Environmental effects of rainbow trout (Oncorhynchus mykiss) farms on Zayandeh-rud River

Objective: Recent advances in intensive aquaculture in flow through systems have caused general public concern over the pollution issues which may occur through the fish farm effluent discharge. Effluent water quality can be affected by many and varied factors such as flow rate, culture species, stocking density, feed quality and quantity, and feeding techniques. Zayandeh-rud River in central Plateau of Iran receives discharge of so many rainbow trout farms, especially in upstream. The purpose of this study was to investigate the potential effect of rainbow trout farms effluents on the river ecosystem using water physicochemical analyses, during one-year period. Method & Materials: Three separate trout farms alongside the river were selected in Dimeh, Nekoabad, Hojatabad and regions with 500, 100 and 60 tons production capacity, respectively. Water samples from inflow and outflow of each farm (with three replicates) were taken seasonally to determine the physicochemical parameters such as BOD5, COD, DO, pH, ammonium, nitrate and phosphate (using Standard methods). Also three sites in river were sampled at each trout farm: site 1, above the farm (control); site 2, approximately 50-100 meters below the outfall; site 3, 1 km downstream of the outfall. Results & Conclusion: Water physicochemical analyses indicated differences between fish farm inflow and outflow. Parameters such as BOD5, COD and total suspended solids (TSS) in outflow were significantly higher than inflow (P < 0.05). Our results indicated an increase in dissolved nutrients (ammonium, nitrate and phosphate) and also a decrease in dissolved oxygen (DO) and pH in outflow compared to inflow. Significant positive relationships were also found between BOD5, COD and TSS and the farm production capacity. The environmental impact of fish farm effluent was evaluated by comparing the amount of each parameter in site 2, 3 with those obtained from site 1 (control). Our findings indicated that the impact of farms effluent on receiving water quality is negligible. Such findings might mostly be due to the large volumes of flow in the Zayandeh-rud River which dilutes the effluents and results in a low nutrient concentrations and apparent improvement of water quality compare to the fish farm outflow. However, each fish farm is unique and would be expected to differ in its discharge volume and characteristics. Thus, using the data from this study to extrapolate applications for other production units and judgment of their environmental impacts should be viewed with caution.

کلیدواژه ها:

effluent ، production capacity ، Zayandeh-rud ، rainbow trout ، nutrient ، water quality