Ovarian cycle and plasma concentrations of estrogen and vitellogenin in brook trout (Salvelinus fontinalis, Mitchill)

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Abstract
Oocyte development and plasma concentrations of estrogen and vitellogenin in brook trout have been investigated. Oocyte development and vitellogenesis resumed immediately after spawning in October, but, up until May, oocytes never developed beyond 1000 .mu.m diameter and yolk deposition only resulted in the appearance of a relatively modest number of fine droplets and globules. A peak occurrence of artretic follicles of about 900 .mu.m diameter was observed in March. In May, many cortical alveoli stage oocytes were seen developing from perinucleolar oocytes. From June to October, oocyte growth and vitellogenesis occurred at a faster rate. By the time of ovulation, the oocytes were about 2500 .mu.m in diameter and became filled with a homogeneous mass of yolk. Throughout winter and spring, plasma level of estrogen was 1-5 ng/mL and that of vitellogenin was mostly below 5 .mu.g/mL of alkali-labile protein phosphorus. In October, the plasma concentrations of estrogen and vitellogenin increased to 40 ng/mL and 96 .mu.g/mL, respectively.