Effects of gametes post-activation, egg storage and sperm-egg ratio on in vitro fertilization outcomes in the brown-marbled grouper (Epinephelus fuscoguttatus).

Due to some biological characteristics of the brown-marbled grouper, there are challenges in aquaculture enterprises focused on production of this fish. With the aim of facilitating captive breeding in brown-marbled grouper, effects on gamete post-activation, post-stripping egg storage and sperm to egg ratio on fertilization success were investigated. Results indicated eggs were fertile for 4 min after placement in seawater, thereafter, there was a reduction in fertilization. Initial curvilinear velocity (VCL) and total motility of fresh sperm was 129.3 ± 3.7 μm/s and 92.9 ± 2.4 %, both of which decreased as time elapsed post-activation, however, there was no significant difference in fertilization until 6 min post-activation of sperm. Compared with fertilization and hatching rates in eggs used immediately after collection (95.0 ± 2.8 % and 90.1 ± 4.2 %), in vitro storage of eggs had no detectable effect on fertilized egg and hatching rates until 60 min post-stripping (92.0 ± 2.8 % and 89.9 ± 2.7 %), indicating that immediate use of brown-marbled grouper eggs for fertilization is not necessary in aquaculture hatcheries. With regard to optimizing the sperm to egg ratio, there was acceptable fertilization with ratios ranging from 103 to 107, whereas there was a marked decrease in fertilization rate when there were lesser sperm concentrations. When the combined results from this study are considered, there could be improvements of artificial fertilization efficiency in the brown-marbled grouper with utilization of these findings in aquaculture enterprises focused on production of this fish.