Coping with unpredictability: Dopaminergic and neurotrophic responses to omission of expected reward in Atlantic salmon (Salmo salar L.).

Comparative studies are imperative for understanding the evolution of adaptive neurobiological processes such as neural plasticity, cognition, and emotion. Previously we have reported that prolonged omission of expected rewards (OER, or 'frustrative nonreward') causes increased aggression in Atlantic salmon (Salmo salar). Here we report changes in brain monoaminergic activity and relative abundance of brain derived neurotrophic factor (BDNF) and dopamine receptor mRNA transcripts in the same paradigm. Groups of fish were initially conditioned to associate a flashing light with feeding. Subsequently, the expected food reward was delayed for 30 minutes during two out of three meals per day in the OER treatment, while the previously established routine was maintained in control groups. After 8 days there was no effect of OER on baseline brain stem serotonin (5-HT) or dopamine (DA) activity. Subsequent exposure to acute confinement stress led to increased plasma cortisol and elevated turnover of brain stem DA and 5-HT in all animals. The DA response was potentiated and DA receptor 1 (D1) mRNA abundance was reduced in the OER-exposed fish, indicating a sensitization of the DA system. In addition OER suppressed abundance of BDNF in the telencephalon of non-stressed fish. Regardless of OER treatment, a strong positive correlation between BDNF and D1 mRNA abundance was seen in non-stressed fish. This correlation was disrupted by acute stress, and replaced by a negative correlation between BDNF abundance and plasma cortisol concentration. These observations indicate a conserved link between DA, neurotrophin regulation, and corticosteroid-signaling pathways. The results also emphasize how fish models can be important tools in the study of neural plasticity and responsiveness to environmental unpredictability

Behavioural indicators of welfare in farmed fish

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.Fundação para a Ciência e Tecnologia, Portugal [SFRH/BPD/42015/2007]info:eu-repo/semantics/publishedVersio

Effects of environmental enrichment on growth, aggressive behaviour and brain monoamines of gilthead seabream Sparus aurata reared under different social conditions

The presence of blue or red-brown substrate on the tank bottom has been previously reported as an efficient means of environmental enrichment for gilthead seabream. The present study aimed to investigate whether this enrichment is still beneficial when gilthead seabream is reared under different social conditions (i.e. a lower 4.9kgm-3 and a higher 9.7kgm-3 density). Water exchange was adjusted according to fish biomass to exclude density effects on water quality. In the enriched tanks single-colour glass gravel was used as substrate (blue and red-brown substrate, or BS and RBS respectively), while control tanks had no gravel. Growth, aggressive behaviour and size distribution results indicated that the lower density created a less favourable social environment. In both densities studied, BS enhanced growth, suppressed aggression and reduced brain serotonergic activity. In the condition of intense social interactions (i.e. the lower density) BS also reduced brain dopaminergic activity. These results along with the negative correlations observed between brain monoamines and fish body mass, indicated that substrate and density effects are socially-induced. However, there may be several biotic and/or abiotic factors interfering with substrate effects that should be investigated before the practical use of a substrate in land-based intensive aquaculture. © 2013 Elsevier Inc

Environmental enrichment induces changes in brain monoamine levels in gilthead seabream Sparus aurata

It is generally accepted that environmental enrichment enhances the performance and improves welfare of animals kept in captivity. Similar results have been obtained for fish. It has been previously reported that the presence of Blue or Red-Brown Substrate (BS and RBS respectively) on tank bottom resulted in growth enhancement and suppression of aggressive behavior of gilthead seabream Sparus aurata compared to Green Substrate (GS) and tanks without modifications (Control-C). In an attempt to identify the underlying mechanisms, in the present study the effects of this environmental enrichment on brain monoamine neurotransmitters and fatty acids of gilthead seabream were evaluated. BS and RBS fish had lower serotonergic activity (5-HIAA/5-HT), resulting mainly from lower 5-hydroxyindoleacetic acid (5-HIAA) levels. BS fish also had lower serotonin levels compared to all other treatments. Brain noradrenaline (NA) levels did not show significant differences between substrate treatments and control. Brain dopamine (DA) levels were lowest in BS and RBS fish, higher in GS fish and highest in C fish. No differences were observed for dopamine metabolites or dopaminergic activity. Moreover, brain NA was negatively correlated with body weight in BS fish and positively correlated in RBS and C fish. A positive correlation was also observed for brain DA with body weight in RBS fish. No differences were observed for brain fatty acids. Present results support the hypothesis that the beneficial effects of the presence of BS and RBS are related to altered social interactions and indicate the establishment of a less stressful social organization in enriched-reared fish groups. © 2014 Elsevier Inc

Acute stress response of European sea bass Dicentrarchus labrax under blue and white light

Recent data suggest that specific light wavelength can alleviate fish acute stress response by counteracting or reducing the stress-induced cortisol increase. The European sea bass Dicentrarchus labrax, widely reared in the Mediterranean, is very sensitive to handling stress, so that typical rearing procedures during on-growing (e. g. grading) are avoided. The present study aimed at investigating whether exposure to blue (480 nm) or white light (BL or WL, respectively) could alleviate European sea bass acute stress response. Fish (initial weight 130.9 +/- 0.4 g) were reared (seawater recirculating system) for 63 days under BL or WL and then subjected to 1 hour confinement or left undisturbed (control). Confinement of fish under BL resulted in a higher cortisol increase, no dopaminergic activation and lower brain serotonergic activity than under WL. In contrast, WL confined fish showed a lower cortisol increase coupled with higher brain serotonergic activity and increased levels of brain dopamine. Stress-induced hematocrit increase was lower when fish were confined under BL and triacylglycerides increase was only observed for WL reared fish. Differences in some parameters between unstressed BL and WL fish suggest that light wavelength had an effect on fish physiological status irrespective of stress. Although present results are not conclusive on which fish groups were more or less stressed, they do confirm that light wavelength can differentiate European sea bass response to acute stressors. Further studies to elucidate biological mechanisms of light spectrum effects will reinforce its efficacy as a tool to manipulate intensively reared fish stress response. (C) 2012 Elsevier B.V. All rights reserved

2000. Effects of background color on growth performance and physiological responses of scaled carp (Cyprinus carpio) reared in a closed circulated system Aquacultural Engineering

Abstract Growth performances and physiological responses of Cyprinus carpio after long-term (14 weeks) background color adaptation were investigated. Six groups of ten individuals each (initial body weight 116 g) were reared in black, green and white tanks (two replicate groups for each color). At the end of the experiment, blood (cortisol, glucose, haematocrit, cholesterol, triglycerides, total lipids, osmolality, electrolytes, pCO 2 , pH), liver (total lipids, glycogen, hepatosomatic index) and growth (body weight, specific growth rate, food conversion ratio, condition factor, proximate carcass composition) parameters were determined. Plasma cortisol levels in white-adapted carp were significantly (PB0.05) lower than those in black, while in green-adapted fish did not differ significantly from those in both other counterparts. White-adapted carp showed the highest specific growth rate and the lowest food conversion ratio, whereas black-adapted fish exhibited the opposite pattern. In addition, mean (%) increase of body weight in white-adapted carp was 4.66 and 3.58% higher than that in black-and green-adapted fish, respectively. Furthermore in white-adapted carp, blood pCO 2 and pH were significantly higher and lower, respectively, than those obtained in black-and green-adapted fish. In black-adapted carp, liver total lipid levels were significantly lower, and plasma total lipid levels were significantly higher, than those in white-and green-adapted fish. No significant variations were observed in the other parameters. It is concluded that different background colors may lead to different growth performances of scaled carp depending upon rearing conditions

Effects of rearing density on growth, brain neurotransmitters and liver fatty acid composition of juvenile white sea bream Diplodus sargus L.

White sea bream Diplodus sargus L. is a fish species that develops dominance hierarchies and aggressive behaviour against its conspecifics. On the other hand, stocking density is known to affect social interactions, while an appropriate density for D. sargus efficient farming remains to be elucidated. For this purpose, juvenile D. sargus (14.3 g) were reared in 88.4 L tanks, for 10 weeks, under six rearing densities (10, 15, 20, 25, 30 and 35 fish tank -1). Water quality was not affected by rearing density. Best growth, in terms of final weight, specific growth rate, weight variation and food utilization, was achieved at 10 fish tank-1. At this treatment the lowest body water content, hepatosomatic and splenosomatic indices, higher body and liver lipid content were also observed. Brain neurotransmitter results indicated increased dopaminergic activity in populations held at higher rearing densities, while serotonergic activity was not affected. Moreover, no significant differences were detected for liver fatty acids. Results of the present study, compared with previously reported data, suggest that, within the range tested, the lowest realistic rearing density for juvenile white sea bream would be 10 fish tank-1. Higher rearing densities led to decreased growth, which seemed to be related to changes in intraspecific competition and social behaviour. © 2005 Blackwell Publishing Ltd

Blue substrate modifies the time course of stress response in gilthead seabream Sparus aurata

Environmental enrichment may attenuate stress response of several vertebrates. In the case of fish, although their stress response is well investigated, the effect of structural complexity as a means of environmental enrichment on stress response is not widely studied. The present study aims to investigate the possible effect of structural enrichment (blue gravel substrate) on gilthead seabream Sparus aurata primary and secondary stress responses during confinement and after recovery. Fish (initial mass 20.3 ± 0.22 g; age 0 +) were reared in tanks with blue substrate (BS) or no-substrate (NS) for 75. days. Fish (triplicated groups) were subjected to 90. min of confinement stress and sampled at 30, 60 and 90. min of confinement, as well as at 2, 6 and 24. h after stress (recovery). Triplicate groups of BS and NS fish were left undisturbed (unstressed fish). During rearing BS fish had better growth performance and less aggressive behavior than NS fish. Plasma cortisol levels and brain neurotransmitters of BS and NS fish were increased during confinement. Cortisol reduction (after stress-induced increase) occurred earlier in NS fish (60 min) than BS fish (90. min), while cortisol levels recovered in 2. h in both treatments. Serotonin metabolite 5-HIAA levels and serotonergic activity (5-HIAA/5-HT) were recovered in 6. h in BS fish, while they remained elevated for NS fish. Dopaminergic system response to confinement showed a transient increase in BS fish (60 min), while no effect was observed in NS fish. Concerning secondary stress response, glucose levels of BS fish decreased after 6. h of recovery while NS fish were not affected. On the other hand, NS fish presented a reduction of triacylglycerides (60 and 90 min) during confinement, while BS fish response was not affected. Osmolality and plasma total protein levels increased at 30. min of confinement and returned to unstressed levels in 24. h in both treatments. Present results indicate that the presence of blue substrate did modify the time course of gilthead seabream stress response to confinement. The overall performance of fish reared with blue substrate suggests that they are in better fitness than fish reared in plain tanks. The efficacy of the blue substrate as environmental enrichment enhancing gilthead seabream welfare is further reinforced and strongly encourages for additional investigations. © 2013 Elsevier B.V