3. FISH PROLACI'lh? AND GROWTH HORMONE
229
F. heteroclitus showed that removal of the pituitary led to failure of formation of new circuli (growth rings) on the scales, corresponding to
cessation of body growth ( Pickford, 1953a). Administration of beef GH
to hypophysectomized fish elicits a resumption of scale growth which
starts with formation of an irregular zone resembling the year mark (Pickford, 1953b, 1954a), and which shows an approximate correlation between the body length increment and the member of new circuli formed
on the scales (Pickford, 1957). Furthermore, Swift and Pickford (1965)
showed that although a body length increment of 3% was required before
any scale growth was detectable, length increments greater than 3% were
associated with proportional increases in scale width. These experimental
findings thus support some of the main assumptions on which a great deal
of fishery biology work is based, that is, the existence of a direct correlation between body growth and scale growth, and a correspondence between spacing of circuli and rate of body growth (see, e.g., Ball and
Jones, 1960, 1962; Ball, 1961). As Pickford ( 1959) pointed out, since temperature affects the response of hypophysectomized killifish to GH,
temperature is probably an environmental factor involved in the establishment of the usual seasonal pattern of scale and body growth in temperate
zone fishes. In addition, food supply (which may be controlled by temperature) may determine the growth pattern in some species in some
environments ( see Pickford, 1957). The importance of the annual changes
in day length as an environmental governor of the annual growth cycle
was suggested by a field study of a population of brown trout, Salmo
trutta (Ball, 196l), but experimental studies on the effects of day length
on fish GH secretion have not been undertaken.
D. Metabolic Effects of GH in Fishes
Beef GH rapidly improves the appetite of hypophysectomized F.
heteroclitw ( Pickford, 1957), which suggests some stimulation of metabolism preceding the growth response. Unfortunately, there are no reported detailed studies of this aspect of GH physiology in teleosts. After
hypophysectomy, the liver in killifish increases in size and is laden with
fat and glycogen (Pickford, 1953a), and GH did not reduce liver size or
stores in hypophysectomized fish ( Pickford, 1953b). Hypophysectomized
Poeciliu also have enlarged livers with increased glycogen stores (Ball
et al., 1965, 1966b), and GH did not reduce liver size or glycogen stores,
although ACTH was effective on both counts (Ball et al., 1966b; Ball,
1968). Matty ( 1962) has reported nitrogen retention following injection
of GH into intact Cottus, which is in line with the protein anabolic effects
229
F. heteroclitus showed that removal of the pituitary led to failure of formation of new circuli (growth rings) on the scales, corresponding to
cessation of body growth ( Pickford, 1953a). Administration of beef GH
to hypophysectomized fish elicits a resumption of scale growth which
starts with formation of an irregular zone resembling the year mark (Pickford, 1953b, 1954a), and which shows an approximate correlation between the body length increment and the member of new circuli formed
on the scales (Pickford, 1957). Furthermore, Swift and Pickford (1965)
showed that although a body length increment of 3% was required before
any scale growth was detectable, length increments greater than 3% were
associated with proportional increases in scale width. These experimental
findings thus support some of the main assumptions on which a great deal
of fishery biology work is based, that is, the existence of a direct correlation between body growth and scale growth, and a correspondence between spacing of circuli and rate of body growth (see, e.g., Ball and
Jones, 1960, 1962; Ball, 1961). As Pickford ( 1959) pointed out, since temperature affects the response of hypophysectomized killifish to GH,
temperature is probably an environmental factor involved in the establishment of the usual seasonal pattern of scale and body growth in temperate
zone fishes. In addition, food supply (which may be controlled by temperature) may determine the growth pattern in some species in some
environments ( see Pickford, 1957). The importance of the annual changes
in day length as an environmental governor of the annual growth cycle
was suggested by a field study of a population of brown trout, Salmo
trutta (Ball, 196l), but experimental studies on the effects of day length
on fish GH secretion have not been undertaken.
D. Metabolic Effects of GH in Fishes
Beef GH rapidly improves the appetite of hypophysectomized F.
heteroclitw ( Pickford, 1957), which suggests some stimulation of metabolism preceding the growth response. Unfortunately, there are no reported detailed studies of this aspect of GH physiology in teleosts. After
hypophysectomy, the liver in killifish increases in size and is laden with
fat and glycogen (Pickford, 1953a), and GH did not reduce liver size or
stores in hypophysectomized fish ( Pickford, 1953b). Hypophysectomized
Poeciliu also have enlarged livers with increased glycogen stores (Ball
et al., 1965, 1966b), and GH did not reduce liver size or glycogen stores,
although ACTH was effective on both counts (Ball et al., 1966b; Ball,
1968). Matty ( 1962) has reported nitrogen retention following injection
of GH into intact Cottus, which is in line with the protein anabolic effects