ABSTRACT
Contamination in Indonesian waters needs to be continuously monitored to prevent serious damage an ecosystem. Environmental monitoring involves not only contamination analyses in water; sediment and organisms but also application in ecotoxicological approach to detect contaminant effects to organism. Selection for bioindicator must consider many factors including abundance, easy to handling, taxonomy is well known, sensitivity and ecological relevance. Java merdeka (Oryzias avanicus meets that requirements and potentially to develop as bioindicator for environmental monitoring in Indonesia.