Ploidy Manipulation and Gynogenesis in Fishes: Cytogenetic and Fisheries Applications

Abstract

Manipulation of fish chromosomes dates back to the early part of this century. The earliest experiments involved induction of gynogenesis with sperm inactivated by radiation or chemical treatments. Temperature or pressure shocks applied soon after fertilization resulted in the retention of the second polar body and reconstitution of diploidy; triploidy resulted from shocks to fish ova fertilized with normal sperm. More recently, it has been possible to suppress the first mitotic division offish eggs with high-pressure or -temperature treatments applied at the time of first cleavage to produce mitotic gynogenetic diploids and tetraploids. Androgenesis has been successfully induced in fish by irradiation of ova, fertilization of eggs with normal sperm, and suppression of the first mitosis with high-pressure treatments. Gynogenetic diploids have been used for cytogenetic studies of meiotic phenomena and gene mapping. The general finding to date is that the arrangement of genes on chromosomes is highly conserved in fish genomes. Inbreeding in successive generations of gynogenetic diploids is not as rapid as was anticipated, due to extensive gene-centromere crossing-over and chiasmata interference. However, isogenic lines can be produced more rapidly from gynogenetic diploids than from inbred lines of normal diploids, which require many generations of sibmating. Mitotic gynogenetic diploids and androgenetic diploids are completely homozygous and similar to inbred or isogenic lines; they can be used to study genetic versus environmental effects on fish. Triploids are of interest because they are expected to be sterile, to grow faster than diploids as they reach the age of sexual maturity, and to live longer than diploids because of the biological costs associated with reproduction; however, results on the performance of adult triploidy have been equivocal. For some species, adult triploidy outperformed diploids in growth and other production characters, whereas the triploidy of other species did not possess superior performance traits.