The reproductive physiology of witch flounder, Glyptocephalus cynoglossus

Short, Constance Elizabeth (2004) The reproductive physiology of witch flounder, Glyptocephalus cynoglossus. Masters thesis, Memorial University of Newfoundland.

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Abstract

The witch flounder (Glyptocephalus cynoglossus), or grey sole, as it is commonly known, is a member of the family Pleuronectidae (right eye flounders) and is found in the Northwest Atlantic near Hamilton Bank off southern Labrador, southward over Newfoundland banks, Gulf of St. Lawrence, Scotian Shelf, Bay of Fundy and Gulf of Maine, to Cape Lookout, NC. The witch flounder has become increasingly important commercially since the 1940's. There was heavy exploitation of witch flounder by foreign ships in the early 1970's but with the introduction of Canada's 200-mile limit in 1977, foreign fishing for the species was reduced and Canada's take increased. -- This study focused on the adaptation of wild witch flounder to captivity and the development of a captive broodstock. Areas of concentration focused on growth and maturation, with emphasis on the reproductive biology (pattern of oocyte development, endocrinology and gamete analysis) of the witch flounder. This information will be used to help determine whether the witch flounder is a good candidate as an aquaculture species. -- The reproductive cycle of both the male and female witch flounder is characterized by distinct seasonal variations and fluctuations in plasma sex steroids associated with reproductive activity. As seen in other teleosts, the circulating levels of sex steroids increased as gamete maturation and gonad growth proceed, reaching peak levels during spawning. -- Oocyte size-class frequency distributions of witch flounder demonstrate the presence of just a single clutch of progressively developing vitellogenic oocytes, indicating group-synchronous development, by far the most common reproductive strategy in teleosts. -- Male witch flounder produce low volumes of viscous milt and sperm is only available for five months of the year (April--August). This correlates with spawning events in the female witch flounder, with ovulated eggs from late June to late August.

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