Are fish what they eat? A fatty acid’s perspective

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA, >C₁₈) for human consumption. In general, it has been widely observed that the fatty acid (FA) profiles of farmed fish are reflective of the diet. However, the degree of tissue FA “distortion” based on incorporation of different dietary FA into fish tissues varies greatly depending on FA type, fish species and environmental factors. In terms of fish FA composition, this variation has not been comprehensively reviewed, raising the question: “Are fish what they eat?”. To date, this remains unanswered in detail. To this end, the present review quantitatively summarized the ‘diet-fish’ FA relationship via an analysis of FA composition in diets and fish tissues from 290 articles published between 1998 and 2018. Comparison of this relationship among different fish species, tissue types or individual FA was summarized. Furthermore, the influence of environmental factors such as temperature and salinity, as well as of experimental conditions such as fish size and trophic level, feeding duration, and dietary lipid level on this relationship are discussed herein. Moreover, as a means of restoring LC-PUFA in fish, an emphasis was paid to the fish oil finishing strategy after long-term feeding with alternative lipid sources. It is envisaged that the present review will be beneficial in providing a more comprehensive understanding of the fundamental relationship between the FA composition in diets, and subsequently, in the farmed fish. Such information is integral to maintaining the quality of farmed fish fillets from the perspective of FA composition.     

Taking account of fish welfare: lessons from aquaculture

This paper explores the possibility that lessons learned from aquaculture might contribute to current debate on welfare and fisheries. After looking briefly at the history of research interest in the welfare of farmed fishes, some implications of using different definitions of and approaches to the concept of welfare are discussed. Consideration is given to the way in which the aquaculture industry has responded to public concern about fish welfare and, for cases where these responses have been effective, why this might be the case. Finally, possible cross‐over points between aquaculture and fisheries in the context of fish welfare, as well as experience and expertise that might be shared between these two areas, are identified.     

The gradual vocal responses to human-provoked discomfort in farmed silver foxes

Vocal indicators of welfare have proven their use for many farmed and zoo animals and may be applied to farmed silver foxes as these animals display high vocal activity toward humans. Farmed silver foxes were selected mainly for fur, size, and litter sizes, but not for attitudes to people, so they are fearful of humans and have short-term welfare problems in their proximity. With a human approach test, we designed here the steady increase and decrease of fox–human distance and registered vocal responses of 25 farmed silver foxes. We analyzed the features of vocalizations produced by the foxes at different fox–human distances, assuming that changes in vocal responses reflect the degrees of human-related discomfort. For revealing the discomfort-related vocal traits in farmed silver foxes, we proposed and tested the algorithm of “joint calls,” equally applicable for analysis of all calls independently on their structure, either tonal or noisy. We discuss that the increase in proportion of time spent vocalizing and the shift of call energy toward higher frequencies may be integral vocal characteristics of short-term welfare problems in farmed silver foxes and probably in other captive mammals.     

The status of farmed fish hearts: an alert to improve health and production in three Mediterranean species

The heart ventricles of farmed gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax) and Senegalese sole (Solea senegalensis) have been examined and we compared them to the corresponding fish from wild populations. These results can help to understand the differences in farmed fish hearts and in the myocardial structure that this condition of growth can produce. Several parameters were measured in the two groups. Numerical comparisons included heart mass, cardiac and ventricular index, ventricle height:width ratio, width and alignment of bulbus arteriosus, ventricular angles and compacta thickness. We confirm that the normal shape of wild fish hearts can be modified as a result from the adaptation to different environments. These changes can modify the structure of myocardium and compromise the cardiac function in farmed species. The ventricle of farmed fish present differences in shape, were misaligned, rounder, with a wider bulbus and thinner compact layer. Further studies are necessary to reveal functional significance and possible causes of these abnormal hearts and improve the cardiac welfare of Mediterranean species in culture as a way of ensuring a level of production compatible with economic benefits.     

Expanding the moral circle: farmed fish as objects of moral concern

Until recently fish welfare attracted little attention, but international and national legislation and standards of fish welfare are now emerging and an overview of these developments is presented in this study. Whereas animal welfare legislation is based on public morality, animal ethics does not automatically accept public morality as normative and elaborates arguments regarding the way humans should treat animals (referred to as moral standards). In this study we present the most common animal ethics theories. For most of these, sentience is considered a demarcation line for moral concern: if an animal is sentient, then it should be included in the moral circle, i.e. receive moral consideration in its own right and some basic welfare should be ensured. As for fish, research has revealed that the sensory system of teleosts can detect noxious stimuli, and that some kind of phenomenal consciousness, allowing the fish to feel pain, seems to be present. This raises the ethical question as to how much evidence we need in order to act on such indications of fish sentience. A simple risk analysis shows that the probability that fishes can feel pain is not negligible and that if they do indeed experience pain the consequences in terms of the number of suffering individuals are great. We conclude that farmed fish should be given the benefit of the doubt and we should make efforts that their welfare needs are met as well as possible. Finally, the way forward is briefly discussed: efforts must be made to understand what fish welfare means in practical fish farming. This will involve the development of research and education, greater accountability and transparency, compliance with and control of policies, and quality assurance schemes.     

Review: Assessing fish welfare in research and aquaculture,with a focus on European directives

The number of farmed fish in the world has increased considerably. Aquaculture is a growing industry that will in the future provide a large portion of fishery products. Moreover, in recent years, the number of teleost fish used as animal models for scientific research in both biomedical and ecological fields has increased. Therefore, it is increasingly important to implement measures designed to enhance the welfare of these animals. Currently, a number of European rules exist as requirements for the establishment, care and accommodation of fish maintained for human purposes. As far as (teleost) fish are concerned, the fact that the number of extant species is much greater than that of all other vertebrates must be considered. Of further importance is that each species has its own specific physical and chemical requirements. These factors make it difficult to provide generalized recommendations or requirements for all fish species. An adequate knowledge is required of the physiology and ecology of each species bred. This paper integrates and discusses, in a single synthesis, the current issues related to fish welfare, considering that teleosts are target species for both aquaculture and experimental models in biological and biomedical research. We first focus on the practical aspects, which must be considered when assessing fish welfare in both research and aquaculture contexts. Next, we address husbandry and the care of fish housed in research laboratories and aquaculture facilities in relation to their physiological and behavioural requirements, as well as in reference to the suggestions provided by European regulations. Finally, to evaluate precisely which parameters described by Directive 2010/63/EU are reported in scientific papers, we analysed 82 articles published by European researchers in 2014 and 2015. This review found that there is a general lack of information related to the optimal environmental conditions that should be provided for the range of species covered by this directive.     

Life in the fast lane: Temperature,density and host species impact survival and growth of the fish ectoparasite Argulus foliaceus

With expanding human populations, the food sector has faced constant pressure to sustainably expand and meet global production demands. In aquaculture this frequently manifests in an animal welfare crisis, with fish increasingly farmed under high production, high stress conditions. These intense environments can result in fish stocks having a high susceptibility to infection, with parasites and associated disease one of the main factors limiting industry growth. Prediction of infection dynamics is key to preventative treatment and mitigation. Considering the climatic and technology driven changes facing aquaculture, an understanding of how parasites react across a spectrum of conditions is required. Here we assessed the impact of temperature, infection density and host species on the life history traits of Argulus foliaceus, a common palearctic fish louse, representative of a parasite group problematic in freshwater aquaculture and fisheries worldwide. Temperature significantly affected development, growth and survival; parasites hatched and developed faster at higher temperatures, but also experienced shorter lifespans when maintained off the host. At high temperatures, these parasites will likely experience a short generation time as their life history traits are completed more rapidly. A. foliaceus additionally grew faster on natural hosts and at lower infection densities. Ultimately such results contribute to prediction of population dynamics, aiding development of effective control to improve animal welfare and reduce industry loss.     

Insights into the concept of fish welfare

Fish welfare issues are predicated on understanding whether fish are sentient beings. Therefore, we analyzed the logic of the methodologies used for studying this attribute. We conclude that empirical science is unable to prove or to disprove that fish are sentient beings. Thus, we propose a combined ethical-scientific approach for considering fish as sentient beings. The most difficult ongoing question is to determine which conditions fish prefer. Approaches to assess fish preferences should be rigorously and cautiously employed. In light of these considerations, attempts to establish physiological standards for fish welfare are discouraged, and a preference-based definition of fish welfare is proposed.     

我国转基因鱼研制的历史回顾与展望

中国自从诞生了首例转基因鱼以来,在后续30多年里取得了一系列重要研究进展。全球范围的转基因鱼研究包括多种养殖鱼类,目标性状涉及快速生长、抗病抗逆和品质改良。现在已经初步建成转基因鱼育种技术体系和安全评估体系,为转基因鱼产业化奠定了重要基础。本文以转基因黄河鲤育种研究为主线,简要回顾了转基因鱼研究的发展历程,并对转基因鱼育种面临的问题和发展前景进行了分析和展望。     

Fish farms at sea: the ground truth from Google Earth

In the face of global overfishing of wild-caught seafood, ocean fish farming has augmented the supply of fresh fish to western markets and become one of the fastest growing global industries. Accurate reporting of quantities of wild-caught fish has been problematic and we questioned whether similar discrepancies in data exist in statistics for farmed fish production. In the Mediterranean Sea, ocean fish farming is prevalent and stationary cages can be seen off the coasts of 16 countries using satellite imagery available through Google Earth. Using this tool, we demonstrate here that a few trained scientists now have the capacity to ground truth farmed fish production data reported by the Mediterranean countries. With Google Earth, we could examine 91% of the Mediterranean coast and count 248 tuna cages (circular cages >40 m diameter) and 20,976 other fish cages within 10 km offshore, the majority of which were off Greece (49%) and Turkey (31%). Combining satellite imagery with assumptions about cage volume, fish density, harvest rates, and seasonal capacity, we make a conservative approximation of ocean-farmed finfish production for 16 Mediterranean countries. Our overall estimate of 225,736 t of farmed finfish (not including tuna) in the Mediterranean Sea in 2006 is only slightly more than the United Nations Food and Agriculture Organization reports. The results demonstrate the reliability of recent FAO farmed fish production statistics for the Mediterranean as well as the promise of Google Earth to collect and ground truth data.     

Interactions between commensal bacteria and viral infection: insights for viral disease control in farmed animals

Viral diseases cause serious economic loss in farmed animals industry. However, the efficacy of remedies for viral infection in farmed animals is limited, and treatment strategies are generally lacking for aquatic animals. Interactions of commensal microbiota and viral infection have been studied in recent years, demonstrating a third player in the interaction between hosts and viruses. Here, we discuss recent developments in the research of interactions between commensal bacteria and viral infection,including both promotion and inhibition effect of commensal bacteria on viral pathogenesis, as well as the impact of viral infection on commensal microbiota. The antiviral effect of commensal bacteria is mostly achieved through priming or regulation of the host immune responses, involving differential microbial components and host signaling pathways, and gives rise to various antiviral probiotics. Moreover, we summarize studies related to the interaction between commensal bacteria and viral infection in farmed animals, including pigs, chickens, fish and invertebrate species. Further studies in this area will deepen our understanding of antiviral immunity of farmed animals in the context of commensal microbiota, and promote the development of novel strategies for treatment of viral diseases in farmed animals.     

Otolith mass marking techniques for aquaculture and restocking: benefits and limitations

The use of farmed and restocked fish to supplement the worldwide human consumption of fish, recreational fishing stocks, and conservation efforts, is growing at a rapid rate. Yet, monitoring the benefits of using hatchery-raised fish for supplementation is lacking, often due to hatcheries not marking or tagging all fish prior to release, despite a range of easy to apply, cost effective and accurate mass-marking methods being available to mark farmed and restocked fish en masse. Here we review otolith marking techniques that have the capability of mass marking millions of hatchery-reared fish that are, or could be, used for monitoring and compliance purposes. The otolith mass marking methods consist of otolith thermal marking and a range of otolith chemical marking methods (tetracyclines, alizarin compounds, calcein, strontium chloride, stable isotopes of Ba and Sr, and rare earth elements). We assessed and compared marking technique in terms of (1) ease of application, (2) cost of application, (3) mark retention and detectability, and (4) fish welfare. In addition, we determine the suitability of different otolith marking techniques for mass marking entire hatchery populations whether it be for restocking purposes, or for identifying and tracing escapees from aquaculture facilities. We conclude that although some techniques have restricted use due to regulations, the majority of otolith mass marking techniques are simple, easy to apply, cost effective and highly suitable for long term monitoring of hatchery produced fish.     

Atlantic salmon (Salmo salar L.) genetics in the 21st century: taking leaps forward in aquaculture and biological understanding

Atlantic salmon (Salmo salar L.) is among the most iconic and economically important fish species and was the first member of Salmonidae to have a high‐quality reference genome assembly published. Advances in genomics have become increasingly central to the genetic improvement of farmed Atlantic salmon as well as conservation of wild salmon stocks. The salmon genome has also been pivotal in shaping our understanding of the evolutionary and functional consequences arising from an ancestral whole‐genome duplication event characterising all Salmonidae members. Here, we provide a review of the current status of Atlantic salmon genetics and genomics, focussed on progress made from genome‐wide research aimed at improving aquaculture production and enhancing understanding of salmonid ecology, physiology and evolution. We present our views on the future direction of salmon genomics, including the role of emerging technologies (e.g. genome editing) in elucidating genetic features that underpin functional variation in traits of commercial and evolutionary importance.     

An analysis of the use of plant products for commerce in remote aboriginal communities of northern Australia

The indigenous people of Australia have a long and well documented history of using native plants as an essential component of their customary economy. However, few have engaged successfully in commerce based on native plant use. Recently there has been an increasing interest in exploring options for use of native plants for food, food additives, botanical medicines, and related purposes. In this paper, we determine the issues important to Aboriginal people in enterprise development utilizing plant products, and we define some of the factors affecting progress in realizing opportunities. The Aboriginal people with whom we have worked appear to prefer small-scale enterprises where they have community ownership of ideas and control of the rate and direction of development. Government could play a larger and more active role through supporting additional research and marketing information, providing training, and better matching policy and legislation to support indigenous development and reduce dependence of welfare.     

Current issues in fish welfare

Human beings may affect the welfare of fish through fisheries, aquaculture and a number of other activities. There is no agreement on just how to weigh the concern for welfare of fish against the human interests involved, but ethical frameworks exist that suggest how this might be approached. Different definitions of animal welfare focus on an animal's condition, on its subjective experience of that condition and/or on whether it can lead a natural life. These provide different, legitimate, perspectives, but the approach taken in this paper is to focus on welfare as the absence of suffering. An unresolved and controversial issue in discussions about animal welfare is whether non‐human animals exposed to adverse experiences such as physical injury or confinement experience what humans would call suffering. The neocortex, which in humans is an important part of the neural mechanism that generates the subjective experience of suffering, is lacking in fish and non‐mammalian animals, and it has been argued that its absence in fish indicates that fish cannot suffer. A strong alternative view, however, is that complex animals with sophisticated behaviour, such as fish, probably have the capacity for suffering, though this may be different in degree and kind from the human experience of this state. Recent empirical studies support this view and show that painful stimuli are, at least, strongly aversive to fish. Consequently, injury or experience of other harmful conditions is a cause for concern in terms of welfare of individual fish. There is also growing evidence that fish can experience fear‐like states and that they avoid situations in which they have experienced adverse conditions. Human activities that potentially compromise fish welfare include anthropogenic changes to the environment, commercial fisheries, recreational angling, aquaculture, ornamental fish keeping and scientific research. The resulting harm to fish welfare is a cost that must be minimized and weighed against the benefits of the activity concerned. Wild fish naturally experience a variety of adverse conditions, from attack by predators or conspecifics to starvation or exposure to poor environmental conditions. This does not make it acceptable for humans to impose such conditions on fish, but it does suggest that fish will have mechanisms to cope with these conditions and reminds us that pain responses are in some cases adaptive (for example, suppressing feeding when injured). In common with all vertebrates, fish respond to environmental challenges with a series of adaptive neuro‐endocrine adjustments that are collectively termed the stress response. These in turn induce reversible metabolic and behavioural changes that make the fish better able to overcome or avoid the challenge and are undoubtedly beneficial, in the short‐term at least. In contrast, prolonged activation of the stress response is damaging and leads to immuno‐suppression, reduced growth and reproductive dysfunction. Indicators associated with the response to chronic stress (physiological endpoints, disease status and behaviour) provide a potential source of information on the welfare status of a fish. The most reliable assessment of well‐being will be obtained by examining a range of informative measures and statistical techniques are available that enable several such measures to be combined objectively. A growing body of evidence tells us that many human activities can harm fish welfare, but that the effects depend on the species and life‐history stage concerned and are also context‐dependent. For example, in aquaculture, adverse effects related to stocking density may be eliminated if good water quality is maintained. At low densities, bad water quality may be less likely to arise whereas social interactions may cause greater welfare problems. A number of key differences between fish and birds and mammals have important implications for their welfare. Fish do not need to fuel a high body temperature, so the effects of food deprivation on welfare are not so marked. For species that live naturally in large shoals, low rather than high densities may be harmful. On the other hand, fish are in intimate contact with their environment through the huge surface area of their gills, so they are vulnerable to poor water quality and water borne pollutants. Extrapolation between taxa is dangerous and general frameworks for ensuring welfare in other vertebrate animals need to be modified before they can be usefully applied to fish. The scientific study of fish welfare is at an early stage compared with work on other vertebrates and a great deal of what we need to know is yet to be discovered. It is clearly the case that fish, though different from birds and mammals, however, are sophisticated animals, far removed from unfeeling creatures with a 15 s memory of popular misconception. A heightened appreciation of these points in those who exploit fish and in those who seek to protect them would go a long way towards improving fish welfare.     

Genetics of salmonid skin pigmentation: clues and prospects for improving the external appearance of farmed salmonids

Skin color is an important commercial trait in fish farming, given that this phenotype influences consumer acceptance, thereby determining the commercial value that fish can reach. This character is genetically determined, either by monogenetic or polygenetic control. Over the past few years, progress has been made in studies of quantitative genetic parameters for commercially important traits related to skin pigmentation and, in the molecular field, the mapping and cloning of some genes involved in fish color determination. This study reviews information regarding the genetic determination of salmonid skin color, along with different strategies to improve this character. Data collected in model fish (medaka and zebrafish) are also considered since this information contributes considerably towards improving understanding of the genes that may participate, and of the mechanisms involved in establishing skin coloration in salmonids.     

Disease interaction between farmed and wild fish populations

This paper reviews the literature on disease interaction between wild and farmed fish and recommends strategies to reduce the disease risks to both populations. Most, if not all, diseases of farmed fish originate in wild populations. The close contact between farmed and wild fish readily leads to pathogens exchange. Aquaculture creates conditions ( e.g. high stocking levels) conducive to pathogen transmission and disease; hence pathogens can overspill back, resulting in high levels of challenge to wild populations. This is exemplified by sea lice infections in farmed Atlantic salmon. Stocking with hatchery reared fish or aquaculture escapees can affect disease dynamics in wild populations. Whirling disease has been spread to many wild rainbow trout populations in the US with the release of hatchery reared stock. The greatest impact of aquaculture on disease in wild populations has resulted from the movement of fish for cultivation. Examples of exotic disease introduction following movement of live fish for aquaculture with serious consequences for wild populations are reviewed. The salmon parasite, Gyrodactylus salaris, has destroyed wild salmon populations in 44 Norwegian rivers. Crayfish plague has wiped out European crayfish over much of Europe. Eels numbers have declined in Europe and infection with the swimbladder nematode Anguillicola crassus has in part been blamed. The impact of disease in farmed fish on wild populations can mitigated. Risk analysis methods need to be refined and applied to live fish movement and new aquacultural developments. Appropriate biosecurity strategies, based on risk assessments, should be developed to reduce pathogen exchange and mitigate the consequences.