Goldfish are omnivorous, feeding on both plant and animal matter, and they need a well-balanced diet in order to grow and remain healthy. For this they will depend upon their environment, but also upon their keeper to a great extent.
Fish require correct amounts of good-quality food containing essential ingredients, consisting mainly of proteins, carbohydrates, fats, vitamins and minerals. Certain of these can be stored by the fish and used as required, but many need to be consumed regularly: for example, the proteins (amino acids) that are used in building tissues. Likewise, not all vitamins can be stored successfully: an example being vitamin C, which is essential for good health in fish as well as humans. In a well-planted-out garden pool, goldfish will be able to feed upon vegetable matter and live foods, but depending on the size of the fish population, these might have to be supplemented by another food source. In an aquarium, however, your goldfish will rely entirely on you for their dietary needs.
There are two main foods that are available, namely prepared foods and live foods. Live foods are by far the best, but it can be difficult to have a constant supply of these. There are many preparations that are available for goldfish and, although it is debatable, continuous feeding on prepared food can provide an adequate supply for all dietary needs, providing, of course, that there is plenty of variation in these.
There are many different types of prepared foods available, ranging from floating and sinking granules to flakes and freeze-dried preparations. If you are using any of these, you must remember that the same menu can become a monotonous diet that could possibly result in complications like constipation, which is seen quite often with fancy goldfish. It is also important to remember that fish are omnivorous and that in the wild they eat vegetable matter. You should occasionally provide either fresh, chopped lettuce or spinach, or readily prepared vegetable food, if available. Remember that prepared foods have a limited storage time.
Live foods are essential to maintain healthy fish, providing all and more of the important nutrients that are not available in prepared foods. They also aid digestion in the intestinal tract, which could be the remedy for a fish that has become constipated from being fed constantly on prepared foods.
Live foods – such as white enchytrae worms, tubifex worms, blood worms, earthworms, daphnia and brine shrimps – can all be obtained on a regular basis from your local pet shop, which will also have a supply of frozen foods. Raw meat and shrimp are also an excellent treat for your fish as long as they are thoroughly washed beforehand.