Abstract
The effects of fertilization and stocking rate on the grow-out phase (123 days) of Penaeus japonicus were studied in earth ponds in a ‘valle’ of the Grado Lagoon (north Adriatic Sea). Water was fertilized by broadcasting poultry manure (2000 kg/ha), ammonium nitrate (8 kg N/ha) and mineral superphosphate (10 kg P 2O 5/ha) in drained ponds. During the trial, half of the initial dose of inorganic fertilizers was also spread fortnightly. Stocking shrimp at 3/m 2 as opposed to 1.5/m 2 lowered the average final weight of the shrimps and negatively influenced the distribution of live-weight classes. Fertilization significantly increased the live weight of the shrimps ( P<0.01) after the 42nd day of rearing. It also significantly lowered the incidence of shrimp weighing less than 16 g but did not affect survival rate. Stomach content analysis confirmed the benthic omnivore habits of P. japonicus, although, within each class, few species were shrimp prey. Both fertilization and stocking density affected shrimp stomach contents.
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