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In pelagic fish species, studying reproductive behaviour and spawning dynamics is challenging. In culture scenarios, these parameters are difficult to investigate for broadcast spawners such as Seriola. Hubbs‐SeaWorld Research Institute has been culturing California yellowtail (S. dorsalis) since 2003 and now it is poised to become one of the first commercial offshore aquaculture marine finfish species in Southern California. Brood fish are typically kept in large tanks and spawn volitionally throughout the spawning season. This method is successful in yielding a consistent supply of eggs; however, it limits the understanding of spawning group dynamics or individual brood fish contribution, information that will be important to scaling production to commercial levels. In this study, genetic‐based offspring parentage analyses were used to evaluate captive spawning dynamics in S. dorsalis over two consecutive spawning seasons. The analyses determined that typically one female released eggs during a spawning event, compared with an average of six males who released milt during these same spawning events. Notably, the analyses revealed that a single female dominated spawning output in both years, participating in 63 spawning events and producing 49.7 million eggs. The largest single spawn contribution by a female was 2.5 million eggs, corresponding to a batch fecundity estimate of 110,000 eggs kg−1. The spawning interval for the most productive females was 5–6 days. Using genetic tools to characterize spawning events will help to improve breeding programme designs for S. dorsalis, and this information can serve as a proxy for estimating spawning capacities of this species in the wild. [ABSTRACT FROM AUTHOR]

One of the key limitations in the use of artificial microdiets for the culture of marine fish larvae and post-larvae is their poor acceptability. The chemosensory systems of adult and juvenile fish are known to serve important roles in the detection and selection of food items; however, the relative importance and functionality of chemosensory detection and responses are less well understood for the larval stages. Many chemical compounds previously found to promote feeding in fish are low molecular weight, water-soluble compounds that are prone to rapid leaching from artificial microdiets. Particle taste, which requires retention of these low molecular weight water-soluble compounds, is difficult to manipulate in currently available larval diets. In the present study, we used liposomes embedded in alginate particles (alginate complex particles), that showed high retention of low-molecular weight water-soluble compounds, as a tool to evaluate the impacts of several water-soluble organic compounds on the feeding of California yellowtail (Seriola dorsalis) and white seabass (Atractoscion nobilis). We also compared the relative importance of including (and retaining) these compounds within the particles (enhanced taste) as opposed to dissolving these compounds in the culture water (enhanced smell). The results of this study showed that alginate complex particles retained >50% of sodium fluorescein and >70% of amino acids after 1 h suspension in seawater. Moreover, we found that feed consumption rates (feeding incidence and fullness) were greatest when a mixture of glycine, betaine and alanine were included in the complex particles suggesting that particle taste was an important factor for influencing the feeding of white seabass and California yellowtail post-larvae. • Alginate complex particles show high retention of liposome-encapsulated, water-soluble substances. • Feeding indices were highest when fish were fed on a mixture of glycine, betaine and alanine encapsulated within alginate complex particles. • Encapsulated substances had a greater impact on fish feeding than those that were dissolved in the water. • These results may inform the formulation of microparticulate artificial diets to improve their acceptability by marine fish larvae. [ABSTRACT FROM AUTHOR]

Two eight-week feeding trials were conducted to evaluate the effect of dietary carbohydrate to lipid ratios on growth performance on juvenile California yellowtail Seriola dorsalis. In Trial 1, groups of twenty California yellowtail (ca. 6.8 g) were fed five iso‑nitrogenous diets that were formulated to contain decreasing levels of crude lipid from 21% to 6% by replacing menhaden fish oil with corn starch on a weight basis In Trial 2, groups of twenty fish (ca. 5.2 g) were fed five iso‑nitrogenous diets that were formulated using a similar matrix, corn starch 0–24% was used to replace lipids (11.3 to 1.3%) at approximately 2:1 ratio to maintain the diets with similar energy content and the nitrogen free extract (carbohydrates) from 10% to 30% of the diet Fish were fed 5–11% body weight per day over the course of both trials. Growth performance metrics including thermal-unit growth coefficients and protein retention efficiencies were measured and compared using a quadratic regression model. Fish that were fed diets containing high levels of dietary lipids (15% or higher) exhibited decreased growth performance in Trial 1. In Trial 2, fish that received diets containing the highest level of carbohydrates exhibited improved feed efficiency and overall performance. The results from both trials demonstrate that juvenile California yellowtail with a starting size of 5–7 g have an energy fraction preference and display increased growth when fed diets containing a carbohydrate to lipid ratio of up to 5.8. • California yellowtail juveniles fed diets containing up to 30% dietary carbohydrate exhibited improved feed efficiency and overall growth. • 15% lipid diets overburdened fish, with carbohydrate replacement of lipids improving overall growth performance. • Carbohydrate to crude lipid ratios as a fraction of dietary energy is important for California yellowtail feed formulations. • California yellowtail have an energy fraction preference. [ABSTRACT FROM AUTHOR]