Sunil Kadri

Coping strategies in a strongly schooling fish, the common carp Cyprinus carpio.

Individual common carp Cyprinus carpio were screened repeatedly for risk taking (rate of exploration of a novel, potentially dangerous environment) and for competitive ability (success in gaining access to a spatially restricted food source). Marked differences in behaviour were evident, and significant consistency in individual responses across trials was found for both risk taking and competitive ability. In addition, there was a significant positive relationship between individual performance in these two contexts, with fish that explored more quickly in the novel environment tending to be among the first to gain access to restricted food. In two follow-up studies, resting metabolic rate, blood lactate and glucose and the expression of the cortisol receptor gene in the head kidney and brain were compared in fish from the two extremes of the risk-taking spectrum. Mass-specific metabolic rate was significantly higher in risk-taking than in risk-avoiding fish, while plasma lactate and glucose concentrations and expression of the cortisol receptor gene were lower. It was concluded that a behavioural syndrome based on boldness and aggression exists in C. carpio, as it does in many other animals, and that this is associated with differences in metabolic and stress physiology (down to the genomic level) similar to those described in animals with different coping strategies.

Daily and seasonal patterns in the feeding behaviour of Atlantic salmon (Salmo salar L.) in a sea cage

Abstract The diurnal and seasonal variation in behavioural indices of appetite in one-sea-winter Atlantic salmon in a sea cage was investigated in relation to environmental variables and fish swimming activity, from autumn to spring. There was marked seasonal variation in feeding behaviour, indicating a reduction in appetite from autumn to winter and a rapid increase in appetite from late winter onwards. Seasonal variation in behavioural indices of appetite was more closely related to day length and change in day length, than to other environmental variables, including water temperature. A feeding regime based on the assumption that water temperature is the most important environmental determinant of the appetite of salmon in sea cages could lead to food wastage in autumn and early winter and under-feeding in late winter and early spring. The responsiveness of salmon to food varied significantly throughout the day, but the diurnal pattern of appetite was different at different times of year. In contrast to a previous study at the same site in summer, there were not marked morning and evening peaks of appetite, and pre-feeding swimming speed was not closely related to appetite.

Differential patterns of feeding and resource accumulation in maturing and immature Atlantic salmon, Salmo salar

Abstract Maturing Atlantic salmon first accumulate nutrient reserves and then cease feeding in the spring/summer prior to spawning. Here we examine patterns of feeding behaviour and reserve accumulation in maturing and immature fish of the same age from the onset of the maturation cycle (autumn) to the onset of anorexia (summer). Two hundred one-sea-winter fish were sampled monthly from sea cage populations of individually marked fish, and their feeding responses, weights, forklengths and body lipid levels were recorded. Maturing fish were larger and in better body condition than non-maturing fish from October until July of the following year. They also had a greater motivation to feed than non-maturing fish from April. The period of greatest differentials in growth rate, body lipids and condition factor between the two groups of fish coincided with the period of differential feeding responses. The results are discussed with reference to the energetic requirements of maturation and breeding in Atlantic salmon, and the aquaculture implications of early differences in appetite of maturing and immature fish.

What controls the onset of anorexia in maturing adult female Atlantic Salmon

1. Atlantic Salmon (Salmo salar) cease feeding before entering their home river to undertake upriver migration and spawning. Here we examine whether the onset of this anorexia is related to body condition and/or gonad development. 2. The food intake and growth rate of 100 individually marked one-sea-winter fish (stocked in an outdoor tank) were monitored regularly over 11 weeks during summer. The relative size of body lipid reserves, lean mass and gonad size were estimated in all maturing females in midsummer and at the end of the experiment. 3. The date on which individual fish stopped feeding varied greatly ; after ceasing to feed all lost weight at a consistent rate of 0.1% per day. 4. The onset of anorexia was significantly correlated with estimates of fat reserves, lean mass and gonad size. However multivariate analysis showed that lean mass was most important. Female salmon thus appear to continue feeding until their lean mass has reached threshold levels. The evolutionary implications of these findings are discussed with respect to inter-population variation in the length and relative difficulty of upriver migration.

Screening for Coping Style Increases the Power of Gene Expression Studies

Background Individuals of many vertebrate species show different stress coping styles and these have a striking influence on how gene expression shifts in response to a variety of challenges. Principal Findings This is clearly illustrated by a study in which common carp displaying behavioural predictors of different coping styles (characterised by a proactive, adrenaline-based or a reactive, cortisol-based response) were subjected to inflammatory challenge and specific gene transcripts measured in individual brains. Proactive and reactive fish differed in baseline gene expression and also showed diametrically opposite responses to the challenge for 80% of the genes investigated. Significance Incorporating coping style as an explanatory variable can account for some the unexplained variation that is common in gene expression studies, can uncover important effects that would otherwise have passed unnoticed and greatly enhances the interpretive value of gene expression data.

Social interactions and the distribution of food among one-sea-winter Atlantic salmon (Salmo salar) in a sea-cage

Abstract In order to test whether the amount of food obtained by individual one-sea-winter Atlantic salmon was related to social status, the feeding interactions of 19 individually marked Atlantic salmon in a sea cage were monitored by underwater video (fish competed for single food pellets presented at regular intervals). Food was distributed unevenly among fish; no significant relationship was found between food intake and either weight or gender. More successful fish fed earlier in a feeding session than their companions, and smaller fish avoided competitors when approaching pellets. There was a positive relationship between food intake and frequency of being beaten to pellets, but no relationship between food intake and proportion of feeding attempts in which a fish was beaten. This suggests that fish of a similar status were scrambling for food. Previous studies have shown a negative relationship between the coefficient of variation in daily food intake and total food intake, but did not control for fish size. Here we found the same relationship after controlling for fish size, showing that more successful fish had less variation in their day to day consumption than did less successful conspecifics. These data suggest that, in order to prevent food monopolisation by few individuals, the food should be presented so that it is unpredictable in time and space.

The effect of competition on the feeding efficiency and feed handling behaviour in gilthead sea bream (Sparus aurata L.) held in tanks

Abstract The aims of this study were to determine whether growth, feed handling and feeding efficiency of gilthead sea bream ( Sparus aurata ) changed in response to imposed competition levels, manipulated by altering ration and feed delivery rate, and to investigate the effect of feed handling on feed conversion efficiency. Triplicate tanks of bream (32 g, 12 kg m −3 ) were fed rations of 3.5%, 3%, 2.5% or 2% BW day −1 at a rate of ca. 10 g min −1 , in three meals. To compare the effect of feed delivery rate, triplicate tanks were fed a 3% BW day −1 ration at a rate of ca. 20 g min −1 . Low rations increased competition levels; feeding intensity, density of fish under the feeder and frequency of sharp-angled turns increased during meals. Increasing the feed delivery rate had a weaker influence on competition; feeding intensity was higher and sharp angled turns more frequently observed but fish density under the feeder increased and swimming speeds decreased during feeding for both feed delivery rates tested. Increasing ration and feed delivery rate led to an increase in feed intake, growth rate, rate of chewing and proportion of feed particles in the stomach. High feed delivery rate also appeared to result in a reduction in waste from chewing. Bream fed the 3% BW day −1 ration (just under satiation) delivered at a high rate had the lowest standard FCR. This was also true for when calculating FCR, taking into account the actual feed intake. However, when taking waste from handling feed into account, the resulting FCRs were higher in treatments where waste from chewing was reduced i.e. for bream fed at the high rate of feed delivery. The results are discussed in terms of improved feeding practices for the intensive culture of this species.

Social hierarchies, growth and brain serotonin metabolism in Atlantic salmon (Salmo salar) kept under commercial rearing conditions

Monitoring social interactions between individuals in large, high-density groups poses several challenges. Here we demonstrate that relative concentrations of serotonin (5-Hydroxytryptamine, 5-HT) and its principal catabolite 5-Hydroxyindoleacetic acid (5-HIAA) in brain tissue of individual fish reflect social organisation in large groups of farmed Atlantic salmon. In the central nervous system of vertebrates, the monoamine neurotransmitter/neuromodulator 5-HT is critical for maintaining adaptive physiological, cognitive and emotional processes. In both teleost fish and mammals it has previously been shown that social interactions in small groups lead to elevated 5-HT release and/or metabolism in subordinate individuals, as indicated by the 5-HIAA/5-HT concentration ratio. In the current study, evidence is presented of non-linear dominance hierarchies in farmed Atlantic salmon (Salmo salar) kept at high rearing densities. The physiological effect of these hierarchies was decreased when food resources were abundant, although some subordinate fish still showed altered brain serotonergic activity and failed to grow even feed was available in excess. The largest effect of decreased feed rations was seen in fish of intermediate size, where competition appeared to increase with reduced access to feed. The largest individuals in each rearing unit showed low 5-HIAA/5-HT ratios independent of feeding regime. A novel observation, with respect to previous studies, was that elevated brain 5-HIAA/5-HT ratios resulted from decreased 5-HT concentrations rather than elevated 5-HIAA in small fish. Thus, in light of the serotonin deficit hypothesis of depression, it cannot be excluded that social stress is important for animal welfare even in large, relatively homogenous groups of animals reared in captivity.

Anorexia in one-sea-winter Atlantic salmon (Salmo solar) during summer, associated with sexual maturation

Abstract During a period of temperature increase from 8.8 to 11.2 °C from May to August, maturing one-sea-winter Atlantic salmon showed decreasing appetite from early June, to little or no food intake by early July. In contrast, non-maturing siblings increased food intake steadily from early June throughout the period. The number of anorexic maturing fish increased throughout the summer, suggesting that anorexia is dependent on an internal cue.

Taking account of fish welfare: lessons from aquaculture

This paper explores the possibility that lessons learned from aquaculture might contribute to current debate on welfare and fisheries. After looking briefly at the history of research interest in the welfare of farmed fishes, some implications of using different definitions of and approaches to the concept of welfare are discussed. Consideration is given to the way in which the aquaculture industry has responded to public concern about fish welfare and, for cases where these responses have been effective, why this might be the case. Finally, possible cross-over points between aquaculture and fisheries in the context of fish welfare, as well as experience and expertise that might be shared between these two areas, are identified.