Temporal Factors and Maturation Status as Determinants of Appetite in Atlantic Salmon

Kadri, Sunil (1995) Temporal Factors and Maturation Status as Determinants of Appetite in Atlantic Salmon. PhD thesis, University of Glasgow.

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Abstract

This thesis examines the patterns of variation in appetite in Atlantic salmon, Salmo salar, their causes and consequences. The emphasis of this study is on both their biological bases and their significance for the aquaculture industry. Chapter II: Experiments are described here that relate to daily feeding patterns and competitive interactions under both ambient and constant light and temperature regimes. Results were as follows: For yearling salmon parr under ambient light and temperature conditions: a) Consistent daily feeding rhythms with an afternoon peak were recorded in spring, while in autumn fish fed synchronously but without a consistent pattern between days. b) There was also a diurnal rhythm in frequency of aggressive interactions that was similar in both seasons. c) In spring aggression and feeding rates were negatively correlated. For salmon smolts under constant light and temperature conditions (12L:12D photoperiod): d) A clear diurnal rhythm was observed in feeding activity, with appetite peaks in early morning and late afternoon. e) When the data described in d) were separated according to fish size categories, significant patterns of diurnal variation in appetite were found for the small and medium fish but not for the larger fish. Medium-sized fish fed in a daily pattern similar to that observed at the population level, while small fish showed the highest level of feeding activity at first light and at the end of the light phase, with a marked reduction in feeding in the afternoon. Large fish maintained a relatively consistent level of feeding activity throughout the day. Chapter III: An experiment is described that was aimed at investigating the relationships between food intake, digestive efficiency and feeding regime, and to examine individual variation with respect to food intake and digestive efficiency. Results were as follows: a) Food intake and digestive efficiency varied widely between individuals under both continuous and meal-feeding regimes. b) However, while digestive efficiency was higher for continuous feeding, there was no difference between feeding regimes for food intake. c) Continuous feeding produced a negative relationship between food intake rate and digestive efficiency but no such relationship was found for meal-feeding. d) Under the meal-feeding regime there was a positive relationship between relative protein intake rate and body weight, with a weaker relationship between these two parameters under continuous feeding, suggesting a more pronounced feeding hierarchy under meal-feeding conditions. Chapter IV: This chapter describes an experiment to test whether the amount of food obtained by individual one sea-winter Atlantic salmon was related to social status. a) Food was distributed unevenly among fish; no significant relationship was found between food intake and either weight or gender. b) More successfiil fish fed earlier in a feeding session than their companions, and smaller fish tended to avoid competitors when approaching pellets. c) There was a positive relationship between frequency of being beaten to pellets and food intake, but no relationship between proportion of feeding attempts in which a fish was beaten and food intake. This suggests that fish scrambling for food were of a similar status. d) Previous studies have shown a negative relationship between the coefficient of variation in daily food intake and total food intake, but did not control for fish size. Here I found the same relationship after controlling for fish size, showing that more successful fish had less variation in their day to day consumption (corrected for body weight) than did less successfiil conspecifics. e) These data suggest that, in order to prevent food monopolisation by few individuals, the food in production cages should be presented so that it is unpredictable in time and space. Chapter V: In this chapter patterns of feeding behaviour, growth and accumulation of lipid reserves were examined in maturing fish and immature fish of the same age from the onset of the maturation cycle (autumn) to the onset of anorexia (summer). a) Maturing fish were larger and in better body condition than non-maturing fish from October until the end of the trial in July. b) Maturing fish were over-represented in samples of feeding fish from April to May (end of trial) suggesting they had a greater motivation to feed than non-maturing fish over this period. c) The period of greatest differentials in growth rate, body lipids and condition factor between the two groups of fish coincided with the period of differential feeding responses. Chapter VI: An investigation of the most useful morphometric predictors of sexual maturation in one sea-winter fish is described here, with results as follows: a) A combination of forklength and condition factor proved to be the strongest and most consistent predictor of maturation (over 88% accurate) from May until August (by which time maturing fish were losing condition and in any case could be easily distinguished by shape and colour). b) Anal height and dorsal height also gave strong predictions of reproductive status, but these parameters were of secondary importance to forklength and condition factor. c) A second trial was performed on a separate stock of fish for which forklength and condition factor were able to predict maturation to a similar level of accuracy. However, the discriminant function derived from one stock of fish did not produce the same discriminatory power when applied to the other stock.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Felicity Huntingford
Keywords: Zoology, Aquatic sciences
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-75703
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 18:44
Last Modified: 19 Nov 2019 18:44
URI: http://theses.gla.ac.uk/id/eprint/75703

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