It's not hard to feed a goldfish. Almost any brand of goldfish flakes will have what your pet needs. However, knowing about fish nutrition is a great way to pick out the best food for your fishy friends.
Proteins are import for your pet goldfish. Goldfish require protein for growth and development. Make sure you adjust the amount of protein for your pet's age. Younger fish need a greater portion of protein in their life; about 45 percent of their diet should be protein. Older fish require a smaller portion of protein in their diet, around 30 percent. Plant proteins are preferable to animal proteins, as they are more easily digested.
Goldfish get most of their energy from fat, unlike humans (on a good day anyway). About 5 to 10 percent of your goldfish's diet should be fat. Unlike protein, animal fat seems to be healthier for goldfish than plant-based lipids. Fish oil is a common ingredient that provides good fats for your goldfish. Since these fats come from salmon, not goldfish, it doesn't count as cannibalism.
Like humans, fish need vitamins to live. They even need many of the same vitamins humans need, like A, D, K and folic acid. Your goldfish can make some vitamins itself, and has to get the rest from its diet. If your fish lacks vitamins, the symptoms are sort of hard to nail down. They can manifest as anything from general tiredness to skin lesions. Fortunately, most fish flakes contain all the vitamins your goldfish needs. Try the occasional frozen or live treat if you have any doubt.
Minerals are pretty similar to vitamins, in that your fish needs small amounts of them to be healthy. Unlike people, fish can absorb many of the minerals they need right out of their water. They do need a few minerals, like magnesium, iron and zinc in their diets, but they need them in such small amounts that it's almost never a problem.
No Carbs, No Fiber
Believe it or not, goldfish need very few carbs and very little fiber in their diet, unlike humans. Fiber, sometimes called "bulk" or "ash" on the label of fish flakes, should be avoided. If fiber exceeds more than 10 percent of a goldfish's diet, it can make it hard for your pet to absorb nutrients by flushing the system. Likewise, carbohydrates -- including starches -- should stay under 10 percent. Excess carbohydrates can build up in the liver, causing disease in your pets.