Date of Award


Degree Type


Degree Name

Doctor of Philosophy


This study tested the hypothesis that the reproductive physiology of brook charr (Salvelinus fontinalis) differed between acidic and neutral lakes. Charr were collected from neutral (pH > 6.5) and acidic (pH < 6.5) lakes in the Sault Ste Marie and Blind River areas of Northern Ontario from June to November of 1981 to 1983. Female brook charr from neutral lakes initiated exogenous vitellogenesis in July. Charr from acidic lakes began exogenous vitellogenesis approximately one month later than neutral lake charr. Charr from acidic lakes had fewer yolky oocytes and more oil droplet oocytes than those from neutral lakes in July and August. However, oocyte development was accelerated from September onwards and the abundance of all oocyte stages was the same in charr from acidic and neutral lakes by October. Charr from the acidic lakes produced significantly more mature ova than charr from neutral lakes, but the average weight and diameter of the ova were decreased. Plasma estrogen and vitellogenin levels did not differ among charr from acidic and neutral lakes. Male brook charr from neutral lakes initiated rapid spermatogenesis in June, as measured by the increase in spermatocyte and spermatozoa cyst diameter and percent of testis area. Charr from acidic lakes initiated rapid spermatogenesis and spermiogenesis in July, one month later than charr from the neutral lakes. The rate of spermatogenesis increased in charr from acidic lakes in September, so by October, the quantity of spermatozoa in their testes was the same as in charr from neutral lakes. Histological evidence indicates that charr from acidic lakes did not spawn in October and November, as did those in neutral lakes. Spawning activity was observed in the neutral lakes by mid-October, but spawning still had not occurred by mid-November in the acidic lakes. This study is the first to demonstrate a change in the reproductive physiology of fish due to pH under natural conditions.



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