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The genetic and environmental basis for external colouration in lake whitefish (Coregonus clupeaformis (Mitchill)) from Southern Indian Lake, Manitoba Johnston, Christine Helga


The purpose of this study was to investigate the nature of the colour difference between light and dark-coloured whitefish from Southern Indian Lake, Manitoba and to examine related differences between them. Subjective assessment of whitefish colour is corroborated by quantifiable differences in melanophore numbers between the two forms. Spatial distribution of lights and darks differs both between and within regions. Lights occur throughout the lake, are slightly more abundant offshore than onshore and are primarily benthic in habit. Darks are restricted to certain areas of the lake, are more numerous onshore than offshore and are somewhat more pelagic than lights. The two forms showed significant differences in several morphometric characters and lower gill raker number, but not in hemoglobin or glycerol-3-phosphate dehydrogenase allele frequencies. Hatchery-reared offspring of dark parents had higher mean dorsal melanophore counts than offspring of light parents. The heritability estimate derived from the regression of offspring (age 111 days post-fertilization) on male parent melanophore count was 0.10. Short and long-term experiments showed that colour of larval whitefish is subject to environmental alteration in response to light conditions and background colour. Short-term change is effected through redistribution of melanin granules in the melanophores, long-term change through changes in numbers of melanophores. Level of infection with Triaenophorus crassus cysts is, on average, higher in darks than in lights. However, the mode for both forms is 0 indicating no direct causal connection between cyst count and pigmentation. Higher mean counts of darks may be related to diet and distribution. Morphometric and meristic characters are subject to. environmental modification, as shown by other studies. This plus the lack of difference between lights and darks in biochemical characteristics suggests no clear-cut separation between the two into non-interbreeding stocks. Whitefish colour is correlated with water colour and clarity and may be an adaptation for concealment.

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