Effects of Light Spectrum and Intensity on Cellular Stress Responses in Baikal Whitefish and Its Hybrid Embryos: A...

The light spectrum is a key factor in aquaculture, but its effects on molecular stress responses during early fish development are unclear. This study examined how light of different wavelengths (spectra) affects embryos of Baikal whitefish Coregonus baicalensis and its hybrid with Yenisei hump-snout whitefish C. fluviatilis. Eggs were incubated from 35 days post-fertilization under white light (1.8 and 20 µmol m^-2 s^-1), darkness, red (peak at 631 nm), green (peak at 507 nm) and blue (peak at 459 nm) light. We analyzed relative telomere length, telomerase activity, blood profiles, and expression of stress-related genes (HSP-90, MtCK) at key developmental stages. Notably, a significant increase in telomere length was observed throughout early development (from embryo to larva to fry), independent of the light spectrum. Red light and darkness acted as potent stressors, indicating proteotoxic stress and energy imbalance. In Baikal whitefish, this was accompanied by notable telomere shortening at the earliest stage and elongation at later stages under certain conditions, potentially mediated by increased telomerase activity, a response that may be metabolically costly. Conversely, green light was the most neutral. The effect of blue light differed between Baikal whitefish and its hybrid, with the hybrid proving more sensitive. Furthermore, high-intensity white light (20 µmol m^-2 s^-1) also induced negative effects in the hybrid, such as increased telomere length, suggesting that excessive irradiance itself can be a stressor, independent of spectral composition. We conclude that darkness or a predominance of red light is suboptimal for incubating these whitefish, while green light provides a more favorable environment, offering a basis for optimizing aquaculture light conditions.