TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

Figure 1. Specific Growth Rate of fingerling sockeye salmon (mean weight, 13 g) in
relation to specific feed ration, at 10° C (Brett 1979) (Data from Brett et al. 1969).
The graph shown in Figure 1 is applicable for one specific size and species of fish, at a
specific temperature. As the fish grows, the specific growth and ration rates decline, but
the general shape of the curve would be expected to remain roughly the same. While a
large amount of information is available for the effect of temperature on Gmax, relatively
little information is available on temperature effects on Gopt and Gstarv.
Brett (1979) has plotted various specific growth curves as a function of temperature. In
general, increasing culture temperature increases the food consumption and growth rate
up to the point where higher temperatures start to inhibit the appetite. Above this
temperature maximum, the lines of Gopt and Gmax should be nearly coincident due to the
rapidly increasing metabolic requirements at elevated temperatures coupled with the
inability to ingest more energy. Below the temperature that produces the maximum
growth rate, difference between optimal and maximum growth rates increases rapidly with
an increasing amount of energy available for growth.
It should be noted that apparently the optimal growth temperature for salmonids, sockeye
salmon (Brett 1974) and brown trout (Elliott 1975, as cited in Brett 1979) remains
independent of size. Brett (1979) also cites the work of Oshima and Ihava (1969) that
shows for the case of yellowtail (Seriola quinqueradiata) that the thermal optima
decreases from 27° C to 21° C for juveniles and adults respectively. Previous growth
experiments coupled with the extremely thermophilic nature of tilapia would tend to
suggest that the optimal growth temperature for tilapia would be near the upper lethal
temperature limit, somewhat in excess of 30° C.
4