Aluminum exposure impacts brain plasticity and behavior in Atlantic salmon (Salmo salar)

Abstract

SUMMARYAluminum (Al) toxicity occurs frequently in natural aquatic ecosystems as a result of acid deposition and natural weathering processes. Detrimental effects of Al toxicity on aquatic organisms are well known and can have consequences for survival. Fish exposed to Al in low pH waters will experience physiological and neuroendocrine changes that disrupt homeostasis and alter behavior. To investigate the effects of Al exposure on both the brain and behavior, Atlantic salmon (Salmo salar) kept in water treated with Al (pH5.7, 0.37±0.04μmol1 −1 Al) for 2weeks were compared with fish kept in under control conditions (pH6.7, <0.04μmol1 −1 Al). Fish exposed to Al and acidic conditions had increased Al accumulation in the gills and decreased gill Na + , K + -ATPase activity, which impaired osmoregulatory capacity and caused physiological stress, indicated by elevated plasma cortisol and glucose levels. Here we show for the first time that exposure to Al in acidic conditions also impaired learning performance in a maze task. Al toxicity also reduced the expression of NeuroD1 transcript levels in the forebrain of exposed fish. As in mammals, these data show that exposure to chronic stress, such as acidified Al, can reduce neural plasticity during behavioral challenges in salmon, and may impair the ability to cope with new environments.

Chronic cortisol and the regulation of food intake and the endocrine growth axis in rainbow trout

“…While fish can habituate to some chronic stressors, sustained plasma cortisol levels similar to those used in this study have been observed in response to diverse stressors of anthropogenic and natural origins. For example, chronic exposure to aluminum, copper, selenium or low environmental pH can result in prolonged elevations in plasma cortisol levels (Craig et al 2009, Wiseman et al 2011, Kennedy & Picard 2012, Grassie et al 2013. In salmonids, sustained increases in cortisol levels are also associated with social subordination (Gilmour et al 2005) and with specific phases of the life cycle such as smolting (Nilsen et al 2008) and sexual maturation (Fuzzen et al 2011).…”

Predation on Fishes in the Sacramento-San Joaquin Delta: Current Knowledge and Future Directions

“…These contaminants are all are present in concentrations that could affect fish behavior (Sloman and Wilcox 2006;Connon et al 2011;Brooks et al 2012;Fong et al, submitted). Aluminum, in particular, affects physiological homeostasis as well as learning and behavioral performance in Atlantic Salmon (Salmo salar, Grassie et al 2013). Similarly, Sandahl et al (2007) demonstrates that copper concentrations commonly found in Delta waters can produce abnormal anti-predator behaviors in Coho Salmon (Oncorhynchus kisutch).…”

Measuring cortisol, the major stress hormone in fishes

“…It is also an important tool in characterising coping abilities of fishes and investigating how the environment can disturb this. In a context of global change it is, for example, increasingly applied to gauge human‐induced rapid environmental change in different contexts: polluted areas (Grassie et al, ), habitat degradation (Jeffrey et al, ), exposure to tourism (Geffroy et al, ) or global warming (Beldade et al, ). In aquaculture, effects of changes in rearing conditions on cortisol titres have been intensively investigated, notably as related to the type of feed supplied (Sadoul et al, ), effects of water recirculation (Colson et al, ), or stocking density (McKenzie et al, ; Vijayan & Leatherland, ).…”