California Sea Grant College Program

The ability to control egg production and have a consistent supply of high quality eggs is critical to the commercial success of any farmed marine finfish species. Here we describe the first documented controlled spawning of California yellowtail (CYT; Seriola dorsalis). The aim for this study was to shift volitional spawning six months ahead of when natural spawning typically occurs for the species using photothermal manipulation. Over the course of one year we tracked spawning for two sibling groups of F1 generation broodstock and recorded relevant metrics for all spawn events (egg production, viability), eggs (egg and oil diameters, hatch rates), and larvae (notochord length at hatch, yolk sac volume, survival to first feeding). The first group was subjected to natural day length and temperature conditions (Natural) and produced eggs from March through October in 2023. The second group had a shifted day length and temperature regime (Controlled) designed to stimulate spawning from October 2022 through April 2023. Egg production for both groups was similar, with the Natural group producing 37 spawns resulting in 25 million eggs (682,086 ± 299,821 eggs spawn−1), and the Controlled group producing 34 spawns resulting in 20 million eggs (604,825 ± 315,412 eggs spawn−1). Egg quality was also similar, with only hatch rate being different between the groups (Natural 48.8 ± 28.9 %; Controlled 75.1 ± 15.5 %). Through the control of temperature and day length, we demonstrated that CYT spawning can occur outside the natural spawning window and that achieving year round egg production is possible. This is an important step forward for commercial production of this high value marine finfish species.