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The critical thermal maxima (T(MAX)) of threadfin shad Dorosoma petenense exposed to standardized stress (30 s handling in a dip-net), simulating stressors endured during fish loading before transport, were measured over a range of holding temperatures (15, 20 and 25 degrees C). Dorosoma petenense T(MAX) showed a significant thermal effect, displaying mean +/-s.d. critical thermal maxima of 26.5 +/- 1.6, 30.9 +/- 1.2 and 33.3 +/- 1.4 degrees C, when tested at temperatures of 15, 20 and 25 degrees C, respectively. Dorosoma petenense T(MAX) levels were also affected by stress, with handled fish showing significantly lower values than control fish exposed to 15 (mean +/-S.D. T(MAX) = 25.6 +/- 2.0 degrees C), 20 (27.6 +/- 2.8 degrees C) and 25 degrees C (32.0 +/- 2.6 degrees C). In addition to providing basic information on D. petenense thermal tolerance, experimental results suggest that fishery managers should consider the whole suite of potential stressors, such as air exposure during handling and fish loading, when developing management criteria.

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Mark-recapture studies are often used at fishscreening 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 CO 2 -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 6 SE total length ¼ 9.9 6 0.6 cm, wet weight ¼ 9.1 6 1.8 g), which were marked in the caudal peduncle or caudal fin. Absolute U crit (64.8 6 5.2 cm/s) and relative U crit (7.0 6 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 markrecapture studies because they are unlikely to affect the capture probability of fish through reductions in swimming performance.