Natural spawning and scaling-up of yellowtail snapper (Ocyurus chrysurus): Larval rearing for the mass production of juveniles

Abstract

The natural spawning and scaling-up the larval rearing of yellowtail snapper (Ocyurus chrysurus) are described. We obtained fertilized eggs via the volitional spawning of broodstock acclimated for two years in two 12-m3 tanks. Of the eggs collected 10 to 14 h after spawning, 87.3% were floating, and 90% of these were transparent and presented a live embryo (egg diameter of 824 ± 77 μm and oil droplet diameter of 137 ± 14 μm). The incubation period was 18 h at 27 °C and 38 g l−1 salinity. The average normal larvae hatching rate was 88.3 ± 3.3%, and the notochord length of the newly hatched larvae was 2.5 ± 0.5 mm. Larval survival at 48-h post-hatching was 48.1 ± 3.7%. The initial mean stocking density in the 2500 l rearing tanks was 206.3 ± 24.5 floating eggs l−1, which resulted in 99 ± 43 larvae l−1 per tank. A total of 261,736 juveniles were harvested at a mean of 50 ± 3 days post-hatching (dph) from ten 4.5-m3 cylindrical fibreglass tanks, which presented a mean of 26,174 ± 3211 juveniles per tank (5.8 ± 0.7 juveniles l−1). The mean survival in the ten tanks was 7.0 ± 1.4% from the time of hatching and 15.0 ± 2.9% as of the first feeding (48-h post-hatching). Two critical periods with high larval mortality occurred during rearing: between 4 and 7 dph and during the third and fourth weeks (20–28 dph). At harvest, the mean total length (TL) was 3.8 ± 0.2 cm (range: 2.9–5.4 cm) and the mean total weight was 0.9 ± 0.2 g (range: 0.3–2.1 g). Larval growth increased from a mean of 0.24 mm day−1 during the first 14 dph (specific growth rate (SGR) of 6.7% day−1) to a mean of 1.73 mm day−1 (SGR of 9.6% day−1) in the subsequent 21 rearing days. The mean final biomass was 4.9 ± 1.3 kg m−3. Finally, the results and current and future larval rearing practices for this species are discussed.