Why do Corydoras take gulps from the surface?

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Matt Clarke explains why Corydoras catfish sometimes take gulps of air from the water surface.

Corydoras use a technique known as aerial respiration — an adaptation for life in low oxygen environments.

They are often found in streams or rivers that flow into larger rivers and these can dry out, forming pools during the dry season. The water in these is warm and shallow, and holds less oxygen.

Most fish wouldn’t be able to withstand this, but Corydoras can gulp air from the surface and use their posterior intestine to extract oxygen from it and pass it into their blood where it’s needed.

Aerial respiration has been shown to occur at all oxygen concentrations, so it isn’t always an indication that the oxygen level of the tank is low.

Fish can take anything between one and 45 breaths from the surface per hour and this is believed to be linked partly to the water depth. It is also more common during or after a meal.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.