Hydropower development in Indonesia poses significant barriers to upstream migration of anguillid eels, particularly during their juvenile life stages. This study evaluates the effectiveness of climbing substrates designed to facilitate passage of juvenile eels (Anguilla bicolor bicolor and A. celebesensis) using a controlled flume system at the River Engineering Institute, Ministry of Public Works, Indonesia, located in Central Java. Two species, two slope gradients (25° and 45°), two size classes (glass eel and elver), and three substrate types (no substrate, mussel rope, and eel tiles) will be tested across replicated treatments. Climbing success, climbing speed, and number of attempts to climb will be quantified, alongside physiological stress responses including cortisol, glucose, BUN, AST, and total protein. This experimental design enables assessment of both climbing performance and physiological responses. The results will inform the development of juvenile eel-specific passage structures in Indonesia, where no functional designs currently exist despite extensive hydropower expansion. This research fills a critical knowledge gap and supports sustainable infrastructure planning for conserving tropical anguillid eel populations and the livelihoods that depend on them.