Long-term ammonia toxicity to the pink-shrimp Farfantepenaeus paulensis
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Juvenile pink-shrimp Farfantepenaeus paulensis were exposed (75 days) to NH(3) (0.016-0.287 mg L(-1)) under static condition with water renewal every 24h. Experiments were performed at 20 degrees C, at a water salinity of 15 ppt, and at pH 7.8. Endpoints analyzed were survival, growth and predation rates. After 75 days of exposure, survival was >or=90% in all concentrations tested. However, growth (carapace length and wet body mass) was reduced after exposure to NH(3) concentrations as low as 0.033 mg L(-1), while the relative growth (dry body mass and ash content) was reduced after exposure to the highest NH(3) concentration (0.287 mg L(-1)). Predatory activity was inhibited after exposure to 0.144 or 0.287 mg L(-1) NH(3). Post-larvae exposed (75 days) to 0.301 mg L(-1) NH(3) under the same experimental conditions also showed a reduced growth (wet body mass) and relative growth (dry body mass). In addition, they showed decreased body lipids content and increased body glycogen and glucose contents. However, no changes in body protein, chitin and uric acid contents were observed. Also, NH(3) did not affect post-larvae feeding response. Altogether, findings suggest that F. paulensis reduces its food intake to limit the internal accumulation of nitrogenous waste products when exposed for long time to high levels of ambient ammonia. As a consequence, shrimp show a marked change in energy metabolism, characterized by a decreased content of body lipids paralleled by an increased content of body carbohydrates, resulting in a significant reduction in growth.
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