Behavioural responses in a net restraint test predict interrenal reactivity in Arctic charr Salvelinus alpinus

In this study, a 1 min net restraint test was evaluated as a method to predict stress-coping style in Arctic charr Salvelinus alpinus, by investigating the relationship between behaviour during the test and levels of plasma cortisol sampled after 30 min confinement. In two separate groups of S. alpinus, general linearized model revealed significant correlations between cortisol levels and principal component scores extracted from principal component analysis, combining measures of activity in the tests. With the use of glmulti, the model selection ruled out any effects of size, sex and order of capture on interrenal reactivity. In general, S. alpinus that were more active in the net restraint test also had low levels of circulating cortisol, suggesting a proactive coping style. The results from two repeated runs were not correlated, but both runs, performed eight days apart, show a negative correlation between post-stress cortisol level and activity in the net. The lack of consistency could be explained by different treatments before each run and individual differences in behavioural plasticity. The net restraint test is thus predictive of stress-coping style in S. alpinus, and has the benefit of being less time-consuming than the commonly used confinement stress test.

Thermal stress in Arctic charr Salvelinus alpinus broodstock: a 28 year case study

Temperature and egg viability data from an Arctic charr Salvelinus alpinus hatchery covering a period of 28 years were analysed. During the study period, there was a significant increase in the mean water temperature in May, July, August and September of c. 2° C. Independent of year, the egg viability showed a negative correlation with the mean monthly temperatures in July, August and September as well as with the temperature difference between October and November. The negative effect of high summer temperatures was further supported by a comparison of egg viability from replicate broodstock reared at two sites differing mainly in summer water temperature. The eggs from the colder site were, on average, significantly larger (4·4 mm compared with 4·0 mm) and had higher hatching rates (57% compared with 37%). These results suggest that unfavourable temperature conditions during the summer and autumn can explain much of the excessive egg mortality experienced at the main facility used for the Swedish S. alpinus breeding programme. The main effect was supra-optimal temperatures during the period July to September, but there also appears to have been an effect from the temperature regime before and during spawning (October to November) that was unrelated to the summer temperatures. These findings emphasize the importance of site selection and sustainable management of aquaculture hatcheries in the light of the ongoing climate change.

Time-place learning and leader-follower relationships in Arctic charr Salvelinus alpinus

Feeding activity from a larger refuge site into two visually separated feeding sites with temporally restricted food availability, one in the morning and one in the evening was studied in duplicate groups of Arctic charr Salvelinus alpinus. A passive integrated transponder (PIT) system enabled continuous monitoring of individual movements between the sites. Both groups synchronized their diel pattern of visit activity to the two feeding sites when food was available. One group showed significant anticipatory visit activity into both feeding sites during the hours before the feed was available, suggesting a time and place learning of resource availability. The anticipatory activity of the other group was, however, less pronounced and only occurred into one of the feeding sites. Individual S. alpinus entered the feeding sites independently and no obvious patterns of leaders and followers were identified. All S. alpinus gained mass and moved between a refuge and the feeding sites. Different strategies of how individual S. alpinus utilized the feeding sites were not correlated with growth.

Behaviour, physiology and carotenoid pigmentation in Arctic charr Salvelinus alpinus

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High-activity individuals had higher plasma cortisol levels following stress compared to low-activity individuals. This indicates that high- and low-activity individuals correspond to reactive and proactive stress-coping styles. Further, a pigmentation analysis showed that high-activity individuals had a higher number of carotenoid spots cm⁻² than low-activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress-coping style in S. alpinus.

Influence of dietary sesamin, a bioactive compound on fatty acids and expression of some lipid regulating genes in Baltic Atlantic salmon (Salmo salar L.) juveniles

The effects of inclusion of sesamin / episesamin in Baltic Atlantic salmon (Salmo salar L.) diets based on vegetable oils were studied. The study was designed as a dose response study with two control diets, one diet based on fish oil (FO) and one diet based on a mixture of linseed and sunflower oil (6:4 by vol.) (MO). As experimental diets three different levels of inclusion of sesamin / episesamin (hereafter named sesamin) to the MO based diet and one diet based on sesame oil and linseed oil (SesO) (1:1 by vol.) were used. The dietary oils were mirrored in the fatty acid profile of the white muscle. Sesamin significantly decreased the levels of 18:3n-3 in the white muscle phospholipid (PL) fraction of all groups fed sesamin, no significant differences were found in the triacylglycerol fraction (TAG). Slightly increased levels of docosahexaenoic acid (22:6n-3, DHA) in PL and TAG were found in some of the sesamin fed groups. Sesamin significantly affected the expression of peroxisome proliferator-activated receptor alpha, scavenger receptor type B and hormone sensitive lipase, in agreement with previous studies on rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar L.) hepatocytes published by our group. No significant effects on toxicological response measured as ethoxyresorufin O-deethylase activity was found. The total cytochrome P450 enzymes were significantly higher in MO 0.29 and SesO group. The amount of alpha- and gamma-tocopherols in liver and the amount of gamma-tocopherol in white muscle were significantly lower in fish fed the FO diet compared to the MO diet, but no difference after inclusion of sesamin was found in this study. Increased inclusion of sesamin increased the levels of sesamin and episesamin in the liver, but did not affect the amounts in white muscle.

Effects of crude rapeseed oil on lipid composition in Arctic charr Salvelinus alpinus

This study investigated the effects of crude rapeseed oil (RO) on lipid content and composition in muscle and liver of Arctic charr Salvelinus alpinus. Triplicate groups were fed diets containing fish oil (FO):RO ratio of 100:0, 75:25, 50:50 and 25:75 until two-fold mass increase. Total lipid content increased significantly in the liver with higher proportion of RO in the diet. Profound effects were seen in the fatty acid composition in the analysed tissues with a reduction in 20:5n-3 and 22:6n-3 and an increase in 18:2n-6 with higher RO content in the diets. A drop in cholesterol content was seen at 25% inclusion of RO in both tissues. Wild-caught fish contained a considerably higher amount of 20:4n-6 in both storage and membrane lipids of white muscle compared with the experimental fish.

Individual responses to predation risk and food density in perch (Perca fluviatilis L.)

Perch, Perca fluviatilis, of different sizes and ages were allowed to choose between two feeding patches differing in food ratio and (or) predation risk (presence versus absence of a pike, Esox lucius). The aim of our study was to test whether food-patch choice and risk-taking behaviour (time with the predator present) were related to size, phenotype (fast- versus slow-growing) and (or) stage of development (mature versus immature). Movements of individual fish were continuously monitored with an automatic system employing passive integrated transponder (PIT) tags. Food distribution did not seem to be important in determining perch distribution. Predation risk, however, had a significant influence. The presence of a predator in a patch significantly reduced the proportion of time spent in that feeding patch by all perch. However, the strength of this effect was dependent on individual characteristics, both the slow-growing phenotype and the mature fish spending a significantly lower proportion of time in the risky patch than the fast-growing and immature fish. Switching rates, which differed between character groups, also had an effect on growth rate, varying with predation risk.

The pineal organ is the first differentiated light receptor in the embryonic salmon, Salmo salar L

The initial appearance of S-antigen, alpha-transducin, opsin and 5-HT during embryogenesis of the pineal organ and retina was studied by means of immunocytochemistry in the Atlantic salmon, Salmo salar L. The presence of these substances may be taken as a good indication of photoreceptor differentiation; alpha-transducin and S-antigen are involved in the phototransduction process, opsin is the proteinaceous component of the photopigment rhodopsin, and 5-HT is a neurotransmitter or neurohormone produced by pineal photoreceptors. Two days after the retinal pigment layer became visible in the eggs, the outer segments of a few pineal photosensory cells showed immunoreactivity to opsin and alpha-transducin. At the same time S-antigen and serotonin were present in pineal cells of the photoreceptor type. The number of immunoreactive cells in the pineal organ increased up to hatching. In the differentiating retina of the salmon, no immunoreactivity to antibodies raised against the mentioned substances were detectable until after hatching. These results indicate that in ontogeny the developing pineal organ of the salmon embryo has the ability to perceive light information much earlier than the retina.