Advancement of sexual maturation and spawning of sea bass, Lates calcarifer (Bloch), using pelleted luteinizing hormone-releasing hormone analogue and 17 α-methyltestosterone

Abstract

The ability of luteinizing hormone-releasing hormone analogue [(D-Ala 6,Pro 9-NEt)LHRH], 17 α-methyltestosterone (MT), and their combination to advance gonadal maturation and spawning in captive sea bass ( Lates calcarifer Bloch) broodstock was tested. Several hormonal therapies were tested including monthly implantations of a low dose (100 μg/kg body weight) of each hormone and a high dose (200 μg/kg) implanted to sexually-quiescent sea bass at 45-day intervals. A high dose of LHRHa alone or in combination with MT induced a significant number of mature females (43–71%) in April, 45 days after a single implantation in early March. A lower dose of pelleted LHRHa and LHRHa plus MT was found effective (78–80%) only in May following three monthly implantations. Two and three monthly implantations of a low dose of MT failed to stimulate oocyte growth in April and May whereas a less frequent mode of application of a high dose of the androgen inhibited ovarian growth in April only. A low dose of MT alone significantly increased the number of mature males in April (90%) and May (100%) after two and three monthly implantations. All male sea bass which received three monthly implantations of a low dose of LHRHa and LHRHa plus MT were sexually mature in May. Sexually mature sea bass obtained from these experiments spawned in early May after a single intramuscular injection of LHRHa. These results demonstrate the potential use of pelleted LHRHa and MT to significantly advance gonadal development and spawning in sea bass earlier than the annual breeding season.