LETHAL LEVELS OF LOW DISSOLVED-OXYGEN AND EFFECTS OF SHORT-TERM OXYGEN STRESS ON SUBSEQUENT GROWTH OF JUVENILE PENAEUS-MONODON

The lethal level (96 h LC50) of dissolved oxygen (DO) for juvenile Penaeus monodon was estimated to be 0.9 mg O2 l-1 (95% confidence limits: 0.8, 1.0 mg O2 l-1). Other replicate groups of P. monodon were subjected to short-term, severe DO stress and then grown under conditions approaching DO saturation. The aim was to simulate the type of event which can occur in ponds when emergency aeration successfully raises DO after an oxygen crisis. Neither the duration (4,8 or 12 h), nor the level (0.5-0.6 or 1.0-1.1 mg O2 l-1) of the DO stress significantly (P > 0.05) reduced subsequent growth or food conversion efficiency at favourable DO levels over 21 days. Prawn pond managers should not need to reduce feeding levels or consider premature harvest after a single, short-term DO crisis when mass mortality is avoided. This is provided that other water quality variables do not reach critical levels during the crisis.