from Lemon
"A very unusual yellow Holacanthus angelfish has turned up at B-Box Aquarium which is not quite a queen angelfish although it does bear some traits of the Rock Beauty angelfish, Holacanthus tricolor. The Queen Angelfish (H. ciliaris) is a staple import from the Atlantic. Fully grown adults are typically blue-green with hints of yellow. Adorned with long trailing filaments and a blue crown on its nape, the common name is aptly quite fitting for this fish. The beauty and grace coupled with its relative ease in captivity makes it arguably the representative member for the Holacanthus genus.
Hybrids and aberrations for H. ciliaris do naturally occur. The species readily hybridises with H. bermudensis in the wild, giving rise to the familiar Townsend’s angelfish. H. ciliaris also very rarely form hybrids with H. tricolor, with only a few specimens ever seen. As with hybridization, aberrations within this particular species is not abnormal. The most famous examples of aberrant Queen Angelfishes are perhaps those from St. Paul’s Rocks in Brazil. Specimens there run the gamut from being pure blue, resembling the Clipperton Angelfish, to all Yellow, all white, Koi, and practically anywhere in between.
The yellow Holacanthus that you see interlacing this post was recently acquired by B-Box Aquarium in Japan. The highlighter yellow colouration of this individual is truly spectacular. Specimens that are typically bright yellow like this are usually xanthic morphs with abnormally yellow colouration. Such individuals tend to revert back to their natural colours after awhile in captivity. However, with the existance of amazingly mutated Queen Angelfishes living in St. Paul’s Rocks, the possibility that this sub-adult individual could be a waif from some far flung isolated reef in the Atlantic is not all that impossible."
"One of the issues with ‘Koi’ and xanthic fish, is that they often change with time in the aquarium; in some cases reverting back to a classic color scheme more in keeping with their kin. Unusual color morphs, being rare and in turn highly desirable, do not always make for good value for money, if your prized mutant is going to change back to a bog standard example of its species!
This being the case, we must look past striking and stable genetic mutations like true piebaldism, and instead question environment, and possibly the specific physiological factors affecting the aberrantly colored individual, as in the case of a fish with vitiligo!
The most frequently encountered color pigments in fish are melanins, carotenoids, and purines. Purines (mostly guanine) are structural colors- crystalline substances that produce the sheen and reflective qualities of fish skin through interplay with light. But it is the melanins and carotenoids that give us the range of yellows to blacks when found in different combinations.
The production of these pigments would be down to the fish’s diet, while the utilization of these pigments is controlled by the fish’s nervous and endocrine systems. The chromatophores, pigment holding cells in the dermis, dictating the spread, or concentration of pigment in localized areas, respond to environmental, and in turn hormonal cues.
Therefore, perhaps fishes sporting ‘Koi’ coloration have a combination of dietary deficiency contributing to loss of one ‘channel’ of color pigmentation, or localized disruption to areas of chromatophores? In people, vitiligo manifests in the loss of melanin in the skin, but in the skin of a fish, with a greater interplay of pigments, perhaps we are seeing a greater variability of outcomes.
Stress, illness, physical trauma, or some other environmental factor, could be leading to the muting, so to speak, of part of their color scheme? Drop out the melanins from a multicolored fish, and we are left with a xanthic individual. Drop the carotenoids and adjust the purines, and we can encounter the blue morphs, most commonly seen in C. bicolor, C. bispinosus and C. potteri.
This could be the reason why the ‘Koi’ coloration is unstable, and changes or reverts over time. Environmental factors are subject to change and often in a state of flux, whereas in a condition like piebaldism, there is a genetic blank, with unpigmented areas left barren indefinitely. A fish with a most human-like case of vitiligo, may, like the aberrant Centropyge, exhibit white patches. But other fishes, tricolor scopas tangs spring to mind, may be showing symptoms of a different magnitude, but of the same condition.
One suggestion as to why angels have adopted a xanthic coloration has been offered due to breeding. Of course many species of fish take on nuptial dress, but it was suggested (by F. Walsh in the Debelius, Tanaka, Kuiter, 2003 book on Angelfishes) that aberrant xanthic morphs of Centropyge bicolor appear at certain times of the year during the peak of spawning. However, if this was the case, surely aberrant individuals would be more greatly noted?
It seems unlikely that such unusual nuptial coloration would manifest in just a handful of individuals, in just a few species of what could be considered a closely related family. However, perhaps collecting pressure, having removed specimens that kept to an archetypal colour scheme, has left fish that display less than perfect colors to breed, raising the percentage of potentially aberrant genetics, and the propensity for a particular fish to exhibit variable coloration.
This theory has been put forward as to the apparent increase in aberrantly colored surgeonfish, and is certainly a plausible one in that case. I think it would be really interesting if the abundance and collection of these fishes, with their appearance in the trade, was noted, against data on their spawning activity, as this seems a good area for study.
In regards to my London piebald angel, we are still unsure as to what species it actually is. C. flavissima is typically a bright lemon yellow fish with blue highlights around the eyes, fin margins and operculum. There seem to be remnants of these on our aberrant individual. At the same time, there is a strong argument for it being a C. heraldi, due to its facial profile, as well as the eye coloration. There is even the possibility of a C. flavissima x heraldi hybrid, upon which case, in regards to colouration, anything goes. It has certainly been observed that female C. flavissima change color to almost white during courtship and spawning.
In the case of this aberrant individual, the strong white patches, if caused by piebaldism, should remain that way. In the case of fish vitiligo, they may spread! Only time will tell. As so often is the case with these Centropyge color morphs, only time will tell."
from Jane
