Effect of constant digestible protein intake and varying digestible energy levels on energy and protein utilization in Nile tilapia
Haidar, M.N. ; Bleeker, S. ; Heinsbroek, L.T.N. ; Schrama, J.W. - \ 2018
Aquaculture 489 (2018). - ISSN 0044-8486 - p. 28 - 35.
Digestible energy - Digestible protein - Energy utilization - Feed evaluation - Protein efficiency - Protein/Energy ratio
In literature, the variability in the estimated optimal digestible protein to digestible energy ratio (DP/DE) is high. The present study aimed to estimate the optimal DP/DE ratio in Nile tilapia (Oreochromis niloticus) using different criteria (performance, energy and nitrogen balances parameters). Duplicate aquaria were randomly assigned to one of 16 diets. These diets covered a wide range of dietary DP/DE ratio (from 16.7 to 27 g MJ −1 ). DP levels ranged between 36 and 50% and DE levels between 17.5 and 22 MJ kg −1 . Fish were fed restrictively based on a similar digestible protein amount at all 16 diets. Initial fish weight was 6.7 g. Broken line analysis showed that no optimal DP/DE ratio was present for Nile tilapia within the DP/DE ratio range studied. Regression analysis showed that growth declined as DP/DE ratio increased and seemed to level off at high DP/DE ratio (25 g MJ −1 ). FCR ranged between 0.8 and 1.1 and increased linearly with increasing DP/DE ratio. Decreasing the DP/DE ratio resulted in a linear increase in protein efficiency to a highest value of 53%. However, protein efficiency did not show a plateau or a maximum value. Moreover, decreasing the DP/DE ratio resulted in a very high fat content of the fish (over 16%). In conclusion, an optimal DP/DE ratio in Nile tilapia being fed restrictively seems to be absent or to be below 16 g MJ −1 . A maximum protein deposition level is not present in 5–40 g Nile tilapia.
The effect of type of carbohydrate (starch vs. nonstarch polysaccharides) on nutrients digestibility, energy retention and maintenance requirements in Nile tilapia
Haidar, Mahmoud N. ; Petie, Mischa ; Heinsbroek, Leon T.N. ; Verreth, Johan A.J. ; Schrama, Johan W. - \ 2016
Aquaculture 463 (2016). - ISSN 0044-8486 - p. 241 - 247.
Energy utilization - Non-starch polysaccharides - Maintenance requirements - Fish
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.