Studies on the Alaskan Blackfish Dallia pectoralis I. Habitat, Size and Stomach Analyses

Abstract

The end-product of evolution via mutation and natural selection frequently results in the establishment of a species well adapted to a limited environment. The distribution of the Alaskan blackfish, Dallia pectoralis Bean, limited to arctic and sub-arctic fresh waters, (Jordan and Everman, 1896; Wilimovsky, 1954), suggests that because of modifications necessary for survival in the cold, this species may have become over-specialized, resulting in an organism suitably adapted to the cold. We successfully maintained 50 live blackfish under refrigeration in the laboratory at Catholic University during 1953 and 1954. A second group of 30 animals was kept at room temperature (250C). The members of this group died within a few weeks even though we attempted to gradually acclimatize them to room temperature. Other factors suggest that this species is well adapted for survival in the cold. For example, Turner (1886) reports that the Alaskan blackfish was frequently collected by natives, stored in grass baskets, frozen, and fed to dogs. Upon being rewarmed, it is reported, the fish was regurgitated alive by the dogs. Such reports are part of Alaskan folk-lore. Scholander et. al. (1953) in an attempt to verify such reports performed critical metabolic and survival studies on the blackfish, the results of which indicated that the fish is, indeed, coldadapted but it cannot survive freezing. The above studies suggested to us that an ecological and physiological investigation of the blackfish was warranted. The physiological study will be published separately. The ecological study included determinations of the total alkalinity, pH, dissolved oxygen and temperature of the environment, and of the total length, weight, and stomach contents of the fish. All these factors are interrelated; the physical environment influences the occurrence of food as well as the distribution of the blackfish.