Swimming Performance of Sacramento Splittail Injected with Subcutaneous Marking Agents

Abstract

Mark–recapture studies are often used at fish-screening facilities near water diversions, such as those in the Sacramento–San Joaquin Delta, to quantify fish salvage efficiency. The accuracy of these salvage estimates and subsequent facility operational criteria are highly dependent on unbiased mark–recapture estimates. Marking techniques and agents that produce reduced swimming performance in marked fish could result in inaccurate estimates of fish salvage and facility efficiency. Two of the most commonly used marking agents and techniques for experimental purposes at these screening facilities are the subcutaneous injection of visual implant elastomers using a hypodermic needle and the subcutaneous injection of fluorescent latex microsphere solutions using a CO₂-powered pneumatic marking gun. We tested the effects of these marking agents and techniques on the critical swimming velocity (U_crit) of age-1 Sacramento splittail Pogonichthys macrolepidotus (mean ± SE total length = 9.9 ± 0.6 cm, wet weight = 9.1 ± 1.8 g), which were marked in the caudal peduncle or caudal fin. Absolute U_crit (64.8 ± 5.2 cm/s) and relative U_crit (7.0 ± 1.1 body lengths/s) were unaffected by marking technique or marking agent (2-way ANOVA). Our results suggest that the tested marking agents and techniques are suitable for use in mark–recapture studies because they are unlikely to affect the capture probability of fish through reductions in swimming performance.