Branchial Na(+)K(+)ATPase activity in brook charr (Salvelinus fontinalis):Effect of gonadal development in hypo- and hyperosmotic environments

Changes in gill Na(+)K(+)ATPase activity were examined following the transf er of brook charr (Salvelinus fontinalis) from fresh water (FW) to seawater (SW). Gonadal development was altered at the hatching stage using three do ses of ionizing radiation (IR): 6.2, 7.8, and 11.4 Gray (Gy). A non-irradia ted control group was also included in the experimental set-up. Following 1 5 and 19 months of growth in FW, assessment of gill activity in regard to g onadal status (sterile vs. mature) and level of IR exposure was realized by conducting two estuarine challenge tests. A first introduction was perform ed during June (period of highest osmoregulatory capacities for this specie s) (summer experiment). A second introduction was conducted during October (period of diminished osmoregulatory capacities) (fall experiment). Gill Na (+)K(+)ATPase activity and water content were measured at different times a nd two FW control samplings were added in October and January. In the summe r experiment (June-December), normal gonadal development of female brook ch arr was related to reduced gill Na(+)K(+)ATPase activity during the spawnin g period as compared to sterile fish (4.0 +/- 1.5 and 7.2, 1.9 mu mole Pi . mg protein(-1) . hr(-1)) (P < 0.0002). Similar results were not observed i n FW conditions, implying that a lack of gonadal growth does not initiate a significant advantage when the osmoregulatory system including the gills a re not highly in demand, i.e. in a FW environment. Ionizing radiation expos ure of I 11.4 Gy at the hatching stage had no significant negative or posit ive effect on Na+K+ATPase activity either in FW or SW conditions. J. Exp. Z ool. 286:647-655, 2000. (C) 2000 Wiley-Liss, Inc.