干旱区生态环境知识资源中心

Temperature is an important factor affecting the distribution of freshwater fishes. The longfin dace (Agosia chrysogaster) is endemic to the Gila River basin of the southwestern USA and northern Mexico and occupies a range of thermal environments from cool mountain tributaries to warm desert rivers but information about its thermal biology is limited, particularly for larvae. We quantified the effect of rearing temperature on survival, growth capacity, and critical thermal maximum (CTM) of larval longfin dace. Broodstocks of longfin dace were collected from two sites in the upper Gila River in New Mexico from which larvae were hatched and reared for 22 days in indoor aquaria at constant temperatures ranging from 18.0 to 31.0 A degrees C. Growth capacity peaked at 27.0 A degrees C and was 21 % greater for larvae hatched from the upstream compared to the downstream broodstock, indicating intraspecific variability in growth capacity. CTM increased with rearing temperature and ranged from 33.9 to 39.9 A degrees C, indicating that thermal acclimation influences maximum thermal tolerance. CTM and acclimation response ratio of larvae are lower than those of adult longfin dace measured in a previous study, suggesting that larvae are more sensitive and less responsive to thermal stress than adults. Water temperatures in 2012 from six sites in the upper Gila River basin did not exceed 27.0 A degrees C and larval growth capacities in May of 2012 ranged from 5 to 28 % of the maximum growth capacity. We assert that rising temperatures may increase larval growth rates, although this will depend on resource limitation and shifts in community interactions.