472
C. B. COWEY AND J. R. SARGENT
Variations in the body composition of young sockeye salmon
(Oncorhynchus nerka) receiving a single diet occurred in response to
both ration size and water temperature (Brett et al., 1969). Extremes
of body composition were 86.9% water, 9.4% protein and 1.0% lipid
in fish starved for 83 days at 20°C to 71.3% water, 19.7% protein and
7.6% fat in fish fed to excess for 99 days at 16°C. Variations were due
to progressive changes in water content; at all temperatures as daily
ration size increased the water content of the body decreased while
lipid and protein increased. Brett et al. were able to derive equations
relating lipid content and protein content to water content. From these
equations measurement of water content alone would enable major
components in the body of the fish receiving the same diet to be
deduced.
VII. FEEDING RATE AND CONVERSION RATE
The importance of daily ration size is clear ; excessive feeding will
be wasteful and possibly deleterious to the water quality while
inadequate rations will limit growth rate. Thus with channel catfish
feeding rates greater than 4% (4g dry WeightllOOg live weight of
fish) led to inefficient utilization (Simco and Cross, 1966) and the best
conversions occurred at feeding rates between 2% and 3% (Swingle,
1964; Tiemeier et al., 1969).
A searching study of the relationship between feeding rate and
growth rate in sockeye salmon fingerlings wasmade by Brett etal. (1969).
Several groups of fish were held at each of a series of temperatures
between 1°C and 24°C. At each temperature different quantities of
the same food (varying from 0 to 6 g of dry food per 100 g dry weight
of fish) were fed to each group. Stable growth was obtained at each
temperature and from plots of growth (weight gain) against ration
size it was possible to determine optimal ration (that providing
greatest growth for the least intake) and maximal ration (that providing maximal growth rate) at each temperature. As water
temperature increased, larger rations were necessary to meet defined
growth parameters, in other words at reduced ration levels optimal
temperatures for growth fell. Thus a ration of 1 6 % dry body weight/
day permitted nearly optimal growth at 6" but no growth at 16".
The fish had a general temperature optimum for growth around 15"
the ration size for optimal growth at this temperature being about
6.2% of the dry body weightiday.
From their data on growth and ration level Brett and his colleagues
were able to distinguish between maximal, optimal and maintenance
levels, the latter being a ration " that just maintains the fish without
C. B. COWEY AND J. R. SARGENT
Variations in the body composition of young sockeye salmon
(Oncorhynchus nerka) receiving a single diet occurred in response to
both ration size and water temperature (Brett et al., 1969). Extremes
of body composition were 86.9% water, 9.4% protein and 1.0% lipid
in fish starved for 83 days at 20°C to 71.3% water, 19.7% protein and
7.6% fat in fish fed to excess for 99 days at 16°C. Variations were due
to progressive changes in water content; at all temperatures as daily
ration size increased the water content of the body decreased while
lipid and protein increased. Brett et al. were able to derive equations
relating lipid content and protein content to water content. From these
equations measurement of water content alone would enable major
components in the body of the fish receiving the same diet to be
deduced.
VII. FEEDING RATE AND CONVERSION RATE
The importance of daily ration size is clear ; excessive feeding will
be wasteful and possibly deleterious to the water quality while
inadequate rations will limit growth rate. Thus with channel catfish
feeding rates greater than 4% (4g dry WeightllOOg live weight of
fish) led to inefficient utilization (Simco and Cross, 1966) and the best
conversions occurred at feeding rates between 2% and 3% (Swingle,
1964; Tiemeier et al., 1969).
A searching study of the relationship between feeding rate and
growth rate in sockeye salmon fingerlings wasmade by Brett etal. (1969).
Several groups of fish were held at each of a series of temperatures
between 1°C and 24°C. At each temperature different quantities of
the same food (varying from 0 to 6 g of dry food per 100 g dry weight
of fish) were fed to each group. Stable growth was obtained at each
temperature and from plots of growth (weight gain) against ration
size it was possible to determine optimal ration (that providing
greatest growth for the least intake) and maximal ration (that providing maximal growth rate) at each temperature. As water
temperature increased, larger rations were necessary to meet defined
growth parameters, in other words at reduced ration levels optimal
temperatures for growth fell. Thus a ration of 1 6 % dry body weight/
day permitted nearly optimal growth at 6" but no growth at 16".
The fish had a general temperature optimum for growth around 15"
the ration size for optimal growth at this temperature being about
6.2% of the dry body weightiday.
From their data on growth and ration level Brett and his colleagues
were able to distinguish between maximal, optimal and maintenance
levels, the latter being a ration " that just maintains the fish without