Effects of dietary supplemented oxytetracycline and vitamin c on the performance of giant freshwater prawn (Macrobrachium rosenbergii): Technical paper no. 1/2000

Giant freshwater prawn diets are routinely supplemented with oxytetracycline (OTC) to increase survival and to stimulate growth. This may result in residual OTC in prawn meat which is potentially hazardous for public health. There has been a continuous effort, therefore, to minimize the OTC content of prawn diets. This experiment was conducted to determine whether vitamin C replacement of OTC in the prawn diet can be accomplished without an offset of performance. Prawns weighing approximately 0.48 g were reared in 12 earthen ponds each 200 cubic m. Five thousand juvenile prawn were randomly allocated to each of the four experimental diets with three replicates per diet. Diet 1 was obtained from a commercial source and contained no OTC. Diets 2, 3 and 4 were prepared in our laboratory to have the same basal composition. The OTC concentration in diet 2 was 0.25 percent. Diets 3 and 4 were devoid of OTC, contained vitamin C to 0.25 percent concentration, and differed for the form of vitamin C used. Diet 3 contained ascorbic acid whereas diet 4 contained coated stable form of vitamin C. The prawns were fed twice daily. Body weight and feed consumption were recorded on monthly basis. The OTC concentration in prawns was determined at the end of the experiment, using HPLC. There were no significant differences between treatments in terms of final average body weight (12.85, 12.52, 15.50 and 14.17 g), FCR (1.72, 1.41, 1.69 and 1.43) and survival (85.33, 84, 78.17 and 82.94 percent), respectively. The average total weight of the prawn fed diets 1, 2, 3 and 4 was 55, 53, 60 and 59 kg/pond, respectively. The concentration of OTC in prawn muscle decreased from 3.27 to 0.01 mg/kg at 15 d post OTC withdrawal from the diet. These data suggest that OTC can be eliminated from the prawn diet without any significant decrease in performance when the diet is adequately supplemented with vitamin C. Such a scenario may offer a better safety of public health that may otherwise be compromised by an OTC inclusion in the prawn diet.