# Proteomic Insights into the Immune and Sex-Specific Proteins in the Skin Mucus of Barramundi (Lates calcarifer)

## TL;DR

This study identifies immune and sex-related proteins in the skin mucus of barramundi, offering a non-invasive way to monitor fish health and reproduction.

## Contribution

The first comprehensive proteomic analysis of barramundi skin mucus, revealing sex-specific and immune-related proteins.

## Key findings

- 1801 protein groups were identified and functionally annotated in barramundi skin mucus.
- 352 immune-related and 24 sex-related protein groups were prioritized based on GO terms.
- 244 protein groups showed statistically significant sex-based differences in abundance.

## Abstract

Background: Fish skin mucus contains proteins involved in diverse biological pathways, representing a valuable non-invasive diagnostic of fish health. Methods: Skin mucus from three male and three female barramundi was analysed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) following protein extraction and S-Trap digestion. Results and Discussion: A total of 1801 protein groups were matched to the L. calcarifer reference proteome and functionally annotated using Gene Ontology (GO) terms via UniProt ID mapping, with representation across Biological Process, Cellular Component, and Molecular Function categories. Functional classification using eggNOG-mapper further associated leading protein group sequences with Clusters of Orthologous Groups (COGs) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways. GO-based screening prioritised 352 putatively immune-relevant protein groups and 24 protein groups associated with sex- and reproduction-related processes, highlighting the functional complexity of the skin mucus proteome. Comparative analysis revealed sex-associated patterns in protein group detection and relative abundance, with differential abundance analysis identifying 244 protein groups exhibiting statistically significant differences between male and female samples. Conclusions: This study provides the first comprehensive discovery-based characterisation of the barramundi skin mucus proteome and establishes a baseline reference dataset for this aquaculture-relevant species. The findings support the utility of skin mucus proteomics for exploring immune and sex-associated molecular patterns and provide a baseline dataset for future validation studies investigating non-invasive health and reproductive monitoring.