Biology Reference
In-Depth Information
McCormick et al. (2000) demonstrated that temperature could
infl uence smolt development, most likely by affecting the rate of response
to an endogenous circannual rhythm cued by changing photoperiod.
They also showed that plasma T4 concentrations decreased following
increased temperatures, whereas plasma IGF1, T3 and cortisol levels were
only moderated affected. In contrast, changes of GH preceded and were
strongly correlated with the physiological changes that resulted from the
manipulations of both temperature and photoperiod.
6.5 Anthropic Factors Impairing Smoltifi cation
6.5.1 Endocrine disruptors
Major declines in Atlantic salmon populations observed in Atlantic
Canada were strongly associated with events of aerial forest spraying with
insecticides containing 4-nonylphenol as primary solvent (Fairchild et al.,
1999). Xenobiotics, such as alkylphenols, may interact negatively with
physiological and biochemical aspects of smoltifi cation in Atlantic salmon
(Madsen et al., 1997), presumably due to their interaction with the estrogen
receptor (White et al., 1994).
In Atlantic salmon, treatment with E2 and 4-nonylphenol (4-NP)
impaired smolting as judged by elevated condition factor, reduced gill
Na+,K+-ATPase activity and α-subunit Na+,K+-ATPase mRNA level,
reduced muscle water content (Madsen et al., 2004). The inhibition of gill
Na+,K+-ATPase activity and α-subunit Na+,K+-ATPase mRNA level by E2
treatment is in accordance with other studies in salmonids (Miwa and Inui,
1986; Madsen and Korsgaard, 1989; 1991; Madsen et al., 1997; McCormick
et al., 2005). SW-transfer of 4-NP-treated fi sh resulted in 90% mortality
within 24h, while no mortality was observed in FW-transferred controls;
this was likely due to hypo-osmoregulatory failure after 4-NP treatment
impairing SW-tolerance (Madsen et al., 2004). Moreover, treated fi sh initiated
downstream migration with a delay of 6 (E2) and 8 (4-nonylphenol) days,
and electro-fi shing of the stream after 9 days revealed a more upstream
position of E2-treated fi sh compared to controls (Madsen et al., 2004). Using
waterborne exposure (30 days) during the peak migration period, Moore et
al. (2003) were unable to confi rm the negative effect of 4-NP on SW-tolerance
in salmon smolts. It was suggested that 4-NP treatment in Madsen paper
was initiated prior to migration, a period during which the developing
smolts may be more sensitive to disruption. In another study, Fairchild et
al. (2000) reported that a portion of Atlantic salmon smolts treated with E2
and 4-NP did not survive the transition from FW to SW.
Combined with impairment of smolt quality, a signifi cant delay in
migration may add to the risk of temperature-controlled desmoltifi cation
