Seriola, like many other marine finfish, are first fed cultured live feeds and then weaned onto formulated microparticulate feeds (microdiets) during the later larval stages. Selecting appropriate microdiets for these early-stage animals is of great importance because early nutrition can affect both short-term production efficiencies (i.e. survival and larval duration) as well as the long-term growth trajectory and robustness of the fish. However, little is known about the specific nutritional requirements of Seriola larvae making it difficult for producers to select appropriate microdiets from those that are commercially-available for marine finfish. Moreover, feed companies do not disclose the complete formulation or nutrient composition of these diets making growth studies difficult to interpret. Open formula diets, on the other hand, are those wherein the formulation and composition are in the public domain and provide valuable research tools in animal nutrition. In addition, open formulas, or aspects of open formulas, can be directly adopted by industry if desired.
A growth trial with Seriola dorsalis larvae was conducted at Hubbs-SeaWorld Research Institute, wherein the growth, survival and biochemical composition of the fish were compared between those fed an open formula microdiet produced at the University of Maine and four microdiets produced by commercial feed companies. The open formula microdiet, made via microextrusion followed by marumerization (MEM), has been proposed as a reference diet (i.e. open formula reference diet; OFRD) that could be used for wide range of marine finfish species. Three of the diets produced by feed companies were commercially available (Algonorse-Trofi [EWOS], Advance [Alltech Coppens] and Otohime [Marubeni Nisshin Feed Co.]) and the fourth was a closed formula experimental diet produced by Zeigler Bros. Larvae were fed these microdiets starting on 17 days post hatch (dph) and were co-fed with Artemia until 34 dph after which the fish only received the microdiets; the trial ended when fish reached 52 dph. Each dietary treatment was reproduced across four replicate tanks. A repeated measures ANOVA (REML personality) indicated that larval dry weights (mg larva-1), measured throughout the growth trial, were the highest for fish fed Algonorse-Trofi (EWOS) and were only matched by those fed Otohime. The open formula microdiet resulted in similar larval dry weights when compared to all microdiets evaluated in this study except Algonorse-Trofi. Larval endpoint survival was not significantly different among treatments and had a grand mean of 45%. The nutrient composition of the microdiets were measured and compared with larval whole body compositions in order to identify specific nutrients that may have contributed to the observed growth trends. Ultimately, this study serves to help producers select from currently available products and provides insight into key nutritional parameters that should be considered when formulating Seriola-specific microdiets. Furthermore, our results support the use of this open formula microdiet as an adequate reference diet for Seriola larvae.