Knowledge of aquaculture–environment interactions is essential for the development of a sustainable aquaculture industry and efficient marine spatial planning. The effects of fish and shellfish farming on sessile wild populations, particularly infauna, have been studied intensively. Mobile fauna, including crustaceans, fish, birds and marine mammals, also interact with aquaculture operations, but the interactions are more complex and these animals may be attracted to (attraction) or show an aversion to (repulsion) farm operations with various degrees of effects. This review outlines the main mechanisms and effects of attraction and repulsion of wild animals to/from marine finfish cage and bivalve aquaculture, with a focus on effects on fisheries‐related species. Effects considered in this review include those related to the provision of physical structure (farm infrastructure acting as fish aggregating devices (FADs) or artificial reefs (ARs), the provision of food (e.g. farmed animals, waste feed and faeces, fouling organisms associated with farm structures) and some farm activities (e.g. boating, cleaning). The reviews show that the distribution of mobile organisms associated with farming structures varies over various spatial (vertical and horizontal) and temporal scales (season, feeding time, day/night period). Attraction/repulsion mechanisms have a variety of direct and indirect effects on wild organisms at the level of individuals and populations and may have implication for the management of fisheries species and the ecosystem in the context of marine spatial planning. This review revealed considerable uncertainties regarding the long‐term and ecosystem‐wide consequences of these interactions. The use of modelling may help better understand consequences, but long‐term studies are necessary to better elucidate effects.

In two laboratory experiments using tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio), we investigated the effect of lipid content in the fish carcass on the stable carbon isotope ratio (δC). In both experiments, a significant negative correlation was found between lipid content in the carcass dry matter and δC of total dry matter, but there was no influence on the δC of fat-free dry matter or lipids. As the lipid content of fish is known to vary with reproductive stage, season or nutritional state, separate analysis of fractions of the proximate composition of dry matter will lead to more reliable results than analysing the whole body. The differences in δC between diet and fish carcass (trophic shift) were different for the two species, calling for feeding trials under controlled conditions using the species and the feeds in question before applying the stable isotope tracer technique in the analysis of food webs.

Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animal's diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp (Cyprinus carpioL.) was carried out to test the influence of the feeding level and individual metabolic rate on delta(13)C and delta(15)N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and delta(13)C and delta(15)N values. delta(13)C and delta(15)N values differed significantly at different feeding levels. While delta(13)C values of the lipids and delta(15)N values decreased with increasing feeding rate, delta(13)C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between delta(13)C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 per thousand for both delta(13)C and delta(15)N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge.

Many scientists use naturally occurring stable isotopes to reconstruct the diets of animals. However, isotopic ratios may be affected not only by the composition of the diet but also by the amount of food consumed. Thus, an experiment using tilapia (Oreochromis niloticus) was carried out to test the influence of feeding level on delta13C and delta15N of fish given a semi-synthetic wheat gluten/wheat starch based diet. In addition, the effect of diet quality was tested by comparing tilapia given this feed with tilapia fed a fish meal/wheat meal based diet. Forty-four tilapia were reared individually. After a prefeeding phase, fish were randomly assigned to five groups, four on the semi-synthetic diet at different feeding levels and one group on the fish meal/wheat meal based diet fed at the equivalent of the highest level of the semi-synthetic diet. The experiment lasted eight weeks. Proximate composition, gross energy content and delta13C and delta15N values were determined in feed and fish, for delta13C separately in the lipids and the lipid-free matter. Delta13C in the lipids and the lipid-free matter and delta15N of tilapia fed the semi-synthetic diet decreased significantly with increasing feeding rate. The absolute values of the trophic shift in fish fed the semi-synthetic wheat based diet were significantly higher than in fish fed the fish meal/wheat meal based diet. The different delta13C and delta15N values in tilapia fed the same diet at different feeding levels and the influence of feed quality on the trophic shift add to the uncertainty involved in the use of stable isotopes in ecological research.

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