Total ammonia nitrogen leaching from feed pellets used in salmon aquaculture

The total amount of ammonia nitrogen ( TAN) leaching from Atlantic salmon ( Salmo salar L.) feed pellets was determined under controlled laboratory conditions. The leaching was successfully explained by means of a first order kinetic equation: y = a . (1 - e(-k.t)), where a was the maximum TAN leached and k was the velocity of the process. Then t(a) was defined as the time at which a was reached, which was obtained from the equation prediction. The interaction between pellet size and immersion length significantly influenced TAN leaching: the smaller the pellet and the longer the immersion times, the higher the leaching (a). However, pellet size did not influence k or t(a), although k tended to be higher and t(a) lower for larger pellets. TAN leaching from feed pellets depends on the protein content and contact surface. As the surface/volume ratio (S/V) increases with pellet size while the protein content decreases, it was hypothesized that S/V influences k whereas the protein content has a greater effect on a.