BackgroundNematodes have lost the ability to synthesise necessary lipids de novo and have complementally evolved the capacity to acquire fatty acids and their derivatives from a diet or host animal. Nematode-specific fatty acid- and retinol-binding protein (FAR) family is one approach that facilitates lipid acquisition, representing an Achilles heel and potential target against roundworms of socioeconomic significance. However, little is known about their detailed functional roles in either free-living or parasitic nematodes.MethodsA genome-wide identification and curation were performed to screen the FAR family members ofHaemonchus contortus. Their transcription patterns in worms were also analysed to identify the targets. Ligand binding assay and molecular docking were conducted to verify the fatty acid binding activities of FAR proteins of interest. RNA interference (RNAi) and heterologous expression (rescuing) experiments were designed to explore the potential roles of the selected FAR protein in nematodes. Localisation of the protein was shown in sections of paraffin-embedded worms after an immunohistochemistry (IHC) assay.ResultsHere, an orthologue offar-6in the model organismCaenorhabditis elegans(Ce-far-6) was functionally characterised in a parasitic nematode,H. contortus(Hc-far-6). It is demonstrated that knockdown ofCe-far-6gene did not affect worm fat content, reproduction, or lifespan, but decreased worm body length at an early life stage ofC. elegans. In particular, theCe-far-6mutant associated phenotype was completely rescued byHc-far-6, suggesting a conserved functional role. Surprisingly, there were distinct tissue expression patterns of FAR-6 in the free-livingC. elegansand parasiticH. contortus. High transcriptional level ofHc-far-6and dominant expression of FAR-6 in the intestine of the parasitic stage ofH. contortuslink this gene/protein to nematode parasitism.ConclusionsThese findings substantially enhance our understanding offargenes and the associated lipid biology of this important parasitic nematode at a molecular level, and the approaches established are readily applicable to the studies offargenes in a broad range of parasites.Graphical AbstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s13071-023-05836-8.