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Penaeids can be divided into three groups on the basis of their burrowing behaviour. Members of the first group live in clear water; they are always burrowed in the day or in bright moonlight and emerge only at night. The group includes P. duorarum, P. Iatisulcatus, P. plebejus and probably P. brasiliensis and P. notialis. Prawns in the second group live in slightly turbid water; they are nocturnal but occasionally emerge during the day. Species in this group include P. aztecus, P. esculentus, P. monodon, P. japonicus and P. semisulcatus. The third group is found in turbid water and seldom if ever burrows. It includes P. indicus, P. merguiensis, P. chinensis [= orientalis], P. setiferus and probably P. occidentalis and P. schmitti (Dall et al., 1990). The prawns in these different groups are clearly responding to light and to factors that affect light intensity. Three factors can be regarded as the major ones influencing light intensity and thus prawn behaviour; these are diel changes, moonlight and turbidity. Ammount of light is influenced by the diel cycle, the moonlight and the turbidity. Amount of light is influenced by the diel cycle, the moonlight and the turbidity (Dall et al., 1990). Shrimp are adapted to survival in turbid waters, and turbidity is not likely to be a significant factor affecting survival in natural-systems unless associated with heavy freshwater runoff. Turbidity in cultures inhibits monitoring of sexual maturation, biomass and survival rates (Hanson & Goodwin, 1977). | |