UTILITY OF STREAMER TAGS TO ASSESS SURVIVAL AND GROWTH OF JUVENILE TIGER PRAWNS (PENAEUS-MONODON) IN AQUACULTURE ENVIRONMENTS

Experiments in tank and pond environments over 5-6 months showed that growth rate of juvenile Penaeus monodon was unaffected by tagging at 1 5 mm carapace length (CL) or at 18 mm CL. The mortality rate of prawns tagged at 15 mm CL was consistently greater than those tagged at 18 m m CL in both environments, suggesting that the minimum size for taggin g to obtain less biased survival estimates is at least 18 mm CL. Survi val in the tank of prawns tagged at 18 mm CL was the same as untagged animals (40-50%), but that of prawns tagged at 18 mm CL in the pond (5 0%) was less than untagged prawns (70%). These results suggest an envi ronment-specific effect on tag-induced mortality: The ability to obtai n independent data from untagged animals in aquaculture ponds allowed the effect to be detected. This has been impossible in wild fisheries work and the results in this paper highlight the inadequacy of tagging methods to obtain mortality estimates from wild prawn populations. Ta g colour also biased tag recovery rates, but no mechanism to explain t he bias was identified. Streamer tags will prove useful in aquaculture as the tags are unlikely to affect important performance characterist ics of the marked animals, such as growth rate, and reasonable relativ e estimates of mortality among tagged groups can be obtained. However, the use of tagged animals to gain accurate estimates of mortality of an untagged group they are meant to represent is unlikely to be succes sful, even in relatively well-controlled aquaculture situations, becau se of environment specific effects on tag mortality.