Silvery fish are extremely prevalent in the entire ocean. From small species of lake chub to the largest barracuda and the most aggressive needle fish, silver seems to be the preferred “choice” of color for most types of fishes. But is there an actual reason behind this fact? What makes silver more of a benefit from an evolutionary standpoint and why do some fish actually change their coat to silver in some circumstances? The answer may be simpler than you think.
Probably the most important significance of silver coats on fish is that they are actually able to make predators and prey less distinguishable than bright colors. Like a type of camouflage coat, silver skin makes it easier for a fish to remain unnoticed. This happens due to the fact that the color itself, as well as the specific ways in which the skin, fins and layers of scales grow on fish species such as barracuda, coho salmon (jacks) and Atlantic spadefish act to prevent the polarization of reflected light. Predators like spadefish and barracuda use this strategic advantage to sneak up on their prey, while silver salmon and chubs are able to fool predators more easily, since many of their predators have polarization-sensitive vision that can be bypassed by this reflection trick.
Although silver is a common color in the ocean, it is by no means a sign of sameness. In fact, the diversity of fish species with silver skin and their anatomical differences are quite staggering. Coho salmon males, also known as jacks, are only silver when they enter the ocean. As they migrate from fresh water to salt water, this “move” of camouflaging themselves for protection becomes far more imperative due to the more prevalent presence of predators. Some species of barracuda, on the other hand, only feature silvery sides, and their skin has largely developed in order to make them less easily detectable by both prey and predators – since they often compete for food with larger species of fish, as well.
Silver fish can be both on the attack and on the defense side, some species being targeted by sharks, dolphins and other large fish and sea mammals, while others – like the barracuda and needlefish – are fast and powerful predators that can sometimes take down fish that are much larger in size than they are. Jacks commonly make the transition from the ocean to freshwater to spawn more frequently, developing a less pronounced pink color during the breeding phase, while retaining their silver skin in the ocean phase to avoid attackers. Fallfish and other species of chubs retain a predominantly silver shade even while living in freshwater areas, preferring fast currents and being easily able to evade larger, slower predators.
Some types of silver fishes have been found to develop two distinct types of guanine crystals as part of their scales. According to researchers, these crystals are largely responsible for neutralizing polarization when the fish reflect sunlight, and have played a significant role in their evolution. Another significant trait of silver fishes is that some species, including barracuda, chubs and jacks, are commonly known to adapt to their environment by changing their camouflage, in some cases even becoming a distinctive sign for different activities, such as hunting or reproduction.