Thomas Torgersen

Food anticipatory behaviour as an indicator of stress response and recovery in Atlantic salmon post-smolt after exposure to acute temperature fluctuation

In this study we evaluated Pavlovian conditioned food anticipatory behaviour as a potential indicator for stress in groups of Atlantic salmon, and compared this with the physiological stress responses of cortisol excretion into water and hyper-consumption of oxygen. We hypothesised that environmental stress would result in reduced feeding motivation. To assess this, we measured the strength of anticipatory behaviour during a period of flashing light that signalled arrival of food. Further, we expected that fish given a reduced food ration would be less sensitive to environmental stress than fish fed full ration. The fish responded to an acute temperature fluctuation with hyper-consumption of oxygen that decreased in line with the temperature, and elevated cortisol excretion up to 1h after the stressor. These physiological responses did not differ significantly between the food ration groups. The anticipatory behaviour was significantly reduced after the stressor and returned to control levels after 1 to 2 h in the reduced ration group, but not until after 3 to 4 h in the full ration group. Our results show that acute stress can be measured in terms of changes to feeding motivation, and that it is a more sensitive indicator of stress that influences the fish over a longer time period than measures of change in cortisol excretion.

Duration of effects of acute environmental changes on food anticipatory behaviour, feed intake, oxygen consumption, and cortisol release in Atlantic salmon parr

We compared behavioural and physiological responses and recovery time after different acute environmental challenges in groups of salmon parr. The fish were prior to the study conditioned to a flashing light signalling arrival of food 30 s later to study if the strength of Pavlovian conditioned food anticipatory behaviour can be used to assess how salmon parr cope with various challenges. The effect on anticipatory behaviour was compared to the effect on feed intake and physiological responses of oxygen hyper-consumption and cortisol excretion. The challenges were temperature fluctuation (6.5C° over 4 h), hyperoxia (up to 380% O(2) saturation over 4 h), and intense chasing for 10 min. Cortisol excretion was only elevated after hyperoxia and chasing, and returned to baseline levels after around 3 h or less. Oxygen hyper-consumption persisted for even shorter periods. Feed intake was reduced the first feeding after all challenges and recovered within 3 h after temperature and hyperoxia, but was reduced for days after chasing. Food anticipatory behaviour was reduced for a longer period than feed intake after hyperoxia and was low at least 6 h after chasing. Our findings suggest that a recovery of challenged Atlantic salmon parr to baseline levels of cortisol excretion and oxygen consumption does not mean full recovery of all psychological and physiological effects of environmental challenges, and emphasise the need for measuring several factors including behavioural parameters when assessing fish welfare.

Role of the GH-IGF-1 system in Atlantic salmon and rainbow trout postsmolts at elevated water temperature.

A comparative experiment with Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) postsmolts was conducted over 35 days to provide insight into how growth, respiration, energy metabolism and the growth hormone (GH) and insulin-like growth factor 1 (IGF-1) system are regulated at elevated sea temperatures. Rainbow trout grew better than Atlantic salmon, and did not show reduced growth at 19 °C. Rainbow trout kept at 19 °C had increased blood hemoglobin concentration compared to rainbow trout kept at 13 °C, while salmon did not show the same hemoglobin response due to increased temperature. Both species showed reduced length growth and decreased muscle glycogen stores at 19 °C. Circulating IGF-1 concentration was higher in rainbow trout than in Atlantic salmon, but was not affected by temperature in either species. Plasma IGF-binding protein 1b (IGFBP-1b) concentration was reduced in Atlantic salmon reared at 19 °C after 15 days but increased in rainbow trout at 19 °C after 35 days. The igfbp1b mRNA level in liver showed a positive correlation to plasma concentrations of glucose and IGFBP-1b, suggesting involvement of this binding protein in carbohydrate metabolism at 19 °C. At this temperature muscle igfbp1a mRNA was down-regulated in both species. The muscle expression of this binding protein correlated negatively with muscle igf1 and length growth. The plasma IGFBP-1b concentration and igfbp1b and igfbp1a expression suggests reduced muscle igf1 signaling at elevated temperature leading to glucose allostasis, and that time course is species specific due to higher thermal tolerance in rainbow trout.

Reply to Diggles et al. (2011): Ecology and welfare of aquatic animals in wild capture fisheries

In their recent review, Diggles et al. advocate the use of ‘‘function-based’’ and ‘‘nature-based’’ welfare approaches instead of the ‘‘feelings-based’’ approach regarding aquatic animals in wild capture fisheries. We disagree with key premises and conclusions in their paper and have a few remarks as to what welfare is and what it is not. The basis for the interest in animal welfare is man’s capacity for empathy and the assumption or suspicion that animals have an experience of life. The term welfare, however it is measured, should be restricted to addressing the quality of the lives of animals that are able to experience it. Since it is commonly accepted that e.g., plants and fungi have no sentient experience of life, the terms ‘‘plant welfare’’ and ‘‘fungus welfare’’ do not exist—they would have no meaning. Still, in order to produce healthy plant crops, offering the plants conditions and care that meet function-based ‘‘welfare’’ criteria is generally a good strategy, as it will ensure healthy, growing plants. As this care is instrumental in the production of plant crops, making a semantic detour via constructed welfare terms is not necessary to justify such practices. Feelings are partially concealed to anyone but the subject itself. However, verbal creatures, like neighbors, friends and family, can talk about their experience of life, and this will often reflect how they feel. Non-verbal communication can be at least as effective in expressing welfare. The welfare of sentient animals and human beings with limited verbal capacities (such as very young children and mentally impaired individuals) can be assessed, more or less directly using emotional expressions (e.g., vocalisations) and tests [e.g., cognitive bias test (Harding et al. 2004)]. In addition, we may check whether they appear fit and agile and with a healthy appetite, i.e., how they function. The reason why the function-based animal welfare approach exists is that it makes welfare measurable under the assumption that an animal that does not function properly, does not or will not have good welfare, provided that it has the capacity for having an experience of life. Function is therefore a welfare indicator; a useful proxy for current and future welfare, but not welfare in itself. The T. Torgersen (&) T. S. Kristiansen Animal Welfare Research Group, Institute of Marine Research, Matre Research Station, 5984 Matredal, Norway e-mail: thomast@imr.no