A wide variety of seafood and vegetables sold for human consumption are of great use to the aquarist in feeding aquatic animals. Particularly rich sources of fish of all sizes and shellfish are the markets serving Asian communities in large cities. If you are not familiar with the species offered, you will likely be pleasantly surprised with some new favorite meals for yourself as well! You may even be tempted to purchase additional pets from the live wells and tanks that are often maintained in such shops, but this is usually a risky proposition. Although much less expensive in price than animals sold in pet stores, those that make their way to food markets are generally in poor condition due to rough handling. You may wish to boil and then freeze any fresh foods that you purchase, particularly if the food item comes from a different part of the world than does the animals to which it will be fed. Often times, microorganisms that cause few or no problems to species that have evolved in the same habitat can be devastating to creatures from other parts of the world.

Another effective method of eliminating parasites and other microorganisms from fresh foods is to soak marine food animals in freshwater and freshwater food animals in saltwater. Doing this for a half-hour or so will kill most potentially harmful organisms.

Many types of marine and freshwater fish and invertebrates relish vegetables and, less commonly, fruits. Kale, spinach, dandelion, cucumber, and zucchini are particularly favored. Most terrestrial plants contain a good deal more cellulose than do aquatic plants. This cellulose is, in general, indigestible to most fish and aquatic invertebrates. Therefore, you should break down the cellulose by soaking the vegetables that you use in hot water for approximately 5 minutes before introducing them into your aquarium. You will find that even the tiniest snails and shrimp will readily devour vegetables that have been treated in this matter. Be sure to thoroughly wash all green plants and vegetables before feeding them to your pets, so as to remove all traces of pesticides and fertilizers.

Naturally growing freshwater aquatic plants and marine algae are an excellent food source for your pets and should be utilized where their collection is legal. Be sure to wash them before use so as to remove potentially harmful microorganisms, or soak the plants as has been described in the section concerning fresh foods. Maintaining growing food plants within the aquarium will allow your pets to benefit from the plants' nutritional value as well as from their potential to produce oxygen and remove nitrogenous wastes. If your fish or invertebrates consume the growing plants too quickly, you may wish to culture the plants in a separate enclosure. Algae scrubbers are an excellent source of food for those keeping marine aquariums.