Hypoxia tolerance of juvenile weakfish (Cynoscion regalis): Laboratory assessment of growth and behavioral avoidance responses

Laboratory experiments were conducted to examine the growth rate and avoidance behavior of juvenile weakfish (Cynoscion regalis) exposed to hypoxia (dissolved oxygen (DO) below saturation). Growth rates were measured under constant (2.0, 3.5, 5.0 and 7.0 mg O2 L− 1) and diel-cycling (2.0–11.0 mg O2 L− 1) DO conditions at three temperatures (20, 25, and 30 °C) over 7 days. Two-way DO choice trials were conducted over the same temperature range to 1) determine the DO level at which juvenile weakfish exhibit hypoxia avoidance and 2) examine whether temperature influences hypoxia avoidance behavior. There was no significant effect of constant hypoxia, or diel-cycling hypoxia, on growth rates of weakfish at any temperature. In the DO choice trials, weakfish avoided 1 mg O2 L− 1 but showed no preference for DO when the low choice was ≥ 2 mg O2 L− 1. Temperature had no significant effect on growth or avoidance responses of juvenile weakfish. Lack of mortality during seven days exposure to hypoxia as low as 2 mg O2 L− 1, moderate to high growth rates, and lack of hypoxia avoidance of DO concentrations as low as 2 mg O2 L− 1 indicates that juvenile weakfish are physiologically capable of tolerating levels of hypoxia commonly encountered in estuarine nurseries during summer months. There was no indication that hypoxia avoidance occurs at a DO level higher than that which negatively impacts growth rate in juvenile weakfish.