Labelling fish diets with 15 N -Leucine for monitoring feed consumption and bio-distribution in Atlantic salmon

Abstract

Feeding represents 50-70% of the cost of production in salmon farming, higher than any other animal farm. The improvement of this percentage is challenging as the food is thrown into the fish tank, there is no quantification of the amount of food that is consumed by the fish. In consequence, it is difficult to adjust the food composition making it more nutritive or promoting food consumption by fish. In this study, to investigate food consumption, bio-distribution and food residues, leucine containing ¹⁵ N (a stable isotope of nitrogen) was used to label the fish food. Atlantic salmon (Salmo salar) weighing 100-120 g were maintained in 30 L tanks at a density of 14 kg/m³ . Fishes were fed daily at 1% of the fish weight with pellet labelled with ¹⁵ N-leucine. The ¹⁵ N incorporation was determined 14 hours after the feeding in all the fish organs. Results showed that 14 hours after the administration of a single dose of labelled food to Atlantic salmon enables the detection of the tracer in the whole organism allowing determining the food consumption. Through the analysis of nitrogen use efficiency (NUE), we showed that the trunk, pyloric caeca and head incorporate the highest level of the marker (72.7, 8.7 and 5.7%, respectively). This methodology would permit monitoring feeding to minimize food loss, improve administration methodologies or select the preferred foods for the fish, among others to reduce production costs.

Keywords: feeding in aquaculture; fish feeding; food marker; nitrogen biodistribution; oral intake.

FIGURE 1

Total nitrogen content in tissues from the gastrointestinal tract and intestinal contents. Fish fed ¹⁵N‐leucine food for 1 or 5 days. Total nitrogen content was quantified in pyloric caeca, oesophagus, stomach, liver, gut and intestinal contents by the Kjeldahl method (n = 2)

FIGURE 2

Quantification of total nitrogen in fish 14 hours after feeding ¹⁵N‐leucine food. Total nitrogen content was quantified by the Kjeldahl method in each tissue from fish. Standard deviation is shown (n = 4)

FIGURE 3

Nitrogen use efficiency on each tissue from fish. NUE (¹⁵N yields per ¹⁵N‐leucine food consumed) was determined in each tissue 14 hours after feeding ¹⁵N‐leucine food (columns). The average NUE and the standard deviation are shown (n = 4). Statistical analysis was performed with Kruskal–Wallis One‐way ANOVA on rank tests followed by post‐hoc Dunn's multiple comparison tests. *p < 0.01 was considered a significant change