Effects of Probiotics on the Aquaculture Performance of Cobia (Rachycentron canadum) and Yellowfin Tuna (Thunnus albacares)

摘要

Effects of probiotics pulse-supplementation on cobia were assessed over two experimental trials carried out with larval and juvenile stages using a commercial blend of Bacillus subtilis, B. lincheniformis, B. magaterium , and Brevibacillus laterosporus. The first trial evaluated the effects of probiotic-enriched live feeds (7x106 and 10x106 colony-forming units (CFU) L--1 for rotifers and Artemia sp., respectively) on the growth and survival of fingerlings during a commercial larval rearing run. The second trial assessed the effects of probiotics supplementation in dry feeds (10 9 CFU kg--1) on the survival, growth, feed conversion ratio (FCR), ammonia excretion of cobia juveniles (58 g to 216 g) and key metabolites measured in whole digestive systems. Results from both experiments showed no significant differences between control and probiotics groups in any of the measured variables, suggesting that pulsed-probiotic supplementation under the present conditions did not affect cobia aquaculture performance. Gas chromatography (GC) and capillary electrophoresis (CE) results evidenced similar profiles between groups for fatty acids and cations, respectively, whereas no values were detected for organic acids of low molecular weight. With regard to the free amino acid profiles, thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) assessments revealed a similar amino acid composition for both experimental groups in each pulse period. However, the concentration of each amino acid increased over time in the supplementation group, whereas the control group showed an opposite tendency. The total free amino acid concentration (ppm) at the end of the experiment was 1.5 and 2.8 times higher than in the control group, as evidenced by spectrophotometry and HPLC analysis, respectively. This increased concentration could be related to higher free amino acid availability from food hydrolysis modulated by probiotics; however, this increment had a negligible effect on feed conversion and growth.;With regards to yellowfin tuna, the effects of probiotics and 1-monoglycerides supplementation on the larval growth and survival at --10 DPH, a common age of acute mortality largely due to nutritional deficiencies, was studied. Two probiotic trials (carried out at different stocking density and different probiotic inclusion) and one trial with 1-monoglycerides were performed. The higher probiotic supplementation (40x106 CFU L--1; Trial 2) yielded a significantly higher total length in the supplementation group with respect to the control in 10 DPH YFT larvae, with no significant differences in survival between groups for both trials. In the case of 1-monoglycerides, no significant differences were found in both variables either, although the supplementation group yielded a two-fold increase in survival compared to the control group, and overall, had higher and less variable values. Probiotics might have assisted digestive processes of the rudimentary digestive system of pre-flexion larvae, whereas 1-monoglycerides might have contributed as additional energy sources, both enabling higher larval nutrient uptake and growth.