Fauna ikan di Sungai Cikawung Kabupaten Cilacap Jawa Tengah [Ichthyofauna in the Cikawung River, Cilacap Regency, Central Java]

Cikawung River is a second order river in Citanduy Watershed. The river is located in the western part of Cilacap Regency, Central Java. Like other rivers in the world, Cikawung River runs through various ecosystems, e.g. Pinus mercusii and Tectona grandis forests, cultivation, and settlement areas. Therefore it is predicted that physico-chemical properties of the river will change from the upstream to the downstream and suggested to impact upon the diversity of fish species inhabiting the river. The objective of this study was to obtain data on fish species and its longitudinal distribution along the Cikawung River. A survey method and cluster random sampling technique was performed according to upper, middle, and lower parts of the river. The observed variables were the number of species and its distribution. During the survey, a total number of 499 fish individuals comprising of 19 species from nine families, were collected. Among these nine families, Cyprinidae had the highest number of species with eight and followed by Bagridae with three species. The most abundant species was Mystus gulio and followed by Osteochilus vittatus. High number of species and families proved that the Cikawung River has high fish diversity. The result also proved that the complex pattern of longitudinal distribution was observed. This different distribution pattern among species could be due to the different physico-chemical characters from upper to lower parts of the river, especially on its dissolved oxygen and carbon dioxide level, acidity (pH), and substrates. Abstrak Sungai Cikawung merupakan sungai ordo dua di daerah aliran Sungai Citanduy. Sungai ini terletak di bagian barat Kabupaten Cilacap, Jawa Tengah. Seperti halnya sungai pada umumnya, Sungai Cikawung mengalir melintasi berbagai tipe ekosistem tepian sungai seperti hutan pinus (Pinus mercusii), hutan jati (Tectona grandis), areal pertanian, dan perumahan. Kondisi tersebut memunculkan dugaan bahwa kondisi fisik-kimiawi Sungai Cikawung akan mengalami perubahan dari hulu ke hilir dan perubahan karakter lingkungan tersebut memengaruhi keanekaragaman spesies ikan yang menghuni sungai ini. Penelitian ini bertujuan untuk mendapatkan data mengenai diversitas spesies ikan (daftar uji) dan persebaran longitudinal ikan sepanjang Sungai Cikawung. Metode penelitian yang digunakan adalah survei dengan teknik pengambilan sampel berdasarkan lokasi daerah hulu, tengah, dan hilir. Variabel yang diamati meliputi jumlah spesies dan persebarannya. Selama penelitian ditemukan ikan sebanvak 499 individu yang termasuk dalam 19 spesies dan sembilan famili. Di antara sembilan famili tersebut, famili Cyprinidae memiliki jumlah spesies paling banyak yaitu delapan spesies diikuti oleh famili Bagridae dengan tiga spesies. Spesies yang cukup melimpah adalah Mystus gulio dan Osteochilus vittatus. Tingginya jumlah spesies dan famili yang ditemukan membuktikan bahwa keanekaragaman ikan di Sungai Cikawung masih tinggi. Hasil penelitian juga membuktikan bahwa telah terjadi pola persebaran longitudinal spesies yang kompleks. Perbedaan pola persebaran antar spesies diduga terjadi karena perubahan kondisi fisik-kimiawi dari hulu ke hilir Sungai Cikawung terutama pada oksigen terlarut, karbon dioksida bebas, tingkat keasaman (pH), dan substrat.