Water Quality Control in Tilapia Closed Culture System Using Filter Feeding Freshwater Clam (Pilsbryoconcha exilis compressa)

Abstract

Evaluation of the possibility of using filter feeder freshwater clam, Pilsbryoconcha exilis compressa, for the improvement of water quality in tilapia closed culture system was evaluated in a 2 month outdoor tank experiment. Tilapia was cultured in a closed system with and without freshwater clam for two months. Average values of turbidity, chlorophyll a, total particulate matter, particulate organic matter, particulate nitrogen and particulate phosphorus in tilapia-freshwater clam treatment were significantly lower (P≤0.05) than those in tilapia only treatment. However, there was no significant difference (P≥0.05) between the average values of total ammonia nitrogen from the two treatments. Average values of turbidity, chlorophyll a, total particulate matter, particulate organic matter, particulate nitrogen, particulate phosphorus and total ammonia nitrogen were 6.0 ±11.6 NTU, 24.3±15.8 μg/L, 7.9±6.1 mg/L, 6.4±5.1 mg/L, 1.419±1.342 mg/L, 0.087± 0.058 mg/L, and 0.473±0.267 mg/L, respectively, in tilapia-freshwater clam treatment. In comparison, tilapia only treatment yielded average values of 22.0±11.6 NTU, 324.1± 222.2 μg/L, 42.5±26.2 mg/L, 34.1±21.1 mg/L, 5.291±5.634 mg/L, 0.305±0.189 mg/L and 0.599±0.752 mg/L, respectively. According to the results of this experiment, P. exilis compressa is effective in removing particulate matter, particulate nitrogen, phytoplankton and particulate phosphorus from water in tilapia culture tanks resulting in the decrease of 72.7% of turbidity, 81.4% of total particulate matter, 81.2% of particulate organic matter, 92.5% of chlorophyll a, 73.2% of particulate nitrogen and 71.5% of particulate phosphorus. There was no significant difference (P≥0.05) between production rate, survival rate and growth rate of tilapia in both treatments.