Fecundity and gonadosomatic index of Macrobrachium australe (Guérin-Méneville, 1838) in Dohinob Dacu River

This study investigated the fecundity and gonadosomatic index (GSI) of Macrobrachium australe in relation to the physical characteristics of Dohinob Dacu River, Zamboanga del Norte, Philippines. Sampling was conducted in January 2024 across three sites. Water temperature, pH, depth, and phosphate concentration were measured alongside morphometric and reproductive traits of ovigerous females. Results showed that river conditions were generally suitable for prawn reproduction, with temperatures ranging from 25.1 to 27.6 °C, near-neutral pH (6.79–7.08), depth (35–49 cm), and phosphate levels below 0.4 mg/L. Total body length ranged from 77–95 mm and weight from 4.8–10.9 g. GSI values (0.39–0.74) reflected asynchronous gonad development. Fecundity varied widely (22–413 eggs) and correlated strongly with gonad weight (r² = 0.938), moderately with body weight (r² = 0.538), and weakly with body length (r² = 0.412). Findings highlight that reproductive capacity in M. australe is more dependent on gonadal development than somatic size, providing baseline information for biodiversity monitoring and management of freshwater prawn populations.