Trophic status index and natural fisheries potential of some Iranian reservoirs.

The Iran Water Resources Management Company constructs many dams to control surface water that provide a new potential for aquaculture activities. Trophic status index and natural potential for fish production were investigated in nine small dam reservoirs from northwest of Iran. Prediction of fish productivity was calculated based on phytoplankton biomass (using chlorophyll a concentration in water; p Chl-a) and benthic macro invertebrate biomass (p BMI). Average p Chl-a and p BMI of reservoirs were estimated as 233.9±479.4 kg ha-1yr-1 and 14.76±19.18 kg ha-1yr-1 respectively. Concentrations of total phosphorus and total nitrogen varied between 0.023-0.345 and 0.42-3.58 mgl-1, respectively. According to Carlson's transformed model (TSIPN) the mesotrophic status was dominant in reservoirs in which TSIPN varied between 38.7 and 51.2. The eutrophication trend seems to be very fast in these reservoirs because of high nutrient input by aquacultures activities. The usage of fertilizers and amounts of food for aquaculture proposes and expansions of exotic species decline the natural fisheries potential of these reservoirs. Maintenance of water quality and investigation of native species should be planned to preserve sustainable fisheries activities in these reservoirs.