LAUSR

AbstractHatchery-reared fingerling Guadalupe Bass Micropterus treculii are stocked into central Texas rivers to restore threatened populations and combat hybridization with Smallmouth Bass M. dolomieu. Fry survival in hatchery rearing ponds has declined by more than 50% in recent years, and pilot investigations indicated that exposure to high dissolved oxygen (DO) concentrations (>20 mg/L; hyperoxia) during tempering might have contributed to fry mortality. To test this hypothesis, Guadalupe Bass swim-up fry (11 d posthatch; 8.45 ± 0.25 mm TL [mean ± SD]) were exposed to normbaric DO concentrations ranging from 7.9 to 33.3 mg/L at 18°C, mimicking the hatchery tempering protocols followed during 2014 and 2015. After a 30-min exposure to the DO treatment (flow rate = 18 L/h), jars were flushed with nonoxygenated water for 1 min to rapidly lower the DO, mimicking the release of fry into ponds after tempering. Jars were then supplied with freshwater at a rate of 36 L/h and were monitored for 72 h. One control...