Investigation of production process and water quality changes in dual-purpose ponds of rainbow trout (Oncorhynchus mykiss) in Sistan area

The most important factors affecting water quality are its physical, chemical and biological properties. Considering how water quality is one of the main and influential factors in aquaculture, in this study, the trend of fish growth and changes in water quality in dual-purpose rainbow trout farming ponds in Sistan region were studied. For this purpose, biometry of fish and water quality conditions were performed by sampling fish and water, respectively from five pools in Zabol, Zahak, Nimroz, Hamoon and Hirmand cities. Sampling was performed monthly from December to April (simultaneously with the breeding period) from all pools. The highest and lowest production rates are related to Hamoon pools (1039.44 kg) and Zahak (913 kg), respectively. The highest final length and weight of fish was recorded in Hamoon pool with 26.3 cm and 366 g. Measured factors included water temperature, dissolved oxygen (DO), pH, salinity, transparency, electrical conductivity (EC), hardness, alkalinity, nitrite, ammonia, sulfate, carbon dioxide (CO2), phosphate and nitrate. The results showed that the amount of dissolved oxygen between 7.76 to 8.34 mg.l-1, phosphate and nitrate between 0.4 to 1.6 and 0.4 to 1.9 mg.l-1 respectively, EC between 1/95 to 5.5 mmhos.cm-1 and pH ranged from 7.5 to 7.93. These results showed that water temperature changes, as the most important factor limiting the breeding of rainbow trout in this region, in the cold seasons of the year is in the optimal range for breeding this fish and in different ponds of Sistan region is not considered a limiting factor. Changes in water temperature during the breeding period in these areas varied between 14.78-15.24. Other water quality indicators were also in the optimal range for breeding this fish and not much change was observed in the pools of this area.