Fishes get their colors from pigment cells. Xanthophyll pigments are yellow, Melanin pigments are black and/or brown, Carotenoids are orange and/or red, Phycocyanin is blue. Fishes cannot produce some pigments such as carotenoids and xanthophylls, therefore it must come from their diet.
The common practice of fish food manufacturer is to lace the foods with artificial colorant or dye especially of the red kind. Once consumed by the fish, it will take the place of carotenoid pigments in the cells beneath the scales, thus displaying the red color. This artificial dye will wreck havoc to the endocrine and nervous system, both that influence coloration in fish. Because of this, the production of certain pigments such as melanin goes hay-wire and black and/or brown pigments will show up at the tail or some parts of the fishes’ body, making the fish look “dirty”.
The red dye pigments which some are bigger in size cannot be absorbed in the intestinal tract, thus blocking it. This will prevent other good nutritions from being digested. That is why it is common that heavily dyed fishes are stunted, unable to breed and grow much less than its fullest potential. It will also affect the reproductive system of the fish.
If the feces of the fish is reddish in color, this means that lots of artificial dye is in the food and cannot be digested and in turn, passed out. This is a telling sign that this food is using the “overwhelming” method to color the fish by pumping as much dye into the body of the fish. Some dyes will stick and some wont, the ones that stick will make your fish so-called red and pretty. The ones that don’t, will only make the water red and color the silicon glue or air pipes in your tank!
The best red colorant in its most natural form is astaxanthin from shrimps,krill or salmon fish. Astaxanthin also acts as an anti-oxidant 10 times stronger that beta-carotene and 100 times stronger than vitamin E.
For yellow color (xanthophylls) corn gluten meal and egg meal is recommended. Where as, for blue/green color, algae or seaweed is known to have the blue color pigments.
Fish coloration using hormones tricks the fishes’ system to belief a false early maturity. The hormone commonly used is Testosterone that allows a premature storage and expression of color pigments. Juvenile fishes do not have the maturity for storage capabilities of color pigments as compared to adult fishes. That is why most juvenile fishes are often pale in color.
If fed with food that contains hormones, the fishes will immediately “mature” to have capabilities to contain color pigments. These treated juveniles will show colors that will only naturally be exhibited by adult fishes.
Because of the false early maturity, the fishes stop growing and become stunted. Its reproductive organs will not develop properly, therefore the fish becomes sterile.