Seasonal variations in the flesh weights and biochemical content of the scallop Pecten maximus L. in the Clyde Sea Area

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Abstract
Monthly samples of Pecten maximus (L.) were obtained from a number of localities in the Clyde Sea Area from May 1966 to March 1968. Statistical analysis of various growth parameters confirm that there are significant differences between populations, and consequently the shell cavity volume has been the parameter used against which other measurements have been compared. The method of volume determination is described. The wet and dry weights of adductor muscle, gonad, and remaining tissue were estimated each month for a ‘standard scallop’ of 75 ml, and the weight of carbohydrate and protein (determined from freeze dried sub-samples), calculated for the dried flesh. The large adductor muscle doubled its weight between March and November, and this was directly related to the increase in the weight of carbohydrate by a factor of 20, and protein by a factor of 1·5. These reserves were depleted during the winter and spring, commensurate with the loss of flesh weights. The digestive gland showed similar weight fluctuations, probably related to the lipid content. Calculation of the calorific value of the reserves indicate that this is only half the equivalent reserve in the large adductor muscle. The gonad showed seasonal variations associated with the sexual cycle, but the biochemical variation was slight. In the main population examined the gonad increased in size during the winter and early spring, whilst other tissue weights and their reserves were falling. Spawning occurred during the early summer, and there was little or no recovery until the following winter. It is suggested that during the winter the carbohydrate reserves form the basic metabolic substrate for the scallop, whilst the nitrogen reserves in the muscle and digestive gland are utilized to produce the gonad. There is some evidence to suggest that following spawning, gametogenesis and release of gametes may occur continuously, without the development of a large gonad until the winter, when the maturation of the gametes ceases. Scallops transplanted from a population in a relatively unfavourable environment to an area with no indigenous population snowed variations in their growth parameters, and a 50% increase in the weight of flesh compared to the parent population. The range of variation of reserve materials was comparable.

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