WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2016 33 Larval nutrition is a key factor in successful marine finfish culture. Typical live prey items such as copepods, rotifers, and brine shrimp are considered necessary for larval culture. In a hatchery setting, production of live prey is expensive, time consuming, and labor intensive, with a high potential for variable nutritional quality. Hence, emphasis has been placed on transitioning larvae from live feed to a formulated microdiet as soon as possible. The use of microdiets with marine finfish larvae has been studied for several decades and, with further improvements in technology, microdiets could be used to evaluate the nutrient requirements of larval marine finfish (Barrows and Lellis 2006, Langdon and Barrows 2011, Hamre et al. 2013). Successful use of microdiets is essential to the development of commercial marine finfish aquaculture. Among the many particle types used, the most common in larval feeding are microbound particles, characterized as crumbled or shaped particles (Langdon 2003, Langdon and Barrows 2011). Shaped microbound particles, unlike crumbled particles, are formed as micron-sized particles that require no additional grinding (Langdon and Barrows 2011). Shaped types include microextruded marumerized particles (MEM) and particleassisted rotational agglomeration particles (PARA). MEM particles can be as small as 500 µm in diameter and PARA particles can be less than 500 µm in diameter (Barrows and Lellis 2006, Langdon and Barrows 2011). California yellowtail Seriola dorsalis, also known as yellowtail amberjack or yellowtail kingfish, is a high-value marine finfish cultured commercially in Japan, Chile, Australia and New Zealand. White seabass Atractoscion nobilis is a popular recreational and commercial species found off the coast of Southern California and Baja California, Mexico. Both species have high-quality flesh and high market value, and thus high Preliminary Comparison of Open-Formula and Closed-Formula Microdiets for Weaning Larval Marine Finfish Kevin Stuart*, Mark Drawbridge, Frederic T. Barrows, Michael B. Rust and Ronald B. Johnson commercial potential, and are considered to have larval stages (Figs. 1 and 2) similar to most marine finfish with commercial potential. This article describes a study that was conducted to determine if feeding larval marine finfish an open-formulation reference diet using a PARA or MEM particle can achieve performance (growth, survival, and feeding) comparable to larvae fed a commercially available diet. Larval Diets In one trial, white seabass larvae were fed open-formulation PARA, open-formulation MEM, or a commercial microdiet (Otohime3; OTO). In a second trial, California yellowtail larvae were fed open-formulation PARA, OTO microdiet, or another commercial microdiet (GEMMA4 wean). Squid and krill meal were the major protein sources in the open-formulation diet (Table 1). The diet preparation method is described thoroughly in Barrows and Lellis (2006). Proximate analysis of diets indicated that moisture was similar among the MEM (5.9 ± 0.01), OTO (6.4 ± 0.2) and GEMMA (6.5 ± 0.1) diets, but significantly less in the PARA diet (5.2 ± 0.2). Fat content of the OTO and GEMMA diets was significantly less than that of the MEM and PARA diets. The protein content of the OTO and GEMMA diets was significantly greater than in MEM and PARA diets (Table 3). The proximate composition of the GEMMA diet was obtained from Bonaldo et al. (2011). Particle Size and Sinking Rate Three types of factors determine a diet’s success: factors that impact ingestion; factors that impact digestion, assimilation, and metabolism; and factors that impact both (Langdon and Barrows 2011). Particle size and sinking rate are two important physical (CONTINUED ON PAGE 34) FIGURE 2. Larval California yellowtail Seriola dorsalis. FIGURE 1. Larval white seabass Atractoscion nobilis.
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