The evaluation of two commercial microbial products on increasing the resistance and survival of rainbow trout (Oncorhynchus mykiss) larvae

Objective: This study investigated the effect of two commercial probiotics bacteria on the resistance and survival rate of rainbow trout larvae in rearing culture. The types of probiotic bacteria basic on metabolic activity and extera cellular substance have different ability on health and resistance in fishes. The aim of our study was to evaluate the effect of three different concentrations of probiotic bacillus and lactobacillus on the promoting of resistance and survival percentage in rainbow trout larvae. The degree of resistance of trout larvae was determined by data on the surviving times in challenged tests with thermal, salinity, alkalinity and acidity. Method & Materials: The blend of Bacillus subtilis, B. licheniformis and Lactobacillus plantarum, L. dlbrueckii, L. acidophilus, L. rhamnosus, Streptococcus salivarius, as commercial probionts were provided from Protexin Co. The microbial blends were incorporated in fish diets at three concentrations, 2 × 106, 2 × 105 and 2 × 104 cells g−1, respectively and Trout larvae in experimental treatments were fed 32 days at the rate of 10% of body weight. The growth and survival rate were monitored at regular weekly intervals and in termination of experiment, total count of bacteria in gut and resistance of larvae in challenge by different stresses was considered. Results & Conclusion: The results determined that the administration of these probiotic bacteria increased the survival percentage of trout larvae during period of experiment. The best results on the resistance obtained from blend of bacillus. The highest surviving time of trout larvae in thermal stress, obtained in treatment B1 (Trout larvae was fed on diet with 2 × 104 Bacillus subtilis and B. licheniformis g−1) (94.33 second) and the maximum surviving time about alkalinity (249 second) and acidity (358 second) test, obtained in treatment B3 (fed on diet with 2 × 106 Bacillus subtilis and B. licheniformis g−1). While the best results in growth parameters of trout larvae, obtained in treatments were fed with supplemented diet by blend of lactic acid bacteria and B. bifidum, S. salivarius, E. faecium. The highest total weight (1.79 g) and food conversion efficiency (113.35%) obtained in L3 (fed on diet with 2 × 106 blend of lactic acid bacteria and S. salivarius, E. faecium g−1). The control treatment had lowest growth performance and surviving times in challenge test. The results showed that the high resistance, healthy and low infectivity recorded in the probiotic feed fed fishes in comparison with control treatment.

کلیدواژه ها:

Commercial probionts ، Rainbow Trout ، resistance ، Surviving time