high allostatic load through physiological changes associated with the HPI axis

High allostatic load through physiological changes

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high allostatic load through physiological changes associated with the HPI axis, which may have led to the observed changes in learning behavior. In addition, exposure to Al toxicity lowered NKA activity in the gill. This is similar to the results of another study in salmon that found negative impacts on ion-regulatory development during smoltification (Nilsen et al., 2010). While Al impairment of ion regulatory development is detrimental for a smolt and has been implicated in low rates of returning adults (Kroglund and Finstad, 2003; Monette et al., 2008), a recent study has shown that ion regulatory capacity can partially recover following episodic acidification and Al exposure (Kroglund et al., 2012). In the present study, the mechanisms through which Al exposure affected gill condition are unknown; Al toxicity may have acted directly on NKA activity, or it may have acted indirectly by stimulating the HPI axis and inducing changes in NKA activity. Our data showing impaired learning in Acid-Al treated fish add a new consideration in terms of how Al toxicity in acidified water affects salmon. The effect appears to extend beyond physiological changes to also altering learning behavior. It is known that smolts have a heightened sensitivity to Al in acidified water compared with parr (Monette and McCormick, 2008). In parr, many of the smolt- related parameters, such as neural plasticity, hormones and NKA activity, are at baseline levels, thus making it difficult to detect impacts on them. We chose to test the fish during a significant developmental period in their life cycle because the toxicity of Al in freshwater is enhanced, potentially leading to detrimental effects later on in life. Certainly, we found effects of Al exposure in terms of increased levels of glucose and cortisol. Taken on its own, however, it is not clear whether an increase in allostatic load, brought about by altered stress physiology, is causing distress or eustress in the fish (Korte et al., 2007; Korte et al., 2009). With the addition of our data on behavioral impairment and decreased neural plasticity, a decrease in cognitive ability suggests that the impact of Al toxicity is playing a negative role, causing distress in the exposed fish. These kinds of negative effects may have consequences for the ability of smolts to imprint on their natal streams (Yamamoto et al., 2010); it has been established that the parr–smolt transformation is a critical period for neural development, including cell differentiation and proliferation (Ebbesson et al., 1996b; Ebbesson et al., 2003; Ebbesson et al., 2007; Ebbesson et al., 2011). Olfactory imprinted memory is formed during smolting and the loss of neural plasticity could therefore impair the ability of Atlantic salmon to return to their natal stream (Dittman et al., 1996).
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  • Winter '20
  • Atlantic salmon

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