The State of Riverine Ecosystem and Fish Exploitation
Opak-Oya river basin and its tributaries physically have been intensively exploited for several purposes such as irrigations, sand mining, embankment as well as garbage and wastewater disposal. The community surrounding has also exploited a riverine fish intensively using electrofishing. Cyprinoformes and Percyformes dominated Fish taxa in the area. The objectives of research were to understand the state of riverine ecosystem and fish exploitation, fish population, and fish microhabitat preferences in down stream parts of the river. Field works and literature review was conducted to test the issues. The characteristic of fish exploitation was analyzed in focus of group discussion. Fish data was collected using electrofishing, while microhabitat criteria were calculated using Nakamura’s procedure (1999) and analyzed using PHABSIM (Stalnaker 1995; Boove et. al 1998).
Awaos personatus was found preferred microhabitat with depth and velocity of about 0.3 – 1.0 m and 0.6 – 1.4 m/s respectively, while adult Caranx ignobilis preferred depth of about 0.1 – 0.3 m and velocity of 0.1 m/s. Liposarcus pordalis and Rasbora agryotaenia were preferred microhabitat with higher depth and velocity, which range of about 1.0 – 1.2 m and 0.9 – 1.4 m/s respectively. In terms of substrate preferences, it was found that A. personatus adult, juvenile L. pordalis and R. agryotaenia preferred microhabitat with sandy substrate, whereas A. personatus juvenil and C. ignobilis adult preferred clayey-silt substrate. Another species such as Dermogenis pusilla preffered microhabitat with depth of about 0.1-0.3 m. Based on chi-squared test (a=95%) fishes were not differ the optimal and usable microhabitat, except juvenile A. personatus for substrates. The rapid changing of riverine habitat might threaten the sustainability of the fish population.
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