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Behaviour represents a reaction to the environment as fish perceive it and is therefore a key element of fish welfare. This review summarises the main findings on how behavioural changes have been used to assess welfare in farmed fish, using both functional and feeling-based approaches. Changes in foraging behaviour, ventilatory activity, aggression, individual and group swimming behaviour, stereotypic and abnormal behaviour have been linked with acute and chronic stressors in aquaculture and can therefore be regarded as likely indicators of poor welfare. On the contrary, measurements of exploratory behaviour, feed anticipatory activity and reward-related operant behaviour are beginning to be considered as indicators of positive emotions and welfare in fish. Despite the lack of scientific agreement about the existence of sentience in fish, the possibility that they are capable of both positive and negative emotions may contribute to the development of new strategies (e.g. environmental enrichment) to promote good welfare. Numerous studies that use behavioural indicators of welfare show that behavioural changes can be interpreted as either good or poor welfare depending on the fish species. It is therefore essential to understand the species-specific biology before drawing any conclusions in relation to welfare. In addition, different individuals within the same species may exhibit divergent coping strategies towards stressors, and what is tolerated by some individuals may be detrimental to others. Therefore, the assessment of welfare in a few individuals may not represent the average welfare of a group and vice versa. This underlines the need to develop on-farm, operational behavioural welfare indicators that can be easily used to assess not only the individual welfare but also the welfare of the whole group (e.g. spatial distribution). With the ongoing development of video technology and image processing, the on-farm surveillance of behaviour may in the near future represent a low-cost, noninvasive tool to assess the welfare of farmed fish.

Sounds produced by male cichlids Metriaclima zebra during aggressive interactions were recorded to conduct a detailed analysis and to search for potential individual acoustic signatures. Fish from two different size groups (small and large individuals) were analysed. The two groups were significantly different for all acoustic variables considered; six of seven features demonstrated a significant interindividual variability and most of them were correlated with the size of the emitter. A cross-validated and permuted discriminant function analysis (pDFA) separated the two groups and correctly classified around 50% of the sounds to the correct individuals. Acoustic features that best distinguished among males were the instantaneous frequency of sounds and the modulation of pulse amplitude. These results suggest that acoustic signals could bear information about individual identity. The long-term stability of this signature is likely to be weak since the signature of a growing individual may change over time. [ABSTRACT FROM AUTHOR]

Abstract: In two experiments, a computerized on-demand feeding system coupled with a PIT tag monitoring device was used to continuously record the triggering activity by ca. 50 individual sea bass for 55 days (Exp. 1, initial average body weight and coefficient of variation, CV: 299 g, 15%) and 69 days (Exp. 2, 157 g, 13%). Each group was stocked in 1 m3 tanks and exposed to a water temperature of 21±1 °C and a light regime of 16:8 LD. Only 5% of the triggering activity was not associated with simultaneous PIT tag detection. Although each individual was detected via PIT tag during the experiment, only 67% and 74% of the fish actuated the trigger at least once in Exp. 1 and Exp. 2, respectively. Moreover, only two fish in Exp. 1 and one fish in Exp. 2 accounted for 82% (43+39) and 77% of the total triggering activity, respectively. These three, high-triggering individuals did not exhibit a higher specific growth rate or agonistic behavior as observed by video monitoring. Indeed, zero-triggering fish had either a slightly higher SGR (Exp. 1) or a higher final body weight (Exp. 2) compared with low- and high-triggering fish. [Copyright &y& Elsevier]

A 12-week study was conducted to examine the influence of light regime on food intake and growth in juvenile (ca. 3.5 g) largemouth bass (Micropterus salmoides). Fish were reared in 15-l aquaria either under an alternated light/dark cycle (12L:12D; L from 6:00) or under continuous light (24L:0D), and were weighed every 3 weeks. They were fed by hand once a day at 8:00, with fish in each aquarium being provided with 2% of the tank biomass (re-calculated every 3 weeks). After each meal, uneaten pellets were counted and food intake estimated. Fish reared under continuous light grew faster than those under day–night alternation, primarily because feed consumption of fish was greater under 24L:0D than under day–night alternation. [Copyright &y& Elsevier]