Evaluation of paraprobiotic applicability of Lactobacillus plantarum in improving the immune response and disease protection in giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879).

Paraprobiotics, also known as ghost probiotics, are non-viable microbial cells which, when administered in adequate amounts, confer a benefit on the host. However, the advantage of non-viable microbes over their viable counterparts is a much debated topic in aquaculture. Therefore, the present study was conducted to evaluate paraprobiotic effect of heat-killed Lactobacillus plantarum on giant freshwater prawn Macrobrachium rosenbergii. A 90-day feeding trial was conducted by feeding prawn juveniles (mean weight ± SE: 0.54 ± 0.03 g) with three experimental diets prepared by supplementing basal diet (Crude protein: 38%; Gross energy: 387 kcal 100 g(-1)) with different concentrations of heat-killed probiotics bacteria viz. HKPB1 (10(7) cfu g(-1) diet), HKPB2 (10(8) cfu g(-1) diet), HKPB3 (10(9) cfu g(-1) diet) and control diet (unsupplemented diet). In the present study, growth parameters viz. WG % and SGR and feed utilization parameters viz. FCE, FCR and PER, though improved marginally in all experimental groups, were found to be insignificant (P > 0.05) compared to the control. The immune parameters viz. total hemocyte count (THC), phenol oxidase (PO) activity, respiratory burst (RB) activity and clearance efficiency were significantly improved (P < 0.05) with concurrent decrease (P < 0.05) in cumulative mortality against Aeromonas hydrophila challenge in all the experimental groups except for HKPB1, where PO and RB activity did not improve significantly (P > 0.05) compared to the control. Among the experimental groups, though the improvement in immune parameters was higher (P < 0.05) in HKPB2 and HKPB3 compared to HKPB1 and the control, no significant difference (P > 0.05) was observed between HKPB2 and HKPB3. The results obtained from the present study indicate that the application of heat-killed L. plantarum at a concentration of 10(8) cfu g(-1) diet, though not effective in augmenting the growth and feed utilization parameters, can significantly improve immune parameters and disease resistance of M. rosenbergii in the laboratory condition.