Genetic improvement of aquaculture finfish species by chromosome manipulation techniques in Japan
K.
Arai-2001
Aquaculture,
197 (1-4): 205-228
(Reproductive Biotechnology in Finfish Aquaculture
Oceanic Institute, Hawaii, USA, 4 - 7 October 1999
Edited by C.-S. Lee, E. Donaldson and N. Bromage)
Abstract:
The
purpose of this review is to introduce recent advances in research,
development and application of chromosome manipulation techniques in Japan.
Triploids have been induced and utilized to improve growth. In most cases,
triploids are produced as all-female populations by using spermatozoa of
artificially sex-reversed males, so as to assure their complete sterility.
In contrast, triploid males show better gonadal development and sometimes
generate functional spermatozoa, which give rise to inviable aneuploids in
most species. Although induced tetraploids can be useful for mass production
of triploids by mating with normal diploids, tetraploid lines have only been
produced in rainbow trout by a few institutes belonging to prefectural
governments. In most cases, the techniques to inhibit the first cleavage
often result in very low survival and mosaicism. In the loach (Cobitidae),
polyploid lines such as hexaploids have been developed by using natural
tetraploid individuals as an intermediate step. Cloned fish can be produced
by the second cycle of gynogenesis in the eggs of completely homozygous
diploids, which were produced by inhibiting first cleavage after induction
of gynogenetic and androgenetic development. The second cycle of
androgenesis, using spermatozoa of completely homozygous males, can also
generate clonal lines. The most serious technical problem of cloning is the
extremely low survival of homozygous gynogenetic and androgenetic diploids,
probably due to the expression of deleterious recessive genes and side
effect of treatments. However, cloned populations have been realized in
commercially important ayu Plecoglossus altivelis, amago salmon Oncorhynchus
masou ishikawae, coho salmon O. kisutch, hirame (Japanese
flounder) Paralichthys olivaceus, fancy carp Cyprinus carpio,
and red sea bream Pagrus major. In hirame, a practical method for
mass production of clones was proposed and better performance has been
reported in a heterozygous clone, produced by hybridization between two
different homozygous clonal lines. Repeated meiotic (polar body) gynogenesis
may be more practical than cloning from homozygous gynogens as a method to
generate isogenic lines. In meiotic gynogenesis, the proximal region of
chromosomes should be homozygous, whereas the distal region should be
heterozygous due to high rates of gene-centromere recombination.
Consequently, similar genotypes are predicted in the second and later
generations of gynogenetic progeny. Their isogenic nature has been confirmed
by minisatellite, microsatellite, and other DNA analyses. Gynogenesis,
androgenesis and cloning can be used for elucidation of genetic sex
determination. The involvement of environmental factors has been indicated
from the sex ratios of chromosomally manipulated populations of several
species. Finally, the regulation of chromosomally manipulated fish by the
guidelines and the integration of such techniques with molecular genetics
for further gene mapping and transgenics are discussed.