In this review, we provide a brief retrospective history of the science of animal welfare and recognize the sentience of non-human animals; however, we emphasize that crucial problems remain regarding how to define and measure animal welfare. In general, the use of physiological measures to assess welfare is discouraged. Furthermore, there is a theoretical background for measures of stress, but not for welfare states because life may not be at risk. Instead, a preference or choice-based approach, which is based on the animal decision, is recommended. To this end, welfare is discussed and then contrasted with disease, health, stress and distress. In addition, the importance of prospective capacities for the welfare of human and non-human animals is discussed.

No abstract

Animals can use social information to detect threat in the environment. In particular, social learning allows animals to learn about dangers without incurring in the costs of trial‐and‐error learning. In zebrafish, both chemical and visual social cues elicit an innate alarm response, which consists of erratic movement followed by freezing behavior. Injured zebrafish release an alarm substance from their skin that elicits the alarm response. Similarly, the sight of conspecifics displaying the alarm response can also elicit the expression of this response in observers. In this study, we investigated if these social cues of danger can also be used by zebrafish as unconditioned stimulus (US) in learning. We found that only the chemical cue was effective in the social fear conditioning. We suggest that this differential efficacy of social cues results from the fact that the alarm cue is a more reliable indicator of threat, than the sight of an alarmed conspecific. Therefore, although multiple social cues may elicit innate responses not all have been evolutionarily co‐opted to act as US in associative learning. Furthermore, the use of the expression of the immediate early genes as markers of neuronal activity showed that chemical social fear conditioning is paralleled by a differential activation of the olfactory bulbs and by a different pattern of functional connectivity across brain regions involved in olfactory processing.

No abstract

Fish gill is a multifunctional organ with role in acid-base balance, elimination of nitrogen waste and mainly gas exchange and ion regulation. There is a high energetic coast for ionregulation in freshwater fish maintained in salt water but a raise in growing taxes was observed for some species. The freshwater Nile tilapia, Oreochromis niloticus, is widely used in aquaculture farmers and the aim of this study was to investigate the changes on the gill filaments ultrastructure in fish kept under different salinities. Alevins were obtained and transported to laboratory of studies in animal stress Federal University of Paraná. Established groups in 0‰, 16‰ and 32‰ salt water with 12 animals in each one. After 30 days of exposition, the animals were anesthetized and the second gill arches were dissected and processed for scanning and transmission electron microscopy. The mitochondrial rich cells fractional area and density in the gill epithelia were determinated. The under scanning electron microscopy (SEM) in 0‰ salinity group reveal changes in the apical ridge of mitochondrial rich cells (MRCs). In all other groups, the observations revealed numerous crypts disposed mainly in the filament epithelia. In transmission electron microscopy (TEM) two distinct types of MRCs were observed. The data of MRCFA and density revealed in 0‰ and 16‰ values significantly elevated in comparison to 32‰. Despite these lower values, the density in the gill epithelia was higher. The main differences found between the groups revealed that fish exposed to 16‰ salinity have less MRCs aperture to the environment and are less related to ion regulation process.