Linuron and carbaryl differentially impair baseline amino acid and bile salt olfactory responses in three salmonids

Abstract

For salmon, amino acid and bile salt detection form the basis for important behaviors including predator evasion and conspecific recognition, respectively. For this reason, decreases in olfactory sensory neuron responses to the amino acid l-serine and the bile salt taurocholic acid (TChA) have been used in studies as indicators of acute olfactory pesticide toxicity to environmental contaminants such as metals and pesticides. In this study, we first compare baseline responses to these two odorant classes across three salmonids, and then explore how two currently used pesticides alter these responses. We found baseline differences in electro-olfactogram (EOG) responses and their sensitivity to pesticide exposure between rainbow trout, coho and sockeye salmon. For example, rainbow trout had lower baseline EOGs than either coho or sockeye (e.g. 10 −5 M TChA EOGs of 1.34 ± 0.17 versus 2.57 ± 0.46 and 2.72 ± 0.43 mV, respectively). At 15 min after exposure to 10 μg/L of the herbicide linuron, rainbow l-serine-evoked EOGs were 49.6% of control versus 78.5 and 69.8% for sockeye and coho, indicating rainbow were more sensitive to linuron. In contrast, at 30 min of exposure to 100 μg/L carbaryl, l-serine-evoked EOGs of sockeye were 49.7% of control versus 60.3 and 62.3% for rainbow and coho, suggesting sockeye were more sensitive to carbaryl. In all species the l-serine-evoked EOGs did not return to baseline by 15 min after 100 μg/L carbaryl exposure, suggesting persisting impairment of amino acid detection. The TChA-evoked EOGs were less affected by carbaryl exposure (i.e. EOGs were 83.3, 84.9 and 66.0% of control 15 min after exposure) and not affected at all by 100 μg/L linuron exposure. Species-specific differences in pesticide sensitivity may limit extrapolation of toxicity across salmonids while the generally greater sensitivity of amino acid olfaction may lead to selective impairment of behaviors such as predator evasion.