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Early life history and possible interaction of five inshore species of fish in Nicola Lake, British Columbia Miura, Taizo


Early life history, distribution, movement, food habits and interspecific relations of five inshore species, largescale sucker (Catostomus macrocheilus), northern squawfish (Ptychocheilus oregonense), peamouth chub (Mylocheilus caurinum), red side shiner (Richardsonius balteatus), and prickly sculpin (Cottus asper), have been studied during the summers of 1959 - 1961 in Nicola Lake, British Columbia. Analyses were based on specimens periodically sampled with three types of seine nets from various inshore waters of the lake, observation of behaviour of the fish both in nature and in aquaria, and study of plankton, bottom animals and temperature conditions. After emerging, the fry of all species move to the head of the lake where there is a tendency to form an early-summer aggregation. Later, they diverge from the head of the lake along the shore. Fry of all four cypriniform species showed similar diurnal movement. They started to move into the shallow water at dawn and moved out at dusk. In the sculpin, fluctuations in numbers near shore had no direct correlation with time of a day. No species was rigorously restricted to one habitat, although different habitat preferences were observed. To a certain extent the species were separated by difference in distribution in relation to depth. These differences increase with age. A close association among fry of all species in the early summer gradually dissipated. Divergence was also observed in feeding habits of these species. In early summer they are typically plankton feeders, but towards the end of summer their interspecific feeding relations gradually become less because of the divergence in food preference, feeding places and feeding manner. These changes are in turn largely due to morphological changes, in particular those of feeding structures. Since the plankton resources seemed to be insufficient in the shallow inshore area, there may have been competition for food in early summer. Moreover, the fry may have been forced into severe competition by an early-summer aggregation at the head of the lake as well as by similarity in behaviour and habitat. An alternative approach to the problem of demonstrating interspecific relationships was made from comparison of species associations in lakes of the Fraser River drainage. A positive correlation between the surface area and the number of species suggests that the larger the lake, the greater the possibility of coexistence between these species, and that competition in small lakes may be a factor in eliminating some of the species. These findings are discussed in relation to the current controversy concerning specialization of temperate and tropical freshwater fishes. It is concluded that in large complex environments freshwater fishes are afforded the opportunity for specialization, whereas in small or simple environments, more generalized behavior leads to competition between species.

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