Investigation of the Factors Influencing Maturation in Atlantic Salmon, Salmo salar L., parr

Simpson, Anna L (1993) Investigation of the Factors Influencing Maturation in Atlantic Salmon, Salmo salar L., parr. PhD thesis, University of Glasgow.

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This thesis investigates the factors influencing maturation in Atlantic salmon (salmo salar L.) parr. Experiments were designed to investigate the relative effects of size and lipid levels as determinants of maturation within sibling groups. The possibility of using these factors to predict which fish would mature and of using them to control maturation rates was also considered. Chapter 2 - Previous work had implicated lipid levels in the control of maturation. Therefore it was necessary to develop a non-destructive method for estimating the fat content of live salmon parr. Two non-destructive methods were used to predict fat content. Total body electrical conductivity (TOBEC) gave a good prediction of lean mass in fish, of wet weights 13.7-151.8g, but could only be used together with wet weight and fork length to accurately predict fat in fish of above 30g. However, the increase in accuracy produced by using TOBEC was small and it was concluded that this technique was not suitable for use in subsequent experiments involving small salmon parr. The biometric method, based on simple body measurements, accurately predicted the fat content of different sized fish (wet weights 1.8-151.8g) at two times of year (November/December and July). Multiple regression equations for fat prediction were based on a combination of the following measurements: wet weight, fork length, opercular height, dorsal height, opercular width, dorsal width, anal width, adipose fin length and condition factor. In every case predictions based on multiple regression equations were more accurate than condition factor alone. This biometric method is easily employed and can potentially be used both in biological studies and on fish farms to assess body condition of individual fish. Since it is non-destructive, it has the additional advantage of allowing repeated monitoring of fat levels in the same fish, and was therefore used in subsequent experiments in this thesis. Chapter 3 - Previous work had indicated that growth rates during late winter / early spring were influential in determining maturation rates. This chapter comprises three experiments in which monthly measurements of body size and lipid levels of a group of sibling 0+ salmon parr were made. In the first experiment, the variables were monitored from January to October 1990. In the second, the lipid level of the diet was manipulated over the early spring period (from January to April 1991) at three treatment levels (Lx)w fat = 7-10%; Medium fat = 12-15%; High fat = 17-22%) to try and influence maturation rates. From May to September (1991) all fish were given a commercial fish food (15-17% fat). In the third experiment a starvation regime was used to try and influence maturation rates. One group of fish (sibling 0+ parr) was fed a reduced ration every fourth week during November and December 1991. Rations were increased gradually from January to March 1992 and from April to September all fish were fed the same ration. Neither of the above treatments were successful in reducing the maturation rates of male parr. Those males that subsequently matured as parr were larger and had a higher fat content than non-maturing males in November of their first year. Neither specific growth rate nor rate of change in fat over the experimental period seemed to be important for maturation. Fat levels were positively correlated with fork length in most months with maturing males tending to have a higher percent fat for a given length than non-maturing males. This relationship became negative towards the breeding season. Logistic regressions based on fat reserves and body size could be used during the winter to predict the probability that a male parr would mature the following autumn. From these experiments it was concluded that maturation must begin prior to the first autumn and therefore experiments designed to reduce maturation rates must target the late summer/early autumn period. Chapter 4 - Previous work had shown that maturing parr tended to be larger than their non-maturing siblings. Since one way of growing larger is by consuming more food, it seemed sensible to look at the appetite of these fish. Therefore, the appetite of parr from the three experiments in Chapter 3 was monitored by two different techniques; behavioural observation and radiography. In all experiments there were no differences in appetite between maturing and non-maturing fish. All results showed a similar peak in appetite in May which did not correspond to a peak in temperature. May was the first month that the temperature rose above the lower critical level for activity in juvenile salmon. It was suggested that appetite peaks in May due to the rise in temperature allowing greater activity and therefore feeding. The decline after May was unexplained since temperatures remained suitable for feeding. The hypothesis that this decline has evolved to enable the fish to survive a period of low prey abundance in the natural stream habitat was tested in Chapter 6. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Neil Metcalfe
Keywords: Aquatic sciences, Animal sciences
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-74784
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 16:30
Last Modified: 27 Sep 2019 16:30

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