The skin, scales and colors of fish
The epidermis is the top layer of the skin and covers the outside of the scales. It generates mucus, a sticky and gluey substance, which plays a protective role against external aggression (physical, infections, parasites) and acts as a lubricant to increase the speed of the fish. Just below is the dermis, which contains the cells responsible for color changes and the appearance of the fish.
These cells are either:
- Chromatophores : Colored with 3 pigments. Erythrophoric cells are orange-red chromatophores; the xantophores are yellow; melanophores are black.
- Guanophores: Contain guanine crystals, and are responsible for the metallic hues of fish.
- Iridophores: Polarize light on the model of a crystal or a prism.
The color of goldfish is influenced first by the environment in which they live, starting with the light. This is why goldfish raised in a dark environment (for example in a river or in a very deep basin) don’t have the most beautiful colors. Stress and aging can also make the color of fish fade (affects the contraction of pigments).
The role of scales
The scales of the goldfish are fixed like roof tiles. The scales grow as the fish does and are replaced if they are damaged but their number remains constant. A microscopic examination will reveal rings, somewhat similar to those of a tree trunk: they can also be used to determine the age of fish if they have been raised in a pond and therefore subject to seasonal variations in temperature (the rings are more spaced apart during the warm season since the fish grows faster during this period. On the contrary, spaced rings mark the winter season, when growth is slower). In the aquarium, the constancy of the parameters means this technique is not needed.