Recombinant gonadotropin induced out-of-season spawning and larval culture of flathead grey mullet (Mugil cephalus)

Abstract

The flathead grey mullet (Mugil cephalus) held in intensive captive condition does not sexually mature. The present study, aimed to apply recombinant gonadotropin (rGth) protocols to advance spawning by three months and demonstrate the protocols potential for juvenile production. Eight females and seven males were divided into an rGth group that was treated with species specific recombinant follicle stimulating hormone and recombinant luteinizing hormone and a control group treated with saline. The rGths-treated males completed spermiation and the females completed vitellogenesis and spawning in June–July, three months before the natural spawning period (September – October). Control females did not advance with oogenesis and control males did not advance to spermiation. Eggs were incubated, and hatched larvae were reared in three replicated densities (16, 32, and 51 larvae/L, 100 L tanks) and in grey and black 500 L tanks at 30 larvae/L. Final survival at 16 larvae/L was 14.13 ± 5.2 % at 42 days post- hatching (dph) and a correlation between survival and stocking density predicted 3 juveniles/L could be obtained at 42 dph with an initial density of 38 larvae/L. Larvae reared in black tanks had a superior growth rate (16.70 ± 0.05 mm) in comparison to the grey tanks (11.40 ± 2.80 mm) at 42 dph (P = 0.01). Together, these findings confirm the high efficacy (close to 100 %) of rGths induction protocols, that out-of-season spawning can be induced, and that rGth induced mullet spawning has good potential as a bases for juvenile production.