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Ecophysiological responses of Litopenaeus vannamei were evaluated as functions of 1) salinity and animal size, 2) temperature and the animal's nutritive state, and 3) dissolved-oxygen concentration and animal size. Growth rate, routine metabolic rate, limiting oxygen concentration for routine metabolism, and marginal metabolic scope were determined for L. vannamei maintained and tested at salinities of 2, 10, and 28 ppt, all at 28 C. Routine metabolic rate (RMR) was not demonstrably dependent on salinity but decreased with increasing shrimp weight. Limiting oxygen concentration for routine metabolism (LOCr) was independent of shrimp weight up to 9 g; but, for larger shrimp, decreased with increasing weight. Marginal metabolic scope (MMS = RMR/LOCr) also decreased with increasing shrimp weight and was independent of salinity for shrimp weighing up to 9 g; but, like LOCr, MMS was dependent on salinity for larger shrimp. Growth rate was significantly less at 2 ppt than at 10 or 28 ppt, which gave similar growth rates. The effects of four temperatures (20, 24, 28, and 32 C) on growth, RMR, LOCr, and MMS were examined for fed and starved L. vannamei. Routine metabolic rate increased with increased temperature both for fed and starved shrimp. Marginal metabolic scope and growth appeared to be positively related and, at 20 C, seemed to induce a state of metabolic torpor. Data from the study of chronic effects of hypoxia (~2 mg O2 L-1) vs. normoxia (> 5 mg O2 L-1) on ecophysiological responses indicated that although low-DO environments can depress RMR and growth in L. vannamei, animals grown under hypoxic and normoxic conditions did not differ in their metabolic responses upon acute exposure to hypoxia, providing no evidence of acclimation to hypoxia in L. vannamei. Data from the above experiments were used to parameterize Ecophys.Shrimp, a computer simulation model of shrimp growth in time-varying environmental regimes. One unified model was able to simulate all my experiments; and, with only minimal adjustment of the model parameter MMSO, it also adequately simulated studies taken from the literature. Thus, Ecophys.Shrimp seems capable of realistically representing the ecophysiological dynamics of shrimp metabolism and growth in various culture systems. |
