3. FISH PROLACTIN AND GROWTH HORMONE
209
of mammalian prolactin (usually the ovine hormone) to teleosts. In this
review, these effects will be discussed in turn, roughly in the order of the
volume of research they have attracted.
B. Prolactin and Osmoregulation in Teleosts
The reader is referred to recent reviews for details that are beyond the
scope of this chapter (Ball, 1969; Ball and Ensor, 1969). As with so much
of modern fish endocrinology, this burgeoning research field stems from
the pioneering investigations of Dr. Grace E. Pickford (see Pickford and
Atz, 1957). Essentially, the situation at present is that certain euryhaline
teleosts, mainly cyprinodonts and other Atheriniformes ( Rosen, 1964),
but including at least two nonatherine species, Betta spkndens and
Tilapiu mossambica (Schreibman and Kallman, 1965; Dharmamba et al.,
1967), are unable to survive in freshwater after hypophysectomy for
more than a limited period (varying from 1 to 12 days); but they can live
for much longer, perhaps indefinitely, in seawater or dilute (1:3) seawater, or in a fish Ringer solution. In some cases (Fundulus heteroclitus,
Poecilia latipinnu, Xiphophorus muculatus, Gambusia sp., and Tilapia
mossambica ), injections of mammalian prolactin have been shown to
prevent this failure and to maintain hypophysectomized fish for long
periods in freshwater (Pickford and Phillips, 1959; Ball and Olivereau,
1964; Schreibman and Kallman, 1966; Chambolle, 1966; Handin et al.,
1964; Dharmamba et al., 1967).
Other teleosts, euryhaline or stenohaline, have been found able to live
in freshwater after hypophysectomy (see Ball, 1969), which perhaps
suggests that the prolactin-mimicked pituitary mechanism is unusual and
of only limited taxonomic distribution. However, investigations concerned
with electrolyte regulation, though limited in extent, point to a more
widespread mechanism, one that may not be essential for life in freshwater but which is necessary for normal electrolyte regulation in this
medium. The data on cyprinodonts indicates that the main deficiency
after hypophysectomy concerns conservation of electrolytes rather than
failure to excrete water; thus, in failing F. heteroclitus, the mean decrease
in serum osmolality or chloride content was about 40-6W, but the average
weight increase (presumably owing to water accumulation) was only
about 6-7%, and when hypophysectomized P . latipinnu fail in freshwater
the 25% or greater fall in plasma sodium occurs in the presence of normal
potassium levels, indicating that hemodilution is not a major factor in
failure.
Failing hypophysectomized F . heteroclitus exhibit a marked fall in
209
of mammalian prolactin (usually the ovine hormone) to teleosts. In this
review, these effects will be discussed in turn, roughly in the order of the
volume of research they have attracted.
B. Prolactin and Osmoregulation in Teleosts
The reader is referred to recent reviews for details that are beyond the
scope of this chapter (Ball, 1969; Ball and Ensor, 1969). As with so much
of modern fish endocrinology, this burgeoning research field stems from
the pioneering investigations of Dr. Grace E. Pickford (see Pickford and
Atz, 1957). Essentially, the situation at present is that certain euryhaline
teleosts, mainly cyprinodonts and other Atheriniformes ( Rosen, 1964),
but including at least two nonatherine species, Betta spkndens and
Tilapiu mossambica (Schreibman and Kallman, 1965; Dharmamba et al.,
1967), are unable to survive in freshwater after hypophysectomy for
more than a limited period (varying from 1 to 12 days); but they can live
for much longer, perhaps indefinitely, in seawater or dilute (1:3) seawater, or in a fish Ringer solution. In some cases (Fundulus heteroclitus,
Poecilia latipinnu, Xiphophorus muculatus, Gambusia sp., and Tilapia
mossambica ), injections of mammalian prolactin have been shown to
prevent this failure and to maintain hypophysectomized fish for long
periods in freshwater (Pickford and Phillips, 1959; Ball and Olivereau,
1964; Schreibman and Kallman, 1966; Chambolle, 1966; Handin et al.,
1964; Dharmamba et al., 1967).
Other teleosts, euryhaline or stenohaline, have been found able to live
in freshwater after hypophysectomy (see Ball, 1969), which perhaps
suggests that the prolactin-mimicked pituitary mechanism is unusual and
of only limited taxonomic distribution. However, investigations concerned
with electrolyte regulation, though limited in extent, point to a more
widespread mechanism, one that may not be essential for life in freshwater but which is necessary for normal electrolyte regulation in this
medium. The data on cyprinodonts indicates that the main deficiency
after hypophysectomy concerns conservation of electrolytes rather than
failure to excrete water; thus, in failing F. heteroclitus, the mean decrease
in serum osmolality or chloride content was about 40-6W, but the average
weight increase (presumably owing to water accumulation) was only
about 6-7%, and when hypophysectomized P . latipinnu fail in freshwater
the 25% or greater fall in plasma sodium occurs in the presence of normal
potassium levels, indicating that hemodilution is not a major factor in
failure.
Failing hypophysectomized F . heteroclitus exhibit a marked fall in