Nutrition plays a major role in keeping your fish healthy and showing their colors to their best advantage. There are many types of fish foods available for both saltwater and freshwater fish that provide basic nutrients. Offering the kinds of food that your fish would naturally consume will increase their activity and life span and help them adapt quickly to the aquarium environment. Supplements and homemade diets add vitamins and minerals that may be lacking in other foods and help acclimate fish with special requirements.
Fish can be categorized as one of three types: vegetarians, omnivores and carnivores. Vegetarians eat from plant sources only. Omnivores will eat almost anything from vegetable matter, insects, crustaceans and meat proteins. Carnivores eat meat only and almost always prefer live food initially, but can be trained to take other meat sources. It is best if you provide the foods your fish prefer for optimum health. In the natural environment, fish can spend a fair portion of the day browsing or hunting for food. Within the space limitations of the aquarium, the food sources they would normally encounter are limited. The hobbyist must provide appropriate quantities of the proper food for fish to thrive.
Fish such as mollies need a diet high in plant material and good quality nutrition can be provided in a number of ways. Prepared flakes, pellets or tablets formulated from vegetable sources are the most common diets offered. Be aware that large containers of dried foods can lose a lot of the nutritional value if used over a long period of time. If you have a small tank with only a few fish, buy a small container of food to prevent it from going stale. Offer your fish fresh greens. Spinach, romaine, lettuce, parsley, endive and arugula are good choices. Blanch a few leaves by placing them in boiling water for 30 to 60 seconds to soften them and then place them in the tank for the fish to nibble on for 1 to 2 hours. Do not leave greens in the tank. They will decompose quickly and foul the water. These green are relished by both freshwater and saltwater fish.
If you have a marine tank, and keep butterflies or tangs, algae is a requirement in the diet. To raise marine algae at home, a separate small tank should be set up near a window with a pump and airstone. Fill the tank with prepared saltwater and some rocks or coral skeletons. Algae will grow on the rocks and sides of the tank, which can then be offered to the fish by placing the rock directly into the show tank. DO NOT keep your show tank in the direct sunlight to grow algae.
These are the easiest fish to feed because their natural diet includes a wider range of foods. They will eat almost anything they encounter. Many types of commercially prepared foods are available and can be offered based on your fish's preferences. Flakes, pellets and tablets are often the staple. Freeze dried foods are readily accepted. These foods retain much of their nutrition and hobbyists find them more convenient than raising live food. Common foods include tubifex worms, bloodworms, brine shrimp and krill. Small portions should be offered as these foods expand and absorb water when placed in the tank.
Omnivores also appreciate some meat proteins, which can be offered in a variety of ways. Small bits of chopped beef heart, shrimp or fish fillets can be offered. Make sure to feed these items sparingly as leftovers will decompose and foul the water. You will soon get to know what your fish prefer. Frozen foods are a convenient option as well. They come prepared from a variety of ingredients and are frozen into individual packages. Small chunks are broken off, thawed in a little aquarium water then added to the tank. You can make your own frozen fish food by blending your own ingredients with some dissolved gelatin, pour into thin sheets and freeze.
Many marine fish require live food such as brine shrimp, mysis shrimp and rotifers, all of which can be raised at home with a minimum of fuss. Starter cultures are available at your local pet fish store. A large jar or separate tank with a heater and airstone is needed. Other food sources for omnivorous fish include cooked egg, earthworms, liver, yeast and oatmeal.
Carnivorous fish such as freshwater Oscars and piranha or saltwater fish such as lionfish or eels thrive on an all protein diet. These fish hunt live food and will consume their tank mates if they don't get a steady supply. Feeder guppies, minnows or goldfish are usual sources. Feeding live prey can introduce disease to the tank so it is beneficial to try and get your fish to accept prepared meat sources. Meat sources are cleaner, more available and less expensive than live food so it is best to get your fish to accept these substitutes. Beef heart is a good lean meat source. Introduce a small piece or two at a time; dangle it from a string or toothpick to attract attention. If the fish reject it, remove it from the tank. Do not feed carnivorous fish with your fingers.