Would you buy Fruit Tetra ?

Since the law does not require them to show how any product is manufactured, the same goes for fish. They have no need to show the fish is a product of (dye) injection.

If you have paid attention to Walmart's fish section, you might have seen those colorful little fish in the following picture.

These colorful little fish are called glofish. They are in fact a product of injecting jellyfish DNA into the eggs of Zebra Danio. Walmart also found no need to tell people they are genetically engineered. I guess most people won't care either.