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Summary
A population of lake whitefish in the Opinaca River (Nouveau Québec, 52°25'N, 77°10'W) was sampled monthly during the ice-free period (end of May to October). Only the specimens whose length was equal to or superior to the length at first sexual maturity (35 cm F.L.) were retained.
In this category 42% of the females and 23% of the males had not reproduced during the year of sampling. In adult non-reproductive females the gonado-somatic ratio remained constant < 1 and the oocytes after a slight increase in size before vitellus formation became atretic in August. In non-reproductive males the gonado-somatic ratio was always > 0.2, no spermatogenesis occurred. During the sexual cycle the hepato-somatic ratio, the weight of viscera, and the water content of muscles, liver and digestive tract remained stable in the non-reproductive individuals, whereas in the reproductive ones these changed in relation to the cycle.
These physiological differences seem to be accompanied by behavioral differences, at least in females, as, starting in July, the reproductive individuals were not found in the same habitats as the non-reproductive ones. The results are discussed in relation to the energetic reserves and the possibility of an alternation in years of reproduction.