Changes in Gill Adenosinetriphosphatase Activity Associated with Parr–Smolt Transformation in Steelhead Trout, Coho, and Spring Chinook Salmon

Abstract

The average Na⁺- and K⁺-stimulated adenosinetriphosphatase (ATPase) activity of microsomes from gills of hatchery-reared coho salmon (Oncorhynchus kisutch) increased from about 12 μmoles ATP hydrolyzed/mg protein per hr during February through mid-April to approximately 24 in mid-May. Larger fish developed higher activities than smaller fish. Hatchery-reared spring chinook salmon (O. tshawytscha) exhibited a similar increase 2–3 weeks earlier.In 2-year-old hatchery-reared steelhead trout (Salmo gairdneri), Na⁺-, K⁺-ATPase activities were elevated in some, but not all, smolt-appearing animals. Parr-appearing fish, including maturing males, showed no activity increase. When held in fresh water to July, steelhead smolts lost their silvery color and became more parr-like in appearance, and the previously elevated ATPase activity decreased to near pre-smolt levels. Yearling steelhead held at the laboratory showed a more consistent rise in ATPase activity.The increase in transport ATPase (Na⁺-, K⁺-stimulated) activity occurring during parr–smolt transformation is probably a preparatory step for saltwater adaption and may also be closely associated with migratory disposition.L'activité moyenne de l'adénosinetriphosphatase (ATPase) stimulée par Na⁺ et K⁺ dans les microsomes des branchies de saumons coho (Oncorhynchus kisutch) élevés en pisciculture augmente de 12 μmoles environ d'ATPase hydrolysée/mg de protéine par h de février à la mi-avril à 24 à la mi-mai. Les gros poissons développent une activité plus grande que les petits. Les saumons chinook de printemps (O. tshawytscha) élevés en pisciculture font preuve d'un accroissement semblable deux à trois semaines avant les saumons coho.