Effect of water temperature on ammonia excretion of juvenile dark-banded rockfish Sebastes inermis

Abstract

A study was carried out to investigate the effect of water temperature on daily pattern and rate of total ammonia nitrogen (TAN) excretion in juvenile dark-banded rockfish Sebastes inermis (mean body weight: 14.8±0.3 g) under fasting and feeding conditions. Fish were acclimated over 10 days under three different water temperatures (15, 20 and 25°C). After 72 hours of starvation, fasting TAN excretion was measured at each temperature. To investigate post-prandial TAN excretion, fish were hand-fed with a commercial diet containing 47.7% crude protein for 7 days, two times daily at 09:00 and 17:00 hr. Water was sampled from both the inlet and outlet of each chamber every 2 hrs over a 24 hr period. Both fasting and post-prandial TAN excretion increased with increase in water temperature (P<0.05). Mean fasting TAN excretion rates at 15, 20 and 25°C were 8.1, 9.0 and 9.2 mg TAN kg fish-1 h-1, respectively. The value of 15°C was lower than those of 20 and 25°C (P<0.05), but there was no significant difference between 20°C and 25°C (P>0.05). Mean post-prandial TAN excretion rates at 15, 20 and 25°C were 20.1, 22.9 and 23.4 mg TAN kg fish-1 h-1, respectively. A peak post-prandial TAN excretion rate occurred after 12 hrs from the first feeding at 15°C (mean 28.7 mg TAN kg fish-1 h-1), 20°C (33.7 mg TAN kg fish-1 h-1) and 25°C (36.8 mg TAN kg fish-1 h-1), respectively. The TAN loss for ingested nitrogen at 15°C (36.2%) was lower than that of 20°C (40.8%) and 25°C (41.7%). Based on overall results, water temperature exerts a profound influence on the nitrogen metabolism of juvenile dark-banded rockfish.