Environmental enrichment (EE) can improve the welfare of captive fish. Its objective is to provide new sensorial and motor stimulation in order to help meet their behavioural, physiological, morphological and psychological needs, whilst reducing stress and frequency of abnormal behaviours. In fish farms, rearing environments are usually designed from a human perspective and based on economic requirements, mainly for practical reasons for the farmer, with little consideration for animal welfare. Throughout aquaculture production cycles, many farming operations can be stressful for fish, and EE may not only help them cope with these stressful events but also improve their overall welfare. In recent years, increasing interest on the effects of EE in captive fish has focussed mainly on structural enrichment. However, there are many other enrichment strategies that merit attention (e.g. sensorial, occupational, social and dietary enrichment) and which may be of interest for fish farming. Here, we review in depth the existing literature on EE and its effects on the welfare of a wide range of farmed fish species, discussing the feasibility and potential applications of different EE strategies to promote fish welfare at a commercial scale. We also present a practical framework to address the design, validation and implementation of EE by the aquaculture industry, taking in consideration the technical challenges of providing enrichment for farmed fish.

19Predation is an important factor during adaptation to novel environments and the feralisation 20 of introduced domestic species often involves responding appropriately to allopatric 21 predators despite a background of domestication and inbreeding. Twenty years ago domestic 22 guppies were introduced to a semi-natural environment at Burgers' Zoo in the Netherlands, 23where they have since been exposed to avian predation. We compared predation-linked 24 behaviours in this feral population and in domestic guppies akin to the original founders. We 25 found that both populations responded to a novel predator and to conspecific alarm cues. 26However shoaling, an important anti-predator behaviour, was higher among feral guppies 27 both at baseline and when exposed to the novel predator. We did not observe a linked suite of 28 anti-predator behaviours across shoaling, predator inspection, alarm substance sensitivity and 29 boldness, suggesting that these responses may be decoupled from one another depending on 30 local predation regimes. As we compared two populations, we cannot identify the causal 31 factors determining population differences, however, our results do suggest that shoaling is 32 either a particularly consequential anti-predator adaptation or the most labile of the 33 behaviours we tested. Finally, the behavioural adaptability of domestic guppies may help to 34 explain their success as an invasive species.

The neural mechanisms regulating social behaviour have received extensive attention in recent years, with much focus on 'complex' forms of sociality. Comparatively little research has addressed fundamental social behaviour, such as grouping, which impacts multiple determinants of fitness, such as foraging and avoiding predation. We are interested in the degree to which brain areas that regulate other forms of sociality are also involved in grouping behaviour, and so we investigated shoal-elicited activation of the brain in the guppy (Poecilia reticulata). Guppies are small, social fish that live in the rivers of Trinidad and, like many social fish, exhibit preferences for larger shoals. We first confirmed that our study population of wild-type guppies preferred to join a larger shoal, and then investigated the activation of four brain regions proposed to be involved in social behaviour and reward (the preoptic area, the dorsal part of the ventral telencephalon, the ventral part of the ventral telencephalon, and the supracommissural part of the ventral pallium). Subjects were exposed to a large shoal, a small shoal, or to a tank empty of conspecifics, and we used immediate early gene expression (egr-1) to assess neuronal activation. We found increased activation in the preoptic area when fish were exposed to a large shoal compared to controls that had no social exposure. There were no significant differences in activation within the other brain areas examined, possibly because these brain areas are not key regulators of grouping behaviour or have only a secondary role. The higher activation of the preoptic area during social exposure suggests functional homology in this highly-conserved region across all vertebrates.

It was thought that tool use in animals is an adaptive specialization. Recent studies, however, have shown that some non-tool-users, such as rooks and jays, can use and manufacture tools in laboratory settings. Despite the abundant evidence of tool use in corvids, little is known about the neural mechanisms underlying tool use in this family of birds. This review summarizes the current knowledge on the neural processes underlying tool use in humans, macaques and corvids. We suggest a possible neural network for tool use in macaques and hope this might inspire research to discover a similar brain network in corvids. We hope to establish a framework to elucidate the neural mechanisms that supported the convergent evolution of tool use in birds and mammals.

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