Percorrer por autor "Silva, T."
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- Cognitive appraisal in fish: stressor predictability modulates the physiological and neurobehavioural stress response in sea bassPublication . Cerqueira, Marco; Millot, S.; Felix, A.; Silva, T.; Oliveira, G. A.; Oliveira, Catarina; Rey, S.; MacKenzie, S.; Oliveira, R.The role of cognitive factors in triggering the stress response is well established in humans and mammals (aka cognitive appraisal theory) but very seldom studied in other vertebrate taxa. Predictability is a key factor of the cognitive evaluation of stimuli. In this study, we tested the effects of stressor predictability on behavioral, physiological and neuromolecular responses in the European sea bass (Dicentrarchus labrax). Groups of four fish were exposed to a predictable (signalled) or unpredictable (unsignalled) stressor. Stressor predictability elicited a lower behavioural response and reduced cortisol levels. Using the expression of immediate early genes (c-fos, egr-1, bdnf and npas4) as markers of neuronal activity, we monitored the activity of three sea bass brain regions known to be implicated in stressor appraisal: the dorsomedian telencephalon, Dm (putative homologue of the pallial amygdala); and the dorsal (Dld) and ventral (Dlv) subareas of the dorsolateral telencephalon (putative homologue of the hippocampus). The activity of both the Dm and Dlv significantly responded to stressor predictability, suggesting an evolutionarily conserved role of these two brain regions in information processing related to stressor appraisal. These results indicate that stressor predictability plays a key role in the activation of the stress response in a teleost fish, hence highlighting the role of cognitive processes in fish stress.
- Cognitive appraisal of environmental stimuli induces emotion-like states in fishPublication . Cerqueira, M.; Millot, S.; Castanheira, Maria Filipa; Félix, Ana Sofia; Silva, T.; Oliveira, Gonçalo; Oliveira, C. C.; Martins, C. I. M.; Oliveira, Rui F.The occurrence of emotions in non-human animals has been the focus of debate over the years. Recently, an interest in expanding this debate to non-tetrapod vertebrates and to invertebrates has emerged. Within vertebrates, the study of emotion in teleosts is particularly interesting since they represent a divergent evolutionary radiation from that of tetrapods, and thus they provide an insight into the evolution of the biological mechanisms of emotion. We report that Sea Bream exposed to stimuli that vary according to valence (positive, negative) and salience (predictable, unpredictable) exhibit different behavioural, physiological and neuromolecular states. Since according to the dimensional theory of emotion valence and salience define a two-dimensional affective space, our data can be interpreted as evidence for the occurrence of distinctive affective states in fish corresponding to each the four quadrants of the core affective space. Moreover, the fact that the same stimuli presented in a predictable vs. unpredictable way elicited different behavioural, physiological and neuromolecular states, suggests that stimulus appraisal by the individual, rather than an intrinsic characteristic of the stimulus, has triggered the observed responses. Therefore, our data supports the occurrence of emotion-like states in fish that are regulated by the individual's perception of environmental stimuli.
- Effects of fertiliser practices on the growth and quality of two table grape cultivars: 'Cardinal' and 'D. Maria'.Publication . Domingos, I.; Silva, T.; Correia, P. J.; Correia, Maribela Pestana; de Varennes, A.In this study, the different fertilliser practices of four commercial vineyards (Vitis vinifera L. cv. 'Cardinal' and cv. 'D. Maria') in southern Portugal were assessed and compared in 2002. The vineyards were established in similar soils under the same climatic conditions and additional water was supplied by drip irrigation. At harvest, the mineral composition of petioles (P, K, Mg, Ca, Fe, Cu, Zn and Mn) and quality parameters of the grapes (total soluble solids expressed as degree Brix, cluster length and weight, number of grapes, grapes weight and rachis weight) were recorded. For the 'Cardinal' cultivar, the nutritional status of the plant was correlated with growth and yield, and the greatest values for most of the parameters studied were measured at Alvisquer farm. For the 'D. Maria' cultivar, a single correlation was found between nutrient levels and growth. Shoot and cluster lengths, and grape weight were similar at all farms, though cluster weight, number of grapes and total soluble solids were smaller at Pedras than at Alvisquer or Gomeira.
- Health status in gilthead seabream (Sparus aurata) juveniles fed diets devoid of fishmeal and supplemented with Phaeodactylum tricornutumPublication . Reis, B.; Ramos-Pinto, L.; Martos-Sitcha, J. A.; Machado, M.; Azeredo, R.; Fernandez-Boo, S.; Engrola, S.; Unamunzaga, C.; Calduch-Giner, J.; Conceicao, L. E. C.; Silva, T.; Dias, J.; Costas, B.; Perez-Sanchez, J.To enhance fish general health, feeds can be supplemented with health-promoting additives, reducing the need to use chemotherapeutics. Incorporation of marine algae biomasses in aquafeeds has been shown to improve fish immune status by enhancing innate immune response. This study evaluated the effects of Phaeodactylum tricornutum incorporation in feed by two different processes, either as freeze-dried biomass or broken cell wall biomass, on fish health status and performance. Triplicate groups of gilthead seabream juveniles (13.3 +/- 0.3 g) were either fed a control diet (CTRL) with an extreme (i.e., 0% fishmeal), nutritionally balanced, formulation, or two experimental diets formulated as the CTRL with 1% inclusion of the microalga P. tricornutum at the expense of wheat meal: BC diet contains P. tricornutum broken cells and WC diet microalgae whole cells. After 2 and 12 weeks of feeding, blood was collected for hematological procedures, whereas plasma and mucus were sampled for immune parameters. Head-kidney, liver, and white skeletal muscle were also collected for gene expression measurements. No major differences were observed in hematological nor plasma humoral parameters after 12 weeks irrespective of dietary treatment. Arrays of 29-31 genes were analyzed in the different tissues, revealing an early dietary effect (2 weeks) in a tissue-specific pattern. In the liver, the major effect was found in the GH/IGF axis and in muscle there was a late downregulation of myostatin (mstn) gene, mainly due to WC diet, even though all fish had similar growth performance. Regarding the head-kidney, BC diet led to alpha-2-macroglobulin (a2m) gene upregulation. Also, the same treatment showed increased mucus alternative complement pathway and bactericidal activity at 2 and 12 weeks, respectively. Hence, it seems that BC diet has a potential stimulatory effect that might be relevant as a prophylactic measure before a predictable stressful event.