Monitoring the influence of marine aquaculture on wild fish communities: benefits and limitations of fatty acid profiles

Abstract

Fatty acids (FA) have been applied as indicators of the influence of coastal sea-cage fish farming on wild fish communities in several recent scientific publications. Due to the relatively high conservation of FA composition throughout the food web, they are useful for characterizing trophic relationships. The increasing utilization of vegetable or alternative animal oils in the production of aquafeeds results in cultivated fish exhibiting higher levels of terrestrial FAs in their tissues. As previously reported, wild fish ubiquitously aggregate around fish farms as a consequence of the introduction of new habitat and the easy availability of food—fish farms act as enhanced fish aggregation devices (FADs). The influence of food pellets on the composition of wild fish has been detected in recent studies on salmon, sea bass and sea bream aquaculture, with increased levels of linoleic acid (18:2n-6) and a low n-3/n-6 ratio as clear indicators of the consumption of food pellets from the farms. The potential ecological and physiological effects on wild fish are presently unknown. In the present article, guidelines are proposed for the investigation and use of terrestrial FAs to track the effects of coastal aquaculture on wild fish communities and local fisheries, as well as the benefits or limitations of this technique

Effects of coastal fish farms on body size and isotope composition of wild penaeid prawn

“…Thus, we speculated that if caramote prawn were feeding on lipid-rich fish food around fish cages, they would become depleted in 13 C and 15 N, and increase their C:N ratios due to lipid accumulation. An increase in fat reserves has been demonstrated before for a number of marine organisms feeding on fish food around fish cages (Fernández-Jover et al, 2011), and our laboratory study shows that the ingestion of fish food in captivity resulted in a significant increase in C:N compared to natural baseline values, though no difference was detected around fish cages.…”

“…Nitrogen isotopic values in this species were significantly higher than fish food but were largely determined by body size, so that prawn appear to become nitrogen depleted as they grow, possibly due to the allocation of energy during reproduction (Lumare et al, 2011;Kevrekidis and Thessalou-Legaki, 2011). Fish assembled around fish farms have been found to have a mixed diet consisting of fish food pellets and natural prey items (Fernandez-Jover et al, 2007;Arechavala-Lopez et al, 2011;Fernández-Jover et al, 2011). The abundance and diversity of epifauna underneath fish cages tend to be lower than those of reference areas due to anoxic conditions (Holmer et al, 2007;Martinez-Garcia et al, 2013), and it is possible that the isotopic nitrogen signature of prawn feeding around fish cages might represent a balance between the ingestion of nitrogen-depleted fish food and the foraging on nitrogen-enriched marine epifauna.…”

Assessing the Influence of Salmon Farming through Total Lipids, Fatty Acids, and Trace Elements in the Liver and Muscle of Wild Saithe Pollachius virens

“…The incorporation and storage of FAs in fish tissues strongly depends on the FA profile of the diet (Sargent et al 2002). The current practice of substituting fish oils with other vegetable lipid sources in farmed marine fish diets leads to notable changes in lipid composition and FA profiles in fish tissues (Fernandez-Jover et al 2011a). Wild Saithe feeding around Norwegian salmon farms had liver and muscle FA profiles similar to the feed pellets used at the farm (Skog et al 2003;Fernandez-Jover et al 2011b).…”

“…Wild U-Saithe could be placed in a higher trophic level as they feed on a wide variety of prey items compared with F-Saithe that usually feed heavily on pellets (Fernandez-Jover et al 2011a). The higher levels of TEs found in U-Saithe liver and muscle tissues compared with F-Saithe might be a result of the accumulation of TEs from natural prey (e.g., As, Se, Zn, Hg, Fe).…”

“…Wild Saithe reside near fish farm facilities for several months (Bjordal and Skar 1992;Bjordal and Johnstone 1993;Uglem et al 2009;Dempster et al 2009Dempster et al , 2010, a sufficient period to cause physiological changes and modification of metabolic profiles due to a diet switch from wild prey to uneaten feed pellets (Skog et al 2003;Dempster et al 2009;Ottera et al 2009;Bustnes et al 2010;Fernandez-Jover et al 2011a, 2011b). Significant differences in body condition, relative liver size, lipid content, and fatty acid (FA) composition in both muscle and liver of Saithe have been reported in previous studies for farm-aggregated and unaggregated fish.…”