Effect of dissolved oxygen on stomach evacuation rate of juvenile red drum (Sciaenops ocellatus)

Abstract

Juvenile red drum (Sciaenops ocellatus) weighing 19,7[]2.5 g, and acclimated to 10 ppt salinity and 25[]1[]C, were subjected to one of three dissolved oxygen (DO) regimes-- 7.5, 4.5, and 2.7[]0.5 mg O₂ 1⁻¹ -- after consuming pelleted feed to apparent satiation under nontoxic conditions, to which they had been adapted. Stomach contents were collected from fish sampled at intervals over the succeeding 24 h, to relate stomach evacuation rate to DO regime. A preliminary experiment had established appropriate experimental design and protocol. Data from the final experiment were analyzed by means of the square-root model and the exponential-decay model for stomach evacuation. Analysis of variance indicated that the square-root model better described the gastric evacuation process for all treatments than the exponential-decay model. Stomach evacuation rate constants (k) under the square-root model were 0.205, 0.138, and 0.156 h⁻¹, for the nontoxic, mesoxic, and hypoxic regimes, respectively. Values of k under both models exhibited significant (p<0.05) differences among DO treatments, with k for the 7.5 mg O₂ 1⁻¹ treatment being significantly greater than for the 4.5 and 2.7 mgO₂ 1⁻¹ treatments, which had ks that did not differ from one another. It is concluded that levels of DO below 55% air saturation can markedly reduce stomach evacuation rate of juvenile red drum fed a commendably formulated enfolded diet.