applied Ichthyology 23(1): 87. doi:10.1111/ j.1439-0426.2006.00788.x
- BBC News published an article on the effects of fish being starved long term and then fed repeatingly. It appears to reduce their lifespan substantially. See BBC News article
- University of Glasgow article on food fluctuation here