Feeding of Some Great Lakes Fishes at Low Temperatures

Field studies on low temperature feeding in freshwater fishes were carried out as follows: (1) Fish Lake, near Picton, Ontario, January–March 1966 and 1967, 1200 fish netted from under the ice at a temperature of 4 C; (2) Little Cataraqui Creek near Collins Bay, April 1966, groups of fish (total, 544 individuals) netted at intervals of several days as the water temperature rose from 6.8 to 11 C; (3) Upper Jones Creek, near Mallorytown, two extensive collections (total, 1005 individuals) made between April 27 and 30, 1966 (at a water temperature of 8 C), and May 15 and 17 (15 C). The following findings resulted.Some members of all six species in Fish Lake contained food but the percentage varied from 50% in Umbra limi down to 10% in Fundulus diaphanus. Hence feeding was erratic. Within species the smaller individuals invariably contained more food (0.005–0.02 g of alimentary contents per gram body weight) than larger fish (0.002–0.005). The same was true of smaller, as compared with larger, bodied species, with the exception of F. diaphanus.After the thaw in Little Cataraqui Creek active feeding commenced at different temperatures in the various species: it was already under way at 6.5 C (when the study started) in Ictalurus nebulosus and Pomoxis nigromaculatus, but did not start in Lepomis gibbosus and Ambloplites rupestris until the water temperature reached 8.5 C. Prior to this the stomachs of species were shrunken, mucous-filled, and drawn far forward in the body cavity. Few Perca flavescens, active winter feeders, fed in April, immediately prior to spawning.In most of the Jones Creek fishes there was a marked increase in weight of alimentary contents (gram per gram body weight) between 8 and 15 C. Exceptions were the larger Semotilus atromaculatus, which were than spawning, and U. limi and Eucalia inconstans, which were sampled before their peak daily feeding times. To the differences in weights of alimentary contents at 8 and 15 C must be added accelerated digestion rates at 15 C.In all the waterways studied the fish consumed a much smaller range of prey items at low temperatures than at higher ones. This applied in midwinter, compared with summer, in Fish Lake, and in April and October, compared with summer, in Jones Creek. A few foods, e.g. chironomid larvae and Cladocera, were especially prominent in the diet at low temperatures, and species food specializations were suppressed. There was probably not, however, any increase in interspecific competition at temperatures approaching zero, because of the relatively low metabolic requirements of the fish.