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ge 1. A. MADDEN AND A. H. HOUSTON
<br />Tissue water content and distribution. Tissue water tended to rise following electro-
<br />anaesthesia and to remain above the control value for most of the 24 h period of
<br />observation. This contrasts with the situation described earlier for the brook trout
<br />in which water content fluctuated irregularly with little evidence of a consistent trend.
<br />Both species were comparable in the sense that the apparent extracellular phase
<br />volume decreased transiently while the apparent volume of the cellular phase expanded
<br />during recovery. While these compartments tended to exhibit a smooth pattern of
<br />recovery in brook trout, both an extensive variation and marked oscillation were
<br />seen following electroanaesthesia.
<br />11
<br />rV. CONCLUSIONS
<br />Like chemical anaesthesia, electroanaesthesia prompts a variety of physiological
<br />changes in the trout. Electroanaesthesia apparently offers some advantages in that
<br />haemoconcentration is avoided or minimized. Deviations in some plasma and tissue
<br />electrolyte concentrations are of lesser magnitude and appear to return more rapidly
<br />to normal values. An advantage is also seen in the spontaneous resumption of
<br />cardiovascular-respiratory activity. This, coupled with the parallel variations seen
<br />in plasma levels of chloride and sodium, suggests that electroanaesthesia may be
<br />associated with less extensive variations in blood gas tensions and acid-base balance
<br />Ethan is the case with tricaine methane sulphonate (MS 222). Against this must be
<br />balanced the greater effects of electroanaesthesia upon some electrolytes and particu-
<br />larly upon water content and distribution. It is concluded that electroanaesthesia
<br />offers a useful, and in some circumstances, a preferable means for the anaesthetiza-
<br />tion of freshwater fishes.
<br />The authors wish to express their gratitude to Mr T. M. Linden for technical assistance in
<br />the design and construction of the electroanaesthesia probe used. The financial assistance
<br />Provided by the U.S. National Science Foundation operating grant G13-17142 is also grate-
<br />fully acknowledged.
<br />References
<br />Field, J. B., Elvejem, C. A. & Juday, C. (1943). A study of blood constituents of carp and
<br />trout. J. Biol. Chem. 148, 261-269.
<br />Garey, W. F. & Rahn, H. (1970). Normal arterial gas tensions and pH and the breathing
<br />frequency of the electric eel. Resp. Physiol. 9, 141-150.
<br />Houston, A. H., Madden, J. A., Woods, R. J. & Miles, H. M. (1971a). Some physiological
<br />effects of handling and tricaine methane sulphonate anesthetization upon the
<br />brook trout, Salvelinus fontinalis. A Fish. Res. Bd Canada 28, 625-633.
<br />Houston, A. H., Madden, J. A., Woods, R. J. & Miles, H. M. (1971b). Variations in the
<br />blood and tissue chemistry of brook trout, Salvelinus fondnalis, subsequent to handling
<br />anesthesia and surgery. J. Fish. Res. Bd Canada 28, 635-642.
<br />Houston; A. H. & Woods, R. J. (1972). Blood concentrations of tricaine methanesulphonate
<br />in brook trout, Salvelinus fontinalis during anesthetization, branchial irrigation and
<br />recovery. J. Fish. Res. Bd Canada 29, 1344-1346.
<br />Houston, A. H., Czerwinski, C. L. & Woods, R. J. (1973). Cardiovascular-respiratory
<br />activity during recovery from anesthesia and surgery in brook trout (Salvelinus
<br />fontinalis) and carp (Cyprinus carpio). J. Fish. Res. Bd Canada, 30, 1705-1712.
<br />Taylor, H. W., Houston, A. H. & Horgan, J. D. (1968). Development of a computer model
<br />simulating some aspects of the cardio-respiratory dynamics of the salmonid fish.
<br />J. exp. Biol., 49, 477-493.
<br />J. Fish Biol. (1976) 9, 463-470
<br />The effects of hypophysectomy, prolactin therapy and
<br />environmental calcium on freshwater survival and
<br />salinity tolerance in the brown trout Salmo trutta L.
<br />S. O. ODULEYE*
<br />Department of Biological Sciences,
<br />University of Lancaster, Lancaster, England
<br />(Accepted 15 June 1975)
<br />Hypophysectomy resulted in a loss of ability of the euryhaline salmonid, Salmo trutta to
<br />survive in fresh water. The mean survival time was 4-5 days. Maintenance in a medium
<br />containing 5 mm calcium increased the mean survival time to 8 days while 10 mM decreased
<br />it. Injection of 0.2 I.U./gm prolactin enabled hypophysectomized fish to survive the 2-week
<br />duration of the experiment.
<br />High environmental calcium, or pre-adaptation to a medium of high calcium, increased
<br />salinity tolerance of the brown trout probably by promoting a quick return of plasma
<br />electrolyte concentration to normal after transfer to sea water.
<br />I. INTRODUCTION
<br />All aquatic organisms maintain an internal environment which is different from their
<br />external environment and they regulate the passage of water and solutes between their
<br />interior and the exterior. The maintenance of a relatively stable body fluid compo-
<br />sition by euryhaline teleosts in varying salinities involves complex physiological func-
<br />tions first described by Smith (1930) and Krogh (1937).
<br />In higher vertebrates, such as the mammals, the complex processes of homeostasis
<br />are under hormonal control, particularly the pituitary hormones. The possibility of
<br />the pituitary involvement in teleost osmoregulation was first proposed by Fontaine,
<br />Callamand & Olivereau, (1949). Conclusive evidence for the involvement of the
<br />pituitary in teleost homeostasis comes from observations on the effects of hypo-
<br />physectomy. Most euryhaline teleosts lose their ability to survive in fresh water after
<br />hypopbysectomy, although they will live indefinitely in sea water. These include Betta
<br />splendens (Schreibman & Kallman, 1965), Tilapia mossambica (Dharmamba, et al.,
<br />1967), Fundulus heteroclitus (Burden, 1956), Poecilia latipinna (Ball & Olivereau, 1964)
<br />l and Ictalarus melas (Chidambaram, Meyer, & Hasler, 1972). A few teleosts (e.g.
<br />I goldfish Carassius auratus, eel Anguilla anguilla and the killifish Fundulus kansae)
<br />are able to survive in fresh water after hypophysectomy (Olivereau & Fontaine, 1965;
<br />Pickford, Robertson & Sawyer, 1966). In all cases of hypophysectomy, there is a
<br />sharp drop in plasma electrolyte level and osmolality (Olivereau & Ball, 1970) leading
<br />to gradual demineralization.
<br />Attempts have been made to demonstrate the pituitary hormones responsible for
<br />the survival of teleosts in fresh water. Pickford & Phillips (1959) were the first to
<br />'Present address: Department of Zoology, University of Ibadan, Ibadan, Nigeria.
<br />463
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