Chemical and physical effects of crowding on growth and survival of Penaeus monodon Fabricius post-larvae

The hypothesis that crowding effects through physical and/or chemical interference may be an important factor in lowering the chance of survival and reducing growth of Penaeus monodon post-larvae under high stocking densities was tested. To separate physical interference from chemically-exerted effects, two-stage systems were used in which shrimps were cultured at different densities (stage 1) and water from these being supplied to individually kept P. monodon (stage 2). Stocking density significantly affected P. monodon survival, body-size and dry-weights over a 4-week experimental period. At high densities of 50 and 100 shrimps/l, strong negative effects traveled into stage 2. Hence, physical interference stress and cannibalism could be excluded as causal factors meaning that the negative impact of crowding (at 50 and 100 shrimps/l) on shrimp growth and survival was due to some chemical compounds or other water quality variable. Among these pH, temperature, salinity, dissolved oxygen, chlorine, nitrite and nitrate appeared of minor influence. In contrast, ammonium toxicity could not be excluded as the causal factor for the observed mortality and reduced growth of P. monodon post-larvae in our experiments.