Investigation on feasibility polyculture of Litopenaeus vannamei with Mugil cephalus in earthen shrimp ponds

This study was conducted in order to optimizing of the biological condition and enhancing of the harvest efficiency for cultured shrimps of Guater site. Experimental design was consisted of three treatments and each treatment with three replications (totally 9 ponds with 600 m^2 area for each pond). After preparing and watering of ponds, the ponds was stocked with shrimp post larves in a density of 0.007±0.001 g (or 20 numbers per m^2) per m^2. After 35 days, the fingerlings of gray mullet were released to shrimp ponds in densities of 0/100 m^2 (T1/), 2/100 m^2 (T2) and 4/100 m^2 (T3). During experiment, the physicochemical parameters of water (temperature, O_2, pH, water transparency and salinity) were measured daily for two times (morning and afternoon). Also, the nitrate, nitrite, ammonia, phosphate and silicate concentrations and BOD5 as well as chlorophyll (a), phytoplanktons and zooplanktons were measured every 15 days one time. To determine the organic values of the bottom sediment of the ponds, monthly sampling was conducted. Health status of shrimps was investigated monthly too. Growth rate, mean weight, survival value, Food conversion ratios (FCR) and total shrimp harvest (Kg) were measured after 107 days rearing in ponds. ANOVA analysis showed significant differences between treatments. The highest (212 Kg, 3533 Kg; weight mean was18.4 g for each shrimp) and lowest (187 Kg, 3116 Kg; weight mean was16.23 g for each shrimp) of harvested shrimps were yielded in T3 and T1 respectively. There was not significant differences between treatments in terms of survival rate (P>0.05). After 107 days rearing, the highest (1.27 0.2) and lowest (1.2 0.1) of FCR were observed in T_3 and T_1 respectively. Although, there were no significant differences between T_2 and T_3 in ammonia, O_2, Total organic material, pH and BOD5, but, T_2 and T_3 had significant differences with T_1 in these parameters. In this study, 27 genus of phytoplanktons belonged to Diatoms (Bacillariophyceae), blue-green algal (Cyanophyceae) and dinoflagellates (Dinophyceae) were identified. Diatoms with 20 genus had more abundance than dinoflagellates (6 genus) and blue-green algal (1 genus). Also, 7 orders of zooplanktons including copepod, mollusks, nauplius of crustacean and rhizopoda were identified. Health investigation of T1 (without shrimp) showed more pathogenic pollution (parasites and bacteria) than in treatments with shrimp. In this regard, among bacteria, the Vibrio genus (V.Alginoliticus and V.Fluvialis) had more abundance and among parasites zoothamnium sp and Epistylis sp were identified which more abundance was for zoothamnium sp. In conclusion, our results concluded that mixed culturing of white shrimp and grey mullet in optimum densities is possible and is caused more production of shrimp