Abstract

Spawning induction in the present study was carried out in two steps. The first treatment consisted of a priming dose of carp pituitary extract with 20 to 70 mg, or 10000 IU of human chorionic gonadotropin (HCG) per fish, while the second dose given 24 h later was the resolving dose of 200 µg/Kg luetenizing and releasing hormone (LHRH-a). After the resolving dose the females were maintained together with males and spawning occurred after 17 to 24 h on average. Running ripe males rated (+2) were used in 3:1 male to female sex ratio, in all spawning trials to optimize fertilization rates. The fecundity varied between 1 - 2.70 million eggs/spawn which represents 1395.3 ± 190 eggs/g bw. The ripe unfertile eggs ofM.cephalus were rounded, colorless and transparent with one oil globule. The surface of the fertilized egg shell is smooth, however; the yolk was unsegmented. After 20 min from fertilization the egg membrane swells up and separated from the previtelline space. The embryo began to be noticed after 13 ± 1 h post fertilization. The egg diameter was 870 ± 30 µm and oil globule was 350 µm. After about 26 ± 4 h post fertilization hatching was started at 25 ± 1°C and water salinity of 34 ppt. The percent of fertilization varied between 75 to 80% and hatching rate was about 90%. The newly hatched M. cephalus larvae was about 1.97 ± 0.23 mm in total length; larvae began feeding 3–5 days after hatching. The time of eye completion is nearly that of mouth opening and body axis becomes straight, which helps the larvae to identify their food as internal-external feeding starts.

Key words: Mugil cephalus, carp pituitary extract (CPE), human chorionic gonadotropin (HCG), luetenizing and releasing hormone (LHRH-a), embryonic and larval stages.