What is in Discus mucus?

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Discus and some other cichlids produce mucus secretions to feed their fry. But why do they do it and what's in their mucus that helps the fry to grow?

Discus and several other South American cichlids, such as Uaru, produce mucus secretions that are used to feed broods of fry. 

These milky secretions are generated during spawning but it was not until relatively recently that scientists learnt what was in them. 

The mucus secretions are produced by cells in the epidermis layers of the skin of both male and female Discus from the genus Symphysodon. 

Recent studies have revealed that 18  different proteins are present in the mucus secretions of Discus whether they’re breeding or not, but the fish produce an additional 17 proteins when they have fry to raise. 

The proteins in the mucus include fructose biphosphate aldolase, nucleoside diphosphate kinase, and heat shock proteins, which are used in energy provision, producing and repairing cells, handling stress and defense during the brooding period. Antioxidants are also present. 

However, perhaps the key thing is the presence of a sugar-binding protein which is believed to provide protection against bacterial infections to both the parents and the fry. 

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