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The present study aims at identifying the lowest number of fish (European seabass) that could be used for monitoring and/or experimental purposes in small-scale fish facilities by quantifying the effect that the number of individuals has on the Shannon entropy (SE) of the trajectory followed by the shoal's centroid. Two different experiments were performed: (i) one starting with 50 fish and decreasing to 25, 13, and 1 fish, and (ii) a second experiment starting with one fish, adding one new fish per day during 5 days, ending up with five fish in the tank. The fish were recorded for 1h daily, during which time a stochastic event (a hit in the tank) was introduced. The SE values were calculated from the images corresponding to three arbitrary basal (shoaling) periods of 3.5 min prior to the event, and to the 3.5 min period immediately after the event (schooling response). Taking both experiments together, the coefficient of variation (CV) of the SE among measurements was largest for one fish systems (CV 37.12 and 17.94% for the daily average basal and response SE, respectively) and decreased concomitantly with the number of fish (CV 8.6-10% for the basal SE of 2 to 5 fish systems and 5.86, 2.69, and 2.31% for the basal SE of 13, 25, and 50 fish, respectively). The SE of the systems kept a power relationship with the number of fish (basal: R-2 = 0.93 and response: R-2 = 0.92). Thus, 5-13 individuals should be the lowest number for a compromise between acceptable variability (< 10%) in the data and reduction in the number of fish. We believe this to be the first scientific work made to estimate the minimum number of individuals to be used in subsequent experimental (including behavioral) studies using shoaling fish species that reaches a compromise between the reduction in number demanded by animal welfare guidelines and a low variability in the fish system's response.

The present study aims at identifying the lowest number of fish (European seabass) that could be used for monitoring and/or experimental purposes in small-scale fish facilities by quantifying the effect that the number of individuals has on the Shannon entropy (SE) of the trajectory followed by the shoal's centroid. Two different experiments were performed: (i) one starting with 50 fish and decreasing to 25, 13, and 1 fish, and (ii) a second experiment starting with one fish, adding one new fish per day during 5 days, ending up with five fish in the tank. The fish were recorded for 1h daily, during which time a stochastic event (a hit in the tank) was introduced. The SE values were calculated from the images corresponding to three arbitrary basal (shoaling) periods of 3.5 min prior to the event, and to the 3.5 min period immediately after the event (schooling response). Taking both experiments together, the coefficient of variation (CV) of the SE among measurements was largest for one fish systems (CV 37.12 and 17.94% for the daily average basal and response SE, respectively) and decreased concomitantly with the number of fish (CV 8.6-10% for the basal SE of 2 to 5 fish systems and 5.86, 2.69, and 2.31% for the basal SE of 13, 25, and 50 fish, respectively). The SE of the systems kept a power relationship with the number of fish (basal: R-2 = 0.93 and response: R-2 = 0.92). Thus, 5-13 individuals should be the lowest number for a compromise between acceptable variability (< 10%) in the data and reduction in the number of fish. We believe this to be the first scientific work made to estimate the minimum number of individuals to be used in subsequent experimental (including behavioral) studies using shoaling fish species that reaches a compromise between the reduction in number demanded by animal welfare guidelines and a low variability in the fish system's response.

The present study aims at identifying the lowest number of fish (European seabass) that could be used for monitoring and/or experimental purposes in small-scale fish facilities by quantifying the effect that the number of individuals has on the Shannon entropy (SE) of the trajectory followed by the shoal's centroid. Two different experiments were performed: (i) one starting with 50 fish and decreasing to 25, 13, and 1 fish, and (ii) a second experiment starting with one fish, adding one new fish per day during 5 days, ending up with five fish in the tank. The fish were recorded for 1h daily, during which time a stochastic event (a hit in the tank) was introduced. The SE values were calculated from the images corresponding to three arbitrary basal (shoaling) periods of 3.5 min prior to the event, and to the 3.5 min period immediately after the event (schooling response). Taking both experiments together, the coefficient of variation (CV) of the SE among measurements was largest for one fish systems (CV 37.12 and 17.94% for the daily average basal and response SE, respectively) and decreased concomitantly with the number of fish (CV 8.6-10% for the basal SE of 2 to 5 fish systems and 5.86, 2.69, and 2.31% for the basal SE of 13, 25, and 50 fish, respectively). The SE of the systems kept a power relationship with the number of fish (basal: R-2 = 0.93 and response: R-2 = 0.92). Thus, 5-13 individuals should be the lowest number for a compromise between acceptable variability (< 10%) in the data and reduction in the number of fish. We believe this to be the first scientific work made to estimate the minimum number of individuals to be used in subsequent experimental (including behavioral) studies using shoaling fish species that reaches a compromise between the reduction in number demanded by animal welfare guidelines and a low variability in the fish system's response.

[EN] The objective of this study was evaluating the effects on the growth rate and flesh quality of separating larvae according to their larval width in cultured gilthead seabream (Sparus aurata, L.). Progeny from two broodstocks (A and B) were divided into two groups according to larval width: heads (being the larger specimens) and tails. After 18months both groups were analysed to evaluate growth, carcass traits and proximal composition. The head specimens reached a larger size and showed a greater level of well-being and degree of nourishment. Total body and fillet composition in general were found to be as expected for this species. Some differences were found in total body composition between head and tail specimens in both batches, and in the fillet composition in batch B (higher fat and lower moisture content in the head specimens). Sensory analyses were carried out using untrained panelists, who were unable to distinguish between the head and tail samples in batch A, whereas differences were noticeable in batch B. Samples from the head group were judged to be tastier and juicier, a consequence of their higher fat content. Hence, fish separation according to larval width is an effective tool to separate progeny into slow and fast growing groups, whereas the total body and fillet analyses and a sensory test ensure that the selection does not generate negative effects on the product quality.

[EN] The objective of this study was evaluating the effects on the growth rate and flesh quality of separating larvae according to their larval width in cultured gilthead seabream (Sparus aurata, L.). Progeny from two broodstocks (A and B) were divided into two groups according to larval width: heads (being the larger specimens) and tails. After 18months both groups were analysed to evaluate growth, carcass traits and proximal composition. The head specimens reached a larger size and showed a greater level of well-being and degree of nourishment. Total body and fillet composition in general were found to be as expected for this species. Some differences were found in total body composition between head and tail specimens in both batches, and in the fillet composition in batch B (higher fat and lower moisture content in the head specimens). Sensory analyses were carried out using untrained panelists, who were unable to distinguish between the head and tail samples in batch A, whereas differences were noticeable in batch B. Samples from the head group were judged to be tastier and juicier, a consequence of their higher fat content. Hence, fish separation according to larval width is an effective tool to separate progeny into slow and fast growing groups, whereas the total body and fillet analyses and a sensory test ensure that the selection does not generate negative effects on the product quality.

This review describes the extant knowledge on the teleostean mucosal adaptive immune mechanisms, which is relevant for the development of oral or mucosal vaccines. In the last decade, a number of studies have shed light on the presence of new key components of mucosal immunity: a distinct immunoglobulin class (IgT or IgZ) and the polymeric Ig receptor (pIgR). In addition, intestinal T cells and their putative functions, antigen uptake mechanisms at mucosal surfaces and new mucosal vaccination strategies have been reported. New information on pIgR of Atlantic cod and common carp and comparison of natural and specific cell-mediated cytotoxicity in the gut of common carp and European seabass, is also included in this review. Based on the known facts about intestinal immunology and mucosal vaccination, suggestions are made for the advancement of fish vaccines. (C) 2014 The Authors. Published by Elsevier Ltd.

It has been hypothesised that, at non-limiting water oxygen conditions, voluntary feed intake (FI) in fish is limited by the maximal physiological capacity of oxygen use (i.e. an ‘oxystatic control of FI in fish’). This implies that fish will adjust FI when fed diets differing in oxygen demand, resulting in identical oxygen consumption. Therefore, FI, digestible energy (DE) intake, energy balance and oxygen consumption were monitored at non-limiting water oxygen conditions in Nile tilapia fed diets with contrasting macronutrient composition. Diets were formulated in a 2 × 2 factorial design in order to create contrasts in oxygen demand: two ratios of digestible protein (DP):DE (‘high’ v. ‘low’); and a contrast in the type of non-protein energy source (‘starch’ v. ‘fat’). Triplicate groups of tilapia were fed each diet twice daily to satiation for 48 d. FI (g DM/kg0·8 per d) was significantly lower (9·5 %) in tilapia fed the starch diets relative to the fat diets. The DP:DE ratio affected DE intakes (P <0·05), being 11 % lower with ‘high’ than with ‘low’ DP:DE ratio diets, which was in line with the 11·9 % higher oxygen demand of these diets. Indeed, DE intakes of fish showed an inverse linear relationship with dietary oxygen demand (DOD; R 2 0·81, P <0·001). As hypothesised (‘oxystatic’ theory), oxygen consumption of fish was identical among three out of the four diets. Altogether, these results demonstrate the involvement of metabolic oxygen use and DOD in the control of FI in tilapia.

The effect of the type of non-protein energy (NPE) on energy utilisation in Nile tilapia was studied, focusing on digestible energy utilisation for growth (kgDE). Furthermore, literature data on kgDE across fish species were analysed in order to evaluate the effect of dietary macronutrient composition. A total of twelve groups of fish were assigned in a 2 × 2 factorial design: two diets (‘fat’ v. ‘starch’) and two feeding levels (‘low’ v. ‘high’). In the ‘fat’-diet, 125 g fish oil and in the ‘starch’-diet 300 g maize starch were added to 875 g of an identical basal mixture. Fish were fed restrictively one of two ration levels (‘low’ or ‘high’) for estimating kgDE. Nutrient digestibility, N and energy balances were measured. For estimating kgDE, data of the present study were combined with previous data of Nile tilapia fed similar diets to satiation. The type of NPE affected kgDE (0·561 and 0·663 with the ‘starch’ and ‘fat’-diets, respectively; P <0·001). Across fish species, literature values of kgDE range from 0·31 to 0·82. Variability in kgDE was related to dietary macronutrient composition, the trophic level of the fish species and the composition of growth (fat:protein gain ratio). The across-species comparison suggested that the relationships of kgDE with trophic level and with growth composition were predominantly induced by dietary macronutrient composition. Reported kgDE values increased linearly with increasing dietary fat content and decreasing dietary carbohydrate content. In contrast, kgDE related curvilinearly to dietary crude protein content. In conclusion, energy utilisation for growth is influenced by dietary macronutrient composition.

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