Use of moist diets for Atlantic salmon (Salmo salar) when transitioning from fresh to sea water

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A study was designed to test the efficiency of a novel moist diet (49% moisture) against a conventional dry diet (3% moisture) during the period when Atlantic salmon transition to seawater. Four experimental diets were produced. A moist diet was produced using fish meal as well as a moist diet containing 50% inclusion of poultry meal and 50% fish meal. Two dry diets were produced using the same formulations. It was hypothesized that the moist diet would alleviate stress due to osmoregulatory pressures experienced by the smolts introduction to seawater and increase palatability and feed consumption, thereby increasing survival. Four experimental groups consisting of four replicates of 40 smolts each were fed to satiation using the four experimental diets twice daily for 109 days. After trial period one (day 0 – day 72), all moist feed groups were switched to the corresponding dry diet (trial period 2; day 73 – day 109). The fish were bulk weighed periodically to obtain average weights and to determine survival. At the conclusion of the study survival and FCR were not significantly different and average weights of the moist feed groups were smaller than the dry feed groups. There were no differences between diets containing poultry meal and diets used containing full fish meal. During trial period one, dry feed groups showed higher dry matter intake while energy efficiency in the moist feed groups was trending towards being significantly higher. Shelf life of the moist feed was also examined and it was determined that vacuum packing shows great promise in increasing the shelf-life of the moist feed. This study has opened new questions that can be used to guide further research in the use of moist feeds during the seawater transition phase in Atlantic salmon smolts.