Effect of temperature on endogenous and postprandial ammonia excretion of dark-banded rockfish Sebastes inermis

Abstract

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 weigh: 14.8±0.3 g) under fasting and feeding conditions was investigated. Fish were acclimated over 10 days under three different water temperatures (15, 20 and 25℃). After 72 hours of fasting, fasting TAN excretion was measured at each temperature. And then, 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 09:00 and 17:00 h. Water was sampled for both the inlet and outlet of chamber every 2 h over a 24 h period. Both of fasting and post-prandial TAN excretion increased with the increase of water temperature (P<0.05). Mean fasting TAN excretion rates at 15, 20 and 25℃ were 8.1, 9.0 and 9.2 mg TAN kg fish-1 h-1, respectively. The value of 15℃ was lower than those of 20 and 25℃ (P<0.05), but there was no significant difference between 20℃ and 25℃. Mean post-prandial TAN excretion rates at 15, 20 and 25℃ 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 hours from the first feeding at 15℃ (mean 28.7 mg TAN kg fish-1 h-1), 20℃ (33.7 mg TAN kg fish-1 h-1) and 25℃ (36.8 mg TAN kg fish-1 h-1), respectively. The TAN loss for ingested nitrogen at 15℃ (36.2%) was lower than that of 20℃ (40.8%) and 25℃ (41.7%). As overall results, water temperature exerts a profound influence on the nitrogen metabolism of juvenile dark-banded rockfish.2