What type of food can I feed to my fish to help them grow faster?
I have goldfish, sharks, and bluegold fish.
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As long as you're feeding your fish an appropriate diet and keeping them in healthy conditions -- with adequate filtration, enough space, good water parameters, and so on -- they'll grow as quickly as they're meant to. If your fish don't appear to be thriving, a poor diet is one possibility, but it's not the most likely culprit: the nutritional balance of most prepared fish foods is usually fine.
Most fish in the pet trade are omnivorous and don't have a single "best" food. In the wild they'll eat insect larvae, random eggs, little worms, algae, aquatic plants, whatever they can find. The name-brand general diets you'll find at your fish store are usually formulated to meet their nutritional needs. (If you're interested in what those actually are, you can learn a lot about the topic in this guide to preparing your own fish food.)
Assuming the sharks you mention are something like bala or rainbow sharks, and that the bluegold fish is just a variety of goldfish, you're not keeping anything with a particularly odd diet. But be aware that some fish in the trade are basically herbivorous and need a lot of plant matter, either through algae wafers or lightly steamed vegetables; others are more carnivorous and need live food or even meat of some kind. So always make sure you understand the broad dietary needs of your fish before you plan out their diet.
Make sure the food you buy is the right size for your fish to eat, and that it'll reach the part of the water column where your fish prefer to feed -- no floating sticks for corydoras, for example -- and that it's not a cheapo no-name brand. I prefer pellets, since they're neater and I suspect that flakes leech their nutrients into the water too quickly. Most frozen or freeze-dried whole foods (tubifex, bloodworms, baby brine, etc.) are best as occasional supplements rather than day-to-day staples, since they're not as nutritionally balanced.
You'll see special diet foods for goldfish, but to be honest, goldfish are such generalists that I suspect this has more to do with marketing than with providing something unique that's lacking in other products. And the "color improving" formulations you'll see usually just have carotenoids or other cosmetic color enhancers added, and aren't necessarily any better for your fishes' health. But I don't know of any reason not to get those products, and don't personally avoid them.
(One exception to this is that I would not feed freshwater fish a product labelled specifically for saltwater fish, or vice versa, since they actually do have different nutritional needs.)
The other half of the equation is the living conditions your fish are kept in. Make sure they've got enough space, keep the tank clean, and stay on top of water changes and other maintenance. Since you're asking about how diet impacts growth, be sure you do not give in to the temptation to overfeed. Your fish, especially your goldfish, will eat whatever you give them, but this is no more healthy for them than it would be for us -- it can lead to issues like constipation, weight problems (or whatever you want to call it when a neutrally-buoyant animal has too much body fat), renal problems, liver problems, swim bladder problems, just about every kind of internal fish problem. It also impacts your overall system as the increased amount of fish waste puts stress on your biofilter, and the increased amount of rotting food and detritus promotes bacterial and parasite growth.
"Sharks" are a nickname for several freshwater aquarium fish, you need to be more specific about what the exact species you have before anyone is going to be able to help you with them.
That said, the speed at which goldfish grow tends to be limited by tank conditions more than their feed, and thus products at your local pet-store of favourite online retailer labelled "goldfish food" should prove sufficient, although general fish food is likely also fine.
The most common growth limiter for all fish is stress. Stress leads to increased levels of epinephrine and norepinephrine which stunts growth in all animals. Common tank conditions that cause stress are dirty water (high organic particulates), low oxygen, high nitrate and/or ammonia levels, poor pH, improper temperature, over crowding, and the presence of chlorine. These things need to be controlled for all fish in your tank, and are best handled via proper tank sizing, proper filtration, and water pre-treatment.
There is another, non-stress related tank condition that specifically affects gold fish, and that's hormone levels. Unlike other fish related by products which can be easily filtered, goldfish secrete the hormones GABA and somatostatin which report back to them about the amount of space available in a tank. More goldfish or less space = higher hormone concentrations and thus smaller, slower growing fish. If you want your gold fish to grow faster give them the largest volume of space per fish (use multiple tanks if needed) possible and replace the tank water often.
For a full review see here: http://injaf.org/articles-guides/do-fish-grow-to-the-size-of-their-tank/