Defining, assessing and promoting the welfare of farmed fish

As currently practised, the culture of fish for food potentially raises concerns about the welfare of farmed fish, and this is a topic that has received considerable attention. As vertebrates, fish share a number of features with the birds and mammals that are more commonly farmed, so many welfare principles derived from consideration of these groups may also be applied to fish. However, fish have a long, separate evolutionary history and are also adapted to a very different, aquatic environment. For these reasons, they have a number of special features that are relevant to how welfare is defined, assessed and promoted and these are discussed. The various methods that are available to researchers for identifying and assessing good and bad welfare in fish are considered, including assessment of physical health and physiological, behavioural and genomic status. The subset of practical welfare indicators that can be used on working farms is also reviewed. Various aspects of intensive aquaculture that can potentially compromise fish welfare are outlined, as are some strategies available for mitigating such adverse effects. Finally, the paper ends by looking briefly to the future, identifying likely changes in aquaculture practices and how these might affect the welfare of farmed fish

Welfare and aquaculture: where benfish fits in

First paragraph: The aim of the final article in this volume is to summarize the main findings of the BENEFISH project and to discuss how the welfare of farmed fish might be managed in the future as the industry develops. However, we start with a brief reminder of the concept of welfare and the particular problems in defining it in fish

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

Three-spined sticklebacks <i>Gasterosteus aculeatus</i> as a model for exploring behavioural biology

Niko Tinbergen chose the three-spined stickleback Gasterosteus aculeatus for his classic behavioural studies because they are small, robust, common and easy to house in the laboratory under reasonably natural conditions and also because their behaviour, while sufficiently simple to be tractable, is still sufficiently complex to be interesting. An analysis of citation records shows that this was an inspired choice. Research on these small fish has addressed all four of Tinbergen's famous questions (causation, development, functions and evolution) and has contributed to the understanding of many different behavioural systems. The G. aculeatus literature is used here to explore several themes in fundamental behavioural biology (diet choice, shoaling, behavioural syndromes and sexual signalling) and the extent to which research using G. aculeatus has informed both fundamental and applied behavioural biology, the latter in the context of aquaculture research

Foraging specialisms, prey size and life-history patterns: a test of predictions using sympatric polymorphic Arctic charr (Salvelinus alpinus)

We use arguments based on optimal foraging theory to predict body size constraints and the consequences of these on a range of life-history traits in three trophic specialist morphs of Arctic charr, Salvelinus alpinus, living in sympatry in Loch Rannoch, Scotland. As predicted, foraging specialists feeding on small prey items with a narrow size range showed evidence of deterministic growth; the ultimate body size of macrobenthos feeders being larger (L∞ = 238 mm) than that of planktivores (L∞ = 216 mm). In contrast, the piscivorous morph showed no evidence of reaching a maximal body size. The two size-constrained morphs (benthivores and planktivores) matured earlier and died younger (living for up to 11 and 7 years, respectively, in this study) than did the piscivorous charr which showed continuous growth up to at least 17 years. The pattern of annual reproductive investment in maturing individuals was complex. Planktivores invested in larger eggs than the other two forms, but benthivores produced a greater number of eggs than planktivores, which in turn produced more than piscivores. Planktivorous males had a greater investment in mean testis weight than the other two forms. Lifetime reproductive output was the greatest in the benthivorous charr, intermediate in planktivorous and the lowest in the piscivorous charr when measured either as fecundity or as gonadal weight. We conclude that constraints imposed upon foraging specialists by foraging efficiency is a significant driver of body size and ultimately reproductive investment in gape-limited foraging salmonids

Fish don't read textbooks: juvenile salmon prove ignorant of foraging theory

The rules governing the selection of feeding patches by foraging animals is an area of intense interest. Much work has focussed on the development of theoretical models that predict when individuals should switch patches. Tests of these models have often been conducted in laboratory environments, but it is not clear how much influence patch-switching decisions have on population-level parameters such as growth and distribution in more complex natural environments. We used juvenile Atlantic salmon as a model species to investigate the effects of randomly fluctuating food levels on growth and site selection. We used PIT technology to monitor in detail individuals’ patterns of patch use and activity in an artificial stream, at natural densities. This allowed us experimental control of food supplies and sufficient replication, while retaining many features of a natural system. Only a few individuals of high social rank switched patches as predicted by an appropriate foraging model; otherwise, although frequent, patch-switching was not related to food availability. Thus, while laboratory experiments indicate that this species has the potential to choose foraging sites on the basis of food availability, it is unlikely that this behavioural mechanism is of great importance in natural systems; further tests of foraging models under natural conditions are essential if we are to understand their effects at the level of populations

Growth, production and fin damage in cage-held 0+ Atlantic salmon pre-smolts (Salmo salar L.) fed either a) on-demand, or b) to a fixed satiation-restriction regime: Data from a commercial farm

This experiment investigated the impact of feeding regime upon the growth performance, production efficiency and fin damage of cage-held 0+ Atlantic salmon pre-smolts. Six groups of pre-smolts (n= 61847 +/- 2620 fish group(-1)) were held in six 12 x 12 x 4 in production cages for 64 days (23rd August until 26th October) at initial and final densities of 4.6 +/- 0.2 kg m(-3) and 9.5 +/- 0.5 kg m(-3), respectively (mean +/- SEM). Fish were subjected to ambient photoperiod (11.67-16.05 h min-max) until 16th October, before being held under 24 h light. Fish were fed throughout the light phase and comparisons were made between three groups fed to an imposed regime (scheduled fixed ration feeding every 10 min) and three groups fed on-demand using commercial interactive feedback systems. The study was divided into primary and secondary phases: during the primary phase (part I) each regime was fed to satiation, whereas during the secondary phase (part II) fish under the imposed regime received a restricted ration that was ca. 20% less than those fed on-demand. During part I there were no differences in ration (g fish(-1)), fish condition and Specific Growth Rate (G,) between regimes (G(w): 1.45 +/- 0.06 vs. 1.44 +/- 0.04 for imposed vs. on-demand fed fish, respectively). During part 11 underfeeding in the imposed regime had a significant and deleterious impact upon fish condition, FCR and growth (G(w): 0.45 +/- 0.04 vs. 0.84 +/- 0.09 for imposed vs. on-demand fed fish, respectively). Fish under the imposed regime also had significantly more dorsal fin splitting than those fed on demand for the duration of the study, and significantly more dorsal fin erosion at the end of Parts I and II. In addition, the smallest fish within each cage suffered the greatest amount of fin splitting and erosion at the end of Parts I and II, irrespective of feeding regime. Daily ration amongst the on-demand cages decreased as winter approached; stepwise multiple regression analyses demonstrated that this was significantly related to a seasonal decrease in temperature

Can juvenile Atlantic salmon use multiple cue systems in spatial learning?

An ability to form a map or spatial representation of a home range should facilitate efficient foraging and promote the use of effective escape routes to shelter. Although a few experiments have shown some species of fish are capable of simple spatial behaviour, little is known about the behavioural mechanisms they use to orient as they forage. Whether juvenile Atlantic salmon,Salmo salar, have the capacity to use conspicuous visual landmarks to help them track a moving resource was investigated. The experiment was then modified to determine whether the salmon could continue to track the resource in the absence of conspicuous visual cues. The salmon followed a moveable food source in the presence and, after retraining, in the absence of distinct coloured landmarks. It is suggested that juvenile salmon may be capable of using multiple forms of cue to help them solve spatial tasks such as tracking a moving resource