Optimizing nursery diets for post‐metamorphic stage black sea bass: Growth performance, body composition, and feed utilization on open‐formulated and commercial starter diets

Abstract

AbstractThe objective of this study was to optimize nursery diets for post‐metamorphic stage black sea bass by evaluating growth performance, whole‐body proximate and fatty acid composition, and utilization of University of North Carolina Wilmington (UNCW)‐formulated and commercial diets under laboratory conditions. A feeding trial was conducted to compare two UNCW‐formulated diets (D1 and D2) for black sea bass (54% crude protein = CP and 14% crude lipid = CL) and two premium, commercial marine finfish fry diets, Otohime (Reed Mariculture Inc., Campbell, CA, CP = 48% and CL = 14%, CD3) and Gemma Diamond (Skretting, Nutreco, Canada, CP = 57%, CL = 15%, CD4). The UNCW‐formulated diet 1 (D1) contained high fish meal (FM, 40% of diet), whereas UNCW‐formulated diet 2 (D2) replaced 50% FM protein by high‐quality poultry by‐product meal (PBM) protein. Post‐metamorphic stage black sea bass (~0.60 g, d40ph) were stocked in each of sixteen 75‐L tanks at a density of 1 fish per L (75 per tank), with four replicate aquaria per treatment. Fish were fed four times per day (0800, 1100, 1400, and 1600 h) to apparent satiation for 30 days. Final body weight (5.70–5.74), specific growth rate (7.40–7.45%/d), and percent body weight gain (834–848%) of fish fed the UNCW‐formulated D1 (FM‐based) and D2 (FM + PBM‐based) were higher (p < .05) than in fish fed the commercial diets CD3 and CD4 (4.66–5.21 g, 6.80–7.15%/d, and 668–756%, respectively). Feed intake (% body weight/d was significantly lower for fish fed commercial diet (CD4) (3.94) compared with fish fed CD3 (4.20), but feed intake for CD3 was not significantly different compared with the UNCW‐formulated diets D1 and D2 (4.10–4.12). Feed conversion ratios (0.76–0.82) were significantly higher for fish fed CD3 (0.82) than for fish fed D1 and CD4 (0.76). Survival was high (99–100%) in all diet treatments. Final whole‐body crude protein content (15.2 to 15.9% wet basis), moisture (68.9–69.6%), and ash (4.31–4.77%) showed no significant differences; however, whole‐body crude lipid was lower in fish fed CD3 (9.67%) than in fish fed the other diets (9.96–10.22%). Final whole‐body fatty acid composition reflected the diet composition. Higher feed consumption and growth of fish fed the UNCW‐formulated diets were attributed to a more optimal combination of marine (fish, squid, and krill meals), terrestrial plant (soybean meal) protein sources, and the addition of chemo‐attractants, which provided both higher nutritional quality and palatability. The study suggests that the species‐specific starter diets may improve growth performance and fingerling quality and may therefore lower production costs under intensive nursery conditions.