Viability, growth and external morphology of meiotic- and mitotic-gynogenetic diploids in red sea bream, Pagrus major

Abstract

Two types of gynogenetic diploids were artificially induced in the red sea bream (Pagrus major Temminck et Schlegel), either by suppressing the first cell cleavage (mitotic-G2N) or by retaining the second polar body (meiotic-G2N). The eggs of red sea bream were inseminated with UV-irradiated (3000 erg mm−2) sperm of Japanese parrot fish (Oplegnathus fasciatus Temminck et Schlegel), and hydrostatic pressure shock of 700 kg cm−2 for 5.5 min at 46 min after insemination (mitotic-G2N) and cold shock of 1 °C for 30 min at 3 min after insemination (meiotic-G2N) were applied to the eggs, sequentially. The total hatching rate and hatching rate of normal larvae of the normal diploid, meiotic-G2N and mitotic-G2N were 86.5 and 94.9%, 38.1 and 45.8%, and 12.8 and 35.0%, respectively. The induction of mitotic-G2N was confirmed by isozyme marker analysis. The standard deviations, variances and coefficients of variation of the body weight, standard length and body depth in 91-day-old juveniles were always large in mitotic-G2N, small in normal-2N and intermediate in meiotic-G2N. The variances in the number of pectoral fin rays and caudal fin rays of mitotic-G2N were significantly higher than those of normal-2N. The incidences of deformities were highest in the mitotic-G2N group. The survival rates and growth performance of the meiotic- and mitotic-G2N were significantly lower than those of normal-2N. Both G2N survived for 3 years to the adult stage.