Biology Reference
In-Depth Information
4.4 Pigmentation Abnormalities During Metamorphosis
Various morphological anomalies have been reported in a variety of wild
fl atfi shes. These anomalies include pigmentation anomalies, eye migration
anomalies, dorsal fi n hooking, abnormally shaped pectoral or pelvic fi ns
of blind side and so on (Norman, 1934; Hubbs and Hubbs, 1945; Dawson,
1962). Norman (1934) categorized pigmentation anomalies as 1) albinism
2) ambicoloration and 3) reversal. Albinism lacks pigment on a part or the
whole of the ocular side of the body. Ambicoloration is further categorized
into following 3 types. (1) Staining: some or greater part of the blind side
looks stained with brownish or grey. (2) Spotting: the blind side bears
varying number of black or brown spots. (3) True ambicoloration: whole
area of the blind side is pigmented as the ocular side. In the case of true
ambicoloration, various other morphological anomalies often accompany,
such as the development of ctenoid scales or strongly spinulated scales on
the ambicolored, blind side, characteristic dorsal fi n hooking above the eye,
or abnormalities in the pectoral and pelvic fi ns. Reversal is the condition that
an individual fi sh is sinistral whereas the normal condition of the species
is dextral, or vice versa. Classifi cations similar to that of Norman (1934)
are also used in pigmentation anomalies of hatchery-reared fi sh with some
modifi cation, such as pseudoalbinism or hypomelanism for albinism.
Morphological anomalies mentioned above are found much more
frequently in laboratory- or hatchery-reared fl atfi shes. These anomalies,
especially pigmentation anomalies, are the commonest defect for the
hatchery-reared fl atfi shes.
Among these pigmentation anomalies, albinism seems to be the most
serious defect in aquaculture, since albinism decreases the commercial
value of the fi sh, and when released for stock enhancement, it will make
predators easier to fi nd the stocked fi sh.
To fi nd the causative factors for malpigmentation in hatchery produced
fl atfi shes, various attempts have been made from genetical, environmental,
and nutritional standpoints. These studies disclosed that the composition of
larval diet is a critical factor for the pigmentation of fl atfi shes (for the review
see Bolker and Hill, 2000).
Artemia
nauplii are convenient and useful diet for
fl atfi sh larval culture. However, feeding
Artemia
nauplii, especially Brazilian
Artemia
, during the early larval period often causes albinism and sometimes
ambicoloration in the Japanese fl ounder (Seikai, 1985a), spotted halibut
(Aritaki and Seikai, 2005), brown sole (Aritaki and Seikai, 2005), and Atlantic
halibut (Naess et al., 1995). Feeding wild zooplankton for the substitution
of
Artemia
nauplii during larval period successfully reduced albinism in the
Japanese fl ounder (Seikai, 1985b) and Atlantic halibut (Naess et al., 1995;
Naess and Lie, 1998). Two nutrients, free fatty acids and vitamin A, have
been shown to be the major factors infl uencing pigmentation in hatchery-
