Tolerance and response of silver perch Bairdiella chrysoura to hypoxia

Silver perch Bairdiella chrysoura are an abundant and ecologically important species that are exposed to major hypoxic events throughout much of their range. Acute sensitivity tests (24 h) were conducted, and the lethal concentration of low dissolved oxygen (DO) determined for B. chrysoura (mean ± SE) 32.5 ± 4.0 mm standard length (SL) at 1.10 mg l �1 (95% CI, 0.43�1.52 mg l �1 ). The avoidance by B. chrysoura to low DO was tested based on size class (mm SL): ≤25, between 26�50, 51�75, and ≥76, with normal DO concentrations (control) throughout a par - titioned aquarium, and later, with an oxygen gradient from low DO ( 5 mg l �1 ). There was a significant difference between the expected and observed distribution for the 3 smaller size classes towards higher DO levels, while the largest size class showed no signif- icant difference in distribution and a G-test showed that oxygen choice levels were significantly different between size classes. The 3 largest size classes of B. chrysoura were tested in a swimming speed apparatus under 3 current speeds (0.17, 0.25, and 0.36 m s �1 ) with both high DO and low DO concentrations. A 3-way ANOVA showed that there was a significant increase in swimming capacity with increasing fish size, decreasing current speed, and increased DO, as well as a significant interaction between all 3 variables. This is one of the first studies to examine size-related responses to low DO in a sciaenid fish.