# Chronic Heat Stress Induces Stage-Specific Molecular and Physiological Responses in Spotted Seabass (Lateolabrax maculatus): Focus on Thermosensory Signaling and HPI Axis Activation

## TL;DR

This study explores how spotted seabass respond to heat stress at different life stages, revealing distinct neuroendocrine and physiological adaptations that could help improve aquaculture practices under climate change.

## Contribution

The study identifies stage-specific molecular and physiological responses to chronic heat stress in spotted seabass, including divergent thermosensory signaling and energy metabolism.

## Key findings

- Larvae relied on skin-based thermosensation, while juveniles used brain-based mechanisms under heat stress.
- Larvae maintained appetite and hyperglycemia, whereas juveniles showed feeding suppression and hypoglycemia.
- Both stages activated the HPI axis and heat shock response, but with stage-specific gene expression patterns.

## Abstract

Global warming poses a significant threat to aquaculture. Marine heatwaves (MHWs), in particular, endanger the spotted seabass (Lateolabrax maculatus), a commercially important marine species in Northeast Asia. We previously did not understand how its neuroendocrine system copes with heat across different developmental stages. So, we conducted an experiment: we exposed late larvae and late juveniles of this seabass to high temperatures for 14 days and tracked their changes. The two stages (late larvae and juveniles) exhibited distinct thermosensory and behavioral responses to heat stress: larvae relied more on their skin to “feel” temperature, while juveniles depended more on their brains. Both activated stress responses (like higher stress hormones), but larvae kept eating normally (with higher blood sugar), while juveniles ate about 80% less (with lower blood sugar). These findings not only help us better understand how spotted seabass acclimatize to heat as they grow, but also provide practical references for its aquaculture—helping farmers take targeted measures to protect seabass survival and yields when MHWs occur, which has implications as regards coping with climate change’s impacts on aquatic production.

Global warming and the increasing frequency of marine heatwaves (MHWs) threaten marine ecosystems and aquaculture. For the economically important spotted seabass (L. maculatus), the neuroendocrine basis of its stage-specific thermal responses has yet to be elucidated. This study examined the transcriptomic, physiological, and behavioral adaptations to chronic heat stress in late larval and late juvenile seabass over 14 days. After thermal acclimation, larvae demonstrated a marked behavioral shift, preferring warmer waters (26–34 °C). While heat stress upregulated key thermosensory genes (e.g., trpv1, trpv4) in the brain across both stages, it induced distinct expression profiles in the skin, suggesting a developmental transition from peripheral to central dominance in thermosensation. Brain transcriptomics revealed stage-specific pathway activation: juveniles engaged in neuroactive ligand-receptor interactions and MAPK signaling, whereas larvae showed enrichment in phosphatidylinositol signaling and protein processing. Both stages showed activation of the hypothalamic-pituitary-interrenal (HPI) axis (upregulation of crh, crhr1, crhr2, pomc) and heat shock response (hsp70, hsp90), accompanied by elevated serum cortisol. Notably, energy metabolism diverged significantly: larvae maintained appetite and developed hyperglycemia, while juveniles exhibited severe feeding suppression and hypoglycemia, which was correlated with differential regulation of appetite genes (npy, orexin, cck). Our results elucidate the distinct neuroendocrine mechanisms underlying thermal acclimation in L. maculatus and provide a scientific basis for developing climate-resilient aquaculture practices for this species.