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Title: Oocyte growth and gonadial maturation in the octopus Eledone cirrhosa
Author: Gnap, M. N.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1987
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In Eledone cirrhosa, egg development proceeds along typical caphalopod lines, but the egg stalks are surrounded by a ciliated columnar epithelium and the eggs go through a phase where the follicular layer forms a tri-lobed structure. Niether of these phenomena have been reported in other species and these specializations may faciliate the exchange of substances between egg and gonadial fluid. Potential fecundity (total number of eggs) is not correlated with either body size or gonadial maturity, but larger body size is associated with an increase in the proportion of eggs which have become vitellogenic (actual fecundity). Egg development is asynchronous and the ovaries of mature animals contain large numbers of immature eggs. Mean egg dry weight is strongly correlated with gonadosomatic index and ovarian maturity can be estimated from the mean dry weight of small biopsied egg samples. The usefulness of ovarian biopsy in Eledone cirrhosa is limited by the relatively short post-operative longevity of these animals. Nonetheless the technique has provided some interesting results and is likely to be even more effective when used with a hardier species. Food intake and gross growth efficiency are greatly reduced in mature females and this seems to be coupled with a decrease in the endocrine activity of the posterior salivary glands so that 5-hydroxytryptamine levels in the posterior salivary glands and blood fall dramatically during gonadial maturation. The decrease in glandular and circulatory levels of 5-hydroxytryptamine can be mimicked by enforced starvation. There is some evidence to suggest that both posterior salivary gland removal and starvation may cause precocious gonadial maturation. The genitoperiocardial ducts drain the ovary but do not resorb glucose or amino acid. Ovarian venous blood contains lower levels of lipid, glucose and amino acid than ovarian arterial blood and these differences between arterial and venous blood are more marked in maturing females.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available