عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The aim of this study was to evaluate the effects of biofloc (with addition of spoilage date palm extract (SDE) and molasses as sugar sources) on bacterial load of water, growth performance and intestine of Litopenaeus vannamei using diets containing different protein levels. Four biofloc treatments were designated including the biofloc treatment with SDE + a diet containing 25% protein (P25), biofloc treatment with molasses + a diet containing 25% protein (M25), biofloc treatment with SDE + a diet containing 15% protein (P15), biofloc treatment with molasses + a diet containing 15% protein (M15) and the control treatment with a diet containing 38% protein (Control). All treatments were conducted in triplicates. A 35-day study was conducted on 35 juvenile shrimp (with average weight of 5.37±0.33 g) which randomly stocked in fifteen tanks (each 300 L) at a stocking density of 175 shrimp m−3. The highest amounts of growth parameters (weight gain, Feed Conversion Ratio (FCR), growth rate and survival) were observed in P25 treatment and the lowest amounts of growth parameters were observed in the control (P<0.05). Moreover, the highest percentages of body weight index, feed efficiency and specific growth rate were observed in P25 and the lowest percentages of those were observed in M15 treatment (P<0.05). Results showed that the number of total heterotrophic bacteria was increased during the study and the numbers of total heterotrophic bacteria in all biofloc treatments were higher than that of the control. The highest and the lowest numbers of fungi, vibrio and bacillus were found in P25 treatment and the control treatment, respectively. The length of the epithelial cells of the intestine was increased in all biofloc treatments as compared to the control but this difference was significant in the first abdominal segment, only. The result demonstrated that the effects of SDE were better than molasses, which could be due to the presence of useful compounds such as the growth and immunity promoters in it.