Stress Response and Avoidance Behavior of Fishes as Influenced by High‐Frequency Strobe Lights

Abstract

We examined the effects of strobe lights on plasma cortisol concentrations and avoidance behavior across a broad range of fish taxa. Representative fish taxa from five families were evaluated and included: Centrarchidae (largemouth bass Micropterus salmoides), Cyprinidae (fathead minnow Pimephales promelas), Ictaluridae (channel catfish Ictalurus punctatus), Percidae (yellow perch Perca flavescens), and Salmonidae (Chinook salmon Oncorhynchus tshawytscha). Mean (±SE) plasma cortisol concentrations for channel catfish (89 ± 22 ng/mL), yellow perch (81 ± 39 ng/mL), and Chinook salmon (173 ± 27 ng/mL) increased significantly compared with those in control groups (50 ± 11, 3.0 ± 1.9, and 102 ± 35 ng/mL, respectively) after 1 h of exposure to strobe lights. After 7 h of exposure, plasma cortisol levels were similar to those in control groups for all fish taxa. Fathead minnow showed no detectable response to strobe lights at either 1 or 7 h of exposure. Behavior experiments showed that the mean distance moved from the strobe light varied significantly between test and control fish and was highest for largemouth bass (mean distance after 1 h = 8.3 m), followed by Chinook salmon (7.3), yellow perch (7.3), and channel catfish (5.1). In contrast, avoidance behavior by fathead minnow exposed to strobe lights did not differ from that of controls. Although a significant increase in plasma cortisol level was useful for predicting an avoidance response, relative change in cortisol concentration was a poor indicator of sensitivity of individual fish taxa to strobe lights. Direct observations of avoidance behavior revealed that largemouth bass, Chinook salmon, and yellow perch were more sensitive to strobe lights than channel catfish and fathead minnow. Lack of both a cortisol response and avoidance behavior by fathead minnow indicates low sensitivity of this species to strobe lights and warrants further investigation into the effectiveness of strobe lights on cyprinids.