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In this study, the effects of different primary stocking densities (45, 50, 55 and 60 shrimp/m²) of whiteleg shrimp postlarvae (PL12) were evaluated on the growth and survival rates. Brackish water (10.52±0.43 psu) was provided from the Caspian Sea. The experiments were performed in 12 circular concrete ponds with a sandy bed (area: 78m²) with four treatments and three replications for each treatment. The culture period was 75 days and the average water temperature was 27.4±1.79°C. The results showed that different stocking densities caused statistical significant difference in growth and survival rates among various experimental treatments (P<0.05). Increasing the stocking density resulted in decreasing the amounts of weight gain, survival rate (SR), specific growth rate ( SGR ) and the average daily growth ( ADG ). However, FCR was significantly different among treatments (P<0.05) and was not dependent on the primary stock density of postlarvae. The highest growth rate ( SGR =11±0.04 and ADG =0.25±0.01 gr/day/ind.), production (43.6±3.3 kg shrimp in 78 m²) and survival rate were observed in the lowest density treatment (45 shrimp/m²). 
 

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In this study, the effect of experimental diets containing different levels of carbohydrate and niacin on growth indices, carcass composition and heamolymph biochemical parameters of juvenile whiteleg shrimp (Litopenaeus vannamei) were investigated for 45 days. Shrimp with mean initial weight of 5±0.33 g were reared in 300 liter tanks with 8 treatments. Feeding was performed 4 times a day using experimental diets containing two levels of carbohydrate 15 and 30% and three levels of dietary niacin 100, 150 and 200 mg kg^-1with two controls. At the end of the period, growth indices, carcass composition and biochemical indices of heamolymph of shrimps were assessed. The best growth performance consisted of the highest final weight (14.05±0.5 g), final length (13.38 ± 0.05 cm) and specific growth rate (2.23±0.07) were in treatment contained 15% carbohydrate and 100 mg niacin kg^-1 diet (p<0.05). Also, the highest glucose (53.66±0.88 mg dl^-1), HDL (27±0.57 mg dl^-1) and total protein values (10.9 ± 0.17 mg dl^-1) were in  treatment contained 15% carbohydrate and 100 mg niacin kg^-1 diet (p<0.05). On the other hand, the highest protein content of carcass was observed in treatments contained 15% carbohydrate and 100-150 mg niacin kg^-1 diet (p<0.05). Also, fat of carcass was reduced by decreasing dietary carbohydrate (p<0.05). Therefore, the results showed that low carbohydrate level with 100 mg niacin per kg of diet had beneficial effects on growth, carcass composition and heamolymph of juvenile whiteleg shrimp.
 

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The aim of this study was to investigate the effects of dietary ethanol extract of Rhizophora mucronata leaves on the growth performance, survival, and biochemical composition of Litopenaeus vannamei. The experiment was conducted using 600 shrimp juveniles (2 g) in a completely randomized design with four treatments and three replicates, with 50 shrimp per replicate for a duration of 60 days. The experimental treatments included: 1- Basal diet (control), 2- Basal diet + 1 mg ethanol extract of mangrove leaves, 3- Basal diet + 2.5 mg ethanol extract of mangrove leaves, and 4- Basal diet + 5 mg ethanol extract of mangrove leaves. At the end of the experimental period, various growth, biochemical, and survival parameters were measured. The results showed that body weight gain, daily growth rate, and specific growth rate were significantly higher in the 1, 2.5, and 5 mg/kg ethanol extract of mangrove leaves compared to the control group (P<0.05). The highest carapace length was mesured in 2.5 mg/kg compared to the other experimental groups (P<0.05). Besides, the survival rate was significantly increased in all extract treatments compared to the control group (P<0.05). The highest crude protein content of the carcass and the lowest moisture content were observed in 2.5 mg/kg (P<0.05). The control group showed the lowest lysozyme activity, while the 5 mg treatment exhibited the highest lysozyme activity, followed by the 1 mg and 2.5 mg treatments (P<0.05). The 1 mg treatment showed the highest phenoloxidase activity (P<0.05). Based on the results, the 2.5 mg and 5 mg treatments were associated with the highest protein and albumin contents, while the control and 1 mg treatments had the lowest contents (P<0.05). Overall, it can be concluded that the inclusion of 2.5 mg/kg of mangrove leaf extract in the diet had positive effects on the growth, biochemical composition, and survival of whiteleg shrimp.