Dose-dependent spawning response of mature female sea bass, Lates calcarifer (Bloch), to pelleted luteinizing hormone-releasing hormone analogue (LHRHa)

Abstract

The induction of sequential spawnings of mature female sea bass following intraperitoneal implantation of various doses of luteinizing hormone-releasing hormone analogue (LHRHa) in a 95% cholesterol pellet was investigated. LHRHa stimulated a dose-dependent increase in spawning rate (number of spawnings per fish over a 4-day period) at doses ranging from 4.75 to 75 μg/kg body weight. Higher doses ranging from 150 to 300 μg/kg resulted in significantly fewer spawnings (62.5%–75%). Untreated control sea bass did not spawn. Sham-implanted fish failed to spawn or did so at significantly lower rates (0%–6.3%) compared to hormone-treated fish. Spawning induction at the highest hormone dose tested (300 μg/kg) resulted in the lowest mean egg fertilization rate of 30.1%. Mean fertilization rates, ranging from 60.5% to 82.2%, at the lower doses of LHRHa were not significantly different. Mean hatching rates ranging from 30% to 76.5% following induction of sequential spawning by several doses of LHRHa were similar. At all hormone doses tested, mean egg production levels of 37.3–58.7×10 4 eggs/kg body weight were highest on the first day of spawning and declined significantly on subsequent days. Mean egg production levels of 1.2–6.9×10 4 eggs/kg were always lowest on the last day of spawning. Similar egg production levels among all hormone doses during each spawning day were observed. These results indicate that the quality and quantity of spawned eggs may, in part, be influenced by sequential spawnings triggered by LHRHa pellet implantation in sea bass.