Reproductive investment, gamete quality and diet in farmed salmonids

Rennie, Shona (2005) Reproductive investment, gamete quality and diet in farmed salmonids. PhD thesis, University of Glasgow.

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This thesis discusses a number of questions relating to life history strategies, gamete quality and nutrition in salmonids. Chapter 1 gives a broad overview of life history strategies and nutrition in aquaculture. An organism's life history strategy determines when it will mature and its reproductive potential. Life histories are diverse with large intra- and inter-species variation; for example in salmonids, some species and individuals within a population remain always in freshwater and some migrate to sea and then return to freshwater to breed. Much research has been conducted with respect to life history strategies in salmonids but there is still a great deal to be learned, in particular about strategies exhibited by post smolt males and females. Currently fisheries, the main source of fish for human consumption, have come under pressure and alternative production sources have been adopted; for example aquaculture, which in recent years has expanded. The future success and expansion of aquaculture is dependent upon the reproductive potential and quality of the broodstock. A better understanding of Atlantic salmon life history strategies and the ability to predict which fish will mature and produce quality gametes could be beneficial to the industry. It is also important to keep aquaculture production costs low. This can potentially be achieved by manipulating diets without compromising the quality of the final product or in the case of broodstock of the gametes. Chapter 2 explores the possibility of predicting which individual Atlantic salmon will mature and their reproductive potential by using morphological measurements taken throughout the year proceeding maturation. Atlantic salmon that matured in a given year had higher body weights than their non-maturing counterparts in the September of the year proceeding maturation, confirming the hypothesised critical autumn maturation 'window'. They remained larger in the following May and June. Weight in May (as opposed to September and June weight) was show to be the strongest predictor of maturity in females. Unlike female maturation, no single predictor was found for male maturation. Body weight in June was shown to have a strong relationship with egg number, indicating that it could be used as a predictor of reproductive investment in females. This chapter also highlighted a gender difference in the reproductive trade offs exhibited by males and females. Ultrasound is used in the aquaculture industry to differentiate the gender of mature fish in a number of species. In chapter 3 it was successfully used to distinguish the sex of immature Atlantic salmon and to estimate gonad length and width of immature female salmon and maturing female rainbow trout and in the case of the latter gonad size. Finding alternative renewable and cheaper dietary sources of lipids would be beneficial to the aquaculture industry considering the present strain fisheries are under. It has been shown that rapeseed oil is a good alternative to fish oil in on-growing Atlantic salmon diets. The study described in chapter 4 showed that a 50% replacement of fish oil with rapeseed oil in an Atlantic salmon broodstock diet had no effect upon the reproductive investment or egg quality (measured as survival of the eggs at each of the developmental stages eyeing, hatching and first feeding). Just as with fish oil, fish meal, the main source of dietary protein for fish food, is also a finite resource that is expensive to produce. Also if it is provided in excess in the food in conjunction with an inadequate level of lipid it can be used inefficiently by the fish producing environmental concerns. Increasing the level of lipid at the expense of protein in large rainbow trout diets was investigated in this chapter. Raising the levels of lipid improved the food conversion ratio and specific growth rate, though it did also increase the levels of fat in the flesh. During the study performed in chapter 5, it was discovered that the majority of the fish had come into reproductive condition and as a result the effects of maturation on growth, flesh quality and energy reserves in female rainbow trout were investigated here. The data in chapter 6 showed that maturation reduces growth and energy reserves as measured by levels of fat in the flesh and size of the visceral and hepato somatic indexes, confirming previous studies. The findings of the studies conducted are summarised in chapter 7 and the implications they have for fish biologists and aquaculture researchers and farmers are described in this final chapter. Future studies that they prompt are also considered.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Felicity Huntingford
Keywords: Aquatic sciences, Animal sciences
Date of Award: 2005
Depositing User: Enlighten Team
Unique ID: glathesis:2005-74055
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Sep 2019 15:33
Last Modified: 23 Sep 2019 15:33

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