EFFECT OF SEDIMENT ON GROWTH AND ACUTE AMMONIA TOXICITY FOR THE SCHOOL PRAWN, METAPENAEUS-MACLEAYI (HASWELL)

The effects of sediment on growth, survival, food conversion efficienc y and acute ammonia toxicity were determined for the school prawn, Met apenaeus macleayi, a species which normally buries in sediment during the day, Survival of prawns in 70-litre acrylic aquaria was high (90-1 00%) regardless of the absence of sediment (bare plastic) or the type of sediment (mud, fine sand or coarse sand) or whether the prawns were confined in mesh cages. Growth (weight gain) and food conversion effi ciency for confined prawns were significantly lower than for non-confi ned prawns in aquaria with or without sediment. Prawns grew 11-22% fas ter in aquaria with sediment than in aquaria without sediment although the type of sediment had no effect on growth. In a 96-h acute toxicit y experiment, mortality of prawns increased with increasing ammonia co ncentration and, at a concentration of 31.5-32.6 mg total ammonia-N (T AN)/l, was higher in aquaria without sediment (30.0 +/- 5.8%; mean +/- s.e., n = 3) than in those with sediment (6.7 +/- 6.7%). Emergence of prawns from the sediment was affected by time of day and ammonia conc entration. During the day, emergence increased from 7.3 to 79.2% with increasing ammonia concentration (<0.05 to 52.8 mg TAN/l), but most pr awns were emergent during the night regardless of ammonia concentratio ns. In aquaria without prawns, ammonia concentrations and pH were alwa ys lower in water extracted from the sediment than in the water column . The effects of different arrangements of sediment, filtration and ae ration on ammonia concentrations in aquaria are described in relation to conducting and interpreting ammonia toxicity experiments with prawn s.