Captive spawning, early development, and larviculture of largescale blackfish, Girella punctata (Gray, 1835), and effects of macroalgae and alternative protein sources on its juvenile growth performance

Abstract

The largescale blackfish, Girella punctata (Gray, 1835), inhabits rocky substrates in the coastal waters of Japan and northeastern Taiwan. Despite its commercial significance, there is limited knowledge regarding its reproductive biology due to the sparse occurrence of broodstocks in its natural environment. This study investigated the reproductive performance and embryonic development of G. punctata, assesses its feeding preferences through controlled feeding trials, and evaluates the impact of various feed types on its growth performance. In total, 124 wild-caught G. punctata were reared for 3-4 years, and their reproductive performance was assessed in 2015 and 2016. Their egg production increased with a sudden water temperature change from 17 degree celsius in 2015-22 degree celsius and 2016. The total and daily average egg production weights were 3589.22 and 40.79 g, respectively, whereas the total and daily average fertilized egg production weights were 1630.72 and 18.59 g, respectively; moreover, the hatching rate was 42.61 %. During embryonic development, the eggs hatched 45 h post fertilization at 19 degree celsius. Newly hatched larvae were 2.26 +/- 0.04 mm in length with a yolk sac of 1.09 +/- 0.02 mm in length. The yolk sac was almost completely absorbed 3 days post hatch (dph), when the larvae grew to a length of 3.42 +/- 0.06 mm. We found that fish meal with 40 % protein was the optimal G. punctata fish diet. The weight gain in juveniles fed Cladophora fascicularis ranged from 47 % to 52 %, which was significantly higher than that in those fed Hypnea charoides (p < 0.05). The present study provided a practical guideline on the conditions required for successful fertilization and early development of G. punctata embryos and other larval stages. This information should help ensure greater survival and a higher proportion of healthy G. punctata larvae for mariculture applications.