Assessing some biological aspects and the stock status of the giant catfish (Netuma thalassina Ruppel, 1837) in Gunungkidul waters

The giant catfish (Netuma thalassina Ruppell, 1837) fishery in Gunungkidul waters has contributed economically to the local community, and the fishery has intensified since the lobster fishery population has declined. However, there is no information on the biological characteristics and stock status of N. thalassina to inform management strategies. This study aimed to assess various biological characteristics and to determine the stock status of N. thalassina in Gunungkidul waters. Biological data and stock status of N. thalassina were collected from March to December 2023. The results revealed that the majority of the giant catfish caught by bottom longline (63% of the catch) were fish below the length at first maturity. This condition can also be evidenced by the length at first capture (Lc50 = 29 cm), which is smaller than the length at first maturity (Lm50 = 37 cm). The length of N. thalassina captured by bottom longline in Gunungkidul waters ranged from 18 to 60 cm, with a mean of 35.44 ± 7.49 cm (± SD). The catfish’s body weight is optimal, indicated by the relative condition factor (Kn) 1.00 and the coefficient of b 3.15. The diet of N. thalassina consists of crabs, stomatopods, shrimps, and fishes, indicating carnivorous feeding habits. Crabs are the dominant prey item, with a preponderance index of 60%. Fecundity was relatively low, with an average of 26 ± 4 eggs (± SD). The as-ymptotic length (L∞) and growth rate (K) were 61.3 cm and 0.22 year–1, respectively. The fishery status of N. thalassina is currently fully-exploited, based on three stock assessment methodologies: length-converted catch curve, yield per recruit, and spawning potential ratio analysis. The current fishing mortality of N. thalassina (Fcur = 0.42 year–1) exceeds the target reference point of F40% (0.28 year–1), indicating recruitment overfishing conditions. Hence, management measures should prioritize protecting immature fish by preventing the capture of individuals under 37 cm to enhance reproductive output.