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 Mar 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.
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."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."
GeneralComparative Endocrinology. 118(3). June, 2000. 461-470.
Hans A. Hofmann and Russell D Fernald. "Social
status controls somatostatin neuron size
and growth. Journal of Neuroscience. 20(12). June 15, 2000. 4740-4744.
Sameer R Phale."The neuroendocrine secretion
regulates growth hormone release in teleost
fish" 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."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. It's the
largest ichthyological collection in the
world. Website is www.nmnh.si.edu/vert/fish.html.
