222
J. N. BALL
water for spawning, and they compare this postulated action of prolactin
with the newt water-drive effect (Section I, A ) . In both cichlids and
Casterosteus, the critical experiments involving hypophysectomy and
treatment with prolactin remain to be done before we may feel certain
that fish prolactin is physiologically involved in inducing egg fanning or
migratory behavior ( see also chapter by Liley, Volume 111).
By far the most complete evidence of the participation of fish prolactin
in aspects of parental care comes from an extensive series of investigations
on the sea horse, Hippocampus, by Boisseau ( 1964,1965,1967). The male
Hippocampus incubates developing eggs in a ventral pouch (marsupium), the development of which is under testicular and gonadotropic
control, The maintenance of the connective tissue structure of the marsupium during incubation appears to depend upon ACTH and corticosteroids. During the incubation, the epithelial lining of the marsupium
proliferates and secretes a protease which breaks down proteins that are
present in the marsupial fluid and derive from the yolk of early developing eggs; the amino acids released are probably absorbed by the embryos.
As it were, the embryo sits in a nutrient broth which is predigested for its
consumption by a paternal enzyme. Secretion of the protease is arrested
by hypophysectomy of the father, and the operation also leads to histological regression of the marsupial epithelium. Prolactin treatment of both
intact and hypophysectomized fish leads to strong histological stimulation
of the marsupial epithelium, and in the intact fish it was shown to accelerate secretion of the protease. The physiological role of fish prolactin
implied by these findings was confirmed by Boisseau (1%7), who showed
by partial hypophysectomy that the endogenous hormone responsible for
maintenance of the marsupial epithelium originated from the rostra1 pars
distalis, known to be the part of the fish pituitary concerned with paralactin secretion ( see chapter by Ball and Baker, Volume 11). Boisseau also
demonstrated that the T, I (paralactin) cells in this region of the gland
displayed cyclical variations in activity which correlated closely with
the development and secretory activity of the marsupial epithelium. The
importance of this most interesting work on Hippocampus cannot be
overemphasized, and it constitutes the most satisfactory demonstration
of a parental role for fish prolactin. It may be significant that this parental
role is in a marine teleost, in which possibly the hormone is not concerned
with regulation of electrolyte exchanges across the body surface (Section
I, B; cf. Ball, 1969).
Other actions of prolactin in the sexual rather than the parental phase
of fish reproduction have been described. The male Indian catfish, Heteropneustes fossilis, has well-developed seminal vesicles that change seasonally in rhythm with the testicular cycle. The seminal vesicles regressed
J. N. BALL
water for spawning, and they compare this postulated action of prolactin
with the newt water-drive effect (Section I, A ) . In both cichlids and
Casterosteus, the critical experiments involving hypophysectomy and
treatment with prolactin remain to be done before we may feel certain
that fish prolactin is physiologically involved in inducing egg fanning or
migratory behavior ( see also chapter by Liley, Volume 111).
By far the most complete evidence of the participation of fish prolactin
in aspects of parental care comes from an extensive series of investigations
on the sea horse, Hippocampus, by Boisseau ( 1964,1965,1967). The male
Hippocampus incubates developing eggs in a ventral pouch (marsupium), the development of which is under testicular and gonadotropic
control, The maintenance of the connective tissue structure of the marsupium during incubation appears to depend upon ACTH and corticosteroids. During the incubation, the epithelial lining of the marsupium
proliferates and secretes a protease which breaks down proteins that are
present in the marsupial fluid and derive from the yolk of early developing eggs; the amino acids released are probably absorbed by the embryos.
As it were, the embryo sits in a nutrient broth which is predigested for its
consumption by a paternal enzyme. Secretion of the protease is arrested
by hypophysectomy of the father, and the operation also leads to histological regression of the marsupial epithelium. Prolactin treatment of both
intact and hypophysectomized fish leads to strong histological stimulation
of the marsupial epithelium, and in the intact fish it was shown to accelerate secretion of the protease. The physiological role of fish prolactin
implied by these findings was confirmed by Boisseau (1%7), who showed
by partial hypophysectomy that the endogenous hormone responsible for
maintenance of the marsupial epithelium originated from the rostra1 pars
distalis, known to be the part of the fish pituitary concerned with paralactin secretion ( see chapter by Ball and Baker, Volume 11). Boisseau also
demonstrated that the T, I (paralactin) cells in this region of the gland
displayed cyclical variations in activity which correlated closely with
the development and secretory activity of the marsupial epithelium. The
importance of this most interesting work on Hippocampus cannot be
overemphasized, and it constitutes the most satisfactory demonstration
of a parental role for fish prolactin. It may be significant that this parental
role is in a marine teleost, in which possibly the hormone is not concerned
with regulation of electrolyte exchanges across the body surface (Section
I, B; cf. Ball, 1969).
Other actions of prolactin in the sexual rather than the parental phase
of fish reproduction have been described. The male Indian catfish, Heteropneustes fossilis, has well-developed seminal vesicles that change seasonally in rhythm with the testicular cycle. The seminal vesicles regressed