Mola Fish (Hypophthalmichthys molitrix) as Plankton Overgrowth Biocontrol Agent in Cirata Reservoir

Abstract

Development in fish aquaculture with floating net cage system (KJA) in Cirata Reservoir have provoked the eutrophication, indicated by the over growth of phytoplankton. The annual restocking initiation of one million plankton feeders fish by the local government was one of the efforts to overcome the massive growth of phytoplankton as consequence of eutrophication in this reservoir. Mola fish, was chosen due to its ecological role as plankton feeder and was expected to control plankton population in the environment. This research was aimed to determine the effectiveness of Mola fish as regulator of plankton overgrowth. Survey method was used with four different location and two sampling time. Materials used in this study were the Mola fish from the KJA and the captured fish from the local fishermen in Cirata reservoir. Fishing gear used in this study was the gill net and regular fish net. In this study, 31 Mola fish were cought in 4 sampling stations and 2 sampling time. Gut content analysis from the gastric and intestine revealed 4 different groups, namely, phytoplankton, zooplankton, crushed pellets and detritus. Additionally, Preponderance Index showed that plankton is the main food of Mola fish during the research with 82.74%, hence this fish was very effective in utilizing plankton. The average plankton’ cell density from all sampling station was 7.529 x 103cellml-1, while the average trophic level of Mola fish in this study was 2.21, indicating the role of Mola fish as herbivore or plankton feeder.