Evaluation of plastic responses to nutritional programming by various feed sources in brown and rainbow trout fry

The possibilities of metabolic programming by nutritive stimuli during early development for using plant-based raw materials in diets for juvenile trout were investigated. Two feeding experiments were carried out with diets differing in their percentage of plant-based raw materials. In a first experiment with wild brown trout the influence of three different diets on amylase and pepsin activities, as well as on the intestinal microbiome was investigated. The results indicated that digestive enzymes are influenced by actual feed intake, but not by diet-type. A dietary share of 50% plant raw materials enhanced growth of brown trout in comparison to exclusive fish meal-based diets. However, nutritional programming with respect to the protein source could not be established. Furthermore, the effects of plant raw materials on the intestinal microbiome of wild brown trout were investigated. It was demonstrated that the bacterial composition strongly adapts to feed composition. In a second experiment, rainbow trout were fed three experimental diets containing several shares of plant-based proteins. It was observed that 50% dietary plant proteins improved the growth of trout fry. In contrast, feedstuffs produced with 97% of plant raw materials resulted in reduced growth. It was also not possible in this experiment to induce nutritional programming. The effects of the three diets on the gastrointestinal microbiome of rainbow trout are consistent with the results of the first experiment. However, the number of bacteria found and the diversity of the different species significantly increase with age in this experiment. A strict separation of the bacterial composition depending on the diet type can be observed here as well. It was shown that during the first months of life, rainbow trout and wild brown trout react highly plastic against nutritive stimuli, which could be observed especially in the composition of the intestinal microbiome.