Biology Reference
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in oceanic environment (skin, eye), in imprinting (olfactory system), in
swimming (metabolism) and in osmoregulation (skin, gills, intestine and
kidney).
6.2 Morphological, Behavioural and Physiological Changes
Occurring During Smoltifi cation
6.2.1
Skin
Gorbman et al. (1982) defi ned a parr as a young salmonid with vertical
dark stripes, while a smolt is a slightly older and larger fi sh in which the
dark stripes are obscured by a deposition of guanine and hypoxanthine in
the scales and the skin, giving a silvery color (Fig. 2). This silvering of the
skin would correspond to an adaptation to the oceanic pelagic adaptation,
limiting the visibility of the fi sh for their predators. Guanine levels correlated
well with changes in common physiological indices of smoltifi cation (Staley
and Ewing, 1992). As they reached maximum level 1 month earlier than
development of seawater tolerance and transfer of juveniles coho salmon did
not cause signifi cant alterations in guanine concentration, it was concluded
that guanine deposition in the skin during smolting may not represent an
adaptation in preparation for an oceanic life (Staley and Ewing, 1992). In
masu salmon (
O. masou
), it was reported that skin and serum guanine levels
increased as smoltifi cation progressed (Kazuhiro et al., 1994).
Figure 2
. Atlantic salmon parr and smolt. Note the silvery color of smolt compared to the
dark stripes of parr.
Color image of this figure appears in the color plate section at the end of the topic.
