Sustainability culture of Grey mullet M. cephalus in freshwater reservoirs, require regular fingerlings supply from hatchery instead of adopted wild catch. However, under intensive conditions of captivity, obtaining larvae from broodstock remains a challenge due to the high level of barriers in gonadal development and spawning in addition to asynchronous of genders.
A captive broodstock of the grey mullet Mugil cephalus has been successfully developed at the aquaculture laboratory facilities of the National Institute of Marine Science and Technology (INSTM - Monastir). A stock of 70 adult specimens consisted by 28 females (BW 1300 ± 218g) and 42 males (BW 655 ± 201g) were acclimated in captivity between 2018 and 2019. A protocol for reducing stress in capturing, selecting fishes, transporting and treatment after stocking in tanks was set up and resulted in significantly enhance survival rate from 40% to 70% in 2019 vs 2018.
Broodstock maintained in captivity was subject of experiments to investigate the effect of hormone-therapy based on GnRHa and dopamine antagonists on vitellogenesis, oocyte maturation and spawning during the spawning season (June - October). During 2021 (year 2), induced to spawn of females did not result in fertilization of eggs due to failed final maturation of males. During 2022 and 2023 (year 3 and 4) oocytes diameter reached maximum size in late September – early October and successful induced breeding trials were conducted using females with average oocyte diameter of 583–630 μm, during the first half of October. Fertilization rates varied from 28 to 93%. Embryonic development and hatching exceed 90%.
Results confirm the possibility of inducing oogenesis from previtellogenesis to the completion of maturation and spawning using combined hormone-therapy based on GnRHa and dopamine antagonists.