Torbjörn Järvi

Differential Stress Coping in Wild and Domesticated Sea Trout

Offspring of wild and sea-ranched (domesticated) sea trout (Salmo trutta) originating from the same river, were reared under identical hatchery conditions from the time of fertilization. At one year of age individual fish were exposed to two standardized stressors; transfer to a novel environment, with or without a simultaneous predator exposure. Blood plasma concentrations of glucose and cortisol were analyzed along with brain levels of dopamine (DA), 3,4-hydroxyphenylacetic acid (DOPAC, a major DA metabolite), serotonin (5-hydroxytryptamine, 5-HT), and 5-hydroxyindoleacetic acid (5 HIAA, a major 5-HT metabolite). Transfer to a novel environment, alone as well as in combination with predator exposure, resulted in elevated plasma concentrations of glucose and cortisol. Moreover, exposure to these stressors resulted in elevated brain levels of 5-HT and 5-HIAA, as well as elevated brain 5-HIAA/5-HT and DOPAC/DA ratios. Wild trout displayed significantly higher post stress plasma glucose levels than domesticated fish. Similarly, following stress, brain 5-HIAA/5-HT and DOPAC/DA ratios were significantly higher in wild than in domesticated fish. These differences were not caused by differences in brain levels of 5-HIAA and DOPAC, but instead by differences in brain 5-HT and DA concentrations. These results suggest that domestication results in attenuated stress responses in trout, and that alterations in brain monoamine neurotransmission are part of this effect.

Male–male competition and female choice in brown trout

In some salmonid species, the females have been assumed to choose their mates on the size of the males adipose fin. This hypothesis was tested in a stream water aquarium, in which 19 brown trout, Salmo trutta, females were allowed to choose between two males of the same body size but with different adipose fin sizes. The two males were separated from each other in cages. After the female had started to prepare her nest close to one of them, the males were released and allowed to fight each other for the opportunity to spawn. Out of 19 females, 14 prepared a nest closest to the male with the larger adipose fin. However, only six of the 14 females spawned with this male. Males that spawned were more dominant (i.e. were more likely to win fights). When the female spawned with the male she chose, he was less aggressive towards her than when she spawned with the other male. There were no significant differences in the plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) between the chosen males and those not chosen. However, the dominant males had significantly higher plasma levels of T and 11-KT both before and after the experiment. The results support the view that female brown trout exhibit mate choice, but their choice is overruled by male-male competition. Copyright 1999 The Association for the Study of Animal Behaviour.

Lack of molecular genetic divergence between sea-ranched and wild sea trout (Salmo trutta).

The supportive breeding programme for sea trout (Salmo trutta) in the River Dalälven, Sweden, is based on a sea‐ranched hatchery stock of local origin that has been kept ‘closed’ to the immigration of wild genes since the late 1960s (about seven generations). In spite of an apparent potential for substantial uni directional gene flow from sea‐ranched to wild (naturally produced) trout, phenotypic differences with a presumed genetic basis have previously been observed between the two ‘stocks’. Likewise, two previous studies of allozyme and mitochondrial DNA variation based on a single year of sampling have indicated genetic differentiation. In the present study we used microsatellite and allozyme data collected over four consecutive years, and tested for the existence of overall genetic stock divergence while accounting for temporal heterogeneity. Statistical analyses of allele frequency variation (F‐statistics) and multilocus genotypes (assignment tests) revealed that wild and sea‐ranched trout were significantly different in three of four years, whereas no overall genetic divergence could be found when temporal heterogeneity among years within stocks was accounted for. On the basis of estimates of effective population size in the two stocks, and of FST between them, we also assessed the level of gene flow from sea‐ranched to wild trout to be ≈ 80% per generation (with a lower confidence limit of ≈ 20%). The results suggest that the reproductive success of hatchery and naturally produced trout may be quite similar in the wild, and that the genetic characteristics of the wild stock are largely determined by introgressed genes from sea‐ranched fish.

Downstream migration in Atlantic salmon (Salmo salar) smolt sibling groups

Previous studies have shown kin recognition abilities in salmonid fish. Some authors have suggested that the attraction of juvenile fish to siblings may indicate preference for shoaling with kin. T ...

Cumulative acute physiological stress in Atlantic salmon smolts: the effect of osmotic imbalance and the presence of predators

Abstract Heavy mortality experienced by sea-ranched Atlantic salmon ( Salmo salar ) smolts during their seaward migration is assumed to be due to predation, caused by a cumulative effect of osmotic stress and physiological stress from the fright reaction of predator-naive smolts to predators. The aim of this study was to test whether osmotic imbalance and the presence of predators have any cumulative effect on plasma chloride, blood glucose and lactate levels. All three of these physiological factors are known to yield a reliable assessment of the degree of physiological stress. Non-acclimated smolts experienced a severe physiological stress when they were exposed to either a hyperosmotic milieu or to a hyposmotic milieu. Predator-naive smolts became likewise physiologically stressed when exposed to a predator. An additive physiological effect was revealed when non-acclimated, predator-naive, smolts were exposed to a predator. A reduction in physiological stress response was noted when the smolts had previously been acclimated either to the osmotic milieu or habituated to predators. The results of this study support the view that the presence of predators and a change in osmotic milieu combined exert a cumulative stress effect, and that this effect is diminished by prior acclimation to the osmotic milieu or habituation to predators.

Synergistic effect on mortality in Atlantic salmon, Salmo salar, smolt caused by osmotic stress and presence of predators

SynopsisThe hypothesis that an increase in the mortality rate of Atlantic salmon would be produced by the synergistic effect of osmotic stress and of stress due to the presence of predators was tested by putting two groups of smolts (one acclimated to seawater and the other not acclimated) into a tank containing predators. These smolts were tested afterwards in a seawater-challenge test, together with smolts of the control groups for both experimental groups. The mortality rate of the non-acclimated and predator-exposed smolts was 90%, and that of the seawater acclimated and predator-exposed smolts 43%, compared to no mortality among the control groups. Lack of acclimation to seawater did not in itself induce any lethal stress, but in conjunction with predator-stress there was a synergistic effect, leading to an increase in the mortality rate. The hypothesis is therefore considered to be valid.

Both contest and scramble competition affect the growth performance of brown trout, Salmo trutta, parr of wild and of sea-ranched origins

The effect of contest and scramble competition on the growth performance of wild and sea-ranched juvenile (0+) brown trout, Salmo trutta, originating from the River Dalälven, Sweden was scrutinised. In a mirror image stimulation (MIS) experiment, and in a 35 000 1 stream-water aquarium the trout was studied for three weeks (20 individuals in each of four replicates). Activity in MIS was correlated with swimming activity in the stream-water aquarium. The MIS results could not be used for predicting any social behaviour patterns or the growth performance of a fish. No behavioural differences between the two strains were noted. However, the sea-ranched strain grew faster than the wild one, both in regard to the RNA/DNA ratio and the weight-specific growth rate. Because the strains had the same genetic background and prior to the experiments were raised under similar hatchery condition, the results of this study suggest that the sea-ranching process selects for faster juvenile growth in brown trout. The ultimate mechanisms underlying the faster growth by the domesticated strain probably involves both contest and scramble competition.

Lower prevalence of fin erosion in mature than in immature Atlantic salmon (Salmo salar) parr

Abstract Samples of hatchery-reared Atlantic salmon parr (age 0+ and 1+) from two different Norwegian river strains were investigated for connections between sexual maturity and prevalence of dorsal fin ray erosion. Mature males showed consistently lower prevalence as well as better recovery than immature males. Among the immature fish, no differences were detected between males and females. The results are discussed relative to morphological and physiological changes in maturing salmon parr.

Multidimensionality of behavioural phenotypes in Atlantic cod, Gadus morhua

Much of the inter-individual variation observed in animal behaviour is now attributed to the existence of behavioural phenotypes or animal personalities. Such phenotypes may be fundamental to fisheries and aquaculture, yet there have been few detailed studies of this phenomenon in exploited marine animals. We investigated the behavioural and neuroendocrine responses of Atlantic cod (Gadus morhua L.), to situations reflecting critical ecological challenges: predator attacks and territorial challenges. Both hatchery-reared and wild fish were tested and behavioural profiles were compared with baseline conditions. We then used an objective, multivariate approach, rather than assigning individuals along one-dimensional behavioural axes, to examine whether distinct behavioural phenotypes were present. Our results indicate that two distinct behavioural phenotypes were evident in fish from each background. In hatchery-reared fish, phenotypes displayed divergent locomotor activity, sheltering, brain monoamine concentrations and responses to competitive challenges. In wild fish, phenotypes were distinguished primarily by locomotor activity, sheltering and responsiveness to predator stimuli. Hatcheries presumably represent a more stressful social environment, and social behaviour and neuroendocrine responses were important in discerning behavioural phenotypes in hatchery fish, whereas antipredator responses were important in discerning phenotypes in wild fish that have previously encountered predators. In both fish types, behavioural and physiological traits that classified individuals into phenotypes were not the same as those that were correlated across situations. These results highlight the multidimensionality of animal personalities, and that the processes that regulate one suite of behavioural traits may be very different to the processes that regulate other behaviours.