Cells with Affinity for Periodic Acid - Schiff Are Present in the Pars-Intermedia of Atlantic Salmon

Abstract

Examination of pituitaries from two populations of Atlantic salmon (Salmo salar) parr held under natural photoperiods revealed at least two histologically distinct cell types. One type has fine granules with affinity for lead hematoxylin (PIPbH). Another type, hitherto believed to be absent in salmonids, has larger granules which are Schiff-positive (PIPAS). These cells are significantly (P < 0.05) shorter and narrower and have significantly smaller nuclei (P < 0.05) than the PIPbH type. No evidence was found for ascribing to the PIPAS cells the functions assigned to them in other species: melanophore control and reproduction. However, PIPAS granules became evident only during fall-winter, when the smolting process begins. The incidence of these cells rose and then declined sharply during this period, suggesting a possible role in some aspect of smoltification. While the role of these PIPAS cells deserves further study, their presence is in itself important from an evolutionary point of view.