THE EFFECTS OF HYPOPHYSECTOMY AND BOVINE PROLACTIN ON SALT FLUXES IN FRESH-WATER-ADAPTED FUNDULUS HETEROCLITUS W. T. W. POTTS AND D. H. EVANS Department of Zoology and Comparative Physiology, University of Birmingham, Birmingham, England, and Department of Biology, Stanford University, Stanford, California 94305 Some of the characteristics of salt balance in the euryhaline killifish Fundnlus heteroclitus have been outlined by us elsewhere (Potts and Evans, 1966). One of the major features of osmotic regulation in this fish is a marked reduction in the sodium and chloride fluxes on adaptation to fresh water. A similar reduction has been observed in several euryhaline teleosts including the stickleback Gasterosteus aculeatus (Mullins, 1950), the rainbow trout Salmo gairdneri (Gordon, 1962), Fundulus kansae (Fleming and Kamemoto, 1963), a blenny Blennius pholis (House, 1963) and the flounder Platichthys flessus (Motais and Maetz, 1964). Measurements of the drinking rate in Fundulus heteroclitus (Potts and Evans, 1966) and in Platichthys flessus' (Motais and Maetz, 1964) show that the larger part of the influx in sea water takes place through the body surface, not through the gut. The site of this influx is uncertain but may well be the gills. Whatever the site it is clear that the body surface of sea-water-adapted fish is relatively permeable to ions but the low fluxes found in fresh-water-adapted fish show that they are relatively impermeable to ions. Burden (1956) first demonstrated that hypophysectomized killifish were unable to survive in fresh water although they could survive in saline solutions. Later Pickford and Phillips (1959) showed that ovine prolactin promoted survival of hypophysectomized killifish in fresh water. Similar results have been obtained with several other genera including Mollienesia (Mollies) (Ball, 1962), Poecilia (Ball and Olivereau, 1964), Xiphophorus (platyfish and sword-tails) (Schreibman and Kallman, 1962) and Tilapia (Handin, Nandi and Bern, 1964). In addition Schreibman and Kallman (1962) and Ball et al. (1965) have demonstrated that pituitary transplants enable hypophysectomized fish to survive indefinitely in fresh water. Schreibman and Kallman (1966) have recently reviewed the problem of hypophysectomy and survival in fresh-water fishes. In the light of this evidence of the influence of prolactin on the osmoregulatory ability of teleosts the effects of hypophysectomy and prolactin on the salt fluxes of Fundulus have been examined. MATERIALS AND METHODS The fish used were Fundulus heteroclitus, weighing between 2 and 5 gm., collected by the Supply Department of the Woods Hole Marine Biological Labora-tory. Sea-water-adapted fish were kept in running sea water which varied slightly 362
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