Effects of bioflocs on water quality,and survival,growth and digestive enzyme activities of Litopenaeus vannamei (Boone) in zero‐water exchange culture tanks

A 30‐day experiment was performed to investigate the effects of bioflocs on water quality, and survival, growth and digestive enzyme activities of the white shrimp Litopenaeus vannamei. Altogether 28 shrimp (7.4 ± 0.1 g) were stocked in each 150 L tank. Two bioflocs treatments and one control were managed: ‘bioflocs 1’ and ‘bioflocs 2’ based on two different densities of the bioflocs, and clean water control without the bioflocs. Brown sugar was added to the bioflocs 1 and bioflocs 2 treatment tanks accounting for 28% and 80% of the shrimp feed respectively (corresponding to proximate C/N ratios of 10 and 14 in daily additions of organic matter respectively), so as to promote bioflocs production and approximately 14 mL L^?1 in treatment bioflocs 1 and 20 mL L^?1 in treatment bioflocs 2 were maintained from day 15. Monitoring of selected water quality parameters throughout the whole experiment period showed that all parameters remained within recommended levels for shrimp culture in the bioflocs treatments at zero‐water exchange, especially low total ammonia nitrogen and nitrite nitrogen levels. By the end of the experiment, shrimp survival rates were above 86%, with no significant differences (P > 0.05) among the three groups. Both weight gain rate and special growth rate tended to increase in the bioflocs treatments compared to those in the control. Meanwhile, the overall specific activities of protease, amylase, cellulase and lipase of the shrimp in the bioflocs treatments were all higher than those in the control; and for the specific activity of the same digestive enzyme, the differences between the bioflocs treatments and the control performed inconsistently among different organs: hepatopancreas, stomach and intestine. Present results suggest that the bioflocs can not only maintain favourable water quality conditions for shrimp culture and help shrimp grow well in zero‐water exchange culture systems, but may also have a positive effect on digestive enzyme activities of the shrimp.     

Juvenile Procambarus clarkii farmed using biofloc technology or commercial feed in zero‐water exchange indoor tanks: A comparison of growth performance,enzyme activity and proximate composition

A 60‐day study comparing the growth performance; proximate composition and the digestive, immune and antioxidant enzyme activities of juvenile red swamp crayfish (Procambarus clarkii) reared using biofloc technology (the biofloc group) or a commercial diet (the control group) in zero‐water exchange indoor tanks was performed. A commercial diet was fed to both groups, and the daily feeding amount in the biofloc group was 40% less than that in the control group. Wheat bran and glucose were used in the biofloc group to ensure a C/N ratio >15 and the same feeding energy as that given to the control group. After 60 days of feeding, the final weight, weight gain and specific growth rate in the biofloc group were significantly higher than those in the control group. Furthermore, proximate composition analysis showed that the total hepatopancreatic lipid and ash contents of the biofloc group were significantly higher than those of the control group, and the intestinal and hepatopancreatic pepsin activities in crayfish in the biofloc group were higher than those in crayfish in the control group. Moreover, higher hepatopancreatic lipase and cellulase activities were observed for the biofloc group than for the control group. Biofloc technology promoted the health of the crayfish in terms of their immune and antioxidant enzyme activities. Based on the results of this study, biofloc technology is more effective than traditional commercial diets for the farming of juvenile crayfish.     

Effect of bioflocs on growth and immune activity of Pacific white shrimp,Litopenaeus vannamei postlarvae

The bioflocs technology (BFT) for shrimp production has been proposed as a sustainable practice capable of reducing environmental impacts and preventing pathogen introduction. The microbial community associated with BFT not only detoxifies nutrients, but also can improve feed utilization and animal growth. Biofloc system contains abundant number of bacteria of which cell wall consists of various components such as bacterial lipopolysaccharide, peptidoglycan and β‐1, 3‐glucans, and is known as stimulating nonspecific immune activity of shrimp. Bioflocs, therefore, are assumed to enhance shrimp immunity because they consume the bioflocs as additional food source. Although there are benefits for having an in situ microbial community in BFT systems, better understanding on these microorganisms, in particular molecular level, is needed. A fourteen‐day culture trial was conducted with postlarvae of Litopenaeus vannamei in the presence and absence of bioflocs. To determine mRNA expression levels of shrimp, we selected six genes (prophenoloxidase1, prophenoloxidase2, prophenoloxidase activation enzyme, serine proteinase1, masquerade‐like proteinase, and ras‐related nuclear protein) which are involved in a series of responses known as the prophenoloxidase (proPO) cascade, one of the major innate immune responses in crustaceans. Significant differences in shrimp survival and final body weights were found between the clear water and in the biofloc treatments. mRNA expression levels were significantly higher in the biofloc treatment than the clear water control. These results suggest that the presence of bioflocs in the culture medium gives positive effect on growth and immune‐related genes expression in L.vannamei postlarvae.     

Nursery performance of Pacific white shrimp (Litopenaeus vannamei Boone, 1931) cultivated in a biofloc system: the effect of adding different carbon sources

Effect of different carbon sources on nursery performance of Pacific white shrimp (Litopenaeus vannamei) cultivated in biofloc system was investigated. Shrimp postlarvae (98.47 ± 8.6 mg) were fed for 32 days in tanks with water volume of 130 L and density of 1 individual L^?1. One control treatment and four biofloc treatments (BFT1, BFT2, BFT3 and BFT4) with adding different carbon sources including molasses, starch, wheat flour and mixture of them, respectively, were considered at equal weight ratios. According to the results, salinity, dissolved oxygen and pH were not significantly different among the biofloc treatments (P > 0.05). Maximum pH (8.27) and maximum dissolved oxygen (6.35 mg L^?1) were recorded in the control. Maximum (0.43 mg L^?1) and minimum (0.09 mg L^?1) ammonia were recorded in the control and BFT2, respectively (P < 0.05). Using simple carbohydrates (molasses and starch) lowered the ammonia concentration significantly. The highest increase in body weight (1640.43 ± 231.28 mg), growth rate, specific growth rate (8.97 ± 0.42% per day) and biomass (190.29 ± 26.83 mg) were found in BFT1 and the highest survival (90 ± 0.77%) was found in BFT4. The highest feed conversion (1.52 ± 0.23) and the lowest feed efficiency (66.81 ± 7.95) were observed in the control (P < 0.05). The proximate composition analysis revealed an increase in lipid and ash in biofloc treatments. Results indicated that using biofloc technology with zero‐water exchange system and adding carbon sources could help to recycle waste and improve the water quality. Moreover, the type of carbonaceous organic matter as a substrate for heterotrophic bacteria would be effective in degradation and metabolization of ammonia and nitrite.     

Dietary thiamin could improve growth performance,feed utilization and non‐specific immune response for juvenile Pacific white shrimp (Litopenaeus vannamei)

This study evaluated the effect of dietary thiamin on growth performance, feed utilization and non‐specific immune response for juvenile Pacific white shrimp, Litopenaeus vannamei. Six isonitrogenous and isolipidic practical diets were formulated with graded thiamin levels of 6.9, 32.7, 54.2, 78.1, 145.1 and 301.5 mg kg^?1 of dry diet, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile shrimp and provided four times each day to apparent satiation. Weight gain (WG) and specific growth rate (SGR) of the shrimp were significantly influenced by the dietary thiamin levels, the maximal WG and SGR occurred at 54.2 mg kg^?1 dietary thiamin level. However, with further increase in dietary thiamin level from 54.2 to 301.5 mg kg^?1, the WG and SGR significantly decreased. Shrimp fed the 54.2 mg kg^?1 thiamin diet exhibited higher feed efficiency, protein efficiency ratio and protein productive value than those fed the other diets. Dry matter and protein content in whole body were significantly affected by the dietary thiamin levels. Thiamin concentration in hepatopancreas significantly increased when the dietary thiamin level increased from 6.9 to 145.1 mg kg^?1. The total protein, glucose, triacylglycerol and cholesterol contents in hemolymph were not significantly affected by the dietary thiamin levels. Dietary thiamin had significantly influenced superoxide dismutase, catalase and lysozyme activities in hemolymph. Results of this study indicated that the optimal dietary thiamin requirements estimated using a two‐slope broken‐line model based on WG and thiamin concentration in hepatopancreas were 44.66 and 152.83 mg kg^?1, respectively.     

Artificial substrates in zero‐water‐exchange culture system regulate the rearing performance of Pacific white shrimp Litopenaeus vannamei (Boone, 1931) under the winter indoor condition

Effects of artificial substrates in zero‐water‐exchange culture system on the rearing performance of Litopenaeus vannamei under winter indoor condition were investigated in this study. Growth, survival, feed conversion rate (FCR), production rate of L. vannamei and water quality were compared between artificial substrate‐treated group (AST) and control group (without artificial substrates presented in the rearing environment). Artificial substrates can significantly improve the water quality, the ammonia and nitrite‐N concentrations in the AST group were significantly lower than in the control group (P < 0.05), and the total heterotrophic bacteria and Vibrio spp. were also significantly lower in the AST group (P < 0.05). The survival, growth and production rate of L. vannamei in the AST group were significantly higher than in the control group (P < 0.05). Significantly lower FCR was observed in the AST group (P < 0.05). Results from this study indicate that the utilization of artificial substrates in the indoor shrimp culture system could effectively control the water quality, improve the survival and growth of shrimp and significantly reduce the FCR. This study provides a guideline for employing artificial substrates in rearing of shrimp in the zero‐water‐exchange culture system under lower temperature, which could be applicable to other similar species.     

Effect of different biofloc system on water quality,biofloc composition and growth performance in Litopenaeus vannamei (Boone, 1931)

The experiment was conducted with three biofloc treatments and one control in triplicate in 500 L capacity indoor tanks. Biofloc tanks, filled with 350 L of water, were fed with sugarcane molasses (BFT_S), tapioca flour (BFT_T), wheat flour (BFT_W) and clean water as control without biofloc and allowed to stand for 30 days. The postlarvae of Litopenaeus vannamei (Boone, 1931) with an Average body weight of 0.15 ± 0.02 g were stocked at the rate of 130 PL m^?2 and cultured for a period of 60 days fed with pelleted feed at the rate of 1.5% of biomass. The total suspended solids (TSS) level was maintained at around 500 mg L^?1 in BFT tanks. The addition of carbohydrate significantly reduced the total ammonia‐N (TAN), nitrite‐N and nitrate‐N in water and it significantly increased the total heterotrophic bacteria (THB) population in the biofloc treatments. There was a significant difference in the final average body weight (8.49 ± 0.09 g) in the wheat flour treatment (BFT_W) than those treatment and control group of the shrimp. Survival of the shrimps was not affected by the treatments and ranged between 82.02% and 90.3%. The proximate and chemical composition of biofloc and proximate composition of the shrimp was significantly different between the biofloc treatments and control. Tintinids, ciliates, copepods, cyanobacteria and nematodes were identified in all the biofloc treatments, nematodes being the most dominant group of organisms in the biofloc. It could be concluded that the use of wheat flour (BFT_W) effectively enhanced the biofloc production and contributed towards better water quality which resulted in higher production of shrimp.     

Effects of Lactobacillus pentosus on the growth performance,digestive enzyme and disease resistance of white shrimp,Litopenaeus vannamei (Boone, 1931)

The objective of this study was to evaluate the probiotic properties of lactic acid bacteria (LAB) strains isolated from digestive tract of white shrimp Litopenaeus vannamei. Eighteen LAB colonies were isolated and one bacterium was found capable of producing three extracellular enzymes (protease, cellulose and lipase) simultaneously and exhibited antagonistic activity against shrimp pathogens (Vibrio vulnificus, V. rotiferianus and V. campbellii). The putative probiotic strain AS13 was identified as Lactobacillus pentosus based on 16S rRNA sequencing. The L. vannamei were fed diet containing 0 (control), 10⁶, 10⁷ and 10⁸ CFU g^?1 bacterial cells of AS13 for 28 days. The results showed that supplementation of L. pentosus significantly improved the growth performance and feed utilization in the treated groups over the control. Similarly, digestive enzyme activities were elevated in the intestines of treated groups. Moreover, feeding of supplemented diets containing AS13 significantly reduced the mortality rate caused by pathogenic Vibrio species (V. vulnificus, V. rotiferianus and V. campbellii). Our results indicated L. pentosus AS13 addition at 10⁷ CFU g^?1 can effectively enhance the growth performance, feed utilization, digestive enzymes and disease resistance of L. vannamei in the laboratory condition.     

Effect of using sodium bicarbonate to adjust the pH to different levels on water quality,the growth and the immune response of shrimp Litopenaeus vannamei reared in zero‐water exchange biofloc‐based culture tanks

The bioflocs technology proved to be a sustainable technique used in zero‐water exchange shrimp culture systems. However, the pH and alkalinity may decrease due to the biofloc formation process and Nitrification. A 48‐day experiment was performed to investigate the effects of different pH (7.1–7.6; 7.6–8.1) conditions on water quality, the growth and the health status of shrimp in biofloc technology (BFT) through using sodium bicarbonate to adjust pH respectively. Two pH treatments and one control were compared: T0 — control, T1 — pH 7.6 — NaHCO₃, T2 — pH 8.1 — NaHCO₃, each treatment consisted of three replicate tanks (90 L water volume) and each replicate stocked with 30 shrimp (equivalent to 333 shrimp m^?3). Significant physical, chemical and biological differences (P < 0.05) were detected among treatments. At the end of the experiment, water quality, the growth and the immune response of shrimp in control were significantly lower (P < 0.05) than the other treatments. Moreover, the T2 treatment had a better performance in these three aspects. The results indicated that it was necessary to adjust the pH and alkalinity in the BFT, and a higher pH as well as alkalinity for shrimp growth and the stability of the BFT were more favourable.     

Dietary protein level and C/N ratio manipulation in zero‐exchange culture of Litopenaeus vannamei: Evaluation of inorganic nitrogen control,biofloc composition and shrimp performance

A 30‐day experiment was conducted to evaluate inorganic nitrogen control, biofloc composition and shrimp performance in zero‐exchange culture tanks for juvenile L. vannamei offered a 35% (P35) or 25% (P25) crude protein feed, each feed supplemented with additional carbohydrate to increase the C/N ratio to 20:1 (CN20) or 15:1 (CN15). Sucrose was used as a carbohydrate to manipulate the two C/N ratios based on the carbon and nitrogen content of both the feeds and sucrose. The four treatments were referred to as: P35 + CN20, P35 + CN15, P25 + CN20 and P25 + CN15. Each treatment consisted of four replicate tanks (125 L), each stocked with 28 shrimp (equivalent to 224 shrimp m^?3). Bioflocs formed and developed based on initial inoculation in all four treatments; and monitored water quality parameters were maintained within acceptable ranges for shrimp culture throughout the experiment. No significant effects (P > 0.05) of dietary protein level, C/N ratio or their interaction were observed on biofloc development (BFV, TSS and BFVI) and inorganic nitrogen (TAN, NO₂^?‐N and NO₃^?‐N) concentrations. At the end of the experiment, proximate analysis of the bioflocs collected from the four treatments showed crude protein levels of 21.3% ~ 32.1%, crude lipid levels of 1.6% ~ 2.8% and ash levels of 43.4% ~ 61.4%. Extracellular protease and amylase activities of the bioflocs were 9.9 ~ 14.4 U g^?1 TSS and 293.5 ~ 403.8 U g^?1 TSS respectively. Biofloc composition and enzyme activity were both affected by dietary protein level (P < 0.01) and C/N ratio (P < 0.05). Survival, per cent weight gain and protein efficiency ratio of shrimp were not affected (P > 0.05) by dietary protein level, C/N ratio or their interaction; however, the feed conversion ratios were significantly lower (P < 0.05) in treatments with high dietary protein (P35) compared with those in treatments with low dietary protein (P25). The results from this study demonstrate that dietary protein level and C/N ratio manipulation can have important implications for water quality, biofloc composition and shrimp performance in intensive, zero‐exchange biofloc‐based culture systems.     

Effects of different carbon sources and dietary protein levels in a biofloc system on growth performance,immune response against white spot syndrome virus infection and cathepsin L gene expression of Litopenaeus vannamei

A 5‐week study was performed to evaluate the effect of spoilage date extract (SDE) as the biofloc carbon source on Litopenaeus vannamei (5.4 ± 0.3 g) performance. The two levels of dietary protein (15% and 25% crude protein) and two carbohydrate sources (molasses‐M and SDE‐P) were tested including: M15, M25, P15 and P25. The minimum (0.2 ± 0.0 mg/L) and the maximum (0.5 ± 0.0 mg/L) of total ammonia nitrogen were observed in the P15 and M25 groups respectively. The highest protein efficiency ratio (6.1 ± 0.3) and protein productive value (112.3 ± 5.8%) were found in the P15 group (p < 0.05). No significant difference was found between biofloc treatments in the expression of cathepsin L gene in hepatopancreas (p > 0.05). The number of total haemocyte count (THC), semigranular cells (SGC) and granular cells (GC) of shrimp in SDE‐based biofloc treatments was relatively higher than those in molasses‐based biofloc treatments. Following the white spot syndrome virus (WSSV) challenge, a significant decrease in THC, SGC, GC and hyaline cell values was observed in all treatments (p = 0.001). Plasma biochemical parameters were significantly influenced by dietary protein levels, biofloc carbon sources as well as WSSV challenge test. In conclusion, SDE successfully could be used as an alternative carbon source for establishing a biofloc system in L. vannamei production.     

Minimum water exchange spares the requirement for dietary methionine for juvenile Litopenaeus vannamei reared under intensive outdoor conditions

We examined if minimum water exchange could spare dietary methionine (Met) required for maximum growth performance of juvenile Litopenaeus vannamei reared in an intensive outdoor system. Shrimp of 1.98 ± 0.13 g were stocked at 70 animals/m² and reared for 72 days in 50 tanks of 1 m³ under flow‐through (14.4% a day) and static (1.4%–2.9% a day) green‐water conditions at 32.0 ± 3.7 g/L salinity. Five diets with a minimum inclusion of fishmeal supplemented with a dipeptide, dl ‐methionyl‐dl ‐methionine, were formulated to contain increasing levels of Met, 4.8, 6.2, 7.2, 8.1 or 9.4 g/kg (on a dry matter basis). Each of the five diets were fed four times daily to five replicate groups. Dietary Met and water exchange significantly influenced shrimp survival, gained yield, apparent feed intake, food conversion ratio and final body weight (p < .05). Raising shrimp under limited water exchange, i.e., static versus flow‐through spared the dependence on higher levels of dietary Met to maximize shrimp body weight, from 9.4 g/kg to 8.0 g/kg (14.0 and 12.6 g/kg Met+Cys respectively). In an intensive rearing system, a reduction in water exchange is desirable as it leads to a lower need for supplemental dietary Met.     

Effects of dietary dl‐methionyl‐dl‐methionine (Met‐Met) on growth performance,body composition and haematological parameters of white shrimp (Litopenaeus vannamei) fed with plant protein–based diets

A 10‐week feeding trial was conducted to evaluate the effects of supplementing different levels of dl ‐methionyl‐dl ‐methionine (AQUAVI^® Met‐Met) in plant protein–based diets on Litopenaeus vannamei. The positive control (PC) and negative control (NC) diets were designed with 20% and 8% fishmeal respectively, and other six diets were formulated with graded levels of Met‐Met from 0.05% to 0.30% with a 0.05% increment on the basis of NC diet (MM 0.05–MM 0.3). Six replicates were randomly assigned to each diet with 50 shrimp each having initial weight of 0.98 ± 0.02 g. The variation of FM concentration from 20% to 8% and supplemented with graded levels of Met‐Met did not affect the survival rate, feed conversion ratio, protein efficiency ratio, whole body and muscle proximate compositions (p > 0.05). However, diets with ≤0.20% Met‐Met supplementation resulted in significantly increased weight gain and specific growth rate, after which both parameters reached plateau. Shrimp fed the NC diet showed significantly lower total essential amino acid (EAA) content in muscle (p < 0.05). Supplementation of Met‐Met significantly improved apparent digestibility coefficients of dry matter, crude protein, lipid, phosphorus and EAAs (p < 0.05). Based on broken‐line analysis, the methionine requirement for white shrimp was estimated to be 0.87% when using Met‐Met as methionine source.     

Effects of different levels of dietary protein on the growth performance,nutrient utilization,digestive enzymes and physiological status of white shrimp,Litopenaeus vannamei juveniles reared in inland saline water

A 60‐day feeding trial was conducted to illustrate the effect of dietary protein levels on the growth and physio‐metabolic responses of juvenile Litopenaeus vannamei reared in inland saline water (ISW). Six isoenergetic (15 MJ/kg) and isolipidic (60 g/kg) diets with graded level of crude protein viz., 240 (T240), 260 (T260), 280 (T280), 300 (T300), 320 (T320) and 340 (T340) g/kg diet were formulated. Significantly higher (p < .05) weight gain (%), specific growth rate, with lower food conversion ratio were found in T320 and T340 groups. The protein utilizing efficiency and whole‐body protein content were significantly higher (p < .05) in the T320 group. Trypsin activity increased with the increasing dietary CP level but amylase activity decreased with the increasing dietary CP level. Transaminase enzymes, haemolymph protein and haemocyanin were elevated in T320 and T340 groups. The lactate dehydrogenase and malate dehydrogenase activities were significantly higher (p < .05) in the T240 group. Shrimp of T240 group had the lowest (p < .05) glycogen and total haemocyte count with highest (p < .05) haemolymph glucose and antioxidant enzymes activities than the other groups. Based on the results, feeding 320 g CP/kg is found to be optimum for supporting maximum growth and health status of L. vannamei reared in ISW at 8 g/L salinity. The finding of the present study will help in developing a low‐cost feed for L. vannamei reared in ISW.     

Effect of different total suspended solids levels on a Litopenaeus vannamei (Boone, 1931) BFT culture system during biofloc formation

In a Biofloc Technology System (BFT), there is constant biofloc formation and suspended solids accumulation, leading to effects on water quality parameters that may affect the growth performance of cultured shrimp. This study aimed to analyse during biofloc formation the effect of different total suspended solids (TSS) levels on water quality and the growth performance of Litopenaeus vannamei shrimp in a BFT system. A 42‐day trial was conducted with treatments of three ranges of TSS: 100–300 mg L^?1 as low (TL), 300–600 as medium (TM) and 600–1000 as high (TH). The initial concentrations of 100 (TL), 300 (TM) and 600 mg L^?1 (TH) were achieved by fertilization before starting the experiment. Litopenaeus  vannamei juveniles with an average weight of 4.54 ± 1.19 g were stocked at a density of 372 shrimp m^?3. Physical and chemical water parameters and shrimp growth performance were analysed. After 6 weeks, TSS mean concentrations were 306.37, 532.43 and 745.2 mg L^?1 for, respectively, TL, TM and TH treatments. Significant differences (P < 0.05) were observed in TSS, settleable solids, pH, alkalinity and nitrite, especially between the TL and TH treatments. Similarly, differences (P < 0.05) were observed in the growth performance parameters, specifically final weight, survival, feed conversion and productivity. The water quality parameters at lower range of total suspended solids concentration (TL) treatment resulted in a better performance of L. vannamei in the BFT system. The maintenance at range of 100–300 mg L^?1 TSS is thus important to the success of shrimp culture.     

Effects of Pediococcus pentosaceus supplementation on growth performance,intestinal microflora and disease resistance of white shrimp,Litopenaeus vannamei

Litopenaeus vannamei is economically important shrimp species in worldwide aquaculture. This study was conducted to assess the effect of different levels of probiotic Pediococcus pentosaceus (PP) on growth performance, feed utilization, digestive enzyme activity, intestinal microflora count and body composition of L. vannamei. Four diets containing different concentrations [0 (PP0), 10⁶ (PPI), 10⁷ (PPII) and 10⁸ (PPIII) CFU/g] of PP were formulated. After 8 weeks feeding trial, the experimental shrimps were challenged with Vibrio anguillarum and noted the surveillance. At the end of the feeding trial, the obtained results revealed a significant increase (p < .05) in final body weight, final length, weight gain (WG), survival rate, protease and amylase activities, lactobacillus sp. and Bacillus sp. intestinal count, total haemocyte counts (THC) and lysozyme activity in PPIII group when compared with the other groups. Similarly, WG, amylase activity, Bacillus sp. count, THC and lysozyme activity were significantly enhanced in case of PPII compared to the control group (p < .05). Interestingly, FCR and Vibrio sp. counts were significantly decreased in case of PPIII group when compared to the other groups (p < .05). Also, significant level of surveillance was noted in the challenging test with V. anguillarum. These results suggested that the P. pentosaceus improved the growth performance, digestive enzyme activity, immunity and tolerance against V. anguillarum of L. vannamei.     

Effect of oxidized fish oil on growth performance and oxidative stress of Litopenaeus vannamei

A 4‐week feeding trial was conducted to determine the effects of oxidized fish oil (OFO, POV: 234.84 meq kg^?1) on growth performance and oxidative stress of Litopenaeus vannamei. Five diets containing various OFO levels (0, 25, 50, 75 and 100 g kg^?1) with the same dietary lipid level were fed to L. vannamei. The results showed that the body weight gain and the specific growth rate of the shrimp fed with 50, 75 and 100 g kg^?1 of OFO diets decreased significantly (P < 0.05), whereas the hepatosomatic index increased significantly (P < 0.05). The malondialdehyde concentrations in the serum and muscle of the shrimp fed with 50, 75 and 100 g kg^?1 of OFO diets were significantly higher than that of the shrimp fed with fresh fish oil (P < 0.05). The total antioxidant competence decreased significantly compared with the control group. Therefore, dietary OFO affects the growth performance and increases the oxidative stress of shrimp.     

The effect of replacement of fish meal by yeast extract on the digestibility,growth and muscle composition of the shrimp Litopenaeus vannamei

Feeding trials were conducted to determine the dietary level of yeast extract (YE) for replacing dietary fish meal for evaluating whether yeast extract was superior to intact yeast as an alternative protein source for shrimp Litopenaeus vannamei. The basal diet (control, D0, containing 25% fish meal), was compared with five isonitrogenous and isoenergetic experimental diets [replacing 15% (D15), 30% (D30), 45% (D45), 60% (D60) or 100% (D100) of the fish meal in the basal diet with IYE]. The digestibility, growth and muscle composition of the shrimp were measured. The results showed that all replacement treatments displayed higher apparent digestibility of crude protein than did the control. The trypsinase activity in shrimp hepatopancreas increased significantly, whereas lipase activity decreased as the amount of dietary YE increased. The shrimp treated with D30 diet displayed the highest amylase activity in hepatopancreas. There was no significant difference in the weight gain (WG) and survival of shrimp between the control and the YE replacement treatments. Feed conversion ratio (FCR) increased as the dietary YE increased, and the FCRs of the D60 and the D100 treatments were significantly higher than that of the control (P < 0.05). The growth performance among the treatments was closely related to the similarity of the essential amino acids in the diets. There was no significant difference in muscle composition of the shrimp between control and other treatments. In conclusion, up to approximately 45% of the fish meal in shrimp diet can be replaced by yeast extract in the presence of supplemental fish oil, phosphorus and calcium.     

Effects of low salinity exposure on immunological,physiological and growth performance in Litopenaeus vannamei

Growth, immunological and physiological parameters of white shrimp Litopenaeus vannamei reared at different salinity levels (1, 10, 15, 25 and 35 g/L) at stocking density of 214 shrimp/m³ were examined at 1, 30 and 63 days. Results showed that the total haemocyte count (THC) of shrimp decreased with time at all salinity levels, indicating a potential reduction in the resistance of shrimp against pathogens, since a low value of THC indicates a perturbation of the immune system. Glucose and protein values observed in the haemolymph throughout the study indicate that shrimp adapted well to low salinities (1, 10 and 15 g/L). Although of those shrimp reared at 10 g/L only 83.3% survived, at this salinity, shrimp depicted a higher glucose concentration in haemolymph at the beginning and end of the study.     

Growth,body composition,ammonia tolerance and hepatopancreas histology of white shrimp Litopenaeus vannamei fed diets containing different carbohydrate sources at low salinity

Juvenile Litopenaeus vannamei farmed at 3.0 psu were fed five diets containing glucose, sucrose, wheat starch, corn starch or potato starch as the carbohydrate (CBH) source. Shrimp were fed for 50 days to explore the effect of dietary CBH source on growth, body composition and ammonia tolerance. The specific growth rate of body length of shrimp fed glucose was the highest and significantly higher than those fed potato starch. The survival rate of shrimp fed glucose was 89.44%, and it was the highest and significantly higher than those fed wheat starch. Whole shrimp body crude protein and lipid of the corn starch group were 140.2 g kg^?1 and 10.1 g kg^?1 respectively. And they were significantly higher than those fed wheat starch. Shrimp fed potato starch had higher hepatopancreas and muscle glycogen. Shrimp fed sucrose had higher glucose‐6‐phosphate dehydrogenase and lower pyruvate kinase activities (P < 0.05). Besides, shrimp fed starch produced more B cells in hepatopancreas tubules than those fed glucose or sucrose. Shrimp fed different sources of CBH differed in the number of R cells. After 96‐h of ammonia nitrogen challenge, the survival rate of the treatments from high to low in turn was glucose, wheat starch, corn starch, sucrose and potato starch, and no significant differences were observed among all treatments. Based on shrimp growth and the economic problems of practical production, we recommend wheat starch as CBH source in practical diets for L. vannamei farmed at low salinities.