Year-round natural spawning, early ontogeny, and larval rearing of the painted sweetlips, Diagramma pictum (Thunberg, 1792) in a hatchery: Potential as a new species for mariculture

Abstract

The painted sweetlips, Diagramma pictum, is an important species for commercial fisheries, game fishing, and the marine aquarium trade. However, limited knowledge is available about the captive breeding and early developmental stages of this species. This study presents the first report on natural spawning, early ontogeny, and appropriate rearing conditions (temperature, salinity, and initial prey) for larviculture of D. pictum. Natural spawning of D. pictum in captivity was observed year-round for two years, from 1 June 2019 to 31 July 2021. During this 792-day period, females produced 127 spawns, with 77.2% ± 27.2% resulting in fertilized eggs. The median fecundity per spawn was 841 eggs with an interquartile range of 1173 eggs, and the average hatch rate was 59.3 ± 22.0%. Fertilized eggs were spherical, buoyant, and had a diameter of 0.78 ± 0.02 mm. Embryonic development lasted 14 h and 30 min at 28.0 °C. Newly hatched larvae measured 1.81 ± 0.20 mm in total length (LT), with 26 myomeres and an oil globule in the ventroanterior area of the yolk sac. Additionally, the ultrastructural observations of the micropyle, accessory openings, neuromast, and head spines of eggs and early larvae were reported for the first time. At 3 days post-hatch (dph), the larvae measured 2.59 ± 0.16 mm LT at full yolk sac and oil globule resorption. First feeding was noted at this stage, as evidenced by the expansion of the digestive tract filled with live feed. The juvenile stage was reached by 25 dph, and juveniles had an average length of 32.54 ± 2.17 mm LT. Based on hatch and survival activity indices (SAI), we propose optimal water quality parameters for D. pictum larval rearing as a temperature of 26–28 °C and a salinity of 32–33 psu. In the first feeding experiment, survival rates were not significantly different between feeding treatments R (Brachionus rotundiformis; 5 rotifers mL−1) and R + C (B. rotundiformis; 4 rotifers mL−1 + Calanopia elliptica; 1 nauplii mL−1), but both were higher compared to treatment C (C. elliptica; 2 nauplii mL−1) at 9 dph. Our study emphasizes the importance of simultaneous consumption of rotifers and copepods as vital initial prey for the first feeding larvae of D. pictum. Additionally, this co-feeding may enhance larval development through an additive effect. These results demonstrate the potential for establishing captive breeding programs for this species.