Freshwater prawn Macrobrachium acanthurus is an American native species suitable for aquaculture. The present investigation was conducted to evaluate the effect of two levels of protein and three lipid to carbohydrate ratios on growth, digestive and antioxidant enzyme activities and thus contribute to the formulation of feeds that improve health and growth of juveniles.
180 juveniles (initial weight of 70.4 mg) were randomly stocked in 18 tanks with a water recirculation system. Six treatments were formulated with two levels of protein (35 and 40%) and three combinations of lipids (L) and carbohydrates (C) to a ratio of 2:1 (L= 15% and C= 8%), 1:2 (L= 10% and C= 20%) and 1:6 (L= 5% and C= 30%) in a 2x3 factorial design. Treatments were tested by triplicate and prawns were fed twice a day for 8 weeks. Length and weight were measured bimonthly for growth calculations. Homogenates of juveniles cephalotorax were prepared at the end of the feeding trial for assaying digestive and antioxidant enzyme activities. Data was tested for normality and homoscedasticity before running a 2 way ANOVA using GraphPad Prism v.8.0.2 software.
Juveniles fed with 35% of protein and a 1:6 L:C ratio attained the highest weight (330.4 mg). Protease activity was higher with 40% of dietary protein associated to the increased amount of substrate (Figure 1). Amilase activity decreased significantly with the 1:6 L:C ratio, suggesting that 30% exceeded carbohydrate requirements affecting digestibility. Total antioxidant capacity was highest with P35 and L:C ratio 1:2, and a ratio of 1:6 increased phenoloxidase, prophenoloxidase and catalase to a peak (Figure 2), suggesting oxidative stress. Results evidence that a diet containing 35% of crude protein, 10% of lipids and 20% of carbohydrates (L:C ratio 1:2) helps to improve health and growth in juveniles of M. acanthurus.