1. Introduction
Under cultivation, farmed chinook salmon have generally higher feed conver- sion ratios FCRs, higher mortality rates and lower growth rates than Atlantic
salmon. The FCR is the ratio of feed fed kg to weight gained kg. Note that throughout this paper, weight a force with the SI unit of Newton will have the
SI unit of kilogram, normally attributed to mass, following the convention used in fishery science. According to the Cooperative Assessment of Salmonid Health
program, which is being conducted through the British Columbia Salmon Farm- ers’ Association, typical FCR values in British Columbia in 1993 were 1.5 for
Atlantic salmon and 2.0 for chinook salmon over the entire production period. Atlantic salmon also had a much higher average harvest weight, at 4.3 as com-
pared with 2.5 kg for chinook salmon over the same growout period BCMAFF, 1993.
Chinook salmon are considered to be more environmentally sensitive than Atlantic salmon. Chinook salmon show symptoms of oxygen stress when dis-
solved oxygen is below saturation, whereas Atlantic salmon tolerate oxygen levels as low as 44 saturation Caine et al., 1987. Chinook salmon are
more sensitive to temperature fluctuations than Atlantic salmon, but Atlantic salmon become increasingly susceptible to Vibrio infections as salinity levels
drop below 15 parts per thousand Caine et al., 1987. Atlantic salmon show somewhat faster growth than chinook salmon at temperatures lower than 14°C,
which is the optimum temperature for growth for both species Pennell, 1992. Atlantic salmon can, therefore, be raised where chinook salmon cannot, for
example at a site with lower dissolved oxygen levels or greater temperature fluctuations.
Drag increases with swimming speed, bodily area exposed to flow and drag coefficient. Drag has been measured on some fishes dead drag, but only over a
small range of size and shape e.g. Blake, 1983. Chinook salmon tend to be deeper bodied with more area exposed to flow than Atlantic salmon. We hy-
pothesized that the higher FCRs and lower growth rates of chinook salmon are due, at least partly, to their higher energy expenditure while swimming. The
objectives of this research were to: 1 compare the swimming speeds and body dimensions of the two species over a wide range of size; 2 calculate drag and
power; and 3 determine whether differences in FCR and growth rate could be accounted for by differences in body morphology, drag and power.
2. Materials and methods
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