River Sapuregel empties into the eastern region of Segara Anakan Cilacap. It is one of the major rivers surrounded by mangrove forests and has various biological resources including fish. This research aimed to observe the diversity and composition of fish in Sapuregel River mouth of Segara Anakan Eastern Area of Cilacap. Recording of fish diversity was carried out from April to September 2018, using purposive random sampling at the Sapuregel estuary. The results showed 1.443 individuals representing 25 families dominated by Engraulidae during the rainy season (42.57%) and dry season (58.49%) followed by Gobiidae (16.82%) in the rainy season and Mugilidae (19.81%) in the dry season. Fish Diversity Index ranged from 1.71 to 1.843 in the rainy, and those during dry seasons was between 1.352 and 1.56. These results indicated fish diversity during the rainy season was higher than that during the dry season.  Evenness Index ranges from 0.1907 to 0.2178 in the rainy season and between 0.2274 and 0.28 in the dry season. The species similarity during the dry season was higher than the rainy season. The fish size obtained varied from juvenile to adult size and was dominated by small fish. Thus, it was presumed that the water of Sapuregel River was used for spawning and feeding grounds by several types of fish.

Nuning Setyaningrum

Agatha Sih Piranti

Dwi Sunu Widyartini

Diana Retna Utarini

Ahmad Ilalqisni Insan

Carmudi Carmudi

Erwin R Ardli