228
J. N. BALL
providing optimal living conditions in order to obtain a good response to
GH, and also the necessity of avoiding too frequent handling or other
stressful procedures which oppose the growth response ( Pickford, 1953b,
1957). The response of hypophysectomized killifish to a standard dose of
beef GH is temperature-dependent, little or no significant length increment being obtained below 15"C, with an optimum plateau for the response between 20" and 25°C ( Pickford, 1957, 1959). Standard beef GH
causes a linear log dose response in the length increase of hypophysectomized killifish (Pickford, 1959) over a dose range from 3 to 30 pg/g
body weight, a finding which permits the bioassay of fish GH in hypophysectomized F. heteroclitus (Swift and Pickford, 1965). The slope of the
log dose growth response is influenced by time after hypophysectomy
among other factors ( Pickford et al., 1959). Hypophysectomized killifish
also respond with linear growth to pig, sheep, monkey, and human GH
(Pickford et al., 1959).
In hypophysectomized P. lutipinna and P. formosa pig and beef GH,
respectively, can induce linear growth; but the responses have not yet
been studied systematically ( Ball, 1968).
Hypophysectomized F. heteroclitis are also reponsive to a purified
crystalline fish GH isolated from glands of pollack, hake, and cod by
Wilhelmi ( 1955). In demonstrating this response, Pickford ( 195aa) found
that even the most highly purified fish GH was less potent that the equivalent dose of beef GH. This may be because the beef GH contained traces
of TSH, which maintained the thyroid, whereas the fish GH preparation
had no stimulatory effect on the regressed thyroid of the hypophysectomized recipient fish ( Pickford, 1954a). This thyroid stimulation probably
potentiated the growth-promoting action of the beef GH, since although
TSH alone has no growth-promoting activity ( Pickford, 1954b) , the addition of small amounts of TSH to hake GH significantly augmented the
growth response in hypophysectomized killifish ( Pickford, 1957).
By bioassay on hypophysectomized F. heteroclitus, Swift and Pickford
(1965) have estimated the GH content of the pituitary of the perch,
Perca fluviatilis, during the annual cycle in Windermere. They found that
during the winter, when the perch do not grow appreciably, the pituitary
contained a low resting level of GH. The GH content of the gland increased in the spring and reached a maximum in June, at about the time
of onset of the natural growth period in Windermere, and then fell to a
very low level in August. This depletion of pituitary GH store corresponded to the period of most rapid growth in the natural cycle and presumably reflects the fact that at this time rapid secretion of the hormone
is only just balanced by synthesis, and little is stored.
A point of special interest to fisheries biologists is that this work on
J. N. BALL
providing optimal living conditions in order to obtain a good response to
GH, and also the necessity of avoiding too frequent handling or other
stressful procedures which oppose the growth response ( Pickford, 1953b,
1957). The response of hypophysectomized killifish to a standard dose of
beef GH is temperature-dependent, little or no significant length increment being obtained below 15"C, with an optimum plateau for the response between 20" and 25°C ( Pickford, 1957, 1959). Standard beef GH
causes a linear log dose response in the length increase of hypophysectomized killifish (Pickford, 1959) over a dose range from 3 to 30 pg/g
body weight, a finding which permits the bioassay of fish GH in hypophysectomized F. heteroclitus (Swift and Pickford, 1965). The slope of the
log dose growth response is influenced by time after hypophysectomy
among other factors ( Pickford et al., 1959). Hypophysectomized killifish
also respond with linear growth to pig, sheep, monkey, and human GH
(Pickford et al., 1959).
In hypophysectomized P. lutipinna and P. formosa pig and beef GH,
respectively, can induce linear growth; but the responses have not yet
been studied systematically ( Ball, 1968).
Hypophysectomized F. heteroclitis are also reponsive to a purified
crystalline fish GH isolated from glands of pollack, hake, and cod by
Wilhelmi ( 1955). In demonstrating this response, Pickford ( 195aa) found
that even the most highly purified fish GH was less potent that the equivalent dose of beef GH. This may be because the beef GH contained traces
of TSH, which maintained the thyroid, whereas the fish GH preparation
had no stimulatory effect on the regressed thyroid of the hypophysectomized recipient fish ( Pickford, 1954a). This thyroid stimulation probably
potentiated the growth-promoting action of the beef GH, since although
TSH alone has no growth-promoting activity ( Pickford, 1954b) , the addition of small amounts of TSH to hake GH significantly augmented the
growth response in hypophysectomized killifish ( Pickford, 1957).
By bioassay on hypophysectomized F. heteroclitus, Swift and Pickford
(1965) have estimated the GH content of the pituitary of the perch,
Perca fluviatilis, during the annual cycle in Windermere. They found that
during the winter, when the perch do not grow appreciably, the pituitary
contained a low resting level of GH. The GH content of the gland increased in the spring and reached a maximum in June, at about the time
of onset of the natural growth period in Windermere, and then fell to a
very low level in August. This depletion of pituitary GH store corresponded to the period of most rapid growth in the natural cycle and presumably reflects the fact that at this time rapid secretion of the hormone
is only just balanced by synthesis, and little is stored.
A point of special interest to fisheries biologists is that this work on