PRODUCTION OF HIGHER POLYPLOID STRAINS FOR AQUACULTURE OF CYPRINIFORMES

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(1)Induction and performance of hexaploid loaches : Hexaploid (6n) loaches were produced by inhibiting the second polar body release after fertilization of diploid (2n) eggs with 2n sperm of a natural tetraploid (4n) line. Hexaploid loaches generated 3n gametes. Egg sizes of 6n were larger than those of 4n and 2n loaches. Hexaploid, pentaploid (5n), and tetraploid lines were produced by fertilization of eggs of 6n loaches with sperm of 6n, 4n, and 2n loaches, respectively.(2)Performance of tetraploid. triploid, and diploid loaches : In communal rearing condition, 2-year-old triploids (3n=2nx4n) showed better growth than 4n and 2n. However, in three-year-old fishes, tetraploids (4n=4nx4n) were smaller than 3n (=4nx2n) and 2n (2nx2n). Gonadal development of 3n was suppressed. Proportion of head length to body length in 4n was larger than those in 2n and 3n.(3)Performance of hexaploid, pentaploid, and tetraploid loaches : In 1-year-old fish, pentaploids (5n=6nx4n) gave better growth than 6n (6nx6n) and 4n (6nx2n). In communal rearing condition, growth of 3-year-old hexaploid was poor ; about half body weight of 5n and 4n loashes. Hexaploids and pentaploids gave 1 : 1 sex ratio, but tetraploids were all-female. Proportion of head length to body length in 6n was larger than those in 5n and 4n.(4)Unreduced eggs in loaches : Triploid (2nx4n) loaches gave unreduced 3n eggs. First generation of triploid gynogens induced from such eggs also produced 3n eggs, but a small number of aneuploid (1.5n) eggs were observed. DNA fingerprinting revealed that second generation gynogens induced from these unreduced eggs were aclonal, but genetically very similar. Diploid loach which generated unreduced 2n eggs was also found in the wild population(5)Production of tetraploid crucian carp : Tetraploidy was induced in gynogenetic triploid crucian carp by incorporating sperm genome into eggs by means of cold, heat and pressure shock of fertilized eggs.