Abstract

Gill-net selectivity is a size and type of fish that caught depending upon specific mesh size of a used gill-net. In this study, four different mesh sizes (4, 6, 8 and 15 cm) were used in al-Kalakla Fishery (KF) and Jabel Awlia Dam Fishery (JADF) in the White Nile for studying their selectivity. The results of a catch per unit effort (CPUE) study showed that meshes 4 and 6 cm had higher productivity in fishing in KF than that in JADF; whereas, meshes 8 and 15 cm caught more fishes in JADF than in KF for the entire year. In KF, autumn season was the best for fishing with meshes 6 and 8 cm. In JADF, summer and autumn were the best for fishing by meshes 4 and 6 cm. The gill-nets of the study were highly selective for fish species according to their body size. Five fishes of small sizes (body depth at around 4 cm) as Tilapias (Oreochromis niloticus: Linnaeus, 1758; Tilapia zilli: Gervais, 1848;Sarotherodon galilaeus: Linnaeus, 1758), Kas (Hydrocynus forskali: Cuvier, 1819;Hydrocynus vittatus: Castelnau, 1861; Hydrocynus brevis: Günther, 1864), Nile Perch (Lates niloticus: Linnaeus, 1758), Dabis (Labeo vulgaris: Heckel, 1847) and Bayad (Bagrus bayad: Forsskål, 1775) were caught intensively by mesh of 4 cm during all seasons in both KF and JADF; whereas, meshes of 8 and 15 cm caught occasionally bigger fishes ranged between 8 to15 cm as Nile Perch and Bayad. The selectivity of these nets reflected over-fishing caused in the White Nile. 

Key words: Fisheries, freshwater fish, River Nile, fishing gear, fishing nets.