fa <span style="color:black;"><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">This study was conducted at the Hanna Reservoir located in the southwest of Isfahan Province</span></span></span><span style="color:#0D0D0D;"><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">. </span></span></span><span style="color:#222222;"><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">According to this study, </span></span></span><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">chemical analyses were conducted to evaluate the magnitude and variations of COD, BOD₅, O₂, NH₃⁺ and NO₂^-concentrations in the Hanna Reservoir. In the headwaters the magnitude values of BOD₅, COD and early morning oxygen minima were quite identical to the recommended optimum levels. However the concentrations of :::union:::ized ammonia in winter and spring and the concentration of nitrite in summer and autumn exceeded the allowable levels cited in different literature and might have exerted some growth retarding or lethal effects on the fish population. Water quality, zooplankton, benthos and sediments were monitored at sites of 20 m depths to determine the effects of rainbow trout cage culture on the lake environment. Oxygen depletion occurred in the vicinity of the farms due to respiration of the farmed fish.</span></span><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;"> Zooplankton had</span></span><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;"> stronger nutritional value</span></span> <span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">in</span></span><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;"> all six ecosystems of the Hanna Reservoir, and in seasons during which fish feed on these nutritional sources, breeding occurs with higher efficiency. </span></span><span style="font-family:times new roman,serif;"><span style="font-size:12.0pt;">Benthic invertebrates were rare at all six sites of the lake. The sediments below the cages had a pH and organic matter comparable to areas of the lake receiving the natural input of allochthonous material.</span></span><br> &nbsp; Hanna reservoir, Fish, Benthos, Zooplankton. 1085 1097 http://jifro.ir/browse.php?a_code=A-10-600-89&slc_lang=fa&sid=1 S.R. Daniali srd169@yahoo.com 100319475328460022560 100319475328460022560 Yes M. Soltani 100319475328460022561 100319475328460022561 No A. Kamali 100319475328460022562 100319475328460022562 No M. Shamsaei 100319475328460022563 100319475328460022563 No