# Effects of Light Spectrum and Intensity on Cellular Stress Responses in Baikal Whitefish and Its Hybrid Embryos: A Basis for Optimizing the Aquaculture Environment

## TL;DR

This study shows that green light is best for fish embryos in aquaculture, while red light and darkness cause stress and harm.

## Contribution

The study identifies green light as a favorable spectrum for Baikal whitefish embryos and highlights hybrid sensitivity to blue and bright white light.

## Key findings

- Red light and darkness caused cellular damage and energy imbalance in embryos.
- Green light had the most favorable effects on embryo health.
- Hybrid embryos were more sensitive to blue and bright white light than pure Baikal whitefish.

## Abstract

Different spectra of light can be a source of stress for developing fish in aquaculture, but the specific effects are not well understood. We incubated the eggs of the Baikal whitefish and its hybrid from fertilization until after hatching under various light conditions: white, darkness, red, blue, and green. The key indicators of stress and health in the embryos, including markers of cellular damage, energy balance, and genetic integrity, were measured. Our results show that red light and complete darkness acted as significant stressors, causing signs of cellular damage and energy imbalance. In contrast, green light had more favorable effects. Interestingly, the hybrid was more sensitive to blue light and bright white light than the pure Baikal whitefish. We conclude that for the incubation of these whitefish forms, red light and darkness should be avoided, while green light provides a significantly more favorable environment, and the predominance of this spectrum range is recommended for use in the artificial cultivation of eggs. These findings offer a practical basis for optimizing light conditions to improve fish health and welfare in aquaculture production.

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.