Jonathan Vaz Serrano defended his thesis on January 20th 2011

Ane Gro Siri Skjelfjord

Variation at early life stages of Atlantic salmon: Relationships between emergence time and stress coping styles

Abstract from the thesis - PhD Thesis 2011:08

Captive fish are exposed to a variety of stressful situations, which can affect growth rates and promote diseases. Identification and selection for stress resistant fish at early stages of the production cycle could be used as a cost-efficient tool to increase productivity, welfare and to reduce disease susceptibility in aquaculture. In different animal groups, two distinctive sets of behavioural and physiological responses to stress, termed proactive and reactive stress coping styles, have been identified. In salmonid fish, emergence time, i.e. the moment when a larva leaves the spawning redd and starts exogenous feeding, has been shown to be related to growth rates, standard metabolic rates, time of smoltification and social status. In this thesis, I have studied whether variability in emergence time could be coupled to differences in stress coping styles. As well, I have investigated the relationships between other early life traits and emergence time in Atlantic salmon (Salmo salar).

In the first part of the thesis, the relationship between hatching time and larval growth were examined. As well, a novel method to sort salmonid larvae according to emergence time was developed to investigate the relationships between family variation in emergence time and egg size, hatching time and larval developmental rate in Atlantic salmon. In the second part of the thesis, fry with different emergence times were screened for divergences in stress coping styles. The results in the first part of this thesis demonstrate that larvae with a late hatching time had higher post-hatch growth rates, thereby compensating for a delayed hatching time. Furhermore, comparisons between families showed a relationship between variation in egg size and hatching time, although these traits were not related to emergence time. In addition, families with a faster larval developmental rate reached emergence earlier.

In the second part of this thesis, where the relationship between time to emerge and stress coping styles was investigated, it was shown that fry with an early time to emerge were bolder compared with a late emerging fry. However, differences in emergence time were not associated to other behavioural and physiological traits of the proactive and reactive coping styles, such as standard metabolic rates, social dominance, or post stress cortisol levels. The decoupling between boldness and such traits could be related to the absence of a strong selection pressure at emergence in captive fish.

To conclude, this thesis demonstrates that the rate of development of the larvae, rather than egg size or hatching time, predicts time to emerge from the spawning redds in Atlantic salmon. Furthermore, this thesis presents a novel method to sort salmonid larvae that could improve rearing conditions of domesticated salmon. As well, it was shown that an earlier emergence was related to boldness behaviour, but earlier emergence was not related to other traits of the stress coping styles in domesticated Atlantic salmon. Future studies should examine if selection of fish according to emergence time is related to other production traits, such as disease resistance, growth rates, fillet colour, occurrence of deformities or feed conversion ratio.

Updated: 10.06.11
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