Plasma thyroxine and cortisol profiles and gill and kidney Na+/K+-ATPase and SDH activities during acclimation of the catfish Heteropneustes fossilis (bloch) to higher salinity, with special reference to the effects of exogenous cortisol on hypo-osmoregulatory ability of the catfish.
When the stenohaline catfish Heteropneustes fossilis was transferred from fresh water (FW) to 30% seawater (SW), the Na(+)/K(+)-ATPase activity significantly increased in the kidney, while in gills it remained more or less constant. A reverse pattern was observed for succinic dehydrogenase (SDH) activity inasmuch as it significantly increased in gills and remained unchanged in the kidney. Plasma osmolality significantly increased within 3 days of transfer to 30% SW and remained significantly higher throughout the duration of experiment. These results suggest that catfish gills may not be able to reverse their function from salt uptake in FW to salt excretion at higher salinity, and that the elimination of monovalent as well as divalent ions is performed by the kidney but not the gills. The significant decline in plasma cortisol (F) levels following transfer to higher salinity may not be due to reduced production but rather to an enhanced utilization and clearance rate, a conclusion supported by the fact that exogenous administration of cortisol acetate (FA) resulted in significant increases in branchial and renal Na(+)/K(+)-ATPase in FW and 30% SW. FA also improved the plasma osmotic regulatory ability of the catfish, possibly due to a change in branchial function from salt-absorption to salt excretion, as was evident from a significant increase in branchial Na(+)/K(+)-ATPase activity in the fish in 30% SW pretreated with FA for 5 days. Consistently higher levels of plasma thyroxine (T4) following transfer to higher salinity suggest the involvement of this hormone at higher salinity.
Department of Zoology, Aligarh Muslim University, Aligarh-202 002, India.
Fauzia Anwar
FA
Sherwani
Iqbal
I
Parwez
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D002397:Catfishes / Q000097:blood / Q000378:metabolism*; D005618:Fresh Water / Q000737:chemistry; D005880:Gills / Q000201:enzymology*; D006854:Hydrocortisone / Q000097:blood / Q000494:pharmacology; D007668:Kidney / Q000201:enzymology*; D012623:Seawater / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013312:Stress, Physiological; D013385:Succinate Dehydrogenase / Q000378:metabolism*; D013974:Thyroxine / Q000097:blood; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology
D012965:Sodium Chloride; D013385:Succinate Dehydrogenase; D000254:Sodium-Potassium-Exchanging ATPase; D013974:Thyroxine; D006854:Hydrocortisone