Page 72 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

70 FRESHWATER FISH: BREEDING

Fish genetics

As fish have been spawned in aquariums over generations,
there has been an understandable tendency to select the
GENETIC MODIFICATION OF FISH
most colorful individuals for breeding purposes. For this
This controversial laboratory method for developing fish with
reason, many of the most popular tropical aquarium unusual characteristics originated in scientific research. By
introducing the luminescence gene from a jellyfish into the genetic
fish kept today are more brightly colored than their makeup of fish (a standard technique used to “visualize” genes),
wild relatives. Modern techniques have allowed the researchers created fish in which every cell in the body emitted a
green glow. Rice Fish that carry this jellyfish gene, pictured below,
development of varieties to be taken to new extremes, were developed in Taiwan during 2001 as part of a medical research
program, but their commercial potential was quickly realized, and
with the first genetically modified fish now available. they became the first genetically modified aquarium fish available to
hobbyists. Subsequently, Zebra Danios (see p.76) that carry the
jellyfish luminescence gene have been developed at the National
The science of genetics is concerned with the way in University of Singapore as part of a scientific study into detecting
which characteristics pass from one generation to the next. environmental pollution. Trademarked as “Glofish,” they also went
The characteristics of all living organisms, including fish, on sale in pet stores in some parts of the US late in 2003.
are contained in the genes, which are carried on rodlike
structures called chromosomes, present within the nucleus
of every living cell in the body. Mutations (or unexpected
changes) in the genetic structure can occur and sometimes
result in a change to the fish’s physical appearance, such as
its color, patterning, or body and fin shape. When mutations
occur in certain cells, such as egg or sperm cells, the change
is passed to the next generation. Most mutations make only
subtle changes, which can be enhanced by selective breeding
(see opposite) over many generations. On occasions, however,
a mutation that creates a radical change can occur. The golden
coloration of the Butterball Angelfish (Pterophyllum sp. var.), for
example, resulted from a mutation that caused the loss of a
dark pigment that normally masks this yellow shade. Mutations A tremendous range of color forms of the Blue Discus (see
can also be harmful; this is clearly illustrated in very large pp.142–143) now exists. Naturally occurring color variants of the
wild Blue Discus have been enhanced and improved by selective
groups of fry, which may contain a few deformed individuals. breeding to create the domesticated strains of today.

Wild Discus Ghost Discus Tangerine Orange Discus

Relatively dull
body coloration

Vertical stripes
provide Vivid blue on the
camouflage sides of the body

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