Induced spawning of captive grey mullet ( Mugil cephalus L.) females by injection of human chorionic gonadotropin (HCG)

Abstract

The possibility of inducing and synchronizing spawning can be very useful to facilitate fish farming, particularly in species that achieve ovarian development in captivity without ovulation occuring. The present study was undertaken to observe the morphological and normal embryonic development of thin-lipped mullet, Liza ramada, after spawning induction of fish reared in freshwater fish farms. The use of pregnyl (HCG) as a priming injection at a dose of 20,000 IU/kg body weight followed by a second injection of 40,000 IU HCG/kg body weight 24 h later, proved to be effective in inducing final oocyte maturation, ovulation and spawning in L. ramada at 52–60 h after hormonal injection. The mean number of the ovulated eggs for each female was 700 ± 80.3 eggs g−1 body weight. The mean rates of buoyancy, fertilization and hatching were 46 ± 7.1, 55 ± 8.4 and 60 ± 6.6, respectively. Fertilized eggs were kept under normal environmental conditions in seawater at 20–21 °C. The first cleavage occurred at 40 min, epiboly began at 5 h, the embryonic body was formed at 24 h and hatching occurred at 48 h after spawning. Newly hatched larvae were approximately 2.5 mm (total length) and similar to those of the other mullet species in terms of external features except no pigment spots were present over the yolk. The mouth and foregut opened on the 5th day after hatching; at which the total length of larvae was 3.5 mm; the hindgut and anus had developed prior to hatching.The induced ovulation technique using acute injections of hormones is an important step in the development of the mullet culture.