THE EFFECT OF PROBIOTIC BACILLUS ON NITROGEN WASTE PRODUCTION OF RAINBOW TROUT FRY
Introduction
In the past, formulation of diets in intensive aquaculture has often been aimed at meeting requirements for maximum growth, while more recently, formulations are being designed to meet other desired production goals. One such goal is to increase the sustainability of various aquacultural enterprises by reducing the environmental impacts they may have on surrounding ecosystems. Aquaculture wastes are largely dietary in origin with estimates of 52-95% of feed nitrogen ending up as waste (Wu, 1995). Therefore, diet manipulations which result in less waste production are an attractive approach to this predicament. One particular aspect of deleterious waste production now being addressed is formulation of diets to minimize ammonia production by cultured species.The main end-product of protein metabolism in teleosts is ammonia and a significant proportion of nitrogenous waste is also excreted as urea (Wood, 1993). Consequently, measurements of ammonia and urea excretion have been used as indicators of the effects of various environmental and nutritional factors on protein metabolism and can give an insight into the nitrogen balance of fish (Jobling, 1981; Perera et al., 1995). There is not information available on nitrogen waste production of rainbow trout fry fed by probiotic bacilli. This study aimed to demonstrating the effect of probiotic bacilli on nitrogen waste production of rainbow trout fry.
Materials and Methods
The probiotic was prepared from Protexin Co (Iran-Nikotak). The five species of probiotic bacillus (Bacillus licheniformis, Bacillus subtilis., Bacillus polymyxa., Bacillus laterosporus and Bacillus circulans) as bacterial blend under the commercial title of Protexin aquatic were used for supplementation of ration. Three concentrations of bacterial suspension, 1×106 (D1 treatment) 1×107 (D2 treatment) and 1×108 (D3 treatment), (single colonies per 100 g food), and the effect of probiotics treatments with a control treatment, which their feeding had no probiotics were compared. The feeding was varied from 5% to 8% of body weight. But During the excretion experiment, fishs were not fed. At the end of experiment (60 days) sixty fish were captured immediately placed into 12 tanks for 24h. Aeration and water flow were stopped during the experiment. Water temperature was 16°C and the experiment was conducted at the natural photoperiod conditions with similar light intensity for all tanks. After 24 h., The concentration of ammonia in samples was determined by the phenol-hypochlo- ride method (Solorzano, 1969). Urea was analysed by the urease method (Elliott, 1976). Total ammonia-nitrogen concentration was calculated using a standard curve prepared from ammonium chloride solution. The difference between ammonia concentration before and after urease treatment was used to calculate urea concentration.
Results
Effects of probiotic treatments on amount of ammonia and urea excretion of rainbow trout fry in probiotic treatments were better than control treatment (p<0.05). The maximum of nitrogenous excretion of ammonia (739.89 mg/Kg) and urea (88.82 mg/Kg) were in control. But the minimum nitrogenous excretion by ammonia and urea were obtained in D2 treatment where the rainbow trout fry fed with supplementated ration by 1×107 (single colonies per 100 g food) of probiotic bacillus. The percentage of nitrogen waste per nitrogen intake, were significantly decreased in experimental treatment in comparison with the control treatment (P<0.05). The growth parameters were significantly changed in experimental trials fed with a diet supplemented by suspension probiotics (P<0.05, Table 2).
All of experimental probiotic treatments had good results in decreasing of nitrogen waste by excretion of ammonaia and urea. Feeds for some fish species typically have a high protein content that supplies a large proportion of dietary energy and results in high nitrogenous excretion. Rychly and Marina (1977) demonstrated an increase in blood ammonia levels within 1 h of feeding rainbow trout and proposed that endogenous circadian rhythms in both ammonia excretion and nitrogen metabolism were dependent upon feeding times and nitrogen intake. Similar results were reported by Faramarzi et al. (2012) on nitrogen waste by excretion of ammonaia and urea nitrogen in Persian Sturgeon using probiotic bacillus with bioenriched Daphnia sp. Probiotic diet supplementation resulted in better growth performance and feed utilisation than in controls. Jafarian et al. (2007) revealed that supplemented diets by probiotic Bacillus sp. enhanced the survival rate of Persian Sturgeon (Acipencer persicus) Larvae. In the present research, the most significant promotion was observed in trails 1 (2×104 CFU ml-1), but other treatments did not show any differences, obviously. The results of this study clearly demonstrate that the probiotc basillus had the best effects on growth and nitrogen waste in Onchorhynchus mykiss fry.
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