Induction of all-female triploids in grass carp (Ctenopharyngodon idella) by integration of hormonal sex inversion and ploidy manipulation.
The herbivorous grass carp (Ctenopharyngodon idella) is an important species for controlling nuisance aquatic vegetation. In the present study, chromosome-set manipulation and hormonal sex inversion were integrated to produce monosex females and males and sterile female triploids. The albino grass carp (AGC) served as a recessive genetic marker for induction of gynogenesis and androgenesis. Sperm of common carp (Cyprinus carpio) or golden tench (Tinca tinca) were examined as activators of albino eggs for gynogenesis. Eggs of common carp and wild-type colored grass carp were tested for androgenesis of AGC. Early shocks (0.15-0.2τ0) were applied to obtain the desired ploidy level in meiotic gynogenesis and triploidy and late shocks (1.6-2.2τ0) in mitotic gynogenesis, androgenesis and tetraploidy. Pressure, heat, and cold shocks at several intensities were examined. Meiotic gynogenotes were obtained (200-600 individuals) in all experiments using UV-irradiated (800 J/m2) sperm of common carp. The highest survival of gynogenotes was obtained from eggs shocked by heat (40±1°C/2 min). In 1994, a group of fish was hormonally sex-inversed with androgen implants. Sex-inversed females (neomales) served as donors of X-bearing spermatozoa for the production of female monosex populations. The timing of late shock, required for induction of androgenesis and tetraploidy, was defined through induction of mitotic gynogenesis. Mitotic gynogenotes were produced by exposing activated AGC eggs to cold shock for different durations (10, 20 and 30 minutes). The survival and hatching of mitogynotes were inversely related to the duration of the shock. Androgenesis was induced in UV-treated eggs of common carp and wild-type colored grass carp, fertilized with intact AGC sperm. Only two diploid albino androgenetic fish survived more than one year. Female (XXX) triploids were produced by fertilizing AGC eggs with sperm of AGC neomales, then shocking them early to retain the second meiotic polar body. The use of neomales provided a mechanism for commercial-scale production of sterile (XXX) all-female AGC. So far, trials to induce tetraploid AGC using cold shocks have failed. Fluorocytometric examination was applied to assess the DNA contents in samples of ploidy-manipulated larvae and fish. Due to the highly applicative importance of tetraploid broodstock, we intend to continue our study on tetraploidy.