Effects of stevia extract on growth, non-specific immune response and disease resistance of grass prawn, Penaeus monodon (Fabricius), juveniles

Abstract

Abstract: Two separate experiments were undertaken on grass prawn juveniles (mean body weight: 0.76 g) and sub-adults (mean body weight: 14.7 g) to study the effects of stevia extract on growth, non-specific immune response and disease resistance. Thirty (30) juveniles and 15 sub-adults were reared in 200-liter tanks for four months and one month, respectively. They were fed with stevia-supplemented feeds at different concentrations (1, 2, 4 and 8%). Control prawns were fed with non-supplemented commercial pellet. For juveniles, growth (body weight) was monitored every 15 days (starting at 45 days of culture). Non-specific immune parameters (total haemocyte count and phenoloxidase, respiratory burst and superoxide dismutase activities of haemocytes) were analyzed at the termination of the experiment. The sub-adults, on the other hand, were used for challenge experiment using the bacterial pathogen Vibrio harveyi. Results show that there was no significant effect on growth among prawns fed with stevia-supplemented feeds and that of the control. Total haemocyte counts of prawns fed with 4 and 8% stevia were significantly higher than the control and those fed with 1 and 2% stevia. Similar results were obtained for respiratory burst activity of haemocytes. For phenoloxidase activity, prawns fed with 2-8% stevia showed significantly higher activities, while those fed with 1% stevia did not differ from the control. Superoxide dismutase activity of haemocytes was not significantly affected by stevia except at the highest concentration of 8%. For the challenge test, complete protection (0% mortality) was observed on prawns fed 8% stevia while 30% mortality was observed on prawns fed 4% stevia. Highest mortality was observed on prawns fed with control diet (60% mortality). Results of this study show that stevia extract can be used as immunostimulant for grass prawn, which can be given through feed incorporation at concentrations of at least 4% or higher.