Biology Reference
In-Depth Information
pseudomesial bar, a unique bone specifi cally found in fl atfi sh. The bone is
formed only on the blind side after the start of metamorphosis. The bone
seems to originate from the ventral dermis beneath the migrating eye.
It elongates toward dorsal direction during metamorphosis (Traquair,
1865; Okada et al., 2001, 2003). Several scientists strongly claim that the
pseudomesial bar, especially in the process of its formation may play an
important role in driving the eye migration, by pushing the migrating eye
to the dorsal direction or at least preventing the eye from moving backward
(Traquair, 1865; Kyle, 1923; Okada et al., 2001, 2003).
Thus, development and transformation of the cranium during eye
migration has been clarifi ed fairly well. Although the exact mechanism of
eye migration needs to be elucidated by further studies, it seems clear that
asymmetrical development of cranium including soft tissues moves the
eye to the other side of the head.
4.1.3 Development of asymmetrical pigmentation
Flatfi sh are well known for their ability to rapidly match their body color to
the background by adjusting their ocular-side pigmentation (Ramachandran
et al., 1996). Such adjustment is mainly achieved by the change in distribution
of melanosomes in the melanophore cytoplasm. This process is controlled
through the sympathetic nervous system and pituitary hormones (Fujii and
Ohshima, 1986; Sugimoto, 2002). The adaptation is reversible.
Apart from above mentioned mechanism of body color change, fl atfi sh
also change pigmentation ontogenetically, especially during metamorphosis,
and the change is irreversible. The overall pattern of fl atfi sh pigmentation
is based on the number and distribution of three types of pigment cells:
melanophores, xantophores and iridophores (Seikai, 1992; Seikai and
Matsumoto, 1994; Bolker and Hill, 2000; Bolker et al., 2005). Melanophores
produce melanin and are responsible for the brown or black body color.
Xantophores appear yellow and contain carotenoids and pteridines, and
iridophores appear white or silvery by light-refl ecting platelets of guanine
(Fujii, 1969, 1993; Bagnara, 1987). Development of fl atfi sh pigmentation has
been studied mainly in the Japanese fl ounder
Paralichthys olivaceus
(Bolker
and Hill, 2000). It is known that all pigment cells in lower vertebrates are
differentiated from the chromatoblast originated from nueral crest (Bagnara,
1987). This is also confi rmed in the Japanese fl ounder by both an
in vivo
study using neural crest markers on pigment cells of developing fl ounder
(Matsumoto and Seikai, 1992) and an
in vitro
study on the development of
pigment cells from dissociated neural cells of fl ounder neurula (Seikai et al.,
1993). In early development of the Japanese fl ounder, chromatoblasts are
evenly delivered to the skin of both left and right side of the body and no
