Spawning response latency and egg production capacity of LHRHa-injected mature female sea bass, Lates calcarifer Bloch

Abstract

Mature female sea bass (Lates calcarifer Bloch) were injected once intramuscularly with 20 μg luteinizing hormone-releasing hormone analogue (D-Ala⁶, Pro⁹-LHRH-ethylamide) per kg body weight (BW) at different times of the day. Following hormone injection, the incidence of initial spawning and the number of eggs spawned by each fish were recorded. Saline-injected fish did not spawn. Fish spawned at dawn or 33.7–40 h after an LHRHa injection at either 11.00 h or 17.00 h. When LHRHa was administered at 23.00 h or 05.00 h, sea bass spawned during the day or at 38–47.3 h post-injection. Mean egg production levels of 26.8–34.4 × 10⁴ per kg BW were higher for fish which spawned at dawn. Low mean egg production levels (6.2–19.9 × 10⁴ eggs per kg BW) were observed when LHRHa-injected fish spawned during the day. These results demonstrate that the time of initial occurrence of spawning varied with the time of day that LHRHa was administered and that the number of eggs shed was influenced by the time of day that hormone-induced sea bass spawned.