Temperature-driven ontogenetic and morphological plasticity in Labeobarbus intermedius larvae from Lake Tana, Ethiopia.

Understanding how temperature influences early developmental stages is critical for predicting fish population responses to environmental change. This study examined the ontogenetic and morphological plasticity of a cyprinid species endemic to Lake Tana, Ethiopia, reared under four constant temperature regimes (18, 22, 24 and 30°C) in controlled laboratory conditions. Fertilized eggs were collected from the Gumara River and reared for 215 days post-hatching. Skeletal development was qualitatively assessed using differential staining (Alcian Blue and Alizarin Red S), while morphometric and meristic traits were quantitatively analyzed. Elevated temperatures accelerated development and growth but were associated with significantly higher mortality, particularly at 30°C (61.2%). In contrast, larvae at 18°C exhibited delayed development but the highest survival (92.6%). Morphological traits, including vertebral count and fin ray numbers, varied significantly with temperature, indicating high developmental plasticity. These findings highlight the sensitivity of this endemic species to thermal variation, offering critical insights for hatchery management, conservation planning and climate adaptation strategies in freshwater fisheries.