Nitrogen content of food as an index of absorption efficiency in fishes

Gravimetric estimation of absorption efficiency in fishes is a time-consuming process and still subject to technical errors. Available marker methods require no quantitative recovery of feces, but their applicability is limited (e.g. chromic oxide method) or their reliability is questionable (e.g. Conover's ash ratio method). From over 100 values reported for about 50 fish species, it has been observed that nitrogen content of food holds a positive correlation to absorption efficiency; the relation is significantly (P<0.001) correlated (r=>0.9). Hence absorption efficiency (Ae) of fishes is predictable from the nitrogen content of food with less than 8% error, using the equation log Ae=1.3706+0.5807 log N.Dedicated to Professor O. Kinne on his 61st birthday, August 30, 1984