Based on the fact that farmed fish experience different environments, stocking densities and feeding regimes compared with wild fish, several techniques have been developed to discriminate the wild or farmed origin of fish. These techniques quantify differences between genetics, chemical characteristics, fatty acid compositions, trace elements, pollutants, stable isotopes, morphology and organoleptic characteristics. Gilthead sea bream and European sea bass are the most important marine fish in Mediterranean aquaculture and are highly appreciated by commercial and recreational fisheries. A total of 60 studies that used techniques to discriminate farmed from wild fish for sea bream and sea bass form the basis of this review. The most common technique used differences in the lipid and fatty acid composition of fish. Many of these studies dealt with food science and product quality, rather than tracing escapees. A wide range of identification tools is useful in determining the correct origin of captures and proper labelling of marketed fish. External appearance and morphometry are useful for rapid assessments and can be achieved with high accuracy and little cost, especially for sea bream. This makes these methods suitable for detecting large and recent escape events, applicable in fisheries studies, and for ensuring that wild and farmed fish are separated in the marketplace. Techniques using differences in chemical or genetic composition are more useful for environmental monitoring, as they have higher accuracy and can detect escapees long after the escape incident. Regulatory bodies should legislate protocols that describe the technique(s) that must be applied in specific circumstances.

Environmental enrichment (EE) can improve the welfare of captive fish. Its objective is to provide new sensorial and motor stimulation in order to help meet their behavioural, physiological, morphological and psychological needs, whilst reducing stress and frequency of abnormal behaviours. In fish farms, rearing environments are usually designed from a human perspective and based on economic requirements, mainly for practical reasons for the farmer, with little consideration for animal welfare. Throughout aquaculture production cycles, many farming operations can be stressful for fish, and EE may not only help them cope with these stressful events but also improve their overall welfare. In recent years, increasing interest on the effects of EE in captive fish has focussed mainly on structural enrichment. However, there are many other enrichment strategies that merit attention (e.g. sensorial, occupational, social and dietary enrichment) and which may be of interest for fish farming. Here, we review in depth the existing literature on EE and its effects on the welfare of a wide range of farmed fish species, discussing the feasibility and potential applications of different EE strategies to promote fish welfare at a commercial scale. We also present a practical framework to address the design, validation and implementation of EE by the aquaculture industry, taking in consideration the technical challenges of providing enrichment for farmed fish.

No abstract

Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than nonpredated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

Coastal aquaculture installations concentrate large numbers of wild ¢sh species of both ecological and economic importance, including schools of bogue, Boops boops (L.), in high abundance and biomass. The aggregated species consume large quantities of the easily available pellets lost from cages. As a consequence, the physical condition of farm-associated wild ¢sh is increased and their physiology is altered. These changes may in£uence local ¢sheries as many of these aggregating species are targeted by ¢shers. We assess whether local ¢shers catch wild ¢sh that have previously aggregated at ¢sh farms by comparing the body condition, trophic indexes, diet overlap and the fatty acid (FA) composition of B. boops obtained from local ¢sh markets and around ¢sh farms. Bogue captured by trammel-nets and around ¢sh farms facilities presented a similar biological condition, as well as high quantities of pellets in the gut, and their FA pro¢le was a¡ected by vegetalderived FAs. In contrast, bogue captured by trawlers were not in£uenced by ¢sh farms, as they consumed natural trophic resources.We conclude that artisanal ¢shers exploit these aggregated ¢sh populations once they have dispersed away from farms, and bene¢t from a 'biomass export' from ¢sh farms at a local scale.