Higher Salinity Environmental Adaptations in Clarias batrachus: Biochemical and Physiological Roles of Hormones (Cortisol and Thyroxine) and Enzymes (Na+/K+-ATPase and Succinic dehydrogenase)
摘要
Salinity is a critical environmental factor that affects metabolism through osmoregulation in all aquatic animals including fishes that serve as an important food source for human beings and a significant indicator of environmental health. The present study investigated the effects of higher salinity on various osmoregulatory parameters of a freshwater stenohaline catfish, Clarias batrachus. Upon being transferred from tap water (TW) to 30% and 35% sea water (SW), Clarias batrachus showed significantly decreased plasma cortisol levels while plasma thyroxine (T4) titres exhibited a significant increase. These biochemical and physiological changes suggest a significant role that these hormones may play at higher salinities. The sodium potassium-dependent adenosine triphosphatase (Na+/K+-ATPase) activity was shown to be significantly higher at the renal level but remained more or less unchanged at the branchial level when the catfish was transferred from TW to higher salinities. On the other hand, succinic dehydrogenase (SDH) activity displayed a contradictory effect and was found to be significantly increased at branchial level but remained more or less constant at the renal level. Plasma osmolality values were also observed to be significantly increased upon transfer of C. batrachus to 30% and 35% SW. These observations suggested that the gills of the catfish may be incapable of altering their function associated with salt absorption in fresh water (FW) to salt-elimination following transfer to higher salinities and that the kidney alone is involved in the excretion of both monovalent and divalent ions. These findings indicated that higher salinities have a profound effect on the osmoregulatory physiology of C. batrachus.