Ammonia excretion of octopus (Octopus vulgaris) in relation to body weight and protein intake

The rate of total ammonia excretion (U, mg TAN d− 1) in relation to body weight (W, 490–3460 g) and absolute protein feeding rate (APFR, 0.00–11.90 g d− 1) was studied in octopus (Octopus vulgaris). Using multiple regression analysis, the data obtained were fitted to the equation U = 13.91 + 0.07W + 0.02W × APFR, which explained 95% of the variance observed. According to this equation, there was a significant interaction between W and APFR (W × APFR), the coefficient of W varying linearly with APFR (b' = 0.07 + 0.02APFR). When U was expressed as a function of body weight (Ur, mg TAN kg− 1 body weight d− 1), Ur basically varied as function of APFR, showing a value of 84 mg TAN kg− 1 body weight d− 1 when the octopus was not fed and 265 mg TAN kg− 1 body weight d− 1 when protein intake was 9 g d− 1. U increases linearly with body weight from 10 to 57 g TAN kg− 1 feed dry matter d− 1 when APFR is 9 g d− 1.