58--67--K. Sivakumar.pmd

The effectiveness of three immunostimulants viz., vitamin C, levamisole and chitin on the prophenoloxidase (proPO) activity of haemolymph, response to challenge studies and growth performance of juveniles of the tiger shrimp Penaeus monodon (Fabricius) was assessed by oral administration of these immunostimulants to the shrimps. The levels of incorporation of these immunostimulants in shrimp feed were vitamin C at 50, 150 and 250 mg /kg; levamisole at 5, 50 and 100 mg/kg and chitin at 50, 100 and 200 mg/kg levels. Juveniles of P. monodon were fed with the experimental diets (9 immunostimulants + 1 control) for 6, 10 and 15 days duration under laboratory conditions. Immune enhancement was recorded as increase in proPO activity in haemocytes and plasma of experimental juvenile shrimps. These diets resulted in relatively better growth rate than the control. The challenge studies were carried out for periods of 6, 10 and 15 days duration. For the cumulative effects of proPO activity in haemocytes and plasma, along with growth increment and survival rate, levamisole at 5 mg/kg, followed by chitin at 100 mg/kg and Vitamin C at 150 mg/kg were observed to be the effective doses to enable “immune enhancement” in shrimps. The ‘prophenoloxidase assay’ standardised in the study proved to be an effective and simple tool for measuring the immune enhancement in penaeid shrimps.