A comparison of the heat tolerance and growth of a selected and non-selected line of rainbow trout, Oncorhynchus mykiss, in Western Australia

Duplicates of a domesticated (H-line) and a naturalised line (S-line) of Oncorhynchus mykiss were examined for growth performance and tolerance to acute exposure to water temperature of 27 °C. After 516 days from hatch, fish from the H-line were, on average, 11% longer and 24% heavier than fish from the S-line. Fish from the H-line also displayed lower coefficients of variation in length and weight than fish from the S-line. H-line fish had a significantly greater tolerance to water temperature of 27 °C than S-line fish and significant logistic models were developed for each line. LT 50's of H-line fish were approximately double the LT 50's of S-line fish. Length or weight within a line was not significantly correlated with survival time at 27 °C. The results indicated that the H-line of O. mykiss is well adapted to the relatively hot summer conditions of Western Australia and that directed selection for faster growth has been effective in selecting for increasing heat tolerance within this line. The implications for establishing an even more heat-tolerant line of O. mykiss are discussed in relation to global warming.