GnRHa-induced spawning of wild-caught spotted rose snapper Lutjanus guttatus

Abstract

The present study examined des-Gly10, [D-Ala6]-gonadotropin releasing hormone ethylamide (GnRHa) implant-induced spawning of recently caught wild spotted rose snapper (Lutjanus guttatus). The effect of implants containing 0 (control), 25, 50, 75 and 100 μg of GnRHa was assessed in ten females that had an oocyte diameter greater than 430 μm. All fish spawned except for the controls and one 100 μg implanted fish. The 75 μg implant-induced the spawning of eggs with a significantly higher percentage hatch (86.1±7.5 and 87.7±5.0%) and twice as many hatching eggs kg−1 body weight (BW). The 75 μg implant was used to induce the spawning of twelve females in two different tank sizes (700 and 1400 L) and with three different female:male densities (1:1, 1:3, 1:5). There appeared to be no significant effect of tank size or male density on egg quality or quantity. Non-linear 3D regressions for the dependent variables total number of eggs kg−1 BW, number of floating eggs kg−1 BW and number of hatching eggs kg−1 BW against the independent variables oocyte diameter (μm) and GnRHa dose (μg kg−1 BW) were significant (P<0.05) and had respective regression coefficients of r2=0.78, 0.80 and 0.85 (n=22). The models described a narrow range of GnRHa doses (240–280 μg kg−1 BW) and a broader range of oocyte diameters (440–500 μm) that predicted a spawn in excess of 100,000 eggs kg−1 BW. As a result, good quality eggs were obtained that enabled experimentation with larval culture.