Some effects of temperature, feeding and body weight on nitrogenous excretion in young plaice Pleuronectes platessa L.

Ammonium-nitrogen accounted for 75–85% of the nitrogenous excretion of young plaice, Pleuronectes Platessa L., prior to feeding. Rates of excretion increased with increasing temperature and in proportion to the body weight to the power 0.67. Following feeding the rate of excretion increased to between 2and 11 times the pre-fed rate and both the peak rate and as the duration of the effect were increased, the greater the amount of nitrogen absorbed from the food. The magnitude of the effect increased with increasing ration and the relationship was best described by an asymptotic equation. Estimates of endogenous nitrogen excretion and maintenance requirements were made from the results of the feeding experiments and were fond to be in close agreement with published data. Estimats of nitrogen requirements obtained from the experiments on fish in the post-absorptive state yielded values intermediate between endogenous and maintenace requirements.