Importance of carrying capacity for sustainable trout culture: the case of “bagci balik”

Trout is a fish species that is produced widely all over the world and it has an important place in the aquaculture industry. For the sustainable development of the trout culture, it is need to determine how much fish can be stocked per unit volume (carrying capacity). Over-stocking could threaten fish welfare and sustainable use of environmental resources. Estimating of carrying capacity is necessary both to minimize these adverse impacts on fish and environment, and in terms of sustainable use of water resources. In this study, carrying capacity of a commercial land based trout farm in Koycegiz (Mugla/TURKEY) was investigated. Two methods were used to calculate carrying capacity and compared with each other: “Oxygen requirement based carrying capacity” and “Metabolic waste based carrying capacity”. The mean values of studied water quality parameters that used in calculations were measured as; 14.12 ± 0.72 °C for temperature, 7.78 ±0.20 for pH, 10.1 ± 0.93 mg/l for oxygen, 3,05 ± 0,84 m3 s-1 for flow rate. The annual production capacity was calculated with these measured parameters. By the observed data, the carrying capacities of the farm were found respectively with based on oxygen requirement as 538.42 ± 196.22 tonnes; and based on metabolic waste as 1113.4 ± 463.7 tonnes per years. According to the results that obtained from the study, there was significant difference between two carrying capacity estimation methods. However when the oxygen levels of the water were examined, in some months the negative values, that could adversely affect the life and growth of the trouts, were observed. Fort this reason, to reduce the limiting effect of the oxygen and reach maximum carrying capacity; it is needed to be integrated oxygenation or aeration systems into the production ponds. On the other hand, for the sustainable use of the environmental sources in the facilities engaged in production according to the metabolic waste based carrying capacity, it is important to use advanced water filtration systems. Keywords: Carrying capacity, land-based trout culture, water quality