Impact of higher temperatures on yolk sac absorption and early development in hybrid catfish between <i>Clarias gariepinus</i> and <i>C. macrocephalus</i>

Abstract Climate change has driven global temperature increases, resulting in severe heat waves, altered precipitation patterns, and extreme weather events. In April 2024, a massive die‐off of hybrid catfish larvae and fry occurred in Thai aquaculture farms, coinciding with elevated temperatures of air (37–41°C) and freshwater (30–32°C). This study aimed to investigate the correlation between elevated temperatures and abnormal embryonic development in hybrid catfish. Controlled mating of male North African catfish ( Clarias gariepinus ) and female bighead catfish ( Clarias macrocephalus ) was conducted in May and June 2024. We examined the effects of water temperature changes in hybrid catfish, focusing on fertilization, hatching, yolk sac absorption, and mouth morphology, while keeping the conditions of water quality, feeding, and disease management constant. The fertilization rate was 67.7% at 29°C, whereas it significantly decreased to 59.0% at 32°C. The hatching rate decreased from 43.4% at 29°C to 26.6% at 32°C. Survival rates plummeted, with no larvae surviving beyond 72 h post‐hatching (hph) at 32°C. Yolk sac absorption was notably accelerated at 32°C, being completely absorbed by 48 hph. Mouth morphometry revealed that a gap in the mouth started to develop 12 hph, and the opening size of the mouth increased out to 72 h. These findings indicate that higher temperatures (32°C) lead to faster yolk absorption, causing embryos to deplete yolk reserves rapidly, potentially before full development and independent feeding. This results in a smaller body size and lower survival rates. Present study provides crucial insights for enhancing breeding practices and creating management protocols for hybrid catfish hatcheries during the period season of high temperature in the context of climate change.