Discus mucus secretions analysed

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Molecular biologists have analysed the mucus secreted by brooding Discus and found that it differs from the mucus of non-breeding fishes.

Brooding male and female Discus, Symphysodon aequifasciata, like many South American cichlids, produce a milky mucus secretion when they are brooding fry and the young fish "glance" at the flanks to gain additional nourishment.

It's long been assumed that this mucus contained something important to the development of Discus fry, but the exact constituents have not been studied before.

A team of scientists working at the School of Biological Sciences at the Universiti Sains Malaysia in Penang used sophisticated molecular techniques to determine whether the mucus secreted by brooding Discus to feed their fry contained anything different to the mucus of non-breeding fishes.

Their findings are due to be published in the journal Proteomics later this year.

By studying the mucus secreted by the epidermal cells of male and female Discus during and outside breeding, they were able to analyse the mucus using proteomics and produced protein profiles showing the differences in the mucus at different times. "The mucus of brooding Discus contains many additional proteins that aren't seen in non-brooding fish..."The analysis showed that the mucus of parental fish contained 35 proteins that weren't present in the mucus of non-breeding fish, as well as 18 others that were present at both stages.

By using mass spectrometry, a technique for identifying the presence of chemicals in a sample, the team were able to identify some of the constituents and found 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.

The team also believes that breeding Discus must be facing oxidative stress while they're producing this mucus, as the analysis also revealed several antioxidant-like chemicals including thioredoxin peroxidase and hemopexin.

Perhaps of most interest to breeders though is the discovery of a C-type lectin in the mucus of brooding fish, which is believed to provide protection against bacterial infection to both the adults and the fry.

For more details on the findings see the paper: Chong K, Joshi S, Jin LT, Shu-Chien AC. (2005) - Proteomics profiling of epidermal mucus secretion of a cichlid (Symphysodon aequifasciata) demonstrating parental care behavior. Proteomics. (In press)