Ammonia excretion rates of the sea bass, Lates calcarifer, in fresh and sea water

Abstract

The weight-specific ammonia excretion rate of sea bass (Lates calcarifer) fry in fresh water is higher than that of those in sea water. The allometric equation \(y = 24.426 \times ^{-0.4714}\) best describes the relationship between the ammonia excretion rate (y, in µg total \(NH_{3}-N/g/hour)\) and body weight (x, in g wet weight) for fry in fresh water and \(y = 19.891 \times ^{-0.6712}\) for fry in sea water. The ammonia excretion rate of sea bass fry in fresh or sea water did not significantly increase or decrease during prolonged starvation.

The pre-feeding ammonia excretion rate of sea bass subadults in fresh water was similar to those in sea water. The ammonia excretion rate of both groups ranged from 3.86 to 4.13 µg total NH₃-N per g per hour. Half an hour after feeding, ammonia excretion rates rose to a significant level over pre-feeding values in both freshwater and seawater-adapted subadults. Both groups also showed the same peaks that were 7.5 times higher than pre-feeding levels 3 hours after feeding. By 10 hours after feeding, the ammonia excretion rate of both groups had returned to pre-feeding levels.