Olfactory sensitivity in fish and ocean acidification
Fish rely on their sense of smell for many behaviours, such as food-search, reproduction, detection of predators and migration, and the evaluation of olfactory sensitivity is essential for understanding fish behaviour. Ocean acidification is one result of increased atmospheric carbon dioxide due to human activity, which leads to a reduction in seawater pH levels. The decrease of the seawater pH can influence the olfactory sensitivity of fish and consequently their behaviour. Therefore, this study was developed to investigate the effects of ocean acidification on olfactory sensitivity in fish.

The method used to assess the olfactory sensitivity in fish
To assess the effects of ocean acidification on olfactory sensitivity in fish, researchers recommend extracellular multi-unit recording from the olfactory nerve of seabream (Sparus aurata), a very important species for aquaculture. This work presents an approach never used by other teams to assess the effects of ocean acidification on olfactory sensitivity fish. The technique used is based on the evaluation of the neuronal response at the level of the olfactory nerve using as an experimental model the seabream (Sparus aurata), a very important species for aquaculture.
Loss of olfactory sensitivity in fish means that they need to get nearer to an odorant source before they can detect it, i.e. food and potential mates will be more difficult to find, predators will be harder to avoid, and migration may be compromised. This study showed that small decreases in seawater pH reduce the olfactory sensitivity in fish to some odorants. 

Can ocean acidification decrease olfactory sensitivity in fish?
The proposed technique presents a complementary and/or alternative method to those usually used in behavioural studies and the evaluation of the effects of acidification on the neuronal system of marine organisms. In this study, seabream was used, but the technique can be used in other fish species and even in other marine organisms (e.g. crustaceans and molluscs). The nerve register can be used to evaluate the effect of other anthropogenic factors on olfactory sensitivity, such as the effect of plastics, pesticides and other pollutants resulting from anthropogenic activity. 
It was demonstrated that a small decrease in the seawater pH (from 8.2 to 7.7) leads to a decrease in the olfactory sensitivity of seabream, but this effect does not occur with all odorants. Thus, occurs a change in the perception of odours that may explain the behavioural changes in many species of marine organisms when exposed to an increase in CO2 and consequent decrease in pH.

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