# Effect of Quinoa Germ Meal as a Replacement for Fish Meal in Diets on Intestinal Health of Juvenile Turbot (Scophthalmus maximus)

## TL;DR

This study explores using quinoa germ meal as a fish meal replacement in turbot diets, finding that high levels negatively affect growth and intestinal health.

## Contribution

The study provides new insights into the effects of quinoa germ meal on intestinal health and gene expression in juvenile turbot.

## Key findings

- High quinoa germ meal inclusion levels impaired growth performance in juvenile turbot.
- Transcriptomic analysis showed modulation of ribosome-related and protein digestion pathways.
- Low quinoa germ meal levels (≤20%) had minimal adverse effects on turbot health.

## Abstract

This study investigates the potential of quinoa germ meal as a dietary alternative protein source for juvenile turbot. Five experimental diets were formulated, comprising a control group and four experimental groups with replacement levels of 10%, 20%, 30%, and 40%. With increasing replacement levels, most growth parameters, notably feed intake, declined significantly. All experimental groups displayed decreased muscle crude lipid content and altered intestinal morphology. Transcriptome analysis revealed that quinoa germ meal modulated gene expression in ribosome-related and protein digestion and absorption pathways, and notably, high replacement levels activated the cellular senescence pathway in the intestine. These findings provide a theoretical basis for optimizing quinoa germ meal as a sustainable protein source in aquaculture.

Quinoa germ meal (QGM) is a protein-rich by-product with potential as an alternative protein source; however, its effects on growth performance and intestinal health in marine carnivorous fish remain unclear. Juvenile turbot (Scophthalmus maximus) were fed five isonitrogenous (45.6% crude protein) and isolipidic (9.8% crude lipid) diets for 8 weeks: a fishmeal-based control diet (C) and four experimental diets in which fishmeal was replaced with QGM at 10% (Q10), 20% (Q20), 30% (Q30), and 40% (Q40). Growth performance, muscle proximate composition, intestinal histomorphology, and intestinal transcriptomic profiles were analyzed. Growth performance parameters, including final body weight, weight gain rate, specific growth rate, daily feed intake, and condition factor, decreased significantly with increasing QGM inclusion levels compared with the control (p < 0.05). Feed conversion ratio increased significantly only when replacement exceeded 30% (p < 0.05), while survival rate was unaffected (p > 0.05). Muscle crude lipid content was significantly reduced in all QGM-fed groups (p < 0.05), whereas crude protein, moisture, and ash contents were unchanged. Intestinal mucosal fold height increased in the Q30 and Q40 groups, while submucosal width decreased in the Q40 group (p < 0.05). Transcriptomic analysis revealed a dose-dependent increase in differentially expressed genes, mainly enriched in ribosome-related pathways, linoleic acid metabolism, and protein digestion and absorption. High dietary inclusion of QGM (>30%) impaired growth performance in juvenile turbot, whereas low inclusion levels (≤20%) exerted minimal adverse effects. Quinoa germ meal represents a potential alternative protein source, yet its effective utilization requires further optimization to maintain growth performance.