Seawater sprinkling promotes swim bladder inflation and reduces lordosis during mass-scale seed production in the leopard coral grouper Plectropomus leopardus

Abstract Lordosis caused by failed swim bladder inflation (SBI) is a major constraint on the production of Plectropomus leopardus . During seed production, an oil film applied to prevent surface trapping impedes air gulping and hinders SBI. We developed a full-surface seawater sprinkling method and evaluated its effects on SBI and survival. In a descriptive preliminary comparison of four oil-film removal methods (one tank each), the sprinkler treatment appeared promising, with SBI and survival rates of 53.6% and 71.4% at 9 days after hatching (DAH), and was therefore scaled up to 10 sprinklers in Experiment 1. During 5–10 DAH, the SBI rate was significantly higher in the sprinkler treatment than in the control with no oil-film removal (51.3% versus 1.3%; 50.0 pp), whereas survival did not differ significantly. At 138 DAH, the incidence of lordosis was significantly lower in the sprinkler treatment (8.5%) than in the control (61.0%; 52.5 pp). In Experiment 2, the SBI rate was 64.0% with 10 sprinklers and 46.0% with four (18.1 pp), and the difference was not significant. Thus, seawater sprinkling promotes SBI without a detectable reduction in survival and offers a practical approach for suppressing lordosis during grouper seed production.