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Some factors affecting the distribution and abundance of the chiselmouth (Acrocheilus alutaceus) Moodie, Gordon Eric Edmund

Abstract

Some features of the biology of Acrochellus alutaceus were investigated with the purpose of explaining the rarity and disjunct distribution of the species in British Columbia. Two populations were compared, one in a lacustrine environment, in which the species is often rare, the other in a riverine environment, in which the species is usually common. Age and growth analysis of the two populations showed that in the river population growth continued for one year longer than in the lake population. Maximum age attained in both populations was 6 years. Observations of feeding behavior in the field and laboratory suggested that the unusual lower jaw of the fish is an adaptation to scraping Aufwuchs, chiefly filamentous algae, from smooth substrates. Analysis of diet in the two habitats showed a much more restricted diet in the river. It is concluded that the growth of the type of food consumed by Acrocheilus and the occurence of a substrate suitable for feeding will be most abundant and commonly found in warm rivers. The temperature required for spawning by Acrocheilus is probably higher than that of other local cyprinids. This may also limit the distribution of the species. In both habitats, diet changes with age; young fish lack the scraper-like lower jaw and eat principally insects,. Diatoms ingested with filamentous algae probably provide the chief source of nutrition. Filamentous algae undergoes little or no digestive breakdown. The possibility of interspecific competition for food and spawning sites in the lake is discussed.

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