In vivo Assessment of Ocimum sanctum and Ciprofloxacin Against Escherichia coli in Oryzias celebensis Embryos Using Heart Rate as a Non-Destructive Biomarker

Oryzias celebensis, a freshwater fish endemic to Sulawesi, is increasingly recognized as a promising model organism in tropical ecotoxicological studies due to its high sensitivity to local pollutants and strong ecological relevance. Among the physiological parameters used to assess embryonic developmental disruption caused by toxic exposure, heart rate is considered one of the most reliable and non-destructive biomarkers. This study evaluated changes in the embryonic heart rate of O. celebensis following exposure to the bacterium Escherichia coli, the antibiotic ciprofloxacin, and ethanol extract of basil leaves (Ocimum sanctum L.), either individually or in combination. Embryos were observed from stage 36 until hatching and divided into five treatment groups: control, E. coli (EC), E. coli + ciprofloxacin (EC+AB), E. coli + basil extract (EC+BE), and E. coli + basil extract + ciprofloxacin (EC+BE+AB). Heart rate was measured under a microscope, and data were analyzed using the Kruskal–Wallis test followed by a post hoc Bonferroni test. Results showed that the median heart rates at stage 36 in the EC, EC+AB, EC+BE, and EC+BE+AB groups were 163, 168, 159, and 136 bpm, respectively, compared to 175 bpm in the control group. Of these, only the EC+BE+AB group showed a statistically significant difference (P< 0.001). This pronounced cardiac depression suggests synergistic effects between the bacterial pathogen, ciprofloxacin, and basil-derived compounds such as eugenol and flavonoids, likely acting through neurodepressive pathways and immune modulation. These findings reinforce the embryonic heart rate of O. celebensis as a valid and sensitive physiological biomarker for assessing complex, multifactorial exposures. Furthermore, they support the ecological suitability of O. celebensis as an in vivo test model and underscore the strategic value of integrating eco-medical approaches within localized ecotoxicology to address emerging environmental challenges in tropical aquatic ecosystems.