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The role of physical structure and micronutrient provisioning in determining egg quality and performance in fish

Murray, David S. (2012) The role of physical structure and micronutrient provisioning in determining egg quality and performance in fish. PhD thesis, University of Glasgow.

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Abstract

This thesis examined novel and previously utilised parameters of egg quality to determine and define reproductive success in farmed and wild salmonids. The effect of holding environment and inter-female variation on salmonid egg quality was also examined. Furthermore, two nutritional feed trials were undertaken to investigate whether organic Se, supplemented into salmonids broodstock diets, was vertically transferred to their eggs and what affect this dietary supplementation had on egg quality. Finally, the possibility that morphological and biochemical adaptations are present on the chorion of eggs from European whitefish (Coregonus lavaretus) was investigated in a resident Scottish population. Chapter 2 examined methods to determine egg quality using eggs from a single population of brown trout (Salmo trutta). Egg survival, provided a biologically relevant definition for egg quality, which was used throughout this study to assess the importance of selected egg quality parameters. Based on a review of the literature and the relationship between parameters of egg quality and egg survival rates, three determinants of egg quality were chosen for further examination. These were chorion breaking strength, elemental concentrations within the egg and the protein profile of the chorion. Brown trout broodstock from a single population were separated prior to spawning and exposed to two different holding units, ‘Ae system’ or ‘S.C.E.N.E. system’ at two sites. Eggs were stripped from females and 13 determinants of egg quality collected, analysed individually, combined by principle components analysis into an integrated egg quality score which was validated against egg survival. The multivariate egg quality score differed significantly between fish held in the Ae and S.C.E.N.E. systems. Egg survival, chorion breaking strength and Se chorion concentrations were higher in eggs produced by broodstock held in the S.C.E.N.E. system compared to those in the Ae system. Alternatively, chorion concentrations of P and K were higher in eggs from fish held in the raceway system. This data highlights the complex interactions between the holding environment and pre-ovulating fish and resultant egg quality. The variation in egg survival in individual Atlantic salmon (Salmo salar) reared in the same environment was assessed and used to examine the suitability of chorion measurements as parameters of egg quality. There was a significant difference in the egg survival rates between individual salmon. Results also show that there was also variation in egg survival, chorion breaking strength, chorion elemental concentrations and chorion protein concentrations and profiles between individual Atlantic salmon. Subsequent analysis of the data showed that there was no difference in these egg quality parameters between high and low egg survival rates. Furthermore, there was no correlation between egg survival and the chorion quality parameters recorded during this study. The results show that individual variation between fish is an important factor affecting egg quality. Broodstock Atlantic salmon were fed a standard commercial diet, with or without the addition of a supplemented nutritional mix, which included 0.5mg/kg of Sel-plex (organic Se). The Se content of the eggs and livers of each fish were assessed as was egg survival rates and proteomic analysis of the egg chorion. Concentrations of Se in the eggs of the individuals fed the supplemented diet were significantly higher than those fed the non-supplemented diet. However, the egg survival rate was also significantly lower in the supplemented group of fish. The assessment of the chorion protein profile and its proteomic structure was inconclusive. These results support the hypothesis that dietary selenium is vertically transferred to immature eggs during oocyte development. The lack of a linear relationship between Se egg concentrations and egg survival suggests that the lower survival rates of eggs from broodstock fed the supplemented diet in this trial was due to another nutritional component of the diet rather than the Se. Selenium enriched eggs from Atlantic salmon fed a supplemented diet and eggs from conspecifics fed a non-supplemented diet were tested for their ability to resist infection by Saprolegnia under incubation conditions similar to those used by the aquaculture industry. There was no significant difference in the presence/absence of infection, infection rate or survival between eggs produced by Atlantic salmon fed the supplemented and non-supplemented diet. Therefore, it was concluded that supplementation of broodstock diet does not alter the resistance of eggs to Saprolegnia. The presence of adhesive mechanisms on the surface of European whitefish eggs was examined from a population found within Loch Eck, Scotland. European whitefish eggs remain non-adhesive in a solution chemically similar to ovarian fluid, but become adhesive seconds after contact with water. Examination of the ultrastructure of the chorion showed that the morphology altered significantly after contact with water with nodule-like protuberances attached to connective filaments on the surface, present in water hardened but not non-water hardened eggs. Biochemical analysis also showed the presence of Chain A, RNase ZF-3e in the chorion of water hardened but not non water hardened eggs. Histochemical staining of the chorion showed that the externa, but not the interna stained positively for the presence of glycoproteins. Egg adhesive mechanisms allow European whitefish eggs to remain in optimal spawning grounds where factors such as mechanical damage, predation, desiccation and hypoxia are minimised.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Fish, egg, quality, reproduction, adhesion, aquaculture, nutrition
Subjects: Q Science > QH Natural history > QH301 Biology
S Agriculture > SH Aquaculture. Fisheries. Angling
Q Science > QL Zoology
Q Science > Q Science (General)
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Veterinary Medicine
College of Medical Veterinary and Life Sciences
Supervisor's Name: Adams, Prof. Colin and Bain, Dr. Maureen
Date of Award: 2012
Depositing User: Dr David S. Murray
Unique ID: glathesis:2012-3563
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Aug 2012
Last Modified: 10 Dec 2012 14:08
URI: http://theses.gla.ac.uk/id/eprint/3563

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