Comparison of two uropod-cutting methods for tagging of juvenile grass prawn Penaeus monodon

Abstract

Two uropod-cutting methods were used and compared for tagging of Penaeus monodon juveniles: LE-cutting half of the left exopod; and WR-cutting the whole right uropods. The treatments were composed of LE, WR, Control (with uncut uropods), and Mixed (equal numbers [5 prawns] of LE, WR and Control in one tank). Fifteen prawns were used for each treatment and the Control, with two replicate tanks for each. Results show that there was no significant difference (P>0.05) on growth and survival among the experimental treatments and the Control after three months of culture. Regeneration of uropods commenced within a week of culture and complete regeneration was evident after one month in LE treatment and after two months in WR treatment. Abnormalities observed in regenerated uropods for LE treatment were composed mostly of hollow type (HT; 65.2%) and flat type (FT; 25.8%). Tag retention rate was 91.0%. In WR treatment, 80.3% regenerated into normal type (N) composed of those with normal pigmentation (33.9%) and with less pigmentation or discoloration (46.4%). Other abnormality observed was incomplete growth (IG; 7.2%) while the rest (10.5%) cannot be classified due to the presence of severe tail rot. Tag retention rate for this cutting method was only 53.3%. In the Mixed treatment, prawns tagged using LE were easily distinguishable from the rest of the prawns (Control and WR) in the same tank. A mean of 73.3% of the LE cut prawns regenerated into HT and 6.7% into FT. For prawns with WR cut uropods, only 40% regenerated into N with discoloration, while the rest (~60%) either regenerated into N which is indistinguishable from the Control, or not classified due to tail rot. Overall, LE method is recommended for tagging juvenile P. monodon as it can produce more distinguishable abnormality in the regenerated uropods compared to WR method. The abnormalities observed can be retained by the tagged prawns even after several molting cycles during their growth.