UTILITY IMPROVEMENT OF BRACKISH WATER CULTURAL EARTH PONDS OF RAINBOW TROUT (ONCORHYNCHUS MYKISS) THROUGH ESTABLISHING ENCLOSURE MEDIUM (NET PEN)

: Considering increase in production of earth ponds in brackish water condition, this research carried out at bafgh fisheries research station to improve efficiency and production of brackish water cultural earth ponds of rainbow trout ( Oncorhynchus mykiss ). This study was performed in four 0.5ha earth ponds in two treatments with two replications. Each treatment included two earth ponds so that fish farmed in two culture mediums consisting open medium and %20 enclosure medium of pond (pen medium).for this purpose 20% of earth pond s space separated via a fixed net wall with 15 mm in mesh. In this research some main growth equations and economical factors were studied. Data were analyzed using SPSS software, Pierson, Toki, Dankan, Dant analysis and also descriptive statistics. The significant differences were determined in %5 level. Since there was a connection between pen medium with free one, no signs based upon disturbance observed in measured environmental factors in this space. Statistical results indicated a significant increase in %WG, %FE, % SGR, %CF and final biomass in pen medium treatment(p>0.05). According to economic results, this treatment also differed significantly from open medium treatment about ratio of marketable size production and net income so that yield quantity and production income increased. Therefore, through pen culture in 0.5 ha earth ponds and likely larger ones, utility and production of farm improve and can be a good approach for farmers in order to better exploitation of possibilities and facilities.