볼락 Sebastes inermis 치어의 암모니아 배설에 미치는 수온의 영향

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: <TEX>$14.8{\pm}0.3g$</TEX>) under fasting and feeding conditions. Fish were acclimated over 10 days under three different water temperatures (15, 20 and <TEX>$25^{\circ}C$</TEX>). 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 <TEX>$25^{\circ}C$</TEX> were 8.1, 9.0 and 9.2 mg TAN kg <TEX>$fish^{-1}h^{-1}$</TEX>, respectively. The value of <TEX>$15^{\circ}C$</TEX> was lower than those of 20 and <TEX>$25^{\circ}C$</TEX> (P<0.05), but there was no significant difference between <TEX>$20^{\circ}C$</TEX> and <TEX>$25^{\circ}C$</TEX> (P>0.05). Mean post-prandial TAN excretion rates at 15, 20 and <TEX>$25^{\circ}C$</TEX> were 20.1, 22.9 and 23.4 mg TAN kg <TEX>$fish^{-1}h^{-1}$</TEX>, respectively. A peak post-prandial TAN excretion rate occurred after 12 hrs from the first feeding at <TEX>$15^{\circ}C$</TEX> (mean 28.7 mg TAN kg <TEX>$fish^{-1}h^{-1}$</TEX>), <TEX>$20^{\circ}C$</TEX> (33.7 mg TAN kg <TEX>$fish^{-1}h{-1}$</TEX>) and <TEX>$25^{\circ}C$</TEX> (36.8 mg TAN kg <TEX>$fish^{-1}h{-1}$</TEX>), respectively. The TAN loss for ingested nitrogen at <TEX>$15^{\circ}C$</TEX> (36.2%) was lower than that of <TEX>$20^{\circ}C$</TEX> (40.8%) and <TEX>$25^{\circ}C$</TEX> (41.7%). Based on overall results, water temperature exerts a profound influence on the nitrogen metabolism of juvenile dark-banded rockfish.