Swimming Performance and Physiological Stress Responses of Splittail Exposed to a Fish Screen

Abstract

Fish screens are designed to divert fish away from potentially life-threatening water diversions, yet little is known of the immediate effects of the screens on exposed fish. To determine the effects of screen exposure, splittail Pogonichthys macrolepidotus swimming performance and survival were measured during exposure to a fish screen and bypass channel in a variable-velocity water flume at 12°C for not more than 1.5 h. Four treatment velocities (range, 0–60 cm/s) were used with 20 fish (standard length (±SD) = 5.9 ± 1.3 cm) per experiment, with three replicate experiments per treatment. The sublethal effects of screen exposure were also assessed by measuring physiological stress responses at −2, 0, 0.5, 2, and 24 h following screen exposure. No losses of equilibrium or mortality were associated with any of the velocity treatments. During the control treatment (0 cm/s water velocity through the 0.6-m-wide × 13.7-m-long flume), screen contacts were infrequent (mean total = 2 ± 2), and the mean swimming velocity was 18.8 ± 3.5 cm/s. At increased velocities, screen contacts increased, mean swimming velocities increased (up to 52.3 cm/s), and the fish displayed significant, positive rheotaxis. The number of fish entering the bypass channel and the physiological stress responses (hematocrit, plasma glucose, and lactate concentrations) did not differ significantly among treatments. Since splittail exposed to a wedge-wire fish screen at elevated water velocities similar to those found at large water diversions did not experience significant sublethal effects or increased mortality, it does not appear that the factors contributing to splittail mortality at diversion screening facilities are related to screen exposure.