Effect of stachyose, raffinose and soya-saponins supplementation on nutrient digestibility, digestive enzymes, gut morphology and growth performance in Atlantic salmon (Salmo salar, L)

This study investigated the effects of raffinose, stachyose either alone or in combination, and the role of soya-saponins in combination with these oligosaccharides, in diets for Atlantic salmon on nutrient digestibilities, growth performance and morphological changes of the gastrointestinal tract. The experiment was carried out using triplicate groups of Atlantic salmon with 0.421 kg initial weight and lasted for 68 days. The experimental diets consisted of a negative control diet based on high-quality fish meal (FM), and a positive control diet containing 300 g kg−1 soybean meal (SBM), and four diets based on the negative control diet added 6.7 g kg−1 raffinose (RA), 29.5 g kg−1 stachyose (ST), a combination of the raffinose and stachyose (RA–ST), or the same combination further supplemented with 2 g kg−1 soya-saponins (RA–ST–SA). The results showed that fish fed the SBM, the positive control, had significantly higher FCR, and tended to have lower weight gain and growth rate compared to fish fed the FM-diet, while fish fed the RA, ST, RA–ST and RA–ST–SA ranked in between the two control diets. The results indicate that feeding the Atlantic salmon the RA, ST, RA–ST and RA–ST–SA did not interfere with protein or fat digestibility. None of the dietary treatments, except for the positive control, caused significant morphological changes in the liver, or mid and distal intestines.