Induced spawning of grey mullet ( Mugil cephalus) by LHRH-a

Abstract

The application of a high potency synthetic analogue of luteinizing hormone-releasing hormone (LHRH-a), des Gly 10 [D-Ala 6] LHRH ethylamide for inducing the final stages of maturation and spawning in the grey mullet was investigated. Two LHRH-a injection strategies were used. The first involved the use of carp pituitary homogenate (CPH) as a priming injection for females with average egg diameters of 600 μm or more. This injection was followed, 24 h later, by a resolving injection of LHRH-a. The second stragegy followed the same time frame but LHRH-a was used exclusively for both priming and resolving injections. A high spawning success rate (94.1%) was achieved utilizing the first strategy. Fertilization rates, hatching rates, and qualitative changes in egg morphology were similar to those reported using traditional methods. In this study, 20 mg/kg CPH followed by 200 μg/kg LHRH-a were the minimum dosages that resulted in fertilized spawns. This is the most cost-effective method developed to date for inducing grey mullet to spawn. A 68.4% success rate was achieved when utilizing the second strategy. The minimum total dosage that resulted in fertilized spawns was between 300 and 400 μg/kg LHRH-a. One-third of the total dosage was administered in the priming dose followed by the remaining two-thirds in the resolving injection.