4. THYROID FUNCTION AND ITS CONTROL IN FISHES
263
mone in the process. La Roche et al. (1966b), who studied trout in particular, concluded: “It remains to be demonstrated that thyroid hormone
administrations will stimulate overall growth in the presence of adequate
iodine intake and thyroid function.” This statement is made in the face of
claims by Smith and Everett (1943), Smith et al. ( 1953), Barrington et
al. ( 1961), Piggins ( 1962), Hopper ( 1952), Gross et al. ( 1963), and
Bjorklund ( 1965) who administered thyroid hormones in various forms
to rainbow trout, guppies, sunfish, goldfish, and young salmon and found
some growth stimulation. Hoar’s review (1957) also expresses uncertainty
concerning the role of thyroid hormone in teleostean growth, and the
earlier data are summarized by Pickford and Atz (1957), Baker-Cohen
(1961), and Olivereau (1957). It should be mentioned that thyroid treatment of some fish retards growth rate (e.g., Dales and Hoar, 1954; Honma
and Murakawa, 1955; La Roche and Leblond, 1952). It may be that
thyroid hormone plays a permissive role in growth regulation of fishes,
as it does in mammals. If so, the analysis of its role in growth may require
more complex experimental design for final definition. Furthermore, as
La Roche et al. (1966b) point out, “chemical thyroidectomy” with goitrogens and radiothyroidectomy (Baker et al., 1955a; Baker-Cohen, 1961;
La Roche and Leblond, 1954; La Roche et al., 1965, 1966a), which inhibit growth, have toxic effects which have not been evaluated adequately
in interpreting their action.
If the complex character of general body growth resists a definition of
thyroxine’s role in it, a somewhat more satisfactory situation obtains when
we consider structural changes in individual systems or organs. It is clear
that skeletal elements, for example, are responsive to thyroid state in
teleosts. Gerbilsky and Saks (1947) have observed accelerated scale and
bone plate formation in thyroxinized sturgeon. La Roche et al. (196Sb),
and in earlier papers of La Roche, specific effects of both thyroidectomy
and thyroxine administration on phases of skeletal growth, calcification,
and differentiation have been described in salmonids. Baker-Cohen
( 1961 ) also observed skeletal changes in radiothyroidectomized platyfish.
In this context, it is of interest that Barrington and Rawdon (1967) found
that thyroxine favors the uptake and incorporation of radiosulfur into the
skeleton of trout.
The positive relationship of thyroid state to integumentary silvering
has been mentioned above. La Roche et al. (196613) have noted the increased melanin pigmentation of the skin of radiothyroidectomized trout
and have found that it is the result of an increased number of melanophores per unit of skin area. Sembrat (1956), using thiouracil, found
increased pigmentation in skin of the carp. Belsare et al. (1966) showed
that in larval Channa punctatus, thiourea not only favors increased in-
263
mone in the process. La Roche et al. (1966b), who studied trout in particular, concluded: “It remains to be demonstrated that thyroid hormone
administrations will stimulate overall growth in the presence of adequate
iodine intake and thyroid function.” This statement is made in the face of
claims by Smith and Everett (1943), Smith et al. ( 1953), Barrington et
al. ( 1961), Piggins ( 1962), Hopper ( 1952), Gross et al. ( 1963), and
Bjorklund ( 1965) who administered thyroid hormones in various forms
to rainbow trout, guppies, sunfish, goldfish, and young salmon and found
some growth stimulation. Hoar’s review (1957) also expresses uncertainty
concerning the role of thyroid hormone in teleostean growth, and the
earlier data are summarized by Pickford and Atz (1957), Baker-Cohen
(1961), and Olivereau (1957). It should be mentioned that thyroid treatment of some fish retards growth rate (e.g., Dales and Hoar, 1954; Honma
and Murakawa, 1955; La Roche and Leblond, 1952). It may be that
thyroid hormone plays a permissive role in growth regulation of fishes,
as it does in mammals. If so, the analysis of its role in growth may require
more complex experimental design for final definition. Furthermore, as
La Roche et al. (1966b) point out, “chemical thyroidectomy” with goitrogens and radiothyroidectomy (Baker et al., 1955a; Baker-Cohen, 1961;
La Roche and Leblond, 1954; La Roche et al., 1965, 1966a), which inhibit growth, have toxic effects which have not been evaluated adequately
in interpreting their action.
If the complex character of general body growth resists a definition of
thyroxine’s role in it, a somewhat more satisfactory situation obtains when
we consider structural changes in individual systems or organs. It is clear
that skeletal elements, for example, are responsive to thyroid state in
teleosts. Gerbilsky and Saks (1947) have observed accelerated scale and
bone plate formation in thyroxinized sturgeon. La Roche et al. (196Sb),
and in earlier papers of La Roche, specific effects of both thyroidectomy
and thyroxine administration on phases of skeletal growth, calcification,
and differentiation have been described in salmonids. Baker-Cohen
( 1961 ) also observed skeletal changes in radiothyroidectomized platyfish.
In this context, it is of interest that Barrington and Rawdon (1967) found
that thyroxine favors the uptake and incorporation of radiosulfur into the
skeleton of trout.
The positive relationship of thyroid state to integumentary silvering
has been mentioned above. La Roche et al. (196613) have noted the increased melanin pigmentation of the skin of radiothyroidectomized trout
and have found that it is the result of an increased number of melanophores per unit of skin area. Sembrat (1956), using thiouracil, found
increased pigmentation in skin of the carp. Belsare et al. (1966) showed
that in larval Channa punctatus, thiourea not only favors increased in-