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Title: Studies on the reproductive biology and culture of two species of Cerastoderma (Lamellibranchia)
Author: Yankson, K.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1983
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Background studies relevant to hatchery and cultivation work were undertaken on two species of cockles. The age structure, settlement, growth, density and mortality of a lagoon population of Cerastoderma glaucum in South Wales were monitored. It was demonstrated that an artificial substrate can be efficiently used to collect and grow spat in the field. The reproductive cycles of C. glaucum and C. edule in discrete populations were studied over two breeding seasons using stereological analysis of their gonads. Both species are "opportunistic" breeders. They normally exhibit a monocyclic reproductive pattern spawning from May through the summer; but following a severe winter (1981-82) C. glaucum exhibited an "epidemic" spawning while C. edule adopted a polycyctic pattern. A method for conditioning cockles for spawning is presented. Using this method it was possible to advance or delay the spawning of C. glaucum but not C. edule. Repeated thermal shock was used to elicit spawning in both species of Cerastoderma. Gametes released by C. glaucum were of good quality enabling satisfactory fertilization and development to be achieved. The response of C. edule was poor. The eggs of C. glaucum retain their fertility longer (30 h or more) than they were previously thought to. The life span of the spermatozoa was prolonged to 6 days by cold storage but this treatment impaired the viability of the eggs. Salinity and egg density ranges for satisfactory fertilization and embryonic development of C. glaucum in laboratory cultures were determined. Some dietary and temperature requirements of spat and larvae (diet only) of this species were also investigated. Observations were made on the byssus systems of the spat of the two species of Cerastoderma and interpreted with reference to their ecology. It was concluded that C. glaucum was more amenable to artificial propagation than C. edule.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available