Use this URL to cite or link to this record in EThOS:
Title: The ecology and reproductive biology of the Pacific oyster (Crassostrea gigas (Thunberg 1795)) in the Daucleddau Estuary, West Wales
Author: Evans, B. S.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
Availability of Full Text:
Access from EThOS:
This thesis is concerned with the ecology and mariculture of the Pacific oyster Crassostrea gigas (Thunberg, 1795) in U.K. waters. Oyster culture in the U.K. is reviewed, with detailed assessment of operations in the Daucleddau Estuary, South-West Wales. Growth performance and gametogenesis of C. gigas were monitored over two seasons (1986 and 1987) at two oyster farms in the Daucleddau Estuary (Carew Oysters and Cosheston Fish Farms Ltd.), and at a control site in the Menai Strait (Tal-y-foel). Environmental water quality was regularly monitored over the same period. Environmental requirements for the mariculture of C. gigas are reviewed and environmental suitability of each study site is appraised. Assessment is made of the environmental impact of tributyltin (TBT) pollution on C. gigas fisheries, with specific evaluations for each site. C. gigas did not present any physiological anomalies, either in the Daucleddau estuary or the Menai Strait. Each year, maximum and minimum condition factors were recorded during summer and winter respectfully, with maximum growth rates between April and November. Annual increments in live weight were less than those predicted, partly because of poor nutritive conditions. These may have been associated with natural deficiencies and TBT pollution. Growth performance was better at Tal-y-foel than at both Daucleddau sites; and was better at Carew Oysters than at Cosheston Fish Farms. Numerous intersite differences in water quality may have contributed to these trends, with quantitative and qualitative differences in food, together with TBT impact, being most important. At each site, water temperature, salinity, dissolved oxygen, and suspended particulates were unlikely to have substantially inhibited growth performance during the study period. The timing of gametogenic phases was similar within each population. Gametogenesis was initiated from a resting state in April (> 8oC), with maximum gametogenic activity during May and June (> 10-15oC). Each population exhibited a marked synchrony in gonad maturation, with a maximum incidence of morphologically ripe individuals during August. Spawning was partial (incomplete) delayed (until late August, September, October) and was succeeded by substantial gamete resorption. A degree of asynchrony in gonad regression was evident within population, especially in males. The proportion of gonads reduced to a resting state increased with progression into the winter. The inability of C. gigas to propagate in the Daucleddau is not entirely a result of spawning failure, but rather a failure of the shed gametes to reach a settled spat stage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available