Effect of elevated winter-spring water temperature on sexual maturation in photoperiod manipulated stocks of rainbow trout (Oncorhynchus mykiss)

The use of artificial lighting on salmonids has successfully reduced levels of early sexual maturation, however variable results between seasons have been observed. Therefore, this work investigated the impact of photoperiod and winter-spring water temperature on maturation in populations of female rainbow trout. Fish were maintained in tanks (from April 2006 to May 2007) under two photoperiod regimes-(1) simulated natural annual photoperiod cycle (41°S) and (2) approximately 5. week advanced annual photoperiod cycle. Two temperature treatments were also employed-(1) simulated natural annual temperature cycle (8-18 °C) and (2) simulated natural annual temperature cycle with elevated mean winter-spring water temperatures (maximum 5 °C elevation). In photoperiod advanced fish, elevated water temperature resulted in a significant increase in maturation rate (39.8 ± 3.3% and 17.5 ± 5.3% for the elevated temperature and natural temperature group, respectively). Maturation rates in fish held under natural photoperiod conditions were significantly higher irrespective of water temperature (79.4 ± 6.6% and 73.3 ± 0.1% for the elevated temperature and natural temperature group, respectively). In addition, gonadosomatic index was significantly higher in photoperiod advanced fish, irrespective of water temperature, at the conclusion of the experiment, with 32% of these fish undergoing ovulation and significantly reduced plasma levels of 17ß-estradiol just prior to ovulation. Significantly greater wet weight, condition factor, specific growth rate and plasma insulin-like growth factor-I were measured in PIT-tagged fish which went on to mature at the conclusion of the experiment compared to those which remained immature. This study demonstrates that elevated winter-spring water temperature results in increased rates of maturation in photoperiod-manipulated stocks of rainbow trout and has important implications for application of artificial lighting on commercial farms which may experience variation in water temperature from year to year. © 2010.