The marine flagellated Chlorophyta Tetraselmis suecica is among the most important live food species in marine aquaculture. In the present study, the effects of dietary supplementation of dried marine microalgae, Tetraselmis suecica, on growth performance; feed utilization; chemical composition; gene expression of superoxide dismutase (SOD), glutathione peroxidase (GPx) and insulin-like growth factor 2 (IGF-II) gene of Pacific white shrimp, Litopenaeus vannamei; muscle protein polymorphism; and microbial count were assessed and evaluated. Three hundred and sixty L. vannamei (postlarvae) Pls (0.124 ± 0.002 g) were randomly stocked into 40-L glass aquaria (30 shrimp/aquarium) and fed three times daily four tested diets: a basal diet (control), diet incorporated with 2.5 g kg −1 dried T. suecica (T1), 5 g kg −1 dried T. suecica (T2) and 7.5 g kg −1 dried T. suecica (T3) in triplicates, for 90 days. At the end of the trial, the survival rate (SR) of L. vannamei fed diets supplemented with different levels of T. suecica was significantly (p < .05) higher than the control diet. The highest weight gain and specific growth rate and the best feed conversion ratio were recorded on L. vannamei fed a diet supplemented with a 7.5 g/kg dried T. suecica. The highest protein, lipid and ash contents were obtained in L. vannamei fed the diet containing 7.5 g/ kg T. suecica, when compared with the remaining tested diets. The gene expression of antioxidant genes SOD and GPx was the lowest in the T3 group in comparison with the control group. Meanwhile, expression level of IGF-II was higher in the T2 group.The total heterotrophic bacterial count was significantly (p < .05) increased with the cumulative T. suecica level, while no significant (p > .05) differences were found in the total Vibrio count among treatments. Overall, the present results have shown that the diet supplemented with the highest inclusion level of dried T. suecica resulted in improved growth and nutrient utilization.

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A biofloc technology-based 75-day indoor growth trial in an 80 L glass aquaria was conducted to evaluate the effects of two different carbon sources (sugarcane bagasse, SB, and wheat flour, WF) on the biofloc composition, bacterial abundance, and growth of whiteleg shrimp (Litopenaeus vannamei) juveniles (0.23 ± 0.04 g). Three different levels of dietary protein content (250, 300, and 350 g protein kg−1 diet) and two carbon sources (SB and WF) were applied (SB250, WF250, SB300, WF300, SB350, and WF350, respectively), comparing to a controlled diet without biofloc and fed on a 450 g protein kg−1 diet (C450). With the addition of SB and WF, water quality was in the ideal recommended ranges for L. vannamei culture. At the end of the experiment, the biofloc volume increased with increasing dietary protein levels. The nutritional value of biofloc in different treatments was influenced by dietary protein and added SB and WF. Increasing dietary protein significantly increased the protein and lipid contents of the produced biofloc. The use of WF as a carbon source significantly increased lipids and nitrogen-free extract in the biofloc. The total heterotrophic bacterial (THB) count was significantly higher (p < 0.05) in WF300 and WF350 than in the other treatments. The mean effect of the protein levels and carbon source was significantly reported, whereas the highest significant THB count was recorded with 300 dietary protein and using WF as a carbon source. The growth performances of L. vannamei fed with biofloc treatments were significantly (p < 0.05) higher than the C450 group. The highest final weight and weight gain were recorded in SB350 treatment. The feed conversion ratio was not affected by reducing dietary protein levels; meanwhile, the protein efficiency ratio increased significantly in biofloc treatments than in the control. Overall, the results demonstrate that, compared to the control treatment of 450 dietary protein, the biofloc treatments using WF as a carbon source could compensate for the reduction in the dietary protein levels in the diet of L. vannamei and maintain higher zootechnical performance.

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The present study evaluated the influence of different commercial agricultural by-products as a carbon source in a bifloc-based (BFT) culture system on growth performance, whole-body proximate composition, digestive enzyme activities, gut microbial abundance, and hepatopancreas histology of Pacific whiteleg shrimp, Litopenaeus vannamei post larvae (Pls). Three groups were designed, the first group was the control group, where the shrimp was reared in clear water (without carbon source addition and water exchange rate of 100% two times a week) and fed with a commercial diet, in the second and third groups shrimp were reared in BFT systems using two different carbon sources, sugarcane bagasse (SB) and rice bran (RB) without additional feeding or water exchange. The initial stocking density was 16 Pls/liter with an average individual shrimp weight of 0.01 ± 0.002g and age (PL20). The experiment lasted 90 days. The water quality parameters were maintained at optimum levels during the experiment. The final body weight and specific growth rate of shrimp were significantly (p ≤ 0.01) higher in the control group than those reared in both SB and RB-based BFT. Meanwhile, the survival rate was significantly (p < 0.05) higher in BFT groups than in the control. The protease activity in shrimp stomach did not differ significantly. Meanwhile, protease, lipase, and amylase in the intestine showed a significant increase (p < 0.01) in BFT groups than those obtained in the control group. The total heterotrophic bacteria were significantly (p < 0.05) higher in BFT groups. Furthermore, the hepatopancreas histological status of shrimp reared in the SB-based BFT group showed an increase in the hepatopancreas tubules in the distal and B-cell zones (blister-like cells) by 16.83 and 34.89%, respectively, compared to the control. This study revealed that BFT could be used as a natural feed without artificial diets, which influenced the gut microbiota of shrimp, increased digestive enzyme activities, as well as improved the histological structure of the hepatopancreas of shrimp. However, the success of this conditions under high stocking density still needs more investigation.