Biological aspects of the endemic eels, Anguilla borneensis, from Lake Semajang, Mahakam Watershed (East Kalimantan, Indonesia)

In order to study biological aspects of the endemic eels from Indonesian Waters, 30 specimens of anguillid eels were collected by gill nets from Lake Semajang, Mahakam Watershed, East Kalimantan (Indonesia) from January to February 2007. The specimens were successfully identified as the endemic species of Anguilla borneensis from Kalimantan Inland Waters, based on morphology and genetic analyses. The endemic species was about 320~780g (Mean ± SD; 519.17±122.26) in BW and 55~74cm (64.20±5.60) in TL, and belong to the long-finned eels with 11.11~15.87 (12.97±1.13) in ADL/%TL. Based on PCR-RFLP analyses, genetic character of the species could be detected by the appearance of double fragment DNA performed by restriction enzymes Alu I (400bp and 500bp), BbrP I (300bp and 500bp), and EcoT14 I (700bp and 600bp) and single fragment DNA performed by restriction enzymes Hha I (500bp), Mva I (700bp) and Bsp1286 I (250bp). Species adjustment was done using DNA mitochondria sequence of the 16S ribosomal RNA gene with specific primer set of the tropical anguillid eels species. Gonado Somatic Index and Eye Index of A. borneensis were about 1.8~10.3 (Mean ±SD; 3.6±2.1) and 3.8~15.9 (8.7±3.1), respectively. It is suggesting that the species were in yellow and silver eel stages when collected. However based on gonad morphology, most specimens (80%) was belong to female immature eels while remain specimen was separated into 10% female mature eels and 10% intersex eels. Positive linear relationship was detected between TL and BW of A. borneensis suggesting the species still in growth phase when collected. The study had proven that Lake Semajang as upper side of Mahakam Watershed was inhabited by the endemic eels A. borneensis. Management and conservation are require in order to keep sustain A. borneensis in the nature since the species also promoted as one ancestor of genus Anguilla in the world.