Fish diversity as bioindicator of downstream pollution in the surabaya river and jagir river

Surabaya City is one of the major cities in Indonesia which has a large number of industries. The industry is suspected of pollution, one of which is water pollution in the city of Surabaya, more precisely downstream of the Kali Surabaya River and Kali Jagir River. The pollution has reduced the diversity of aquatic biota, one of which is fish, the decrease in diversity of fish can reduce the stability of river ecosystems and the loss of potential fish whose existence is not yet known but is lost due to pollution. This study aims to determine the number of fish species found, find out whether or not the differences in fish species found, the index value of fish species dominance, know the value of river pollution by bioindicators, know the stability profile of the two river ecosystems based on the value of fish diversity. This research was conducted in 2018 in March, June, September, and December. Fish sampling results were calculated and identified, then determined whether there were differences between fish species found at each location using similarity and dissimilarity indexes, determining the dominance index value (Simpson’s diversity index) and fish diversity value (Shannon-Wiener), then the results were matched with the category of degree of pollution according to Lee and the stability profile of the ecosystem using the Odum. The results of this study are found as many as 19 species of fish in the Lower River Kali Surabaya and 16 species of fish in the Kali Jagir River. There are differences in fish species found downstream of the Kali Surabaya River and Kali Jagir River. The results of the dominance index value of fish species found downstream of the Kali Surabaya River and Kali Jagir River are included in the low dominance category. The results of the fish diversity index value are known that in the downstream of the Kali River in Surabaya, including mildly polluted and Kali Jagir River included in the category of medium polluted. Based on Odum the ecosystem profile of the two rivers is included in the category of moderate diversity, productivity is quite balanced, the ecological pressure and the stability of the ecosystem is moderate.