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Abstract: Submersible sea-cages represent an alternative method to standard surface-based cages, and could help solve several production problems that exist in surface-based farming, such as heavy storms, algal and jellyfish blooms and attacks by predators. In this study, we investigated growth, haematological, biochemical and immunological parameters of European sea bass (Dicentrarchus labrax) farmed in surface and submersible cages, to compare the physiological status under different rearing conditions. In addition, we evaluated the use of erythrocyte HSP70 levels as a biomarker of fish welfare. The study was conducted in two submerged and two surface cages filled with D. labrax. No significant differences were observed in the growth rate and the relative condition factor between the two groups. Significantly higher levels of serum cortisol, haematocrit plasma glucose and total plasma proteins were measured in surface-based cages. Conversely, fish in submerged cages showed higher haemolytic activity and lysozyme levels in both mucus and kidney than surface reared sea bass. Results obtained in this study indicate that submergence could be a favorable condition for sea bass farming, suggesting mariculture in submerged net cages as a promising system that allows producers to minimize stress (included that from predation by fish-eating birds) and therefore favor animal welfare. [Copyright &y& Elsevier]

Reared sea bass were submitted to six stressful situations: hyperoxia with or without hypercapnia, increased stocking density in an open flow or recirculating system, transfer to another tank and nodavirus injection. The potentially negative impact of these factors on the lives of sea bass was investigated by measuring 9 water parameters and 19 fish parameters including total serum protein (TSP). TSP has already been used to evaluate stress. The present study investigates data of previous and new experiments, concentrating on the potential use of TSP as a routine indicator to assess welfare in sea bass reared on fish farms. In the current experiment, oxygen and carbon dioxide were seen to affect levels of TSP, but alterations were too erratic to enable proper comparison, probably because they are normal components of the fish environment and become toxic only by dose increase. TSP decreased when stocking density increased. After transfer to another tank, TSP decreased to 14% for three weeks and then increased during the fourth week through compensative overproduction, before returning to normal levels after 2 months. The results confirmed that transfer is an important stress factor for fish, with cumulative effects for successive transfers. TSP alteration of nodavirus-injected fish depends on the type of symptoms, which can be divided into 3 groups: (i) dying fish, in which TSP increased sharply due to over-production of protein involved in non-specific defences and inflammation, then decreased dramatically before death; (ii) whirling fish, a group that included both fish that later died, in which TSP decreased, and fish that subsequently survived, in which TSP increased due to development of specific immunity; and (iii) asymptomatic fish, in which TPS was similar to control levels and which were probably insensitive to nodavirus and/or had developed defences. In this paper, different mechanisms of TSP alteration are proposed and the interest of TSP as a field parameter is discussed. TSP is a non-destructive parameter that is robust, easy to measure everywhere and cheap, representing a suitable way of monitoring the overall welfare of fish by its regular increase. It can be used only as a “warning” of poor rearing conditions, however, and further investigations would be needed to identify the specific stress or health disorder. [ABSTRACT FROM PUBLISHER]

Butcher, P. A., Broadhurst, M. K., Hall, K. C., and Cooke, S. J. 2011. Post-release survival and physiology of angled luderick (Girella tricuspidata) after confinement in keeper nets in an Australian estuary. – ICES Journal of Marine Science, 68: .The study was initiated in response to concerns about the post-release welfare of angled luderick (Girella tricuspidata) after protracted confinement in keeper nets. In all, 111 fish were angled and confined for 2–250 min before being released into holding cages (with 87 controls) and monitored for 4 d. Blood was taken from fish angled and brought on board immediately (n = 11), angled and held in keeper nets (n = 25), and angled and held in monitoring cages for 4 d (n = 12). Blood was also taken from controls held in monitoring cages for 4 d (n = 12). No controls and only one angled fish died. Compared with immediately sampled angled fish, those confined in keeper nets had significantly elevated cortisol, glucose, lactate, chloride, sodium, and aspartate aminotransferase. Most of the variables returned to pre-stress levels in caged fish after 4 d. Despite this recovery, the short-term stress associated with capture and keeper-net confinement has welfare implications and justifies avoiding such a practice and/or reducing the personal daily angling quota of the species. [ABSTRACT FROM PUBLISHER]

Abstract: The effect of hydrodynamics on fish distribution (Danio rerio) was studied in two tank configurations: rectangular, with three waterfalls, and circular. The flow pattern of each tank was characterised in a previous paper by using particle tracking velocimetry (PTV) techniques. Image analysis was used as a non-intrusive method to determine spatial fish distribution in the tank by collecting fish position coordinates from the recorded sequences. The tank was divided into cells in order to establish the fish distribution pattern. A ratio of fish occupation in each cell was determined and statistically analysed for three replicates of the experiment. The fish occupation ratio was also correlated with the average velocity in the corresponding cell. Furthermore, a fish distribution coefficient of uniformity (FCU) was defined to evaluate the homogeneity of fish distribution in the tank volume. The rectangular tank showed a strong gradient in the fish distribution pattern from water inlet to outlet, where the average velocity was very low, and a low uniformity in fish distribution was obtained in the whole tank (FCU=0.26). The circular tank showed a gradient in the fish distribution pattern and in velocities from the centre to the outer perimeter, providing velocities from 0.54 to 1.76BLs−1, respectively. A more uniform fish distribution in the tank was obtained (FCU=0.70), indicating a better use of the entire rearing volume. Velocity in this tank strongly influenced fish occupation, with a positive correlation (r =0.85) and a significant linear regression (P <0.05). [Copyright &y& Elsevier]

Among the strategies that can be used to improve fish welfare in a rearing environment, domestication and/or selective breeding was proposed to minimize fish responsiveness to husbandry practices. To verify this hypothesis on a recently domesticated species, the sea bass Dicentrarchus labrax, two experiments were realized, each using two populations differing according to their level of domestication or selection. For the first experiment, we used one population produced from wild parents (Wild; initial body mass: 106 ± 3 g), and one population from parents selected for growth for one generation (Selected 1; initial body mass: 129 ± 4 g). For the second experiment, we used one population produced from parents domesticated for two generations (Domesticated; initial body mass: 72 ± 3 g), and one produced from parents selected for growth for two generations (Selected 2; initial body mass: 89 ± 4 g). The first experiment was carried out over 112 days with 240 fish (60 fish per tank, 120 fish per population), and the second one over 84 days with 200 fish (50 fish per tank, 100 fish per population). Two variables, self-feeding behavior and growth performance, were measured over the time of the experiments. After a control period, the fish were submitted twice, at three-week intervals, to an acute stress treatment consisting of draining the tank and leaving the fish out of water for one minute. Both self-feeding behavior and growth performance were altered by the acute stress treatment. During the first post-stress period, the Domesticated and Selected (1 and 2) groups showed more pronounced post-stress exposure responses than the Wild fish: they modified their feeding rhythm, their feed intake, and their growth rate. During the second post-stress period, feeding rhythm was still affected (being more diurnal with a well defined peak), but the feed intake and growth rate results showed that the Domesticated and Wild groups seemed less affected than the Selected (1 and 2) populations, which continued to express a high post-stress response. According to these results, it can be concluded that: (1) an application of two acute stress treatments, at three-week intervals, modified fish feeding behavior and growth performance; (2) the domestication process seemed to improve fish adaptation abilities to this kind of stress; and (3) the process of selection for growth led to a final, better growth, but did not seem to improve fish acute stress tolerance. [ABSTRACT FROM PUBLISHER]

Abstract: Social status affects access to food, mates and shelter and has consequences for the physiology of individuals and their health status. In the zebrafish (Danio rerio), an emerging model for studies into animal behavior, the possible consequences of social hierarchy to an individual''s physiology and health are unknown. To address this, in this species we assessed the effects of social interaction (for periods of 1–5days) on growth, stress, immune function and reproductive condition. Wide-ranging differences in physiology occurred between the social ranks, some of which were sex-related and time-dependent. In both sexes, dominant fish were larger than subordinates and dominant males had a higher growth rate during the trials. Subordinates had higher plasma cortisol and in males higher telencephalic corticotrophin-releasing hormone, neuropeptide y and glucocorticoid receptor gene expression. Splenic cytokine expression suggested differences in immune status between ranks in both sexes and hematocrit was elevated in subordinate males. In both sexes, dominants and subordinates differed in the expression of genes for various gonadal sex steroid receptors and steroidogenic enzymes and in dominant females the ovary was larger relative to body mass compared with in subordinates. Dominant males had higher plasma 11-ketotestosterone than subordinates and there was an increase in the number of spermatids in their testes over the duration of the study that was not seen in subordinate males. The wide-ranging physiological differences seen between dominant and subordinate zebrafish as a consequence of their social status suggest negative health impacts for subordinates after prolonged durations in those hierarchies. [Copyright &y& Elsevier]

The aim of the present study was to investigate the cataract preventive effect of dietary histidine regimes in adult Atlantic salmon (Salmo salar L.) in seawater, both through manipulating the dietary histidine level and feeding period. Mean body weight of individually tagged Atlantic salmon at the start of the experiment was 1662 (sd 333) g. Low prevalence of mild cataracts were recorded in the beginning of June. Three fishmeal and fish oil-based extruded diets (crude protein: 375 g/kg and fat: 342 g/kg), differing only in histidine content (low (L): 9·3, medium (M): 12·8 and high (H): 17·2 g histidine/kg diets), were fed to duplicate net pens in seawater. The experimental period was divided into three seasons (June–July; July–September; September–October), each starting and ending with individual cataract examination, assessment of somatic data, and sampling of lens and muscle tissues for analysis of histidine and histidine derivatives. In July and September, a part of the population fed L- and H-histidine feeds were transferred (crossed over) to respective series of replicate net pens fed L-, M- and H-histidine diets (i.e. eleven experimental feeding groups at trial conclusion). The fish doubled their body weight from June to October, with no systematic effects on weight gain of dietary histidine feeding regimes. Development of severe cataracts was observed between July and September. The cataract severity was directly related to the dietary histidine level fed during the first and second periods. Feeding histidine-supplemented diets (M or H) in the first period from June to July mitigated later cataract outbreaks. The status of selected free imidazoles in muscle and lens tissues reflected the dietary histidine feeding regimes, relative to both feed concentration and feeding duration. The study shows the risk for cataract development for adult Atlantic salmon, 1 year after the transfer of salmon smolts from freshwater to seawater, which to a major extent can be prevented by histidine supplementation just before and during the early phase of cataract development. [ABSTRACT FROM PUBLISHER]

Abstract: The fish welfare debate is intensifying. Consequently, more research is carried out to further our knowledge on fish welfare in aquaculture. We define here a series of key parameters to substantiate an acute response to a supposedly painful stimulus: a standardized tailfin clip. Ultrastructural analysis of common carp (Cyprinus carpio) tailfin indicates the presence of A-δ and C-type axons, which are typical for transmitting nociceptive signals in (higher) vertebrates. In Nile tilapia (Oreochromis niloticus), responses to a tailfin clip were studied and the unavoidable acute stress associated with the handling required for this procedure. A series of key parameters for further studies was defined. The responses seen in ‘classical’ stress parameters (e.g., changes in plasma cortisol, glucose and lactate levels) did not allow discrimination between the clipping procedure and the handling stress. However, three parameters indicated a differential, stronger response to the clip stimulus itself: first, swimming activity increased more and clipped fish spent more time in the light (in a tank where half the volume is covered by dark material); second, the gill''s mucus cells released their content as observed 1h after the clip, and this response is transient (no longer observed at 6h post clipping). Third, branchial Na+/K+-ATPase activity assayed in vitro was not affected by the procedures, but a remarkable migration of Na+/K+-ATPase immunoreactive (chloride) cells into the lamellar epithelium was observed as of 6h post clipping. We conclude that the differential response to clipping supports that this is a painful procedure that evokes a transient specific physiological status. [Copyright &y& Elsevier]

An in-depth explanation of selected content of the European Inland Fisheries Advisory Commission’s ‘Code of Practice for Recreational Fisheries’ (CoP) is presented. The focus is on core areas that were intensely debated in the drafting the CoP. These include definition of recreational fishing, recreational fishing practices, fish welfare, recreational fisheries management and research. It is anticipated that the CoP for recreational fisheries promotes best practice and management principles for sustainable recreational fisheries, within the recreational fisheries sector and ancillary industries/sectors regionally, nationally, and ultimately globally. To be viable, the CoP for recreational fisheries must be adopted by the international community complementing the Code of Conduct for Responsible Fisheries of the Food and Agriculture Organization of the United Nations. [ABSTRACT FROM AUTHOR]

Fundamentally, in land based mediterranean aquaculture, two techniques are applied to supply water with oxygen: paddling water aeration and application of pure oxygen. The two oxygenation techniques result in quite different PO2 regimens and, consequently, different fish growth performance and gill morphology. Data exist showing a reduction in total respiratory surface (RSA) and increasing gas diffusion distance (GDD) in gills of sea bass (Dicentrarchus labrax, L.) farmed under elevated PO2 regimens. That such a modification might have an effect on the ion regulation has been defined elsewhere as osmorespiratory compromise. In this study, European sea bass previously acclimatized to two PO2 regimens, mild hypoxia and mild hyperoxia (70-80% and 130-140% of the saturation value, respectively), were challenged for 1 hour with hypo-osmotic plus manipulation stress in two separate trials. During the first trial, when only Na+ loss was determined, the ion efflux during the first 5 min resulted in a rate of 163.72±31 and 112.23±87 nmol g-1min-1 from hypoxia and hyperoxia sea bass groups, respectively, and, if sustained, would approach 15.3 and 11.2% per hour of the total body Na+, respectively. During the second trial, in which both Na+ and Cl- loss were determined, after 60 min the Na+ loss was shown to be 76.86±12 and 179.28±32 nmol g-1 min-1 for the fish previously acclimatized to hyperoxia and hypoxia regimens, respectively, whereas for Cl- this loss was 62.02±11 and 157.28±28 nmol g-1min-1, respectively. Our data are compatible with the hypothesis of an osmotic advantage of sea bass exposed to an elevated PO2 regimen, achievable with application of pure oxygen, instead of simple water aeration. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to identify possible metabolic molecular indicators of chronic stress in gilthead sea bream Sparus aurata. Two potential stressful conditions were tested: repeated handling and crowding at high stocking density. Gilthead seabream kept under optimized rearing conditions were used as control fish. Cortisol was measured as primary stress indicator and the liver proteome of stressed fish was compared to that of control fish using comparative proteomics. Plasma cortisol levels in sea bream repeatedly handled and crowded at high stocking density were significantly higher than in undisturbed control fish. A total of 560 spots were detected and the statistical analysis revealed a differential expression in about 50% of all detected proteins. Spots with greater than 2-fold or lower than 0.5-fold changes were identified by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Proteins like fatty acid binding protein (lipid transport and antioxidant role), heat shock cognate protein (chaperoning), calmodulin (Ca2+ signaling), mitochondrial porine — voltage-dependent anion channel (lipid oxidation), glutamine synthetase (ammonia metabolism), cofilin and beta-tubulin (cytoskeleton), hemoglobin and several other proteins involved in carbohydrate metabolism (triose-phosphate isomerase, pyruvate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase, alfa-enolase) were differentially expressed in fish under chronic stress. Some of these proteins may be used in the future as chronic stress and/or part of a panel of welfare biomarkers, after validation studies using RT-PCR and ELISA assays. [Copyright &y& Elsevier]

How can stakeholders within the fisheries community engage in constructive ethical discussions? Drawing on experiences from previous debates surrounding the human use of animals, this paper presents a proactive approach whereby stakeholders can create a framework for ethical discussion of capture fisheries. [ABSTRACT FROM AUTHOR]

The ability to respond to stress is vital to the survival of any living organism, though sustained reactions can become detrimental to the health and welfare of animals. Stress responses of vertebrates are known through several studies in their physiological, behavioural and psychological components, under acute and chronic contexts. In fish, the physiological and behavioural aspects of stress are considerably well known phenomena and show striking similarities to those of other vertebrates. However, the psychological component is not well known. Some authors deny mental experiences to fish on the basis of their lack of neocortex. Nevertheless, recent studies have shown neuroendocrine, cognitive and emotional processes in fish that are not only equivalent to other vertebrates, but also allow inferring some forms of mental representation. The integration of psychological elements in fish stress physiology is insufficiently studied, but, as discussed in this article, there is already indirect evidence to admit that some form of stimuli appraisal can take place in fish. This fact has profound implications on the regulation of the stress response, as well as on fish welfare and its management. [ABSTRACT FROM AUTHOR]

Increased use of plant oils with different origins and quality in fish feed needs to be approached from a food safety and fish welfare point of view. Plant oils contain a number of bioactive minor lipid compounds that may affect the fish’s metabolism and taste perception. This study focuses on the effect of replacing fish oil (FO) with different levels of cold-pressed rapeseed oil (RO) on the lipid composition in muscle and liver as well as on the preference by the fish. Rainbow trout ( Oncorhynchus mykiss) were fed diets with a FO : RO ratio of 100 : 0, 75 : 25, 50 : 50 and 25 : 75 until twofold weight increase. In self-selecting feed trials of single rainbow trout, fish preferred the diet composed of only FO compared with the diets with RO but did not discriminate between different levels of RO. Plant sterols and their metabolites were found in liver of the fish fed RO diets, suggesting an effect on the sterol metabolism different from fish fed a 100% FO diet. The largest effects were seen in the fatty acid composition of the edible tissue of the fish with a decrease in 22:6n-3 and 20:5n-3 and an increase in 18:2n-6 and 18:1n-9. [ABSTRACT FROM AUTHOR]

Abstract: In the search for alternative farming methods, we investigated whether large salmon submerged below 10m in winter conditions behaved normally and performed as well as control fish held in standard surface cages. On average, 2345 salmon of ~3.5kg were kept in each of six 2000m3 sea-cages for 6weeks; three of which were submerged to 10–24m depth and three acted as surface controls (0–14m). Behaviour during both day and night was studied with echo-sounders, and underwater video cameras fitted with infra-red lamps. A sub-sample of fish from each cage was weighed, measured and assessed for fin and snout condition prior to and after the experimental period. In addition, the vertebral column of 50 fish from the control and submerged treatments were dissected and X-rayed to assess vertebral deformities. The submerged salmon seemed unable to re-fill any gas into the swim bladder, as a linear decrease in echo reflection to <5% of pre-submergence levels after 22days of submergence indicated loss of almost all gas from the physostomous swim bladders and negatively buoyant fish. Around day 22, submerged salmon swam at night time with a distinct ‘tail-down, head-up’ tilt (26°) compared to the horizontal swimming position of control fish (−3°). Average swimming speed (body length per second) of submerged salmon were 1.3–1.4 times faster (day: 0.77±0.02; night: 0.46±0.02, (mean±SE)) than control fish (day: 0.54±0.01; night: 0.37±0.02) both during day and night. Almost no mortality was seen, and the submerged salmon maintained similar diurnal vertical migrations as the surface fish, indicating that deep submergence did not exhaust the fish. However, submerged fish fed less efficiently, resulting in lower growth and reduced feed utilization. Fins and snouts of the submerged fish had small, but significantly more erosion than the control fish. Vertebrae in the tail region were significantly compressed in the submerged fish compared to control fish. This could be an early symptom of development of vertebral deformities. The results suggest that continuous submergence below 10m for longer than 2weeks reduces the welfare and performance of Atlantic salmon. [Copyright &y& Elsevier]

Abstract: Further growth in Atlantic salmon (Salmo salar) aquaculture production is expected, and as a response to limited freshwater resources, recirculating aquaculture systems (RAS) are increasingly applied in smolt production. Knowledge of the general composition and quality of inlet-water is important for designing water-treatment to obtain optimal water quality in both flow-through and RAS systems. Based on water quality surveys in Norway (96 water sources, 1999–2006) and Chile (120 water sources, 2006–2008) inlet-water quality was evaluated. Norwegian smolt production is characterized by almost exclusively utilizing surface waters as inlet-water sources, with lake inlets constituting 88% and river inlets 12%. This results in large seasonal variations in both temperature, and inlet-water quality. In Chile, production is based on inlet-water from groundwater wells (32%), natural springs (40%) and rivers (28%). Norwegian inlet-water quality shows significantly lower pH and buffering capacity. The content of total organic carbon and total nitrogen is generally higher in Norway, while the levels the main metals of concern, aluminium (Al) and iron (Fe), show large between-site variability in both countries. In low pH waters in Norway, the concentration of inorganic (labile) aluminium exceeds recommended level (10μg/L) in 15% of the samples. The Norwegian database documents highly variable production intensity in smolt production. The measured levels of carbon dioxide (CO2, 11.6±6.2mg/L) and total ammonia nitrogen (TAN, 499±485μgN/L) (mean±SD), exceed current legislative recommendations in 30% and 10.5% of the cases, respectively. RAS technology has the potential to improve a variable water quality if it proves reliable for the time intervals and production volumes needed. Thus, if necessary adjustments in water treatment to the local water quality are implemented, RAS production may well constitute a substantial part of smolt production in the future. [Copyright &y& Elsevier]

Abstract: Many cichlid species dig spawning pits or nests in soft bottoms and exhibit many substrate oriented activities. Despite this fact being of general knowledge, captive cichlids in laboratory and aquaculture set-ups are often kept in the absence of a soft substrate that they can manipulate. This raises a potential welfare issue, depending on how the substrate is valued by cichlid fish. The aim of this study is to assess the importance of substrate for male Mozambique tilapia (Oreochromis mossambicus) in social and non-social contexts. Preferences were established as a measure of time spent in two choice compartments, before and after the presence of a female. Locomotory activity, social interactions and substrate-related behaviours were recorded. Results show that dominant males prefer the area with substrate regardless of social context, and that female''s presence strengthens this preference. The same preference is not apparent in the subordinate males, except for foraging. To draw conclusions on the importance of substrate to subordinates, preferences should also be assessed in agonistic contexts, during which substrate may serve to displace aggression. These results, together with related previous studies, show that the lack of substrate is particularly deleterious in a reproductive context, and thus it is likely to decrease the welfare state of breeding males of Mozambique tilapia. [Copyright &y& Elsevier]

Abstract: We examined the physiological and behavioural consequences of, and recovery from, catch-and-release related stressors using a combined laboratory and field study in northern pike (Esox lucius L.). A laboratory experiment was conducted to investigate the recovery dynamics of physiological indicators of stress resulting from a simulated angling event resulting in exhaustion, with and without additional air exposure of 300s. In addition, a field study using a combination of physiological and behavioural assessment was conducted to assess the long-term consequences of exhaustive exercise and various air exposure durations. Exhaustive exercise for 60s led to increased muscle lactate, decreased tissue energy stores, and alterations in plasma ionic status. Recovery from physiological disturbance was rapid with all physiological variables except plasma glucose returning to baseline levels after 6h. The recovery profile was largely unaffected by air exposure of 300s that simulated extended de-hooking time. The field component of our study verified the impact of exhaustive exercise on blood lactate values, but did not detect any impact of air exposure varying between 0s and 300s on physiological stress indicators. However, pike exposed to air for 300s were behaviourally impaired in the first hour post-release indicating that despite limited effects on physiological status air exposure resulted in significant impairment of organismal performance. Behavioural patterns returned to normal within several hours. In a three-week post-release monitoring period no mortality occurred. Our results emphasize that angling-induced stressors result in physiological and behavioural disturbances, but that recovery is quick. This suggests that pike are relatively resilient to catch-and-release related stressors but air exposure durations should be kept <300s to minimize behavioural impairment. [Copyright &y& Elsevier]

Simple Summary: Due to the implementation of a landing obligation in fisheries in the European Union (EU), with an exemption for species with "high survival", discard survival studies (henceforth DSSs) have become one of the most politically prioritized fisheries research areas in European fisheries. In contrast to most fisheries science research areas, DSSs are embedded by the EUs animal research welfare directive. This is a challenge, and there has not been any focus on how to implement animal welfare (AW) regulations experimentally in DSSs. This paper focuses on AW regulations in relation to conducting DSSs, but the outreach is much broader. We investigate experimental procedures by bringing in relevant examples, using the output results, and relating this information to relevant AW guidelines and regulations by focusing on implementing 3R principles. Globally, it is estimated that around 10% of the fish that are caught are discarded. This is considered to be a wasteful human marine activity since these fish are often dead or dying. To reduce the high discard rates of commercial fisheries, the European Union (E.U.) has enacted a landing obligation that includes the ability to exempt "species for which scientific evidence demonstrates high survival rates". Therefore, discard survival studies (henceforth DSSs) have become one of the most politically prioritized fisheries research areas in European fisheries. International expert groups have produced guidance reports to promote best practices and to harmonize the methodologies. Nevertheless, there has not been any focus on how to implement animal welfare (AW) regulations experimentally. Discard survival studies are "frontrunners" in fisheries science research areas that are embedded by animal research welfare requirements and are expected to be more restrictive in the future because of an increased public focus on fish welfare. This paper focuses on AW regulations in relation to conducting DSSs, but the outreach is much broader. We investigate experimental procedures by bringing in relevant examples, using output results, and relating this information to relevant AW guidelines and regulations by focusing on implementing 3R principles. [ABSTRACT FROM AUTHOR]

Structural modification of sea cages is continually changing to counter major production issues associated with commercial salmon farming. For example, snorkels and skirts are added to cages to reduce salmon lice infestations, and submerging cages can reduce salmon-lice encounter rates, minimise the effects of storms or avoid other unsuitable sea surface conditions. Unlike snorkels and skirts, the uptake of submerged cages has stalled due to negative effects associated with salmon buoyancy, as salmon require frequent access to the surface to gulp air and fill their swim bladders. Fitting submerged cages with underwater air domes provides an underwater air surface and appears to resolve buoyancy associated issues, but they have not been tested over a full production cycle. Here, we used three 1728 m3 cages submerged to 15 m fitted with air domes and three standard surface cages (i.e. control cages) to grow ~6000 fish per cage from sea transfer (~ 0.2 kg) to harvest size (~5 kg). We tested if growth rates, swimming behaviour, key SWIM (Salmon Welfare Index Model) welfare parameters and lice infestation levels differed between control and submerged cages. Submerged cages had 93% lower lice levels than controls during a large lice pulse event in mid-winter, which was visible through the subsequent lice stages. Swim bladder fullness, swimming behaviour and surface activity rates indicated submerged fish competently used the underwater airdome to maintain neutral buoyancy for the full production cycle. However, after 12 months, harvested mean fish weight was far smaller in submerged (2.8 kg) than control (5 kg) cages and overall mortality 2.5 times higher. Likewise, SWIM welfare scores for eye condition and mouth jaw wounds were worsened in submerged than control cages. The poorer outcomes in submerged cages reflect the suboptimal environmental conditions experienced deeper in the water column, where colder water and/or lower oxygen levels for long periods may have compromised growth. We conclude that while submergence can reduce lice infestation rates, strategies to do so must ensure that fish do not encounter sub-optimal environments for fish growth and welfare. • First study of full production cycle of Atlantic salmon in submerged sea cages fitted with air domes. • Submerging sea cages can reduce salmon lice infestation levels. • Salmon exhibited normal swim behaviour and buoyancy over 5 months in submerged cages. • Salmon growth and welfare were affected by suboptimal environmental conditions in submerged cages. [ABSTRACT FROM AUTHOR]

Social animals commonly establish dominance relationships by means of aggressive interaction, leading to hierarchical stability and priority of access to limited resources by high-ranked individuals. In poikilothermic animals, temperature is a major abiotic factor influencing social and non-social behaviors, including aggression. Here, we investigated the effect of cold temperature on aggression in dominance hierarchies of the commercially important tropical fish Nile tilapia (Oreochromis niloticus). Aggression components were examined in fish shoals during hierarchy formation (T 1) and after hierarchy establishment (T 2) under optimal (26 °C) or cold (14 °C) temperatures, and 24 h afterwards (T 3) following gradual temperature increase (14–26 °C, IT treatment), decrease (26–14 °C, DT treatment) or constant optimal conditions (26 °C, CT control). During dominance hierarchy formation, fish in cold water showed reduced aggressive interactions involving lower-intensity behaviors whereas fish under warm temperature exhibited high aggression involving escalated fighting. Following temperature alterations, at T 3 , aggression levels increased in the IT groups, decreased in the DT groups and remained similarly high in the CT groups. However, despite the drop of temperature in the DT treatment, aggression level at T 3 in cold temperature in this treatment was similar to that in the IT treatment and CT control in warm temperature. Likewise, despite the increase of temperature, aggression level in the IT treatment at T 3 was lower than that observed under the same warm temperature conditions in the DT and CT groups. Our results demonstrate that in addition to the acute effect of the current temperature on aggression in dominance hierarchies, there is a significant carryover effect of prior thermal conditions under which dominance hierarchy has been formed. Thus, cold temperature can possibly be applied during hierarchy formation for mitigating adverse social effects arising from fish grouping under captive conditions. • Aggression during dominance hierarchy formation in Nile tilapia is low in cold water. • Hierarchy formation in cold water attenuates subsequent aggression in dominance hierarchies after temperature increase. • Using cold water during fish introduction may mitigate adverse social effects under captive conditions. [ABSTRACT FROM AUTHOR]

In this study, two experiments were performed to investigate the anesthetic efficiency, hematological and biochemical effects of thymol on Nile tilapia, Oreochromis niloticus. In the first experiment, in order to estimate thymol anesthetic efficacy, tilapia juveniles were exposed to anesthetic baths at six different concentrations of thymol (10, 20, 40, 60, 80, and 100 mg L−1) and the induction and recovery times were recorded. The second experiment was performed with five treatments: CON (non-anesthetized fish), TH1 (anesthesia with 80 mg L−1 thymol within 1 min), TH5 (anesthesia with 30 mg L−1 thymol within 5 min), EU1 (anesthesia with 80 mg L−1 eugenol within 1 min), and EU5 (anesthesia with 30 mg L−1 eugenol within 5 min). The results showed that thymol at 10 mg L−1 concentration failed to induce anesthesia; however 20–100 mg L−1 concentrations induced anesthesia within 491–56.3 s. A strong negative relationship was detected between thymol concentrations and induction times (R2 = 0.906). Anesthesia had no significant effects on plasma albumin, triglyceride, cholesterol, alanine aminotransferase, and the blood mean corpuscular hemoglobin levels. The anesthetized fish exhibited significant elevations in plasma cortisol, glucose, lactate, and the blood hematocrit and mean corpuscular volume; these parameters exhibited significant elevations in the fish anesthetized by 30 mg L−1 anesthetics, compared to the 80 mg L−1. Plasma globulin, total protein, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, catalase, superoxide dismutase, and the blood hemoglobin and red blood cell significantly increased, as mean corpuscular hemoglobin concentration decreased, in the fish anesthetized by 30 mg L−1 anesthetics, compared to the CON fish. The anesthetized fish showed similar plasma glutathione levels, all significantly lower than the CON fish. The EU5 fish exhibited significant elevation in the plasma malondialdehyde levels, compared to the CON fish. In conclusion, thymol anesthetic efficacy was similar to eugenol in Nile tilapia weighing ~40 g at water temperature of 26 °C. Considering the physiological responses, slight but significant elevations in plasma proteins, lactate, lactate dehydrogenase, and malondialdehyde levels attest that thymol may induce less stress, hypoxia, and oxidative stress in the fish than eugenol, but further studies are needed to provide robust and clinically applicable data to support this hypothesis. • Thymol at 80 mg L−1 is suitable for Nile tilapia anesthesia. • Thymol effects on plasma enzymes and stress responses are similar to eugenol. • Thymol induces less hypoxia than eugenol after 5-min anesthesia. • Thymol anesthesia leads to lower plasma MDA, compared to eugenol after 5-min anesthesia. [ABSTRACT FROM AUTHOR]

The aquaculture industry is still expanding to provide human beings with healthy and nutritious protein sources. Infectious diseases, deteriorated water quality parameters, and other environmental stressors are from the main obstacles that threaten fish farming and reduce its profitability. Vibriosis is one of the most common bacterial diseases that negatively affect shrimp, marine fishes, and some freshwater fish causing high mortalities and severe economic loss. Chemotherapeutic agents as antibiotics are commonly applied for treatment strategies; however, their numerous drawbacks to fish and the aquatic environment have limited their use. Moreover, FDA has prohibited certain antibiotics from being used for food fish to avoid their negative consequences on human consumers. Water quality control and biosecurity protocols are traditionally applied to combat vibriosis. Nowadays, immunomodulators are greatly used and described throughout the globe to enhance the fish immunity. In this concern, probiotics, prebiotics, and synbiotics have become common solutions to increase the fish resistance against vibriosis. They were approved to be current alternatives to limit the usage of antibiotics in aquaculture resulting in less mortality and increased health and welfare of the aquatic organisms. Many studies speculated that probiotics, prebiotics, and synbiotics could be efficiently and effectively used as food or water additives to increase immunity, thereby reducing the mortality caused by several fish pathogens such as Vibrio species. Comprehensively, this review article presents the latest knowledge on the potential roles of probiotics, prebiotics, and synbiotics to boost immunity and reduce the impacts of vibriosis in several finfish species. This review article will also provide new findings and possible mechanisms of action of probiotics, prebiotics, and synbiotics to control vibriosis in fish. These literature will be helpful to increase the sustainability of aquaculture and health welfare of farmed fish. • Vibriosis is one of the most common bacterial diseases that causing high mortalities and severe economic loss in infected fish. • Chemotherapeutic agents as antibiotics have numerous drawbacks to fish and the aquatic environment. • Probiotics, prebiotics, and synbiotics have become common solutions to increase the immunity and resistance of fish against diseases. • This review article provides new findings and possible probiotics, prebiotics, and synbiotics mechanisms to combat vibriosis. [ABSTRACT FROM AUTHOR]

Individually tagged Atlantic salmon postsmolts (≈1200 g, 46 cm) reared in triplicate indoor holding tanks were fasted for 8 weeks at 12 °C and subsequently refed for 5 weeks, whereafter they were transferred to triplicate sea cages in a common garden setup together with a continuously fed control group until harvest size of ≈6100 g and 73 cm. At the end of the fasting period fish had lost 7.3% mass and the condition factor had decreased from 1.23 to 1.06. Furthermore, fasted fish were 544 g lighter and 3.8 cm shorter than fed controls, corresponding to a size difference of 50%. Following refeeding, feed intake gradually increased and surpassed the feed intake of controls. As such, fasted fish eventually showed compensatory growth and at harvest weight and length were similar to controls. At harvest, males were larger than females, and immature fish were larger than maturing fish in both treatment groups. The proportion of maturing fish was 25% higher in the fed control group. During the fasting period fish behaviours were video monitored, but no aggressions were observed. After the 8-week fasting period, fish welfare was scored based on the salmon welfare index model. Only minor deviations were found and at similar regularities between fasted and control fish. To assess potential long-term impacts on welfare status, vertebral deformities were quantified with radiology at harvest. Occurrence of vertebral deformities were low and similar between treatments. In conclusion, this study shows that Atlantic salmon are highly flexible with regards to growth patterns in response to food availability, and that a prolonged fasting period neither cause signs of reduced welfare in the short or in the long term. • Atlantic salmon fasted for 8-weeks showed full compensatory growth before harvest. • The fasting period did not induce aggressive behaviour or cause lower welfare scores. • Occurrences of vertebral deformities were low and similar to fed controls. • Fasted fish had a lower incidence of sexual maturation at harvest. • In conclusion, fasting by itself is not a welfare concern in salmon aquaculture. [ABSTRACT FROM AUTHOR]

Imprinting, an early learning process that can determine later preferences for particular types of stimuli, is usually not a consideration in many activities related to fish. However, disruption of such learning and/or absence of suitable conditions for the development of preferences are frequent despite the lack of appropriate knowledge regarding the effects that these practices may have on later behaviour and health. The present study reviews the phenomenon of imprinting in fish and discusses its possible influence on fish welfare. Although there is also potential for acoustic imprinting, here we discuss how sexual, filial and olfactory imprinting should be considered when addressing welfare issues in fish. The review focuses on the relatively few fish species in which this phenomenon has been mainly researched, the results often proving that it may affect some behaviour patterns and social preferences. A diversity of factors, including species, context, behavioural repertoire and social systems may affect the actual existence of the phenomenon, although conditions normally prevailing in husbandry and other systems are not adjusted to allow the emergence of the process. Likewise, the effects of imprinting (or its absence) on fish welfare have still to be demonstrated in many fish species and should constitute a matter for further studies. The conclusion is drawn that much more needs to be learned. However, a better understanding of the relationship between this early learning process in fish and welfare is essential if a complete analysis of conditions promoting fish welfare is to be made. [ABSTRACT FROM AUTHOR]

Abstract: Little is known about the influence of hook size on fishing success, hooking performance and injury associated with recreational angling for large freshwater fish such as common carp (Cyprinius carpio L.). Yet, such information is crucial in the context of the management and conservation of these highly valuable specialised fisheries resources. We compared two different sizes of conventional carp hooks (small, size 6, and large, size 1) baited with corn and found that small hooks caught more and larger carp at similar landing rates. Moreover, small hooks caused less tissue damage compared to large hooks. However, there was no evidence that small hooks reduced incidences of bleeding. For both hook sizes, most carp were hooked in the lower jaw (size 1: 81%; size 6: 64%) and the side of the mouth (size 1: 16%; size 6: 36%), and not a single fish out of 88 fish landed was hooked deeply in vital organs. These results suggest that more widespread use of small size hooks in carp fisheries might be promoted for conservation, fish welfare and angling quality reasons. [Copyright &y& Elsevier]

Abstract: The present study evaluates the biofloc technology (BFT) in light-limited tank culture of Nile tilapia (Oreochromis niloticus). Two biofloc treatments and one control were managed in 250 l indoor tanks: BFT fed a diet of 35% crude protein (CP), BFT fed a diet of 24% CP, and clean water control without biofloc with 35% CP. BFT tanks were aerated and agitated using a dome diffuser. Three kg of Nile tilapia were stocked in each tank. Feed was applied at 1.5% of the total fish biomass daily in each tank. Wheat flour was added in BFT tanks to maintain an optimum C:N ratio for heterotrophic production. The total suspended solid (TSS) level was maintained at around 500 mg l−1 in BFT tanks. The nutritional quality of biofloc was appropriate for tilapias. Fish survival was 100%. Net fish production was 45% higher in the BFT tanks than in the control tanks confirming the utilization of biofloc by fish as food. There was no difference in fish growth/production between 35% and 24% CP fed tanks under BFT. Welfare indicators in terms of fin condition, gill histology, proximate composition, blood haematocrit and plasma cortisol levels were compared and no significant differences between BFT and control tanks were recorded indicating no increased fish stress due to the presence of biofloc. However, overall fish growth and production was poor in terms of commercial feasibility. A modified system design that would allow enhanced feed and biofloc utilization is proposed. [Copyright &y& Elsevier]

The behaviour and survival of pike, Esox lucius L., released with a retained lure in the mouth was studied relative to control fish, which simulated line breakage prior to landing. Behaviour was monitored during the first hour post-release with the aid of visual floats attached to the fish, and longer-term for 3 weeks, by means of externally attached radio transmitters. Lure-treated pike were less mobile during the first hour post-release, but exhibited greater mobility and travelled further distances from the release area in the first 24 h after release than controls. From the second day after release, the behaviour of lure-treated pike was similar to control fish. No mortality occurred in a 3-week monitoring period. These results are indicative of only short-term behavioural impairments resulting from a retained lure and rapid resubmission of normal behaviour after simulated break-offs. [ABSTRACT FROM AUTHOR]

Eleven commercial processing lines for the slaughter of Atlantic salmon were evaluated to investigate the efficiency of the refrigerated seawater live chilling method with respect to stunning fish and reducing body temperature. The method is commonly used in the Norwegian salmon industry to both stun and chill fish before killing. Carbon dioxide gas was added to the live chilling tanks, or in some cases, to a subsequent carbon dioxide stunning tank. Criteria used for evaluation were water quality parameters (dissolved oxygen, carbon dioxide, pH, temperature, total ammonium, ammonia, alkalinity, color, total organic carbon, and ferric ion), fish behavior, white muscle pH, and body and core temperatures. At two processing plants, fillet quality (Roche color, texture, ultimate pH, and water content) was also determined. The results are discussed in terms of fish acclimation temperatures, water quality, welfare, handling stress, chilling efficiency, pre-live chilling factors, refrigerated seawater live chilling process parameters, and fillet quality. Even though the live chilling method can be used to minimize fish handling stress during slaughter and may serve as an efficient chilling method, it was found in most cases that under commercial conditions when large biomasses were slaughtered, both handling stress and chilling efficiency were less than optimal. However, no adverse effects on the fillet texture and color were observed as a result of fish processing. [ABSTRACT FROM AUTHOR]

Abstract: A crucial problem in halibut farming is low and variable growth during the on-growing phase. Individual halibut may have different abilities to adapt to different aspects of the farming environment, including the feed distribution mode. In this study, 30 individually tagged halibut (mean weight 1.5kg) were moved from a larger tank and kept for 3 months in six 7m3 tanks with five fish in each tank. Individual feed intake and behaviour were compared in two periods, when either sinking or floating food was offered. Individual fish within a tank showed large variations in behaviour and feed intake, but both individual swimming behaviour and feed intake were positively correlated between periods. On the basis of differences in stereotypic surface swimming activity and feed intake, the halibut were classified in four behaviour categories that were suggested to reflect reactive or proactive stress coping styles. Floating food seemed to be an additional stressor and decreased feeding and increased stereotypic swimming activity. When floating food was replaced by sinking food, proactive fish that exhibited frequent surface swimming turned into “well-adapted” fish. The indication of different coping styles in individual halibut and the ability of fish applying a stress coping style to adapt when the situation changes suggests the possibility of improving halibut farming by both selective breeding and tailoring the tank environment to the demands of the fish. [Copyright &y& Elsevier]

Nearly half of the fish consumed as food worldwide are raised on fish farms rather than caught in the wild, as shown by FAO statistics. The increasing aquaculture of predatory carnivorous fish demands new sources of feed constituents, particularly oils at the moment. Common terrestrial plant oils contain only traces of the long‐chain polyunsaturated fatty acids. In connection with fish feed, especially the lack of n‐3 "marine fatty acids" is obvious. Recommendations on the required amounts of the fatty acids DHA (22:6n‐3) and EPA (20:5n‐3) exist from 1994. When plant oil‐based diets are fed during the growing phase and replaced by a fish oil‐based diet during a period prior to slaughter, most of the beneficial lipid composition of fish in terms of human dietary recommendations is restored. Little attention has been focused on the fish welfare in connection to substitution of dietary oil sources, and studies are still scarce. New fish diets will rely heavily on the use of alternate ingredients such as plant oils also for carnivorous cold‐temperate water fish species. In the future, an addition of synthetic or GMO‐produced "marine" fatty acids is a possible scenario. The aim of this review is to highlight some plant oils used in fish feeds, with special emphasis on compounds other than fatty acids. We also include some results from an ongoing study, where the effect of dietary soy oil on gonad maturation in Atlantic cod (Gadus morhua) is indicated. [ABSTRACT FROM AUTHOR]

Abstract: Within fish farming grading, i.e. the process of sorting to approximate size, changes the group composition from heterogeneous to homogeneous. Although this procedure is considered an acute stressor, the long-term consequences of grading on aggression and stress levels have not yet been investigated. The objective of this study was to quantify the consequences for welfare of rearing African catfish (Clarias gariepinus) in groups of homogeneous low-, middle- and heavy-weight fish as compared with a heterogeneous group. Two thousand fish were grown for 8 weeks. Afterwards, fish were individually weighed, tagged and manually selected. Four treatments were established according to weight (mean±S.D.): homogeneous low- (L, 83.0±8.2g), homogeneous middle- (M, 140.2±8.7g), homogeneous heavy-weight (H, 198.0±8.1g) and a heterogeneous group (HET, 139.7±48.4g). Fish were sampled three times (days 13, 27 and 34) to determine aggression levels (number of skin lesions and percentage of fish bitten). Blood samples (for cortisol and glucose analysis) were taken at the end of the experiment before and after a stress test (netting). Despite all treatments exhibited high aggression levels (>50%), the H treatment exhibited the lowest aggression levels (58.34±0.92% of fish bitten as compared with 74.13±2.52% in L; 69.70±4.38% in M and 69.94±3.29% in HET, P =0.002). Aggression significantly decreased over time in the M and H treatment but not in the L and HET treatments. In addition, heavy fish reared in heterogeneous groups exhibited higher number of skin lesions in the body (2.0±0.1) than fish with similar weight reared in homogeneous groups (1.4±0.1) (P =0.002). Also, middle-weight fish showed lower cortisol values (before the stress test) in the homogeneous group (45.7±7.5ng/ml) as compared with middle-weight fish in heterogeneous groups (73.5±13.3ng/ml). The stress response in low-weight fish was also affected by the group composition. After a stress test, the glucose levels were higher for low-weight fish reared in homogeneous (7.1±0.4mmol/l) than in heterogeneous (5.1±0.7mmol/l) groups. This study suggested that the group composition affects welfare in African catfish, particularly in the L treatment where aggression levels were as high as 74%. Middle-weight and heavy fish seemed to benefit from living in homogeneous while light fish from heterogeneous groups. [Copyright &y& Elsevier]

Abstract: We are unaware of any assessments of fish welfare during live-hauling of adult salmon in very high numbers (>10,000 fish) and at high density (∼100 kg/m3) and yet live transport of adult salmon from sea cages to processing plants is now a common practice. Here we report on the bulk metabolic rate of adult Atlantic salmon (Salmo salar L.) during transport from a sea farm off the west coast of Vancouver Island, BC, Canada, on board a state-of-the-art live-haul vessel, the Sterling Carrier. Monitoring the oxygen concentrations of the water entering and leaving the flooded holds revealed that oxygen uptake decreased from >8 mg O2/min/kg to an average <4 mg O2/min/kg within the first 20 min of the vessel being underway. During the fourth hour of transport, oxygen uptake averaged 3.1 mg O2/min/kg, a value comparable with routine oxygen uptake values measured under laboratory and field conditions for single adult salmon in a swim respirometer. This finding suggests that adult Atlantic salmon quickly recovered from the stress of loading on to the Sterling Carrier. This conclusion was corroborated by visual observations of the fish in the live holds, which revealed that fish faced the water flow and ventilated lightly while slowly cycling their position in a schooling behavior during the 11-h journey. Thus, the live transport conditions on board the Sterling Carrier appeared to promote good welfare of adult Atlantic salmon during the 11-h journey from a sea farm to a processing plant. [Copyright &y& Elsevier]

Abstract: To assess the effects of environmental stress conditions on fish, the examination of a suite of biomarkers, including endocrine parameters, has been suggested. In teleosts, glucocorticoids, including cortisol and corticosterone, are known to mediate stress response. Inside the cell, they bind to a high-affinity cytosolic glucocorticoid receptor (GR), which acts as ligand-dependent transcription factor to control and regulate gene expression. Receptor number or affinity may directly influence the degree of reactivity of target cells. GR transcripts have been cloned and characterized in different fish species, but no studies, to date, are available on the quantification of GR in sea bass (Dicentrarchus labrax, L.), although this is one of the most important species in Mediterranean aquaculture. These considerations prompted our interest in cloning the GR in this species and investigating the impact of long-term exposure to crowding stress on GR expression in the liver of sea bass. Our data clearly demonstrate that a high rearing density stress affects GR mRNA, whose abundance in the liver decreased inversely with blood cortisol levels. [Copyright &y& Elsevier]

Abstract: Modern technologies may improve fish production and quality and, at the same time, reduce environmental impact with benefits on the public perception of the industry. To be economically profitable, these modern technologies request an increase of rearing density that, however, could affect fish welfare. With the aim to search for molecular biomarkers to describe fish welfare, we have recently compared gene expression of sea bass farmed at different population densities by differential display obtaining six bands differentially expressed. In this paper, we have cloned the mRNA corresponding to one of those differentially expressed bands obtaining a 3860-bp sequence with an ORF of 2664 bp. Its virtual translation originated a 887-aa polypeptide that, by comparison with the other sequences available in the public data bases, resulted to be the 3-hydroxil-3-methyl-glutaryl coenzyme A reductase (HMGCR). In sea bass, as for the other species, the N- and C-terminus portions are the most conserved and are linked by an hydrophilic region that appears to be quite variable. Due to its role in the synthesis of cholesterol, HMGCR mRNA could be a good biomarker for detecting fish welfare. For this reason, we also followed, by real-time PCR, its expression after crowding stress comparing it with mRNA levels of HSP 70 and 90: HMGCR mRNA resulted highly expressed in the fishes farmed at 100 kg/m3. [Copyright &y& Elsevier]

An experiment was conducted to measure swimming activity of rainbow trout (254.0±33.7 g) held in outdoor tanks under three culture conditions with stocking density used to generate differences: 27 (Culture Density 1, CD1), 80 (CD2) and 136 kg m-3 (CD3). Fish were fed dry pellets at 1% of tank biomass from 9h00 to 13h00 with automatic feeders. Using acoustic telemetry, fish positions were monitored every 5 s during 48 h for nine fish (three in each treatment). Swimming behaviour was analysed in terms of trajectories: they varied between (i) holding position (high turning angles), (ii) chaotic trajectories (equal use of all turning angles) and (iii) circular swimming (average turning angle of 60°). Space utilisation differed for each culture condition: CD3 conditions induced a prolonged residence time in the central zone of the tank. Rainbow trout swimming activity patterns and levels differed depending on both day–night alternation and culture conditions. All fish reared at CD1 and one reared at CD2 were day-active. All the other fish showed high activity pattern variability and a higher swimming level was observed under CD3. These results illustrate that monitoring fish swimming activity is feasible even under high densities and provide relevant insights on fish activity which can lead to behavioural welfare indices in relation to constraints imposed by culture conditions. [Copyright &y& Elsevier]

The worldwide decline of ocean fisheries stocks has provided a rapid growth in fish farming and the problems connected to animal welfare in aquaculture gained importance. In this context, we have looked for molecular markers among those genes whose expression could reasonably result modified by the different farming conditions. With this purpose, we have evaluated, in liver and brain of sea basses, grown for 3 months at different biomass density (<10, 80 and 100 kg/m3), the expression of those genes coding for proteins related to stress such as Heat Shock Proteins (HSPs), Metallothioneins (MTs) and Cytochrome P4501A (CYP4501A).In liver, the expression of MT and CYP4501A mRNA resulted induced in animals reared at 80 and 100 kg/m3. Inducible HSP70 appeared significantly over expressed only at the biomass of 100 kg/m3, while apparently, no induction was detectable for HSP90. In brain tissue instead, MT and HSP90 were induced already at 80 kg/m3; CYP4501A and HSP70 were influenced only at the higher population density of 100 kg/m3.In the last three decades, there has been an exponential increase in the interest concerning the description, classification and functional significance of stress-related proteins, in particular HSPs. These proteins represent precious biomarkers to evaluate the welfare conditions when they are still recoverable; detecting their mRNA by PCR is fast, easy and relatively inexpensive. Therefore, we propose this method as a good alternative to monitor fish welfare. [Copyright &y& Elsevier]

Peracetic acid (PAA) is an organic peroxide that produces free radicals, which contribute to its potent disinfection power. At therapeutic doses, PAA is considered a mild stressor that can trigger transient local and systemic oxidative stress in fish, but the resulting consequences in the brain have yet to be identified. Therefore, we report the brain transcriptome of Atlantic salmon ( Salmo salar ) smolts that have been periodically exposed to PAA. Fish were treated three times (every 15 days) with PAA with either short (15 min) or long (30 min) exposure periods. After the third treatment, the whole brain was collected and subjected to biochemical and transcriptomic analyses. The level of reactive oxygen species in the brain was not significantly affected by recurrent PAA treatments. Microarray analysis was performed on the whole brain and revealed 205 differentially expressed genes (DEGs), regardless of the duration of the treatment. The short exposure duration had a more considerable impact on the brain transcriptome, correlating with 70% more DEGs than the long exposure. Strikingly, the brain transcriptome was characterised by the downregulation of gene expression, especially in the short exposure group, and around 82% of the identified DEGs were downregulated. Some of the highly affected genes were key molecules of the vasotocinergic and isotocinergic systems and the corticotropin-releasing factor signalling system, indicating interference of the stress axis but could also suggest an anxiolytic effect. In addition, there were alterations in genes involved in cellular metabolism and processing, signalling and trafficking, and innate immunity, which underscores the physiological changes in the brain following recurrent PAA treatment. Overall, the transcriptomic data reveal that recurrent oxidant treatment could influence brain functions, and although the magnitude was marginal, the alterations suggested neurological adaptations of fish to PAA as a potential chemical stressor. The results identify the risks of PAA, which would be valuable in drafting a framework for its empirically driven use in fish farming., Competing Interests: No conflict of interest., (© 2022 The Authors.)

Probiotics for freshwater fish farming can be administered as single or multiple mixtures. The expected benefits of probiotics include disease prophylaxis, improved growth, and feed conversion parameters, such as the feed conversion rate (FCR) and specific growth rate (SGR). In the current work, we review the impact of probiotics on freshwater finfish aquaculture. Data were gathered from articles published during the last decade that examined the effects of probiotics on fish growth, FCR, and water quality in freshwater fishponds/tanks. While the expected benefits of probiotics are significant, the reviewed data indicate a range in the level of effects, with an average reduction in ammonia of 50.7%, SGR increase of 17.1%, and FCR decrease of 10.7%. Despite the variability in the reported benefits, probiotics appear to offer a practical solution for sustainable freshwater aquaculture. Disease prophylaxis with probiotics can reduce the need for antibiotics and maintain gut health and feed conversion. Considering that fish feed and waste are two significant parameters of the aquaculture ecological footprint, it can be argued that probiotics can contribute to reducing the environmental impact of aquaculture. In this direction, it would be beneficial if more researchers incorporated water quality parameters in future aquaculture research and protocols to minimize aquaculture's environmental impact. [ABSTRACT FROM AUTHOR]