Replacement of fishmeal with alternative proteins in diets for Atlantic salmon (Salmo salar L.): A study on the microbiota, morphology and function of the intestine

Abstract

The research presented in this thesis aims to gain knowledge on the impact of a variety of alternative feed ingredients for which there is an increasing use for in Atlantic salmon feed. In focus were effects on the community population and metabolism of intestinal microbiota, its ability to compete with pathogens, gut physiology and health as well as fish performance and feed utilization. The results of the study revealed that the autochthonous microbiota was dominated by Corynebacteriaceae and the allochthonous microbiota was dominated by Lactobacillaceae regardless of diet, indicating a more stable intestinal microbiota than previously reported. Furthermore, results indicate that Atlantic salmon has the ability to compensate for low digestible feed ingredients by increasing the specific activity of leucine aminopeptidase and as such provide growth following feeding with feather meal close to that of fishmeal. By using ex vivo exposure of the intestine to pathogen bacteria, the effect of alternative feed ingredients was also investigated for their potential to make the host more susceptible to disease through intestinal invasion. The result from this trial revealed that use of alternative feed ingredients may intensify the damage resulting from the exposure of pathogen bacteria, but also that these damages can be alleviated by pre-exposing the intestine to probiotic bacteria. In conclusion pea protein concentrate and poultry by-product are highly useful for use as fishmeal replacements, soy protein concentrate and extracted sunflower should be used with caution due to potentially negative effects on the digestive physiology and feather meal merits further study due to its potential to modulate the digestive enzyme activity.