California yellowtail (CYT; Seriola dorsalis) is considered as a commercially ready species in the United States. The hatchery technologies for this species have been developed over the last twenty years with reliable spawning of high quality eggs yielding high larval survival rates. Swim bladder inflation remains a main area of focus relative to the quality of surviving fish. Swim bladder inflation occurs in a finite window during larval development and failure to inflate can compromise the larvae, and ultimately juvenile performance. Many factors can influence swim bladder inflation including environmental conditions, which can be species-specific across different parameters. Here we investigated environmental parameters that are known to influence swim bladder inflation.
Four separate trials were conducted to examine: surface access, methods of surface cleaning (no skimming, hand skimming, and mechanical skimming), light intensity (5,000, 10,000, and 20,000 lux) and photoperiod (24L:0D and 18L:6D), turbidity agents (Chlorella paste, Nannochloropsis paste, bentonite clay, and live algae). Trials were conducted from -2 to 10 days post hatch in an experimental RAS with twenty-four 320L tanks supplied with 20º C seawater. Results showed non-significant differences between treatments (Table 1). The best treatment combinations were: mechanical surface skimming (34.0 ± 7.2% inflation), turbidity using Nannochloropsis paste (30.8 ± 12.2% inflation), and light intensity of 10,000 lux and photoperiod of 18L:6D (80.8 ± 34.5%).
When applied on a commercial scale (i.e. 5,300 L tank), optimizing these conditions yielded SBI rates of 70.27% (± 0.45) (n=3 cohorts), which can be further improved but is generally acceptable. Future research will explore the interactive effects of light intensity and water temperature.