Egg and sperm production and quality of sharpsnout sea bream (Diplodus puntazzo) in captivity

Abstract

Egg production from captive-reared sharpsnout sea bream (Diplodus puntazzo) was monitored during the spawning seasons of 2003 to 2005, and sperm production during 2003. Spawning took place between September and December under water temperatures of 21.0–18.5 °C. Daily fecundity varied without a consistent trend and peak egg production occurred in October. Mean (±S.E.M.) number of spawning days per month was 20±3 in 2003, and 14±3 in 2004 and 2005. A significant (ANOVA, DNMR, P<0.01) drop was observed in mean total annual relative fecundity from 4.9±0.08 million eggs kg−1 female body weight in 2003, to 2.4±0.07 million eggs kg−1 in 2004 and 2005. Mean monthly fertilization success also dropped significantly from 81±1% in 2003 to 76±2% in 2004 and 78±2% in 2005. Annual hatching success did not vary significantly and was around 86±2%. Finally, 5 day larval survival decreased significantly from 85±2% in 2003 to 44±3% in 2004. The first spermiating males were found in August and sperm production continued until December. Mean total volume of expressible sperm was maximal in November (3±1 ml kg−1) and the gonadosomatic index (GSI) ranged between 0.6 and 2.0% in spermiating fish, reaching its peak in September–November. Sperm motility (%) remained unchanged during the season, whereas motility duration (6.2±1.7 min) and sperm density (2.7±0.2×1010 spermatozoa ml−1) peaked in October. Mean sperm survival ranged between 9 and 13 days during most of the spawning season, and decreased significantly to 5 days in December. The study suggests that egg production is stable for the first 3 months of the spawning season, with relatively unchanged egg quality. On the contrary, sperm production and quality peaks in the middle of the reproductive season in October.