Diversity and biological characterization of anguillid eels in Pangani and Rufiji river systems, Tanzania:...

Tropical rivers in the western Indian Ocean are under significant human activity pressure, impacting the aquatic fauna, including freshwater eels. However, conservation efforts are hindered by a lack of comprehensive knowledge of these species. This study used a combination of morphological characters and molecular markers (mitochondrial cytochrome oxidase subunit I) to identify anguillid eel species unambiguously. The study revealed the presence of Anguilla bengalensis, Anguilla bicolor and Anguilla marmorata, with the last being a new report for the Pangani River. The study also established length-weight relationships for A. bicolor and A. bengalensis and observed significant differences in gonadal development and physiological indices among maturity levels. No study was performed for A. marmorata due to an insufficient sample size (n = 2). The eye index and pectoral index provided measures of maturity, indicating significant morphological changes during maturation. Understanding the biology and ecology of anguillid eels is crucial for developing effective conservation and management strategies. Due to the vulnerability of these migratory species to various human pressures, concerted efforts are needed to protect their populations and the integrity of freshwater ecosystems in the region. This study provides valuable insights into the diversity and biological characteristics of anguillid eels in East Africa, filling crucial knowledge gaps and providing a foundation for informed conservation actions. The findings of this study have broader implications for regional freshwater conservation, particularly in regions facing similar environmental challenges. They can serve as a reference point for international efforts to protect freshwater biodiversity, in general, and catadromous anguillid species, in particular.