Evaluation of microdiets versus live feeds on growth, survival and fatty acid composition of larval haddock (Melanogrammus aeglefinus)

Two newly developed microdiets for the culture of marine fish larvae were compared to the control ICES Standard Weaning diet and the traditional live foods, rotifers (Brachionus plicatilis) and Artemia nauplii, in a feeding study with larval haddock. Haddock larvae were reared from hatch to 20 days post hatch (dph) in a 5000-l tank and fed algae-enriched rotifers. Between 21 and 24 dph, 1000 larvae were transferred to each of the 20 tanks. From 25 until 45 dph, the larvae were fed five different diets: (1) B. plicatilis enriched with mixed algae species; (2) Artemia nauplii enriched with Algamac 2000 (Aquafauna-BioMarine, California, USA); (3) ICES Standard Weaning Diet; (4) IFREMER-INRA microdiet; and (5) microdiet produced by Louis D'Abramo, Mississippi State University, MS, USA. Survival was significantly higher (P<0.001) in the rotifer and Artemia nauplii treatments (meanłS.E.; 24.9±4.2% and 21.3ł±.3%, respectively) than in the microdiet treatments (ICES, 2.2±1.1%; IFREMER-INRA, 4.3±1.8%; and D'Abramo, 4.0±1.2%). Survival was not significantly different (P<0.05) among the microdiet treatments. Mean larval weights were significantly different (P<0.001) between rotifer (1.61±0.12 mg) and Artemia nauplii (2.14±0.14 mg) treatments. The weights of larvae fed microdiets (ICES, 0.75±0.05 mg; IFREMER-INRA, 0.85±0.04 mg; and D'Abramo, 0.86±0.05 mg) were not significantly different from each other; however, all microdiet treatments were significantly smaller than the live feed treatments (P<0.01). There were also significant differences in the fatty acid composition of the larvae fed the different diets although no correlation was found between dietary fatty acid composition and growth or survival of the larvae. The highly unsaturated fatty acid (HUFA) 22:6n-3 showed a dramatic proportional increase in larval tissue relative to its proportional composition in both the live and formulated diets. Dietary proportions of the HUFA 20:4n-6 were similar among the Artemia, ICES and D'Abramo diets (average 1.2-1.3%); however, the proportions of 20:4n-6 in the larvae were significantly higher in larvae fed Artemia (meanłS.E.; 5.4±0.11%) compared to larvae fed either ICES or D'Abramo diets (mean±S.E.; 4.0±0.04% and 4.4±.08%, respectively). Proportional increases of other HUFA, specifically 20:5n-3 and 22:5n-6 in larvae relative to dietary HUFA, suggest important physiological roles for these fatty acids. It appears that under the current rearing conditions, none of the microdiets examined is a suitable replacement for live feeds in the culture of haddock larvae from 25 to 45 dph and factors other than fatty acid composition must be considered.