Photophase and Illumination Effects on the Swimming Performance and Behavior of Five California Estuarine Fishes
Photophase and illumination affect many fish activities. In this study, we examined their effects on the critical swimming velocities (Ucrit), swimming gait patterns, and oral grasping behavior of five California estuarine fishes. All species (4–5 cm SL) swam similarly (mean Ucrit range: 30–36 cm/sec) under day/light conditions. However, both nighttime photophase and darkness decreased Delta Smelt (Hypomesus transpacificus) swimming velocities. Congeneric Wakasagi (Hypomesus nipponensis) swimming performance also decreased at night/dark conditions. Regardless of photophase and illumination, Delta Smelt, Wakasagi, and Splittail (Pogonichthys macrolepidotus) exhibited three swimming gaits: intermittent stroke-and-glide at low velocities, continuous stroking at moderate velocities, and intermittent burst-and-glide at high velocities near Ucrit. In contrast, Chinook Salmon (Onchorhynchus tshawytscha) used only two swimming gaits: continuous stroking and burst-and-glide under all conditions. Inland Silversides (Menidia beryllina) used these two gaits under light conditions and all three gaits under dark conditions. Some Wakasagi, Splittail, and Chinook Salmon orally grasped the upstream screen in the flume at moderate to high water velocities. Oral grasping does not require jaw teeth and may represent adaptive behavior in natural habitats. Regarding vulnerability to water diversions that operate in the dark at night, the threatened Delta Smelt and introduced Wakasagi, comparatively, may be more at risk than the other species.Abstract
Mean (± SEM) critical swimming velocity (Ucrit) of different California estuarine fishes under the four photophase and light conditions. Superscripted letters show significant differences: (A) Delta Smelt at D/L conditions; (B) all other species at N/L conditions; (C) all other species except Wakasagi at N/D conditions; (D) Wakasagi at D/L and N/L conditions; number on top of bar indicates sample size
Mean (± SEM) swim velocity ranges (from minimum to maximum velocities) at which different swimming gaits were exhibited by different California estuarine fishes under the four photophase and light conditions
Mean (± SEM) water velocity range, number of events and duration at which oral grasping behavior was observed in Wakasagi, Splittail, and Chinook Salmon under various photophase and light conditions. Fractional number indicates the number of fish that exhibited oral grasping behavior over number of total fish used; white circle indicates the mean Ucrit value for total fish used; #: one fish grasped for > 120 sec; ##: two fish grasped > 120 sec
Contributor Notes
Department of Wildlife, Fish, and Conservation Biology; and Center for Aquatic Biology and Aquaculture, University of California, 1 Shields Avenue, Davis, California 95616-8521. (PSY) psyoung@ucdavis.edu Send reprint requests to PSY.