Immunological responses of customised probiotics-fed marron, Cherax tenuimanus, (Smith 1912) when challenged with Vibrio mimicus.

A two-phased experiment was conducted to investigate the effects of dietary supplementation of customised probiotics on marron physiology. During the first phase marron were fed probiotic supplemented feed for 70 days, while in phase two the same marron were challenged with Vibrio mimicus and their physiological responses were investigated for 4 days post-challenged. The experiment was carried out in a purpose-built room, designed for aquaculture research, using 18 of 250 L cylindrical plastic tanks. Five species of isolated probiotic bacteria from commercial probiotic products and marron's intestine were tested in this experiment. The probiotic bacteria were (Bacillus sp.); A10 (Bacillus mycoides); A12 (Shewanella sp.); PM3 (Bacillus subtilis); and PM4 (Bacillus sp.), which were added to the formulated basal marron diet (34% crude protein, 8% crude lipid, 6% ash) at a concentration of 10(8) cfu/g of feed. Immune responses of marron fed probiotics were evaluated by investigating organosomatic indices, growth rate, survival, intermoult period, total haemocytes counts (THC), proportion of granular cells (GC), bacteraemia, bacteria load in the intestine and water quality. The results showed that dietary supplementation of probiotics in marron had no significant impact on growth, intermoult period and survival of the marron. However, their supplementation improved the physiological condition of marron in terms of significantly higher tail muscle indices, THC and proportion of granular cells (GC) and reduced bacterial load in the haemolymph. The addition of probiotics in marron diets also increased the bacteria load in the marron intestine. In addition, dietary supplementation of the customised probiotics was effective in improving the resistance of marron against V. mimicus as they had higher THC, higher proportion of GC and lower presence of bacteria in their haemolymph, after marron were challenged with V. mimicus. The results also showed that probiotic Bacillus mycoides (A10) and PM4 are the most beneficial dietary probiotics for marron health.