Hans Magnus Gjøen

Genetic origin of Norwegian farmed Atlantic salmon

Abstract Soon after farming of Atlantic salmon began in Norway, a selection experiment was started in 1971. Over a 4-year period, broodstock of Atlantic salmon were sampled in 41 different rivers and localities resulting in four populations. In forming the base population (generation 0), mating was done within strains to produce full- and half-sib families. In later generations mating was done both within and between strains. Data from the first three generations of selection have been analysed to study the genetic origin of the four populations. One to three strains dominate each population. The importance of selective breeding in fish farming is stressed.

Genetic variation in susceptibility of Atlantic salmon to furunculosis.

The purpose of this experiment was to study the magnitude of genetic variation in mortality due to experimental furunculosis; furunculosis is the most serious salmon disease in Norway at present. Fifty fulisib- and 25 paternal halfsib groups of Atlantic salmon, in total 5000 fish, were infected with Aeromonas salmonicida ssp. salmonicida at Vikan AkvaVet, Namsos. Infection was by means of cohabitation, and all fish were marked and kept in the same tank during the experiment. The death rate averaged 68% with large variation between family groups. Heritability of mortality was high, h2 = 0.48 ± 0.17 for the sire component and h2 = 0.32 ± 0.10 for the dam component estimates. It is concluded that resistance to furunculosis can be effectively improved by selective breeding.

Genetic correlations between survival of Atlantic salmon in challenge and field tests

Abstract Four sub-samples of 171 full-sib groups of Atlantic salmon presmolts (the offspring of 96 sires and 171 dams) were tested for survival after challenge with the pathogenic bacteria Areomonas salmonicida, Vibrio salmonicida, Vibrio anguillarum and the viral disease Infectious Salmon Anaemia (ISA). Another sub-sample of 123 of the full-sib groups was tested as postsmolts at a marine test-site (field test) where infection with A. salmonicida prevailed causing high mortality during a two-month summer period. A full-sib group mean MINQUE model was used to estimate the variance and covariance components for survival in each test environment. Estimated heritabilities on the underlying liability scale for survival in the challenge test with A. salmonicida was 0.53 (at 50% survival) and in the field test 0.38 (at 65% survival). The genetic correlation between survival in the two tests was 0.95. Thus, the results give good prospects for genetic improvement of resistance to furunculosis when survival data from challenge tests of presmolts are used as the selection criterion. The results also indicate a positive genetic correlation between resistance to each of the bacterial diseases, but a weak negative genetic correlation between resistance to the viral disease ISA and resistance to each of the bacterial diseases.

Consistent boldness behaviour in early emerging fry of domesticated Atlantic salmon (Salmo salar): Decoupling of behavioural and physiological traits of the proactive stress coping style

Individual variation in the way animals cope with stressors has been documented in a number of animal groups. In general, two distinct sets of behavioural and physiological responses to stress have been described: the proactive and the reactive coping styles. Some characteristics of stress coping style seem to be coupled to the time to emerge of fry from spawning redds in natural populations of salmonid fishes. In the present study, behavioural and physiological traits of stress coping styles were compared two and five months after emergence in farmed Atlantic salmon (Salmo salar), using individuals with an early or late time to emerge. Initially, compared to late emerging individuals, early emerging individuals showed a shorter time to resume feeding after transfer to rearing in isolation. Resumption of feeding after isolation was suggested to be related to boldness behaviour, rather than hunger, in the present study. This observation was repeated five months after emergence, demonstrating behavioural consistency over time in this trait. However, in other traits of proactive and reactive stress coping styles, such as social status, resting metabolism or post stress cortisol concentrations, early and late emerging individuals did not differ. Therefore, this study demonstrates that boldness in a novel environment is uncoupled from other traits of the proactive and reactive stress coping styles in farmed salmonids. It is possible that this decoupling is caused by the low competitive environment in which fish were reared. In natural populations of salmonids, however, the higher selection pressure at emergence could select for early emerging individuals with a proactive coping style.

A practical evaluation of metomidate and MS-222 as anaesthetics for Atlantic halibut (Hippoglossus hippoglossus L.)

Abstract Metomidate and MS-222 were tested as anaesthetics for Atlantic halibut (Hippoglossus hippoglossus L.) at temperatures of 9.5±0.3°C and 10.5±0.3°C. An effective concentration of the drug was defined as one giving a sure state of anaesthesia for 75% of the fish after an exposure time of less than 5 min. The lowest effective concentration of metomidate was 10 mg l−1; with MS-222, concentrations of 250 mg l−1 were required. Doses should further be kept below 60 mg metomidate l−1 or 480 mg MS-222 l−1. There was interaction between anaesthetic and dose for both drugs with respect to the required exposure time, which focuses on the necessity of testing several doses when a new anaesthetic is to be used on a given species. It is concluded that metomidate gives a broader safe anaesthetic range with a lower effective dose than MS-222.

Genetic variation in red cell membrane fragility in Atlantic salmon and rainbow trout

Abstract The strength and flexibility of cell membranes are of particular importance for fish which routinely experience changes in the surrounding temperature. 496 fingerlings of Atlantic salmon from 50 full-and 25 halfsib groups and 133 fingerlings of rainbow trout from 14 fullsib groups were used to study the total as well as the genetic variation in cell membrane Strength, measured as red cell membrane fragility. Fragility is defined as the salinity at which 50% of the red cells are hemolyzed, and gradient as the regression coefficient of the fragility curve at the turning point. Both parameters showed significant differences between Atlantic salmon and rainbow trout. The mean fragility curve for rainbow trout was similar to the fragility curve for the family of Atlantic salmon which had the strongest cell membranes. Heritability was high for fragility and medium for gradient. There was no significant genetic correlation between red cell fragility and susceptibility to experimental infection with furunculosis.

Coupling between stress coping style and time of emergence from spawning nests in salmonid fishes: Evidence from selected rainbow trout strains (Oncorhynchus mykiss)

Correlations between behavioral and physiological traits, often referred to as stress coping styles, have been demonstrated in numerous animal groups. Such trait variations often cluster in two contrasting styles, with animals characterized as either proactive or reactive. In natural populations of salmonid fishes, emergence from spawning nests, when fry establish a territory and shifts from exogenous to endogenous feeding, is a crucial niche shift with a high selection pressure. The timing of this event is correlated to behavioral and physiological traits such as aggression, boldness/shyness, dominance, and metabolic rate; resembling those of proactive and reactive stress coping styles. In farmed fish populations, however the relation between emergence and stress coping styles seems to be absent, an effect which has been related to lack of selection pressure during emergence. In the present study two rainbow trout strains genetically selected as LR (low-responsive) and HR (high-responsive) trout, characterized with proactive (LR) and reactive (HR) stress coping traits, was used to further investigate the relationship between the time of emergence and stress coping style in salmonid fishes. For this task LR and HR larvae were hatched in mixed batches, and thirty individuals from the earliest and latest 25% of emerging larvae were randomly collected. Thereafter, a line specific genetic marker was used to distinguish the proportion of LR and HR occurring in early and late fractions. The result demonstrates a higher proportion of LR fry in the early fraction in comparison to the HR fry, which emerged at a higher proportion during the late period. Early emerging individuals had larger yolk reserves at emergence, lending further support to a relationship between emergence times, yolk reserves at emergence and stress coping styles in salmonids. Smaller larval bodies in early compared to late emerging individuals suggest that this difference in yolk size reflects differences in developmental stages at emergence. These data suggests that a genetic link between emergence time and stress coping style persists in captive salmonid fishes.

Stress and fear responses in the teleost pallium.

Evolution has resulted in behavioural responses to threat which show extensive similarities between different animal species. The reaction to predator cues is one example of such prevailing responses, and functional homologies to mammalian limbic regions involved in threat-sensitive behaviour have been found in the teleost telencephalon. The dorsolateral (Dl) and dorsomedial (Dm) regions of the pallium are thought to perform hippocampus and amygdala-like functions respectively. To what degree these regions are involved in the neuroendocrine responses to stress and predator cues however remains largely unknown. In the present study the involvement of Dl and Dm in such responses was investigated by exposing Nile tilapia (Oreochromis niloticus) to a standardized confinement stress and to skin extract from conspecifics. Nile tilapia develops a characteristic anticipatory behaviour to hand feeding, and effects of skin extract on this behaviour and locomotor activity were studied to characterise threat sensitive behaviour. Nile tilapia responded behaviourally to conspecific alarm cues by reducing feeding anticipatory behaviour. This may reflect a general elevation of alertness, and further studies combining skin extract with other challenges are needed to reveal neuroendocrine effects associated with this predator cue. Confinement stress resulted in an elevation of cortisol and serotonin (5-hydroxytryptamine, 5-HT) metabolism in both Dl and Dm. A similar tendency was observed in fish exposed to chemical alarm cues, but this effect did not reach the level of statistical significance. Hence, limbic responses to stress and fear, akin to those seen in extant mammals, are also present in the teleost lineage.

Genetic analysis of vibriosis and viral nervous necrosis resistance in Atlantic cod (Gadus morhua L.) using a cure model1

The aim of this study was to investigate whether observed time-until-death of Atlantic cod (Gadus morhua L.) juveniles in separate challenge tests with Vibrio anguillarum (causes vibriosis) and nodavirus [causes viral nervous necrosis (VNN)] are due to differences in susceptibility (whether at risk or not) or increased endurance (individual hazard, given that the animal is susceptible) using a cure mixture (CURE) model with Gibbs sampling. Observed time-until-death, prepared as sequential binary records, were analyzed with the CURE model and results were compared with cross-sectional threshold (SIMPLE) and an ordinary longitudinal survival score (NAÏVE) model (i.e., assuming that all animals are susceptible). Overall mortality at the end of the test was 86 and 71% for vibriosis and VNN, respectively. But the CURE model estimated 92 and 82% of the population to be susceptible to vibriosis and VNN, respectively. Hence, a substantial fraction among the survivors were considered to be susceptible but with high endurance. The underlying heritability of susceptibility was moderate for vibriosis (0.33) and extremely high for VNN (0.91), somewhat greater compared with classical SIMPLE model (0.19 and 0.76 for vibriosis and VNN, respectively), analyzing end survival as a cross-sectional binary trait. Estimates of the underlying heritability were low for single test-day scores of both endurance (0.02 and 0.15 for vibriosis and VNN, respectively) in the CURE model and for the NAÏVE model (0.02 and 0.18 for vibriosis and VNN, respectively). Based on the CURE model, the genetic correlation between susceptibility and endurance was low to moderately positive and significantly different from unity (P < 0.01) for both vibriosis (0.13) and VNN (0.47). Estimated breeding values from the SIMPLE and NAÏVE models showed moderate to high correlations (0.41 to 0.96) with EBV for susceptibility and endurance in the CURE model. The analyses indicate that susceptibility and endurance are apparently distinct genetic traits. Still, the genetic variation estimated in the SIMPLE and NAÏVE models seems to a large extent to be controlled by susceptibility and an efficient genetic selection for reduced susceptibility to vibriosis and VNN is therefore likely feasible even when using classical (noncure) models. Earlier termination of the challenge test or back truncation of survival data is not recommended as this likely shifts the focus of selection towards endurance rather than susceptibility.

Conspicuous carotenoid-based pelvic spine ornament in three-spined stickleback populations-occurrence and inheritance.

Reports on reddish carotenoid-based ornaments in female three-spined sticklebacks (Gasterosteus aculeatus) are few, despite the large interest in the species’ behaviour, ornamentation, morphology and evolution. We sampled sticklebacks from 17 sites in north-western Europe in this first extensive study on the occurrence of carotenoid-based female pelvic spines and throat ornaments. The field results showed that females, and males, with reddish spines were found in all 17 populations. Specimens of both sexes with conspicuous red spines were found in several of the sites. The pelvic spines of males were more intensely red compared to the females’ spines, and large specimens were more red than small ones. Fish infected with the tapeworm (Schistocephalus solidus) had drabber spines than uninfected fish. Both sexes had red spines both during and after the spawning period, but the intensity of the red colour was more exaggerated during the spawning period. As opposed to pelvic spines, no sign of red colour at the throat was observed in any female from any of the 17 populations. A rearing experiment was carried out to estimate a potential genetic component of the pelvic spine ornament by artificial crossing and rearing of 15 family groups during a 12 months period. The results indicated that the genetic component of the red colour at the spines was low or close to zero. Although reddish pelvic spines seem common in populations of stickleback, the potential adaptive function of the reddish pelvic spines remains largely unexplained.