On Rhythmic Periods in Shell-growth in 0. edulis with a Note on Fattening

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Abstract
Continuous observations on the Upper Fal Estuary oyster beds during the years 1925, 1926, and 1927 have established the fact that 0. edulis exhibits on these beds two definite periods of shell-growth, i.e. increase in shell-area, in one year; one period of general shell-growth occurs in the spring, beginning early in April, and the other in autumn at the end of September or early in October. There is some evidence-but as yet incomplete-that internal shell-growth occurs solely and simultaneously with the deposition and thickening of the new shell-shoots in a period of one to two months.These general bursts of shell-growth occur in the pre-breeding and post-breeding part of the seasonSimilar periods of shell-growth occur on beds in the River Blackwater (AVest Mersea), and also occur mainly in the pre-breeding and postbreeding part of the season; but shell-growth begins in the spring in April-May on these beds, a few weeks later than on the Upper Fal Estuary, and in the autumn in August-September a few weeks earlier than on the Upper Fal beds.Spring and autumn periods of shell-growth are also known to occur on many other estuarine beds.