Diplodon chilensis Gray, 1828 (Bivalvia : Hyriidae) a potential residual waters depurator on inland water salmonid, fish-farms: A laboratory scale study

The aim of the present study was to experimentaly evaluate the capability of the freshwater mussel Diplodon chilensis as a potential depurator of residual waters in fish farming. With this purpose, the present study was carried out at the fish farm of the School of Aquaculture of the Catholic University- Temuco, Chile (38 degrees 46'S; 72 degrees 38'W). The experimental design consisted of 12 poly vinyl chloride trays of 50x20x20cm corresponding to 3 treatments with 3 replicates each treatment and their respective controls. Each tray contained sterilized sand substratum and running water from a trout feeding tank. The treatments 1, 2, 3 contained 15, 30 and 60 mussels respectively, while the control trays contained no mussels. The growth tank contained 5,2k/m(3) of Oncorhynchus mykiss. The trouts were fed daily with 37g of fish food during the time of the experiment duration. At time 0 the wet weight and length of each mussel was measured to determine the physiological state of the specimens through the Condition index. At the onset of the experiment it was determined the mortality and the Condition index of each individual. Also water samples from each tray corresponding to the 3 treatments, their respective replicates and controls were taken at time 0, 30 and 60 days to determine: total suspended solids, total dissolved solids, dissolved oxygen, total phosphorous, ammonium, nitrite, nitrate, conductivity, temperature, pH and chemical oxygen demand (COD). In a parallel way the percentage of organic matter and COD in the substratum of each of the treatment trays and their respective controls were determined. D. chilensis showed more efficiency in diminishing the concentrations of total Suspended solids, total phosphorous, nitrite and the chemical oxygen demand. Values of the mentioned parameters decreased in direct relation to mussel density and time elapsed. Water COD data showed a high system efficiency percentage, corroborated by the Substrate organic matter and substrate CDO data. These results, valid for an experimental scale show that D. chilensis is efficient in water depurator used on fish farming activities, Suitable for rural fish farming.

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