Relation Between Temperature and Incubation Time for Eggs of Chinook Salmon (Oncorhynchus tshawytscha)

Abstract

With data assembled from the literature, relations are examined between incubation temperature and rate of development from fertilization to hatching for chinook salmon (Oncorhynchus tshawytscha) eggs. Ten forms of three empirical relations are used, based on the thermal sums hypothesis, Bělehrádek's equation, and a form of the logistic curve. In each case comparisons are made using constant, ambient, and combined (constant + ambient) incubation temperatures. In most cases the rules of minimum variance curve fitting are somewhat violated, although results using the log-inverse form of Bělehrádek's equation are superior to those from the other models. Early imposition of low, constant incubation temperatures (below 6–7 °C) appears to slow egg development below those rates occurring at ambient temperatures having the same mean values. Time–temperature relations based on the unmodified thermal sums hypothesis and its associated "degree-days" are compared with predicted values obtained using the log-inverse Bělehrádek model as a standard. The former model tends to underestimate the length of the incubation period by an average of about 5 days at incubation temperatures above 4 °C; below 4 °C the former model increasingly overestimates the incubation period. Based on the log-inverse Bělehrádek model, a table is provided of predicted daily rates of development in relation to temperature. The table may be used to predict hatching time in a manner similar to that employing degree-days. In general, the enquiry points to a lack of data on development time at temperatures below 5 °C; to be meaningful, further analyses will require such data. Key words: prediction, modeling, development rates, hatching time