EFFECTS OF GROWTH-HORMONE ON GILL CHLORIDE CELLS IN JUVENILE ATLANTICSALMON (SALMO-SALAR)

Experiments were performed to investigate the effects of ovine growth hormone (oGH) on both the ultrastructural features of chloride cells a nd the ability of gills to extrude Na+ after transfer into seawater. F ebruary presmolts and June parrs of the Atlantic salmon (Salmo salar) were implanted with oGH. In such animals, spontaneously showing a poor ability to adapt themselves to seawater Life, GH significantly increa sed gill Na+-K+-adenosinetriphosphatase activity as well as gill sodiu m efflux into seawater. When examined by electron microscope, two type s of chloride cells (alpha- and beta-types) were identified in control parrs and presmolts. GH treatment induced an increase in size and num ber of alpha-cells that displayed an extensive tubular system, while t he beta-cells, thought to be specific to freshwater life, decreased in number. There was, concomitantly, an increase in number of accessory cells associated with the apical portion of the alpha-cells and, as a result, the formation of extensive shallow junctions between these cel l types. Such functional and ultrastructural modifications that mimick ed those naturally occurring during the last steps of the smoltificati on strongly suggest that GH stimulates the differentiation of freshwat er chloride cells toward a seawater type.