Over the years we’ve featured a myriad of “koi” aberrations, which mostly seem to inflict large fully grown adults of the surgeonfish genus Zebrasoma, as well as the dwarf angel genus Centropyge. While not always aesthetically pleasing, from a genetic and fish geek point of view, this phenomena warrants much study and curiosity. Here we see this koi pattern showing up on a Ctenochaetus tang, as well as a Pseudochromis.
Putting aside the distasteful appearance (to each their own; personally I find these fascinating), here’s what we know so far. Most, if not all koi aberrations we see occur in adult sized fish. Large piebald or tricolor or koi Zebrasoma tangs usually occur as fully matured specimens. We’ve seen this affecting Z. flavescens, Z. scopas and Z. xanthurum. Acanthurus tangs occasionally sport this koi aberration as well. Another genus that is commonly inflicted by the koi aberration is Centropyge, the dwarf angelfishes. We’ve seen this in C. eibli, C. bispinosa, C. nox, C. tibicen as well as C. multispinnis. Scattered and isolated reports of koi colored fish in other families have been reported as well such as Butterflyfishes, and other large Angelfish.
Another highly unusual trait that we currently know is that this koi pattern is transient. None of these koi aberrations are able to keep their colors and patterns to the fullest degree after capture. Two phenomena are documented to occur in such fishes. The first scenario involved the koi patterns and colors “changing” with time. The patterns shift, the colors change, but the fish never or seldom ends up looking like how it did initially, but still retaining some or majority of its aberration. The second scenario involves the pattern reverting to normal wild type coloration associated with the particular species fully with time.
What we do not know is why these fishes attain such coloration in the first place? Why are they usually found on large matured specimens, and lastly, why do the colors morph or revert in captivity? Looking at things beyond the perspective of beauty puts things in a new light. If you know, or happen to know someone who knows, or have an idea why these koi fishes are as such, do leave your thoughts in the comments.