The anaesthetic effects of clove-oil-derived eugenol were studied in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Acute lethality and the effects of multiple exposures to eugenol were measured. The estimated 8-96 h LC 50 for eugenol was found to be approximately 9 p.p.m. Times to induction and recovery from anaesthesia were measured and compared with MS-222 under similar conditions. Eugenol generally induced anaesthesia faster and at lower concentrations than MS-222. The recovery times for fish exposed to eugenol were six to 10 times longer than in those exposed to similar concentrations of MS-222. Clove oil eugenol was determined to be an acceptable anaesthetic with potential for use in aquaculture and aquatic research. Doses of 40-60 p.p.m. eugenol were found to induce rapid anaesthesia with a relatively short time for recovery in juvenile trout.

In contrast to other major forms of livestock agriculture, there is a paucity of scientific information on the welfare of fish raised under intensive aquacultural conditions. This reflects an adherence to the belief that these animals have not evolved the salient biological characteristics that are hypothesised to permit sentience. In this review, we evaluate the scientific evidence for the existence of sentience in fish, and in particular, their ability to experience pain, fear and psychological stress. Teleost fish are considered to have marked differences in some aspects of brain structure and organization as compared to tetrapods, yet they simultaneously demonstrate functional similarities and a level of cognitive development suggestive of sentience. Anatomical, pharmacological and behavioural data suggest that affective states of pain, fear and stress are likely to be experienced by fish in similar ways as in tetrapods. This implies that fish have the capacity to suffer, and that welfare consideration for farmed fish should take these states into account. We suggest that the concept of animal welfare can be applied legitimately to fish. It is therefore appropriate to recognize and study the welfare of farmed fish.

Knowledge of the quantitative and qualitative properties of salmonid faeces is necessary for aquaculture waste dispersal models, and the design of integrated multi-trophic aquaculture (IMTA) systems. The amount and proximate composition of salmonid faeces can be estimated using a mass-balance, nutritional approach. Indigestible components of salmonid diets have the potential to a¡ect faecal'cohesiveness'or 'stability' . Nutrient content and density of faeces can vary depending on diet and submersion time. Faecal density has a greater in£uence on settling velocity than faecal size. Published settling velocity data on salmonid faeces are highly variable due to di¡erences in ¢sh size, rearing systems, collection time, water density, methodology, the mass fraction tested and diet. Most faecal settling data used in published salmonid waste dispersal models are rudimentary and recent information suggests that such models are highly sensitive to this input. The design of open-water IMTA systems and estimation of nutrient capture and recovery from co-cultured ¢lter feeders is di⁄cult due to limited information on particle size, digestibility, settleable and non-settleable mass fractions of salmonid faeces at cage environments. Implications of faecal properties on the accountability for the e¡ects of aquaculture nutrient loading are discussed.

Live yeast can replace 40% of FM without disrupting bacteria communities in the gut of rainbow trout, while increased water temperature due to seasonal fluctuations and/or climate change may result in a gut dysbiosis that may jeopardize the health of farmed fish.

The anaesthetic effects of clove‐oil‐derived eugenol were studied in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Acute lethality and the effects of multiple exposures to eugenol were measured. The estimated 8‐96 h LC50 for eugenol was found to be approximately 9 p.p.m. Times to induction and recovery from anaesthesia were measured and compared with MS‐222 under similar conditions. Eugenol generally induced anaesthesia faster and at lower concentrations than MS‐222. The recovery times for fish exposed to eugenol were six to 10 times longer than in those exposed to similar concentrations of MS‐222. Clove oil eugenol was determined to be an acceptable anaesthetic with potential for use in aquaculture and aquatic research. Doses of 40‐60 p.p.m. eugenol were found to induce rapid anaesthesia with a relatively short time for recovery in juvenile trout.