# The Injection of Lipids Into Yolk Sac has Been Shown to Alter the Lipid Metabolism of Adult Nile Tilapia (Oreochromis niloticus)

## TL;DR

Injecting oils into young Nile tilapia affects their lipid metabolism and growth into adulthood, with lasting changes in fat and gene activity.

## Contribution

This study reveals long-term metabolic and epigenetic effects of early n−3 PUFA enrichment in Nile tilapia.

## Key findings

- Linseed oil injection increased weight gain and n−3 PUFA utilization in adult fish.
- Both oil treatments reduced plasma lipids and altered gene expression related to lipid and carbohydrate metabolism.
- Fish oil injection led to increased muscular n−3 LC-PUFA deposition and epigenetic changes in the liver.

## Abstract

Nutritional programming (NP) of n−3 polyunsaturated fatty acids (PUFAs), achieved by injecting linseed oil into Nile tilapia alevins, influences lipid profiles and associated metabolic processes during the juvenile stage. However, the persistence of these effects into adulthood is unknown. In this study, we investigated the long‐term NP effects of early n−3 PUFA and n−3 long‐chain (LC)‐PUFA intervention via linseed and fish oil injection, respectively, during the alevin stage on lipid metabolism and associated pathways in adult Nile tilapia. The experimental design included randomized treatment groups of 0.85% NaCl (control), linseed oil, and fish oil, each with six replicates. Linseed and fish oil were microinjected into the yolk reserves of Nile tilapia alevins, while control fish received NaCl injections. Following dietary challenge with a linseed oil‐rich diet (weeks 37–40), linseed oil‐injected fish exhibited higher weight gain, suggesting that early linseed oil enrichment enhanced n−3 PUFA utilization for growth. Both interventions reduced plasma lipemia, promoted hepatic fat accumulation, and downregulated mlxipl and acaca expression in the muscle, potentially modulating interactions between carbohydrate and lipid metabolism. While these effects were more pronounced in the fish oil‐injected group, long‐term NP effects differed between the liver and muscle, including decreased hepatic but increased muscular n−3 LC‐PUFA deposition, and downregulated hepatic but upregulated muscular β‐oxidation in fish oil‐injected adult fish. Gene expression analysis revealed altered hepatic enzymes involved in DNA (de)methylation and histone modification, implicating epigenetic mechanisms in the long‐term NP effects of early n−3 PUFA and n−3 LC‐PUFA exposure. Thus, linseed and fish oil enrichment during the alevin stage induces long‐term alterations in lipid metabolism and enhances muscular n−3 LC‐PUFA deposition in adult Nile tilapia.