NONTJI Anugerah Research and Development Center of Limnology, Indonesian Institute of Science (L, 陸水学研究開発センター, 所長
SOEROTO Bambang Faculty of Fisheries, Sam Ratulangi University, Indonesia, 水産学部, 講師
OKINO Tokio Faculty of Science, Shinshu University, 理学部, 教授 (50020681)
UWA Hiroshi Faculty of Science, Shinshu University, 理学部, 教授 (20020662)
NARUSE Kiyoshi Faculty of Science, University of Tokyo, 理学部, 助手 (50208089)
|Budget Amount *help
¥2,500,000 (Direct Cost : ¥2,500,000)
Fiscal Year 1991 : ¥2,500,000 (Direct Cost : ¥2,500,000)
Two species of ricefishes (O. nigrimas and O. orthognathus) and one species of adrianichthyid (X oophorus) were collected from Lake Poso in the present survey. They seemed to be littoral and inhabit shallow water areas of the lake. They were easily collected by means of small scoop nets in day time and/or light fishing by nets at night. A single specimen of X. poptae (SL 154 mm, female) was donated by Mr. A. Sigilipu who collected this specimens by hook from the outlet of the lake in April 1991. This specimen is preserved at UNSLAT. However, no specimens was found in A. kruyti. These two species are pelagic and inhabit at the depth of 20 - 30 m. An introduced species Tilapia sp. also lives in the same habitat. So, native adrianichthyids seem to be suffered with severe competition by introduced Tilapia, since Lake Poso is oligotrophic.
Karyotype of O. nigrimas was 2n=38, NF=48, 6M+4SM+28A. It has 6 large biarmed chromosomes (6 LBC) and nucleolus organizer regions (NORs) were located on t
he short arms of a submetacentric pair (NORs-SM). This karyotype is similar to that of O. celebensis ; 2n=36, NF=48, 8M+4SM+26A. This species also have 8 LBC and NORs-SM. So, O. nigrimas seems to be a member of the fused chromosome group and closely related to O. celebensis.
Limnological data revealed that Lake Poso was oligotrophic : transparency was 10 m and amount of chlorophyll-a was 0.99 mg/l. The surface water showed pH 8.45, conductivity 118 uS/cm and contained a trace of NO_2-N, NO_3-N and PO_4-P. Amounts of dominant phytoplankton and zooplankton were 0.760 cells/ml (Staurastrum limneticum) and 3.4 inds/l (Thermocyclops uenui).
We agree with the conclusion by Kottelat (1990) that there is evidence that there has been a strong decline of populations of the native fishes, but it is probably still premature to consider these fishes as extinct, since we could confirm a specimen of X. poptae collected from this lake in 1991. Now, we are planning about appropriate fishing gears to be used for obtaining A kruyti and X. poptae, i. e. gill nets, bottom traps, angling for pelagic and light fishing with scoop net, for the next sampling. Less