7.11). Extirpation of the pituitary gland from killifish, Fundulus heteroclitus, results
in their death within 10 days if they are kept in fresh water, though they survive
when in sea-water (BURDEN, 1956). Death in fresh water is accompanied by an excessive loss of salt from the body. In another species of killifish, Fundulus kansae,
hypophysectomy is not fatal but these fish, like eels, suffer a decline in their plasma
sodium levels when they are kept in fresh water (STANLEY and FLEMING, 1967a).
In other fishes including Poecilia (BALL and OLIVEREAU, 1964; BALL and ENSOR,
1967) and Tilapia (DHARMAMBA et al., 1967), hypophysectomy is fatal if the fish
are kept in fresh water and this is due to a loss of sodium. PICKFORD and PHILLIPS
in 1959 showed that the effects of hypophysectomy in Fundulus heteroclitus could
be overcome by injecting the fish with prolactin; no other pituitary hormones have
been found to be effective . This effect has since been confirmed in the other species
described above, but in the eel complete replacement is dependent on the additional
administration of corticotrophin (CHAN, CHESTER JONES, and MOSLEY, 1968).
Transplantation of the rostral parts of the fish adenohypophysis, rich in eta cells
but poor in other endocrine cells, ensures the survival of hypophysectomized Poecilia latipinna (BALL, 1965). Thus the adenohypophysial secretion prolactin ('paralactin') of teleost fish plays a vital role in their ability to adapt to fresh water, but
corticotrophin may also be involved. SCHREIBMAN and KALLIMAN (1966, 1969)
have demonstrated the fatal effects of hypophysectomy in more than a dozen species of teleosts kept in fresh water, indicating that the importance of this gland in
osmoregulation is widespread in this group. In contrast, hypophysectomy in the
cyclostome fish, Lampetra fluviatilis, has no adverse effect on its survival in fresh
water (LARSEN, 1969). These lampreys were in the fasting condition which they
exhibit after their migration to breed in fresh water and their survival was prolonged
after removal of the pituitary. This is due to a decrease in the rate of tissue cata -
bolism.
In spring, sticklebacks, Gasterosteus aculeatus, migrate from the sea into rivers
in order to breed. The following autumn they swim back into the sea where they
spend the winter. Such marine winter fish die if they are placed in fresh water. These
fish thus apparently undergo a cyclical change in their ability to tolerate salt solutions, just as observed in the steelhead trout described earlier. However, when
winter sticklebacks are injected with prolactin they can survive when placed in fresh
water (LAM and HOAR, 1967; LAM and LEATHERLAND, 1969). This fascinating observation suggests that such cyclical changes in salinity tolerance may reflect the
ability of these fish to synthesize or secrete 'paralactin'. In winter they may be
deficient in this hormone, but with the onset of spring it can be secreted and allow
the fish to make their annual nuptial migration into the rivers.
As the adrenocortical tissues influence the regulation of electrolytes in mam -
mals, the possible significance of the homologous interrenal tissues in osmoregulation of fish has been the source of speculation for some time . The interrenal tissues of teleost fish are rather diffuse in their distribution so that surgical
removal is very difficult. This operation has, nevertheless, been performed in eels
(CHESTER JONES, HENDERSON, and MOSLEY, 1964b) . The procedure involves the
removal of certain blood vessels to which the tissues are attached and replacement
of these with plastic tubing. This operation has since been slightly modified in
an effort to remove the last vestiges of the interrenal tissues (CHAN el al., 1967 a;
240
in their death within 10 days if they are kept in fresh water, though they survive
when in sea-water (BURDEN, 1956). Death in fresh water is accompanied by an excessive loss of salt from the body. In another species of killifish, Fundulus kansae,
hypophysectomy is not fatal but these fish, like eels, suffer a decline in their plasma
sodium levels when they are kept in fresh water (STANLEY and FLEMING, 1967a).
In other fishes including Poecilia (BALL and OLIVEREAU, 1964; BALL and ENSOR,
1967) and Tilapia (DHARMAMBA et al., 1967), hypophysectomy is fatal if the fish
are kept in fresh water and this is due to a loss of sodium. PICKFORD and PHILLIPS
in 1959 showed that the effects of hypophysectomy in Fundulus heteroclitus could
be overcome by injecting the fish with prolactin; no other pituitary hormones have
been found to be effective . This effect has since been confirmed in the other species
described above, but in the eel complete replacement is dependent on the additional
administration of corticotrophin (CHAN, CHESTER JONES, and MOSLEY, 1968).
Transplantation of the rostral parts of the fish adenohypophysis, rich in eta cells
but poor in other endocrine cells, ensures the survival of hypophysectomized Poecilia latipinna (BALL, 1965). Thus the adenohypophysial secretion prolactin ('paralactin') of teleost fish plays a vital role in their ability to adapt to fresh water, but
corticotrophin may also be involved. SCHREIBMAN and KALLIMAN (1966, 1969)
have demonstrated the fatal effects of hypophysectomy in more than a dozen species of teleosts kept in fresh water, indicating that the importance of this gland in
osmoregulation is widespread in this group. In contrast, hypophysectomy in the
cyclostome fish, Lampetra fluviatilis, has no adverse effect on its survival in fresh
water (LARSEN, 1969). These lampreys were in the fasting condition which they
exhibit after their migration to breed in fresh water and their survival was prolonged
after removal of the pituitary. This is due to a decrease in the rate of tissue cata -
bolism.
In spring, sticklebacks, Gasterosteus aculeatus, migrate from the sea into rivers
in order to breed. The following autumn they swim back into the sea where they
spend the winter. Such marine winter fish die if they are placed in fresh water. These
fish thus apparently undergo a cyclical change in their ability to tolerate salt solutions, just as observed in the steelhead trout described earlier. However, when
winter sticklebacks are injected with prolactin they can survive when placed in fresh
water (LAM and HOAR, 1967; LAM and LEATHERLAND, 1969). This fascinating observation suggests that such cyclical changes in salinity tolerance may reflect the
ability of these fish to synthesize or secrete 'paralactin'. In winter they may be
deficient in this hormone, but with the onset of spring it can be secreted and allow
the fish to make their annual nuptial migration into the rivers.
As the adrenocortical tissues influence the regulation of electrolytes in mam -
mals, the possible significance of the homologous interrenal tissues in osmoregulation of fish has been the source of speculation for some time . The interrenal tissues of teleost fish are rather diffuse in their distribution so that surgical
removal is very difficult. This operation has, nevertheless, been performed in eels
(CHESTER JONES, HENDERSON, and MOSLEY, 1964b) . The procedure involves the
removal of certain blood vessels to which the tissues are attached and replacement
of these with plastic tubing. This operation has since been slightly modified in
an effort to remove the last vestiges of the interrenal tissues (CHAN el al., 1967 a;
240