The effect of type of carbohydrate (starch vs. nonstarch polysaccharides) on nutrients digestibility, energy retention and maintenance requirements in Nile tilapia

For Nile tilapia, the energetic value of non-starch polysaccharides (NSP) was compared to starch. It was assessed if carbohydrate type (NSP vs. starch) affected the energetic utilization for growth (KgDE) and the energy requirements for maintenance (DEm). Eighteen groups of fish were assigned in 2 × 3 factorial design: two diets, with either a high NSP or high starch content; and three feeding levels (low, medium or satiation). The NSP diet contained 70% of the starch diet supplemented with 30% dried distillers grains with solubles. Nutrients digestibility, nitrogen and energy balances were measured. All nutrients digestibility decreased with increasing feeding level (P < 0.001). Diet type (NSP vs. starch) affected the digestibility of all nutrients except for dry matter and fat. NSP of both diets were digested and the NSP digestibility ranged between 23% and 73%. Averaged over feeding levels, 5% and 17% of the total digestible energy originated from NSP at the starch and NSP diet, respectively. Although the digestible energy intake was similar, the contrast in type of carbohydrates between the diets resulted in lower energy retention with the NSP rich diet (P < 0.05). Despite this impact on energy retention, both DEm and kgDE were not significantly influence by diet. However, DEm was numerically higher (96 vs. 110 kJ kg-0.8 BW d-1) and kgDE was numerically lower (65% vs. 58%) at the NSP diet compared to the starch diet. In conclusion, NSP are digested by Nile tilapia. Digested NSP are less well utilized for growth, which is reflected by a lower energy retention in fish and is due to the slightly higher DEm in combination with a slightly lower kgDE. Statement of relevance: Scarcity of fishmeal and -oil combined with the fast growing aquaculture sector, result in diversification of feed ingredients in fish-feeds. Plant ingredients as protein source become more important, which also increases the dietary carbohydrate content including non-starch polysaccharides (NSP). This paper provides information on the nutritional value of NSP in tilapia. This will eventually lead to improved fish-feed formulations.