Biology Reference
In-Depth Information
to thyroid hormone, as well as the dynamics of the hormone during
fl ounder metamorphosis seems to be comparable to those of amphibian
metamorphosis.
Expression level of growth hormone gene during metamorphosis of
the Japanese fl ounder changed similarly to that of prolactin (de Jesus et al.,
1994). However, administration of growth hormone
in vitro
did not affect
shortening of fi n rays stimulated by thyroid hormone, and microinjection of
growth hormone to prometamorphic larvae did not affect any metamorphic
parameters, including resorption of the dorsal fi n rays (de Jesus et al., 1994).
Thus, there is so far no evidence that growth hormone is involved in the
regulation of fl ounder metamorphosis.
4.3 Effect of Temperature on Metamorphosis
In various fl atfi sh species reared in laboratories, it is known that water
temperature markedly affect metamorphosis: larvae reared at higher
temperatures initiate and complete metamorphosis earlier than those reared
at lower temperatures (Laurence, 1975; Policansky, 1982b; Seikai et al. 1986;
Aritaki et al., 1996; Aritaki et al., 2004). The ambient water temperature also
markedly affects the size of juveniles immediately after metamorphosis:
higher rearing temperatures result in smaller metamorphosed juveniles
in the Japanese fl ounder (Seikai et al., 1986) and spotted halibut,
Verasper
variegates
(Aritaki et al., 2004), though Policansky (1982b) did not fi nd
such effect of temperatures on the size of metamorphosed juveniles in
starry fl ounder,
Platichthys stellatus
. These temperature effects on fl atfi sh
metamorphosis seem to be comparable to amphibian metamorphosis.
In amphibians, normal tadpoles kept in cool water grow to a larger size
than they do when they are kept in warm water (Etkin, 1955). The effect
of temperatures on amphibian metamorphosis is considered to be largely
or entirely caused by the effect of temperatures on tissue sensitivity to
thyroid hormone (Kollros, 1961). Kollros (1961) states that for any given
metamorphic event at colder temperature not only much more time is
required for its completion at a fi xed thyroid hormone level, but also the
minimal thyroid hormone levels required for the events are higher in both
control and hypophysectomized
Rana pipience
.
In several laboratory-reared fl atfi sh species, extremely low and high
ambient water temperatures induced metamorphic anomalies such as
ambicoloration (the blind side also becomes dark) or albinism (the dark
pigmentation does not develop on the ocular side). These abnormal
colorations are often accompanied by incomplete eye migration (Aritaki
et al., 1996; Aritaki and Seikai, 2004). These authors suggest that the
metamorphic anomalies are related to the temperature-modulated thyroid
hormone action.
