Lake trout (Salvelinus namaycush), initial weight 2.25 g, were reared at population densities of 25, 50, 75, 100, and 125 fish in 6.55‐L cylindrical jars for 20 weeks with a mean water flow of 2.45 L/min. All fish survived the experiment. A significant (P < 0.05) reduction in growth occurred between population densities of 25 fish and those of 50 fish or more per jar, but differences among further increases beyond 50 fish were not significant. Total fish weight at the end of 20 weeks ranged progressively upward from 51.5 to 233.9 kg fish/m³ rearing space for fish at population densities of 25 to 125 per jar. Loading values were light at all densities, ranging upward from 0.14 to 0.62 kg fish/L per min flow. Total consumption of oxygen by fish in each jar increased with time (weeks) and population density. Oxygen consumption per unit weight of fish decreased significantly, however, with each successive 25‐fish increase in number of fish per jar. Mean specific gravity of the 25‐fish groups was less than that of fish of the other groups. Differences in population density did not significantly affect water flow rates, feed conversion, or condition factor (K) of the fish. The number of water exchanges per hour, ranging from 23.8 to 29.3 for the 25‐ to 125‐fish densities, tended to increase with each increase in population density.
