Physical fishes

Physical fishes. Colors of fishes. Black pigment cells, called "melanophores" because they bear the black pigment melanin, occur in almost all freshwater fishes except albinos and a few depigmented ("amelanic") cave fishes. When melanophores are placed near iridocytes or leucophores, which bear the silvery or white guanins, they produce structural colors of blue and green. These structural colors are often intense, because they are formed by the refraction of light through the needle-like crystals of guanin, when red and yellow wavelengths are absorbed by melanin. Think of the structural colors of changeable blue-green on some tropical butterfly wings; those colors are produced by diffraction-grating effects on the surprisingly intricate surface of wing scales, structures that are visible only with the electron microscope. On a fish, light is reflected back through successive ultra thinly-layered films contained within the dermis. Whether the colors appear variously iridescent or not depends upon the relative thickness of the layer and the interlaminar spaces. The giveaway is in the slight changeableness that depends on your viewing angle. A good example of a structural color is the black green of "Mossy Green" Tiger Barbs. This effect is called the "Tyndall effect" for John Tyndall (1820-1893), the British physicist who first explained the phenomenon. (I get stuff like this out of the Encyclopædia Britannica.) How melanin affects the colors that are produced by erythrophores is clear if you compare normal fish colors with their amelanic-- melanin-free "semi-albino"-- mutations in Tiger Barbs, "Rainbow" Shark-Minnows, Paradisefish, etc. Without melanin, brown becomes red or orange, olive green becomes gold.
 
Painted fish. This miserable Singapore practice, which began around 1980 with Indian glassfish Chanda ranga streaked with day-glo colors, is successful because people like us continue to buy fishes that have been injected with colorant or stripped of their slime coat and dipped or streaked with fluorescent dyes. An article by S. MacMahon and P. Burgess in Practical Fishkeeping March 1998, which described the injection of dye and subsequent exposure to Lymphocystis virus in painted fish was the impetus finally for a 2002 Australian consumer boycott of these practices, described by David Midgley at his website.
 
Keith Seyffarth wrote a good brief description of this practice while he was managing the fish department of a pet store in Bozeman MT. If you see painted or dyed fish in a LFS that has any pretensions to respectability, it's worth mentioning quietly to the manager (not to a salesperson) that it seems out of character for a store of such a caliber to be carrying such deceitful and low-end-of-the-market merchandise. Tell the manager that when you see painted fish, you wonder if there's any authentic difference between that store and a chain outlet. Don't lose your temper. Don't make the manager defensive. Just give the manager something to think about.
 
Growth-repressing hormones. Nernst posted at AC, Nov. 2000: "The growth-inhibiting“hormones” whose levels could be lowered with water changes are, in diminishing order of importance: Somatostatin, Norepinephrine, Serotonin, Nitric Oxide. Thyroid-releasing hormone and thyronines haven't been proven to have a direct relation; neither have estrogens/testosterones. There are of course other non-chemical things that affect growth, like stocking density and “social interactions” among fish." He gave the following references to publications: Peng Chun and Richard E. Peter, "Neuroendocrine regulation of growth hormone secretion and growth in fish." in Zoological Studies. 36(2). 1997. 79-89. Aubrey D. Uretsky and John P Chang. "Evidence that nitric oxide is involved in the regulation of growth hormone secretion in goldfish." in General Comparative Endocrinology. 118(3). June, 2000. 461-470. Hans A. Hofmann and Russell D Fernald. "Social status controls somatostatin neuron size and growth." in Journal of Neuroscience.  20(12). June 15, 2000. 4740-4744. Sameer R Phale."The neuroendocrine secretion regulates growth hormone release in teleost fish" in Fishery Technology. 35(1). Jan., 1998. 1-8.  H. Martin Oyama, E J. Sussman, K. Weir G C. and A.Permutt ."The biological activity of catfish pancreatic somatostatin." in Regulatory Peptides. 1 (6). 1981. 387-396. This article shows how somatostatin could be freely secreted via the gut into the surroundings.
 
Museum collections of fishes. The four largest American collections are these, in order of size:
 
1. U.S. National Museum of Natural History (Smithsonian), Washington: Division of Fishes. It's the largest ichthyological collection in the world.
 
 2. University of Michigan Museum of Zoology, Ann Arbor.
 
3. California Academy of Sciences, San Francisco: Department of Ichthyology
 
4. American Museum of Natural History, New York: Department of Ichthyology.