Diet and environmental factors shape retinal lipid composition in common carp (Cyprinus carpio)

Polyunsaturated fatty acids (PUFA), particularly long-chain and very-long-chain PUFA (LC- and VLC-PUFA), are essential structural and functional compounds of the vertebrate retina. Their availability depends on dietary supply and endogenous biosynthesis, yet how environmental factors modulate retinal lipid composition fish species remains poorly understood. Here, we investigated the effects of diet quality, light regime, and temperature on retinal lipid composition in common carp (Cyprinus carpio), one of the most consumed fish species worldwide, using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to resolve lipid distributions across retinal layers. Carps were exposed for six months to a fully factorial combination of low vs. high LC-PUFA diets, light vs. dark conditions, and stable vs. fluctuating temperature regimes. Retinal lipidomes showed strong layer-specific organization, with outer retinal layers enriched in docosahexaenoic acid-containing phospholipids and VLC-PUFA. Across all layers, diet exerted the strongest influence: high-LC-PUFA diets increased n-3 PUFA-containing phospholipids while consistently reducing arachidonic acid-containing species. Only two VLC-PUFA (30:6 and 32:6) were detected in the photoreceptor-associated regions of the retina. Low light conditions reduced the lipid abundance in the outer retina, including VLC-PUFA, suggesting reduced photoreceptor membrane turnover under diminished visual demand. Elevated temperatures induced subtler shifts, favouring shorter and less unsaturated fatty acids. These results demonstrate that the lipid composition of the retina in carp is highly plastic and sensitive to dietary PUFA supply, while light and then temperature act as secondary modulators. Our findings connect dietary lipid supply to retinal structure and function, offering an ecological perspective on sensory plasticity in heterogeneous aquatic habitats, such as shallow and turbid fishponds.