effects of water current on some water quality factors in a closed trout culture system

considering the lack of sufficient fresh water resources for aquaculture and at the same time the pollution of fresh water through the process of fish farming, a project was carried out within 15 days to survey the effects of water flow increment on rainbow trout culture by reusing the outlet effluent under a complete random design with 4 treatments and 3 replicate. the water quality factors including: no2-, no3-, nh4+, o2, co2, ph, alkalinity (alk), carbonate hardness and general hardness were examined. fry initial weight and body length were 5.5±0.9 gr and 6.7±0.7cm. the treatments consisted of various water velocities including 0, 3.5, 7 and 10.5 cm/s. the result of the simple correlation of water chemical factors revealed that the treatments displayed significant correlation on the level of 0.01 within these factors. concerning the factors of no2, o2 and ph with the increment of the water virolance the correlation between time, and these factors were increased while the correlation was negative for the factor of no2-. but concerning the factors of no3-, nh4+ and co2-, the correlation was decreased with the increment of water speed while the correlation was negative for the factor of no3- in the fourth treatment which had the fastest water virolance. the amount of o2 and co2 was increased and decreased respectively with the increment of water virolance,, and the amount of no2- and no3- was increased gradually by passing the time with the increase of water flow rate. despite of slight changes on the correlation coefficient(r) of ph and nh4+, totally their changes could be ignored with the consideration of water speed. totally, in this project, treatment 4(10.5 cm/s) with the lowest pollution increasing rate, in comparison with the other treatments known as the best performance (p<0.05).