PHYSIOLOGICAL RESPONSES AND MORTALITY OF HYBRID STRIPED BASS Morone chrysops × Morone saxatilis SUBJECTED TO ACUTE STRESS AFTER BEING FED DIETARY PREBIOTIC AND PROBIOTIC SUPPLEMENTS

Physiological changes and mortality of hybrid striped bass were monitored following two experimental stressors to study the effects of dietary prebiotic and probiotic supplementation on acute stress responses. Hybrid striped bass averaging 440 g were kept in 1200-L fiberglass round tanks in a recirculating culture system. A basal diet with 42.9 % crude protein and 13.1 % crude lipid (as fed) was formulated. Two supplemented diets with either 2% prebiotic (GroBiotic^®-A, International Ingredient Corporation) or 10⁷ CFU/g probiotic (Aquablend, BIO-CAT Microbials) and the basal diet were fed to 16 fish in each of two replicate tanks.  An acute stress challenge was conducted after 8 weeks of feeding. Fish were maintained under low water condition with aeration for 30 min. Blood samples were collected at 0 (pre-challenge), 30 min (post-stress), and 12 h (recovery). Parameters measured were: hematocrit, blood neutrophil oxidative radical production (at time 0), as well as plasma glucose, cortisol, lysozyme, total protein/immunoglobulin, and osmolality. Experimental fish were given 1 week to fully recover, after which a transportation stressor was applied. Mortality was recorded until fish resumed normal feeding activity.

Results to date showed that: (1) All dietary groups displayed a general decreasing trend in hematocrit following the acute stress challenge (p<0.05). No differences among treatments were found at any sampling time; (2) Prebiotic group had lower blood neutrophil oxidative radical production than both basal and probiotic groups (p=0.005); (3) Lysozyme activity in plasma had a post challenge decreasing trend but no statistical differences were found among sampling times nor treatments. (4) No difference was found in the survival following the transportation stress. But it was worth pointing out that, numerically, the survival results agreed with a previous study in which basal group had more mortality compare to the other treatments, most of which occurred in an earlier post-challenge stage.  Analysis of this experiment is ongoing and more results will be evaluated such as plasma glucose, cortisol, and osmolality.