Effect of dietary inclusion of dried Tetraselmis suecica on growth, feed utilisation and fillet composition of European sea bass juveniles.

Several marine microalgal species offer a valuable source of long chain PUFA’s that have the potential to become a sustainable alternative dietary source and therefore may help to meet the increasing demand for fish oil that is a critical limiting factor for the future expansion of aquaculture activities. Oil extracted from the algae have proven to successfully replace marine fish oil in diets for Atlantic salmon or sea bream (Miller et al., 2007; Ganuza et al., 2008). Microalgae may also offer much potential as sources of protein, bio-active compounds, antioxidant and vitamins to supplement the diet of high-value fish species or in organic-based aquaculture systems. Significant advances have recently been made in the field of photobioreactor technology that significantly improved microalgae productivity in comparison to the traditional culture systems. This technology makes microalgae production of interest for aquaculture beyond its consolidated role in hatcheries for most fish and shellfish larval stages. A study was carried out to evaluate growth response, feed utilization and quality traits of the edible portion of sea bass (Dicentrarchus labrax) fed diets including dried Tetraselmis suecica. Three test isoproteic (50.3% DM) and isolipidic (17.9% DM) diets were compared. All preparations were formulated using "organic" ingredients. T. suecica was incorporated to replace 10% (TETRA10) and 20% (TETRA20) protein supplied as dried fish trimmings which were the major protein source in the control diet (BIO). All diets were offered to apparent satiety to 9 groups of 21 European sea bass juveniles (72 g IBW) under controlled environmental conditions (temperature 20.4°C; salinity 28 psu; light-dark cycle 12L:12D) according to a completely random design. Feeding the test diets over 63 days resulted in similar fish growth (SGR 0.82; weight gain 68.8%; P>0.05) and feed utilisation (feed intake 1.04 g/d/fish; feed:gain ratio 1.39; P>0.05). Dietary algae inclusion significantly affected the apparent digestibility coefficients (ADCs) as measured in vivo using acid insoluble ash as indigestible marker. Compared to the control diet (BIO), fish fed diet TETRA20 resulted in significantly lower ADCs of protein (93.3 vs 95.3%; P<0.05), lipid (79.7 vs 99.3%; P<0.05) and organic matter (87.4 vs 89.1%; P<0.05). The effects of the dietary algae inclusion on the fillet composition were also considered.