Functional effects of quercetin via the haematology–gut axis: Resistance to Lactococcus petauri in Oncorhynchus mykiss

Özay Köse

doi:10.3153/AR26012

EN

Functional effects of quercetin via the haematology–gut axis: Resistance to Lactococcus petauri in Oncorhynchus mykiss

Abstract

This study evaluated the effects of low-fat (LFD), high-fat (HFD), and quercetin-supplemented high-fat (HFD+Q; 0.2 g/kg) diets on the haematological responses, intestinal histomorphology/histopathology, and resistance to Lactococcus petauri infection in rainbow trout (Oncorhynchus mykiss). A total of 270 fish (initial mean weight: 38.37 g) were randomly distributed into three dietary groups with three replicates per treatment (30 fish per tank) and fed the experimental diets for eight weeks. At the end of the trial, haematological parameters were determined using an automated analyser; histomorphometric measurements (muscle layers, villus parameters, and goblet cell counts) and histopathological evaluations were performed on intestinal samples. Furthermore, an intraperitoneal challenge with L. petauri was conducted to evaluate disease resistance. The HFD group exhibited significant suppression of leukocyte profiles (WBC, LYM, MID, GRAN) and a downward trend in HGB/HCT and erythrocyte indices. This group also displayed intestinal alterations consistent with muscular layer irregularities, submucosal oedema, and loss of goblet cells. In contrast, the HFD+Q group maintained more balanced haematological parameters and intestinal barrier indicators, contributing to the recovery of mucosal defence by increasing goblet cell counts compared to the HFD group. In the challenge trial, the survival probability was significantly higher in the HFD+Q group. In conclusion, quercetin is a functional feed additive with the potential to enhance resistance to L. petauri infection by supporting haematological homeostasis and intestinal integrity under high-fat feeding conditions. Further immunological and molecular studies are recommended to elucidate the mechanism of action and optimal dosage.

Keywords

Supporting Institution

Scientific Research Projects Coordination Unit of Recep Tayyip Erdogan University

Project Number

FBA-2023-15

Ethical Statement

The animal study was approved by Recep Tayyip Erdoğan University Experimental Animals Ethics Committee (decision number: 2023/30, date: June 13, 2023). The study was conducted in accordance with the local legislation and institutional requirements.

Thanks

The author, Dr. Ö.K., would like to thank Dr. Salih KUMRU for proofreading the manuscript in its original language. Special thanks are also extended to Dr. Akir ER for his assistance with the challenge test protocol and to Yusuf Demir, our Data Collection Assistant, for his assistance with record keeping during data collection

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Details

Primary Language

English

Subjects

Fish Physiology and Genetics

Journal Section

Research Article

Authors

Özay Köse ^*
0000-0002-3565-160X
Türkiye

Early Pub Date

March 30, 2026

Publication Date

March 30, 2026

Submission Date

December 26, 2025

Acceptance Date

February 9, 2026

Published in Issue

Year 2026 Volume: 9 Number: 2

DOI

https://doi.org/10.3153/AR26012

IZ

https://izlik.org/JA44YS64DW

Cite

RIS / Bibtex

APA

Köse, Ö. (2026). Functional effects of quercetin via the haematology–gut axis: Resistance to Lactococcus petauri in Oncorhynchus mykiss. Aquatic Research, 9(2), 129-147. https://doi.org/10.3153/AR26012