碩士 國立中山大學 生物科學系研究所 103 Silver moony (Monodactylus argenteus) is a common aquarium ornamental species in Taiwan. Due to study on nitrite toxicity in silver moony is lack, an acute toxicity test was carried out by exposing the juvenile fish to 0, 25, 50, 75, 100 and 150 mg/L NO2−N for 96 h. The determined median lethal concentration (96 h - LC50) was 54.5 (42.5-67.9) mg/L NO2−N. The impacts of sublethal nitrite exposure were further investigated. After exposure to 28 mg/L (2 mM) NO2−N for 7 days, decrease of hepasomatic index and increase in plasma glucose levels, osmolality and chloride concentration were observed. Gill Na+/K+-ATPase (NKA) response elevated in silver moony when exposed to sublethal nitrite. In protein quality control (PQC) mechanism, expression of branchial and hepatic heat shock protein (HSP) 90 and 70 up-regulated in response to sublethal nitrite exposure while the levels of ubiquitin-conjugated proteins were constant. The present study showed that sublethal nitrite exposure might be a stressor to affect ionic balance and homeostasis of cellular proteins, and then activation of NKA responses and PQC mechanism was essential for ionoregulatory adjustment and protein stability. This study provided the information to clarify the potential treats of sublethal nitrite toxicity to multi-physiological regulation of seawater teleosts.