Biology Reference
In-Depth Information
Gill GHR mRNA levels peaked in early June, in parallel to branchial
Na+, K+-ATPase activity in Atlantic salmon (Kiilerich et al., 2007).
6.3.2.1.2 IGF1
During salmon smoltifi cation, liver and plasma IGF-1 levels increase (Duan
et al., 1995; Agustsson et al., 2001) and hepatic mRNA levels are signifi cantly
correlated with plasma T4 levels in coho salmon (Duguay et al., 1994). The
levels of gill IGF1 mRNA increase during smoltifi cation of coho salmon
(Duguay et al., 1994) and in response to GH (Sakamoto and Hirano, 1993).
Beckman et al. (1999) reported that plasma IGF1 concentrations were good
indicators of smolt quality and had signifi cant relationships with smolt-to
adult returns (SAR) in hatchery reared Chinook salmon. Smolts of poor
quality (i.e., behaviourally dysfunctional, physiologically compromised
and disease prone) were found to have poor post-release survival and
lower plasma IGF1 concentrations than higher quality smolts (Beckman
et al., 1999).
6.3.2.1.3 GHRH
In chum salmon fry, the expression of GHRH in the preoptic area of the
brain is not seen until the dowstream migratory period and is associated
with the peak in plasma T4 levels (Parhar and Iwata, 1996).
Increased GH and IGF1 may also infl uence osmoregulatory capacities
through their stimulation of cortisol production. Indeed, Young (1988) has
shown that injection of coho salmon with GH enhances the sensitivity of
the interregnal to ACTH. GH may also act via TH as it stimulates hepatic T4
5'monodeiodinase activity and T3 levels in rainbow trout (
Salmo gairdneri
)
(MacLatchy and Eales, 1990).
6.3.2.2 Experimental induction
Administration of GH to Pacifi c salmon induces smoltifi cation-related
changes in condition factor and skin pigment, and improves hypo-
osmoregulatory ability and seawater survival of parr (for review: Donaldson
et al., 1979; Wedemeyer et al., 1980).
6.3.2.2.1 Body silvering
Intramuscular injection of ovine GH for 72 days to underyearling amago
salmon resulted in body silvering (Miwa and Inui, 1985). Komourdjian et
al. (1976b) have reported that porcine GH administration induced marginal
black color of the dorsal fi n in Atlantic salmon.
