jeered to haemorrhage, vasotocin could not be detected in the blood. Possibly isotocin appears under these conditions but this would not have been detectable by the
methods used .
c) Putative Endocrine Tissues in Fishes Possibly Involved in Osmoregulation
The caudal neurosecretory system (urophysis) and corpuscles of STANNIUS may
produce endocrine secretions that influence the electrolyte metabolism of some
fish . These tissues were introduced earlier (page 78).
a ) Urophysis. The caudal urophysial, or DAHLGREN cells of teleost, chondrostean
and chondrichthyean fishes react to changes in the osmotic environment (see FRIDBERG and BERN, 1968; and page 79). The evidence that they produce a secretion(s)
that influences osmoregulation is equivocal.
Some fish die more readily if they are transferred to strange osmotic situations
after their urophysis has been removed. Certain caudal neurosecretory fibres have
also been shown to respond to changes in the external salt concentration (YAGI
and BERN, 1963; 1965). Whether such responses reflect a reaction to specific stimuli
associated with osmoregulation is, nevertheless, not clear . The cichlid fish, Tiiapia
mossambica, and the stickleback, Gasterosteus acuieatus, suffer increased rates of
mortality when they are transferred from fresh water to saline solutions after extirpation of their urophyses (TAKASUGI and BERN, 1962; IRELAND, 1969). This effect in Tiiapia was not, however, found by STANLEY and FLEMING (1964) but it
is considered likely that the tissue may have regenerated in these fish. Recently
CHAN et al. (1969a) removed the urophysis from freshwater eels, but this did not
alter the renal losses of water or sodium, though urinary potassium, calcium and
magnesium excretion initially increased, but later subsided. Some interesting observations of the histological appearance of the urophysis of fish living in different
osmotic conditions have been made by FRIDBERG, BERN, and NISHIOKA (1966).
The Hawaiian 'oio', Albula uulpes, is often kept for extended periods of time in
salt-water ponds adjoining the sea. The salinity in these pools varies considerably,
due to evaporation and periodic flooding with fresh water. The fish kept under
these conditions were found to have a hyperactive caudal neurosecretory system
when compared with those taken directly from the sea. FRIDBERG et ai. consider
that this tissue may be involved in osmotic adaptations to the changes in salinity
which are continually taking place in the ponds.
Extracts of the urophysis have yielded materials that have been characterized
by a variety of biological actions. MAETZ et al. (1963) showed that extracts of the
goldfish urophysis, when injected into goldfish, promoted a (net) accumulation
of sodium by the fish. This was mainly due to an increased rate of uptake across
the gills, but there was also a decrease in the renal losses. This effect is not to be
confused with that of neurohypophysial peptides, which, although they stimulate
branchial sodium uptake in these fish, produce a net loss of this ion due to prominent urinary losses (MAETZ et al., 1964). LEDERIS (1969) has also demonstrated an
effect of urophysial extract on a piscine preparation; it contracts the urinary bladder
of the rainbow trout in vitro. Urophysial extracts from mullet, Mugil, and eels,
when injected into eels, elevate their blood pressure and produce an increased
244
methods used .
c) Putative Endocrine Tissues in Fishes Possibly Involved in Osmoregulation
The caudal neurosecretory system (urophysis) and corpuscles of STANNIUS may
produce endocrine secretions that influence the electrolyte metabolism of some
fish . These tissues were introduced earlier (page 78).
a ) Urophysis. The caudal urophysial, or DAHLGREN cells of teleost, chondrostean
and chondrichthyean fishes react to changes in the osmotic environment (see FRIDBERG and BERN, 1968; and page 79). The evidence that they produce a secretion(s)
that influences osmoregulation is equivocal.
Some fish die more readily if they are transferred to strange osmotic situations
after their urophysis has been removed. Certain caudal neurosecretory fibres have
also been shown to respond to changes in the external salt concentration (YAGI
and BERN, 1963; 1965). Whether such responses reflect a reaction to specific stimuli
associated with osmoregulation is, nevertheless, not clear . The cichlid fish, Tiiapia
mossambica, and the stickleback, Gasterosteus acuieatus, suffer increased rates of
mortality when they are transferred from fresh water to saline solutions after extirpation of their urophyses (TAKASUGI and BERN, 1962; IRELAND, 1969). This effect in Tiiapia was not, however, found by STANLEY and FLEMING (1964) but it
is considered likely that the tissue may have regenerated in these fish. Recently
CHAN et al. (1969a) removed the urophysis from freshwater eels, but this did not
alter the renal losses of water or sodium, though urinary potassium, calcium and
magnesium excretion initially increased, but later subsided. Some interesting observations of the histological appearance of the urophysis of fish living in different
osmotic conditions have been made by FRIDBERG, BERN, and NISHIOKA (1966).
The Hawaiian 'oio', Albula uulpes, is often kept for extended periods of time in
salt-water ponds adjoining the sea. The salinity in these pools varies considerably,
due to evaporation and periodic flooding with fresh water. The fish kept under
these conditions were found to have a hyperactive caudal neurosecretory system
when compared with those taken directly from the sea. FRIDBERG et ai. consider
that this tissue may be involved in osmotic adaptations to the changes in salinity
which are continually taking place in the ponds.
Extracts of the urophysis have yielded materials that have been characterized
by a variety of biological actions. MAETZ et al. (1963) showed that extracts of the
goldfish urophysis, when injected into goldfish, promoted a (net) accumulation
of sodium by the fish. This was mainly due to an increased rate of uptake across
the gills, but there was also a decrease in the renal losses. This effect is not to be
confused with that of neurohypophysial peptides, which, although they stimulate
branchial sodium uptake in these fish, produce a net loss of this ion due to prominent urinary losses (MAETZ et al., 1964). LEDERIS (1969) has also demonstrated an
effect of urophysial extract on a piscine preparation; it contracts the urinary bladder
of the rainbow trout in vitro. Urophysial extracts from mullet, Mugil, and eels,
when injected into eels, elevate their blood pressure and produce an increased
244