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Background: The Temengor Reservoir is the second largest reservoir in Peninsular Malaysia. Located in the northwestern state of Perak, it was selected to develop a large-scale tilapia (Oreochromis niloticus) aquaculture facility within the Aquaculture Industrial Zone (AIZ) in 2008 due to its favourable environmental conditions. No record of tilapia has ever been reported in the natural waters prior to this. However, a post-establishment study recorded tilapia sightings in the natural waters of this lake. The cultured tilapia was easily recognizable with the elongated mouth and body, and long caudal fin. It is postulated that these were escapees from the floating cages that had invaded the natural waters and would negatively impact the native fish species. To test our hypothesis, we investigated the impact of the aquaculture facility on native fish diversity through a spatial design. Methods: The study was focused on assessing the impact of tilapia culture at sites nearer to the AIZ vs more distant sites, the former with a greater likelihood of receiving escapees. Two major sites were chosen; within 5 km (near-cage) and within 5-15 km (far-cage) radii from the AIZ. Fish sampling was conducted using multiple mesh sizes of gill nets (3.7, 5.1, 6.5, 7.6, and 10.2 cm) deployed at the littoral zone of the sampling points. Species diversity, abundance, dietary habits, and habitat preference were investigated. Results: The CPUE (individual/hour) of native fish species at the far-cage site of the AIZ Reservoir was found to be significantly higher (p < 0.05) than that at the near-cage site. Principal component analysis (PCA) based on diet and habitat preferences showed that the tilapia, O. niloticus had almost overlapping diet resources and habitat with native fish species. Conclusion: We conclude that there is a correlation between the reduced catches of native species (based on CPUE) and the high presence of tilapia. Thus, appropriate actions must be implemented for strategic and effective planning in terms of native fish conservation. [ABSTRACT FROM AUTHOR]

An inventory study of fishes was carried out from June 2003 to May 2004 at Sungai Enam and Sungai Telang, which was last logged 40 years ago. In spite of the negative impacts of logging, the study recorded a total of 21 fish species in these headwaters, comprising nine families. Sungai Telang recorded 19 species with 11 species classified as "locally rare", whereas Sungai Enam recorded 11 species with nine species classified as "locally rare". When species from previous studies were included, the total number of species recorded in Sungai Enam and Sungai Telang was 28 and 27 species respectively. The presence of Devario regina, Neolissochilus soroides and Poropuntius smedleyi in all inventory studies conducted indicate that both headwaters are healthy, and function as sources of clean water, nutrient supplies and fish recruits for Temengor Reservoir. [ABSTRACT FROM AUTHOR]