Effects of Ammonia, Salinity and Oxygen on the Growth and Energetics of the Grass Shrimp, \u3ci\u3ePalaemonetes pugio\u3c/i\u3e

The growth and energy budget of juvenile grass shrimp, Palaemonetes pugio, were examined under various combinations of ammonia, salinity and dissolved oxygen. Experiments were performed to determine the effects of multiple stresses on the growth and physiological processes of the shrimp. The experimental design also allowed an evaluation of the effectiveness of several techniques for determining the productivity potential of aquatic animals exposed to stress. A flow-through system was used to produce combinations of ammonia concentrations (0, 3, 6 and 12 mg/l) and salinities (20, 25, 30 and 35 ppt) for 21-day tests. The tests were conducted at high (\u3e5 mg/l) and low (1.7 mg/l) dissolved oxygen (D.O.) conditions. The oxygen consumption rates were elevated for shrimp exposed to high ammonia and high salinity combinations under high D.O. conditions. However, under low D.O. conditions the oxygen consumption was depressed for all treatments involving low D.O. Molting was prevented by high ammonia concentrations, but did not appear to be affected by salinity. Feeding rates were directly affected by salinity and, to a lesser degree, by ammonia. Feces production rates were directly affected by ammonia concentrations and, to a lesser degree, by salinity. Excretion rates were lower under high ammonia and high salinity conditions. The growth rates of the shrimp were significantly reduced in treatments with high ammonia and high salinity combinations. The adverse effects of the ammonia-salinity interaction were particularly evident under low dissolved oxygen conditions. The findings also indicated that commonly used scope for growth estimates may significantly overestimate the productivity potential of stressed populations, particularly when natural stresses are not taken into account. Even more comprehensive energy budget models may underestimate actual growth rates under stressful conditions, particularly those involving low D.O. Processes such as anaerobic respiration, which are not addressed in these models are probably responsible for the lack of balance in the energy budgets of stressed populations