Using seasonal variability of water quality parameters to assess the risk of aquatic pollution from rainbow trout fish farms in Greece

Sustainable development of fresh water (FW) aquaculture requires minimal environmental impact, by reducing the waste discharged into the surrounding waters. To assess the water quality status and impact of flow-through trout farming in the Louros river (NW Greece), a seasonal evaluation of the trout production in the river was performed. Seasonal samples of river water entering and discharged were obtained to monitor some water quality parameters. The parameters were temperature, pH, ammonium, phosphate, dissolved oxygen (DO), biochemical oxygen demand (BOD5), electrical conductivity (EC), total dissolved solids (TDS), total nitrogen (TN), and total phosphorus (TP) of flow-through trout farms alongside the river. All monitored parameters indicated minimal environmental impact of the fish farms; pH ranged from 7.57 to 8.03, TDS ranged from 151.43 to 242.56 mg/L, DO ranged from 6.28 to 9.16 mg O2/L, BOD ranged from 0 to 2 mg O2/L. As for the nutrients, mean values were below each limit set for freshwater systems. NH4-N ranged from 0 to 0.28 mg/L, and PO4-P ranged from 0.15 to 0.42 mg/L. Based on the comparison of water quality parameters in the outlets and on the Environmental Impacts and Environmental Quality Standards (EQS), it can be concluded that trout fish farms had no significant environmental impact on the river water quality during any of the tested seasons. All parameters presented strong increasing trends during spring and summer and low decreasing trends in autumn and winter. In conclusion, the results indicated minimal aquaculture impact on river Louros water quality.