EFFECTS OF SALINITY ON CHLORIDE CELLS AND NA+, K+-ATPASE ACTIVITY IN THE TELEOST GILLICHTHYS-MIRABILIS

1. Longjawed mudsuckers, Gillichthys mirabilis, in 30 ppt seawater (SW) were transferred to 1.5, 30 and 60 ppt SW. 2. In the first 1-3 days after transfer, plasma chloride level and plasma osmolarity rose in the 60 ppt SW fish, and decreased in the 1.5 ppt SW fish. 3. By day 21, however, plasma chloride and osmolarity were at or near the levels seen in the controls (30 ppt). 4. Branchial and jawskin Na+, K+-ATPase activities were high in all salinities, and did not differ significantly among treatments. 5. The vital fluorescent stains DASPEI and anthroylouabain were used to detect mitochondria and Na+, K+-ATPase, respectively, in chloride cells. 6. Both stains indicated that jawskin chloride cell density did not differ among treatment groups. 7. In contrast, chloride cell size increased significantly with increasing salinity. 8. The chloride cells of fish in 60 ppt SW were noticeably angular in outline, whereas those of both the 1. 5 and 30 ppt SW fish were circular. 9. The results are discussed in relation to the ion transport requirements encountered in the intertidal habitat of the mudsucker.