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Traditional sources of protein in fish feed for salmonids, such as fishmeal, face sustainability problems. Therefore, ingredients not attractive for human consumption are increasingly being considered for the development of future feeds. However, it is uncertain how this alternative range of ingredients will affect fish growth, quality and consumer opinion. In this experimental study, we tested a new fish feed on Arctic charr, containing a protein mixture from the Baltic Sea and yeast, all ingredients unattractive for human consumption. This feed comprised of sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), blue mussels ( Mytilus edulis ) and baker's yeast ( Saccharomyces cerevisiae ), in a ratio of three parts to the whole. Fish fed with this feed grew 11.5% less than the control group. The digestibility and microscopy analysis of the faeces suggested a lower digestibility of the test feed, presumably caused by the fish's inability to utilize the nutrients from the yeast cells. Consumers' perceptions of the final product were evaluated through a sensory evaluation, indicating no differences in scores of fillet quality between the two treatments. Potential implications of these results are discussed in context of feed composition, quality and other factors including species biology and season, which are relevant topics in the discussions on feed sustainability. Statement of relevance Evaluating a feed mix unattractive for human consumption. [ABSTRACT FROM AUTHOR]

The evaluation of new diet composition is commonly achieved by performing time-consuming growth trials, which may negatively impact the welfare of a large number of fish if the feed is not accepted. Instead, the fish's behavioural responses to a new diet composition can be used as a first step in the evaluation of new diet composition. The taste acceptance of a new diet by Arctic charr ( Salvelinus alpinus ) was evaluated over 16 days based on the self-selection of a test diet and a control diet. The test diet contained ingredients from the nutrient-enriched Baltic Sea, and it is hoped that this diet can contribute nutrients to the nutrient-poor waters in northern Sweden in which Arctic charr are farmed. The main ingredients in the test feed were blue mussel meat ( Mytilus edulis ), meat from sprat ( Sprattus sprattus ) and herring ( Clupea harengus ), baker's yeast ( Saccharomyces cerevisiae ), fish oil and regionally produced rapeseed oil. Individual fish ( n = 15) were allowed to choose between abundances of both the test diet and a fishmeal based control diet that mimicked a standard feed for Arctic charr. After only a few days, the fish demonstrated a significant preference for the Baltic Sea test feed. These results may depend on betaine, which was found at concentrations that were four times higher in the test feed than in the control feed. Betaine is a known attractant for many fish species and is abundant in marine animals, such as mussels. Thus, the test diet can be evaluated further without additional taste stimulants before the new feed formula can be used commercially to ensure fish welfare, the product quality and the economic feasibility of the new formula. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates how simulation of condensed winter light conditions effects the growth of wild caught Arctic charr (Salvelinus alpinus L.) held in culture. After capturing from Altevatn, Northern Norway, juvenile Arctic charr were cultivated and subsequently individually divided into two groups. The fish were held under identical conditions from May to October including continuous light. Starting from week 41 after capture (October) one group was subjected to a winter light regime of 6 h light and 18 h dark per day (Winter Light group—WL), while light regimes in the second group remained continuous (Light group). After an eight weeks treatment period the WL-group was reverted to the continuous light regime until the experiment ended in May 2007. Results revealed no pre-treatment differences in growth between the two groups. However, starting from two months after the short day treatment, fishes from the WL group had significant higher growth rates compared to L group fish. At the end of the experiment, e.g. five months after the light treatment, fishes from WL group had increased their average body weight by 353 g as compared to 252 g in the L group. Consequently, results show that simulation of winter light conditions can increase the productivity of land-based Arctic charr (Salvelinus alpinus L.) cultivation by 25 to 30%. Thus, management of wild caught charr farming, great care should be taken as to what light regimes the fish are exposed to. [Copyright &y& Elsevier]