Growth Response of European sea bass (Dicentrarchus labrax) fed diets varying in origin and quality of fish meal

Although fish meal (FM) still represents a major protein source in practical diets for the European sea bass (D. labrax), very little information is currently available on the nutritive value to this fish species of fish meals varying in origin and quality attributes such as raw material freshness, processing and storage conditions. The aim of the present investigation was to test and compare a representative set of commercial fish meals widely used by the national feed mill industry. Growth response of juvenile sea bass was used as criteria for evaluating diets where the various FMs were the sole protein source. The study used seven batches of commercial fish meals: two North European white fish meals (labelled as standard and LT, respectively); three Chilean fish meals: labelled as regular, prime and super prime; two Peruvian fish meals, labelled as FAQ and prime). All batches of fish meals (25-50 kg) were supplied by two national aquafeed mill companies. They were analysed and characterised for proximate analysis, levels of total volatile nitrogen and biogenic amines. Seven complete pelletted diets, each including one of the test fish meals plus a control casein-based feed as the sole protein sources, were prepared. All diets were formulated to be grossly isonitrogenous (7.4% DM) and isolipidic (18% DM). The diets were tested in a 124-day growth trial with juvenile sea bass kept in an indoor, partially recirculating, marine water system (daylenght, 12h; temperature, 21±1°C; DO, 7±1 mg/L; salinity, 28±1‰; pH, 7.3±0,2; total ammonia nitrogen <0.08 mg/L). Fish (init. body weight, 47 ± 2 g) were distributed among twenty four 200-L tanks (35 fish per tank) and assigned to the eight diets according to a random design with triplicate groups per treatment. They were hand-fed twice daily nearly to satiety. The actual feed intake of each unit was recorded daily. Fish groups were weighed in bulk and random fish samples were collected at the beginning and the end of the trial from each tank for whole body N analysis. Data were subjected to regression analysis, and ANOVA. If appropriate the Duncan's multiple range test was applied for mean comparison at a significance level of 95%. The diets based on the South American fish meals resulted in slightly different growth performance, feed-gain ratio, PER and gross N retention efficiency according to their putative quality label (DGC: 0.86-0.95; FGR, 1.42-1.54, PER, 1.50-1.65, gross N retention, 27-29 %, p>0.05) which did not differ from those exhibited by fish fed the diet including the LT-white fish meal or the casein-based preparation. On the contrary, feed intake and all response parameters were significantly impaired (p<0.05) in sea bass fed the diet including the standard white FM as this particular batch of FM resulted in very poor quality as assessed through TVN (95 mg/100g) and biogenic amines levels (>3000 mg/kg). A regression analysis between protein-quality parameters of the various FMs and growth performance, showed growth response and N utilisation efficiency in sea bass fed the different FM-based diets to be mostly correlated with levels of biogenic amines, such as putrescine (r = -0,90/-0.94, p<0.01) and cadaverine (r = -0.88/-0.95, p<0.01) in fish meals. The results here obtained suggest that the freshness of raw material used to produce fish meals plays a major role in affecting growth response, feed and N efficiency in sea bass as in other carnivorous fish species investigated to date. Hence conventional chemical parameters such as levels of biogenic amines in FMs seem to provide a first indication on their nutritive value to this fish species.