Water quality changes in rainbow trout (ncorhynchus mykiss) cage farms in the southern part of the Caspian Sea: Kiashahr and Abbasabad

The environmental effects of rainbow trout cage culture were studied on different physicochemical parameters of water quality in two fish farms, Kiashahr and Abbasabad The concentrations of total phosphorus (TP), total Kjeldahl nitrogen (TKN), nitrate, total organic carbon (TOC), chlorophyll-a, oxygen saturation, and dissolved oxygen (DO) was measured beneath, eastward and westward of the cages. In phase II, a significant increase in the concentrations of TKN, nitrate, TOC, and chlorophyll-a beneath and 50 m east and west of the cages was detected compared to the control and the other stations (P<0.05). A significant higher concentration of these variables was observed in the final sampling campaign in both breeding sites (P<0.05). Unlike other variables, TP concentration in both sites decreased at the end of the breeding period compared to the beginning and also cage station didn’t show a significant difference compared to the control station (P>0.05). In conclusion, rainbow trout cage farming in the southern Caspian Sea can cause a significant increase in water quality parameters up to a radius of 50 m of cages, which indicates an organic enrichment in the water surrounding the cages. Due to the growing trend of fish aquaculture in this region, proper management practices such as high-quality food and low feed conversion ratio are needed to reduce its negative effects on the marine environment.