The relationship between the effects of UV light and thermal shock on gametes and the viability of early developmental stages in a marine teleost fish, the sea bass (Dicentrarchus labrax L.)

Abstract

To improve the efficiency of gynogenetic induction, the effects of UV light and thermal shock on gametes were investigated in the sea bass. Exposure of sperm to UV light (>/=15 000 erg mm-2) reduced the amount of motile spermatozoa, without affecting the duration of motility in the spermatozoa that remained motile. The Hertwig effect was elicited in eggs fertilized with sperm exposed to >/=35 000 erg mm-2 of UV light, indicating the inactivation of the DNA of the spermatozoa while retaining their ability to trigger development. Resulting embryos (24 chromosomes; one NOR) exhibited the haploid syndrome and died at hatch. Diploidy was restored in eggs fertilized with irradiated sperm by blocking meiosis II with a thermal shock (0 +/- 0.5 degrees C for 10 min, starting 5 min after fertilization). Resulting larvae ( approximately 35% survival at hatching) had 48 chromosomes, one or two NOR and no paternal chromosome fragments (gynogenetic diploids). In eggs fertilized with sperm not exposed to UV light, the same thermal shock induced 100% triploidy (72 chromosomes; one, two or three NOR), with 70% survival at hatching. Multifactorial ANOVA showed that, compared to external factors (sperm diluent, UV light and thermal shock), the contribution of broodstock to the viability of the early developmental stages was not significant (P > 0.05). Effects of the thermal shock were most evident after fertilization (30.7%) but disappeared (0%) at hatching, suggesting that the lower survival of triploids is a consequence of handling, not of the triploid condition per se. However, effects of UV light increased through development (42.5-69.7%), probably reflecting cumulative deficits in protein synthesis.