been tested. Aldosterone has not been found in the circulation of fish but when
thi s steroid is injected it, nevertheless, promotes accumulation of sodium across
the gills of eels (HENDERSON and CHESTER JONES, 1967) and goldfish (F AVRE, 1960)
and reduces the rate of branchial sodium loss in lampreys (BENTLEY and FOLLETT,
1962; 1963) (Table 7.10). Cortisol, wh ich appears in the circulation of fish , when
injected, increases sodium loss from the gills of eels but in small doses can promote
sodium accumulation in the hypophysectomized fish (HENDERSON and CHESTER
JONES, 1967). H ypophysectomy results in an increased rate of sodium loss in fish
and in many cases this can be prevented by the injection of prolactin (Table 7.11).
b) The Kidney
The kidney is not a major site for the exchange of osmotically important ions in
fish .
In sea-water, the flounder and sea perch excrete only about 0.1 % of the total
accumulated sodium in their urine (MOTAIS and MAETZ, 1965). When euryhaline
fish such as the flounder and eel are transferred from fresh water to sea-water the
total renal sodium and potassium excretion changes little, if anything it may decrease in the latter medium (Table 7.7). In fresh water, sodium and potassium are
lost in the copious dilute urine that is formed . In goldfish this daily sodium loss
equals about 8% of the total sodium in the body, an amount similar in magnitude
to the total accumulated by the fish (MAETZ, 1963). Lampreys lose a similar
proportion of their sodium in this manner. The pike, Esox lucius, loses as little as
0.02 % of its body sodium each day (HICKMAN, 1965). These renal losses can be
replaced by active branchial uptake of sodium, but in some feeding fish this may
not be necessary. Potassium is also excreted in the urine of fish but in smaller quantities than sodium. Eels and flounder in fresh water lose less than 0.1 % of their
total body potassium in th is way each day, and this declines in sea-water (Table
7.7). Urinary potassium losses in fasting fish probably largel y reflect those which
arise in the body as a result of tissue catabolism.
Fish that are feeding in fresh water may gain an excess of potassium in their
food , and the kidneys , most likely, have some role in its excretion . The kidneys
of fish do not appear to respond dramatically to excesses of sodi um chloride but
this is unlikely to occur in fresh water. HOLMES (1959) observed that sodium loads
were mainly excreted extrarenally in rainbow trout. The urinary losse s of sodium
are little affected when sodium chloride solutions are injected into goldfish, indeed
if these are hypertonic there is a decreased renal loss (BOURGUET et al., 1964). In
lampreys we (BENTLEY and FOLLETT, 1963) found that only 10% of a dose of injected sodium chloride was excreted in the urine after 24 hours.
Sodium is absorbed from the glomerular filtrate of fish. In the goldfish and lamprey 93% of this is reabsorbed (MAETZ, 1963; BENTLEY and FOLLETT, 1963) while
in the pike 99.95% may pass back into the plasma (HICKMAN , 1965). Potassium
is also reab sorbed from the glomerular filtrate of fish and as observed, for instance,
in the pike and the white sucker, Catostomus commersoni, it may be secreted into
the urine across the wall of renal tubules (HI CKMAN, 1965). The sites of such transfers along the renal tubules of fish are unknown and must await collection of this
225
thi s steroid is injected it, nevertheless, promotes accumulation of sodium across
the gills of eels (HENDERSON and CHESTER JONES, 1967) and goldfish (F AVRE, 1960)
and reduces the rate of branchial sodium loss in lampreys (BENTLEY and FOLLETT,
1962; 1963) (Table 7.10). Cortisol, wh ich appears in the circulation of fish , when
injected, increases sodium loss from the gills of eels but in small doses can promote
sodium accumulation in the hypophysectomized fish (HENDERSON and CHESTER
JONES, 1967). H ypophysectomy results in an increased rate of sodium loss in fish
and in many cases this can be prevented by the injection of prolactin (Table 7.11).
b) The Kidney
The kidney is not a major site for the exchange of osmotically important ions in
fish .
In sea-water, the flounder and sea perch excrete only about 0.1 % of the total
accumulated sodium in their urine (MOTAIS and MAETZ, 1965). When euryhaline
fish such as the flounder and eel are transferred from fresh water to sea-water the
total renal sodium and potassium excretion changes little, if anything it may decrease in the latter medium (Table 7.7). In fresh water, sodium and potassium are
lost in the copious dilute urine that is formed . In goldfish this daily sodium loss
equals about 8% of the total sodium in the body, an amount similar in magnitude
to the total accumulated by the fish (MAETZ, 1963). Lampreys lose a similar
proportion of their sodium in this manner. The pike, Esox lucius, loses as little as
0.02 % of its body sodium each day (HICKMAN, 1965). These renal losses can be
replaced by active branchial uptake of sodium, but in some feeding fish this may
not be necessary. Potassium is also excreted in the urine of fish but in smaller quantities than sodium. Eels and flounder in fresh water lose less than 0.1 % of their
total body potassium in th is way each day, and this declines in sea-water (Table
7.7). Urinary potassium losses in fasting fish probably largel y reflect those which
arise in the body as a result of tissue catabolism.
Fish that are feeding in fresh water may gain an excess of potassium in their
food , and the kidneys , most likely, have some role in its excretion . The kidneys
of fish do not appear to respond dramatically to excesses of sodi um chloride but
this is unlikely to occur in fresh water. HOLMES (1959) observed that sodium loads
were mainly excreted extrarenally in rainbow trout. The urinary losse s of sodium
are little affected when sodium chloride solutions are injected into goldfish, indeed
if these are hypertonic there is a decreased renal loss (BOURGUET et al., 1964). In
lampreys we (BENTLEY and FOLLETT, 1963) found that only 10% of a dose of injected sodium chloride was excreted in the urine after 24 hours.
Sodium is absorbed from the glomerular filtrate of fish. In the goldfish and lamprey 93% of this is reabsorbed (MAETZ, 1963; BENTLEY and FOLLETT, 1963) while
in the pike 99.95% may pass back into the plasma (HICKMAN , 1965). Potassium
is also reab sorbed from the glomerular filtrate of fish and as observed, for instance,
in the pike and the white sucker, Catostomus commersoni, it may be secreted into
the urine across the wall of renal tubules (HI CKMAN, 1965). The sites of such transfers along the renal tubules of fish are unknown and must await collection of this
225