Effect of dissolved oxygen on swimming ability and physiological response to swimming fatigue of whiteleg shrimp (Litopenaeus vannamei)

The swimming endurance of whiteleg shrimp(Litopenaeus vannamei, 87.66 mm ± 0.25 mm, 7.73 g ± 0.06 g) was examined at various concentrations of dissolved oxygen(DO, 1.9, 3.8, 6.8 and 13.6 mg L-1) in a swimming channel against one of the five flow velocities(v1, v2, v3, v4 and v5). Metabolite contents in the plasma, hepatopancreas and pleopods muscle of the shrimp were quantified before and after swimming fatigue. The results revealed that the swimming speed and DO concentration were significant factors that affected the swimming endurance of L. vannamei. The relationship between swimming endurance and swimming speed at various DO concentrations can be described by the power model(ν·tb = a). The relationship between DO concentration(mg L-1) and the swimming ability index(SA∫ 9000I), defined as SAI =vdt( cm), can be described as SAI = 27.947 DO0.137(R2 = 0.9312). The 0level of DO concentration directly affected the physiology of shrimp, and exposure to low concentrations of DO led to the increases in lactate and energetic substrate content in the shrimp. In responding to the low DO concentration at 1.9 mg L-1 and the swimming stress, L. vannamei exhibited a mix of aerobic and anaerobic metabolism to satisfy the energetic demand, mainly characterized by the utilization of total protein and glycogen and the production of lactate and glucose. Fatigue from swimming led to severe loss of plasma triglyceride at v1, v2, and v3 with 1.9 mg L-1 DO, and at v-11 with 3.8, 6.8 and 13.6 mg L DO, whereas the plasma glucose content increased significantly at v3, v4 and v5 with 3.8 and 6.8 mg L-1 DO, and at v5 with 13.6 mg L-1 DO. The plasma total protein and hepatopancreas glycogen were highly depleted in shrimp by swimming fatigue at various DO concentrations, whereas the plasma lactate accumulated at high levels after swimming fatigue at different velocities. These results were of particular value to understanding the locomotory ability of whiteleg shrimp and its physiological changes, further contributing to the improvement of capture and rearing technique.     

Peritrophin-like protein from Litopenaeus vannamei(LvPT) involved in white spot syndrome virus(WSSV) infection in digestive tract challenged with reverse gavage

The peritrophic membrane plays an important role in the defense system of the arthropod gut. The digestive tract is considered one of the major tissues targeted by white spot syndrome virus(WSSV) in shrimp. In this study, the nucleotide sequence encoding peritrophin-like protein of L itopenaeus vannamei(Lv PT) was amplified from a yeast two-hybrid library of L. vannamei. The epitope peptide of Lv PT was predicted with the Gen Script Optimum Antigen? design tool. An anti-Lv PT polyclonal antibody was produced and shown to specifically bind a band at ~27 k Da, identified as Lv PT. The Lv PT protein was expressed and its concentration determined. L v PT ds RNA(4 μg per shrimp) was used to inhibit Lv PT expression in shrimp, and a WSSV challenge experiment was then performed with reverse gavage. The pleopods, stomachs, and guts were collected from the shrimp at 0, 24, 48, and 72 h post-infection(hpi). Viral load quantification showed that the levels of WSSV were significantly lower in the pleopods, stomachs, and guts of shrimp after L v PT ds RNA interference than in those of the controls at 48 and 72 hpi. Our results imply that Lv PT plays an important role during WSSV infection of the digestive tract.     

Pharmacokinetics and tissue behavior of enrofloxacin and its metabolite ciprofloxacin in turbot Scophthalmus maximus at two water temperatures

Turbot Scophthalmus maximus, an important aquaculture species in China, currently suffers from epizootic diseases because of high density aquaculture. Enrofloxacin has been used to treat various systemic bacterial fish infections. However, studies concerning the pharmacokinetics of enrofloxacin in turbot are limited. In this study, the pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin, were investigated in the turbot following intravenous and oral administration at 10 mg enrofloxacin/kg body weight, at 16°C and 10°C water temperatures. The concentrations of enrofloxacin and ciprofloxacin in the main tissues (plasma, muscle, liver and kidney) were detected by HPLC. The results show that the plasma concentration-time data for enrofloxacin were best described as a two-compartment open model after intravenous and oral administration. Three pharmacokinetic equations were established between the concentrations and temperatures. The kinetic profile of enrofloxacin was temperature dependent. The absorption half-life of enrofloxacin was 1.99 h and 2.17 h after oral administration, whereas the elimination half-life of the drug was 98.63 h and 136.59 h at 16°C and 10°C, respectively. The peak concentration of enrofloxacin in plasma and tissues was higher at 16°C than that at 10°C, and the peak plasma concentration time in the liver was the shortest at both temperatures among those of other tissues. The plasma C max /MIC ratio varied between 11.08 and 5 540.00 at 16°C; and between 7.92 and 3 960.00 at 10°C. The AUC/MIC ratio was 467.82-280 690.00 at 16°C, and 359.48-215 690.00 at 10°C. These ratios indicate that it is possible to obtain therapeutic efficacy. Very low levels of ciprofloxacin were detected. The AUC ratios of ciprofloxacin and enrofloxacin in plasma suggest that plasma ciprofloxacin might play a minor role in enrofloxacin treatment for turbot.     

The Effect of Three Culture Methods on Intensive Culture System of Pacific White Shrimp （Litopenaeus vannama）

Different culture methods may affect the intensive culture system of Pacific white shrimp （Litopenaeus vannamei） re- garding water quality and growth and economic performance. This study evaluated the potential effects of three culture methods through cultivation of juvenile shrimps under consistent tank management conditions for 84 d. The three methods involved shrimp cultivation in different tanks, i.e., outdoor tanks with cement bottom （mode-C）, greenhouse tanks with cement bottom （mode-G） and outdoor tanks with mud-substrate （mode-M）. Results showed that water temperature was significantly higher in mode-G than that in mode-C （P 〈 0.05）. In contrast to the other two treatments, mode-M had stable pH after 50 d cultivation of shrimps. In the mid-late period, the average concentrations of TAN, NO2-N, DIP and COD were significantly lower in mode-M and mode-G compared with those in mode-C （P 〈0.05）. Despite lack of differences in the final shrimp weight among different treatments （P 〉0.05）, mode-M had significantly higher shrimp yield, survival rate and feed conversion rate （P 〈 0.05） than other modes. There were significant dif- ferences in revenue and net return among different treatments （P 〈 0.05）. These demonstrated that the treatments of mode-G and mode-M were conductive to the intensive culture system ofL. vannamei.     

INTERACTIONS BETWEEN AMMONIUM UPTAKE AND NITRATE UPTAKE BY NATURAL PHYTOPLANKTONASSEMBLAGES

Measurements of ammonium and nitrate uptakes by natural phytoplankton assemblages from Jiaozhou Bay at various combinations of ammonium and nitrate concentrations with 15N trace techniques showed that uptake rate of either nitrogen was influenced by the presence of the other but that the influence of ammonium on nitrate uptake was much greater than, that of nitrate on ammonium uptake. The influence mechanism of ammonium on nitrate uptake manifested as competition at lower concentrations and as inhibition at higher concentrations (ammonium concentration >0.6 umol/L), but no total inhibition appeared within the concentration.range of the experiments (0-10umol/L). The influence of nitrate on ammonium uptake seems to be a result of competition for uptake sites on the cell surface. In view of the in situ nutrient concentration in the given marine . environment, it is believed that both nitrogen sources are utilized by phytoplankton. Nitrate uptake in the presence of ammonium and ammonium uptake in the presen     

Low temperature stress on the hematological parameters and HSP gene expression in the turbot Scophthalmus maximus

To study the effect of low temperature stress on hematological parameters and HSP gene expression in the turbot( Scophthalmus maximus),water temperature was lowered rapidly from 18 to 1°C.During the cooling process,three individuals were removed from culture tanks at 18,13,8,5,3,and 1°C.Blood samples and tissues were taken from each individual,hematological indices and HSP gene expression in tissues were measured.The red blood cell count,white blood cell count,and hemoglobin concentration decreased significantly( P 0.05) as temperature decreased.Enzyme activities of plasma alanine transaminase and creatine kinase increased as temperature decreased,whereas aspartic transaminase and γ-glutamyl transpeptidase activities displayed no obvious changes above 1°C and lactate dehydrogenase activity increased first and then decreased.Blood urea nitrogen and uric acid levels were highest at 8°C,and creatinine concentration was highest at 3°C.The concentrations of plasma cortisol,cholesterol,and triglyceride all increased significantly( P 0.05) as temperature decreased.The serum glucose concentration increased first and then decreased to the initial level.The HSP70 m RNA expression showed various patterns in different tissues,whereas HSP90 m RNA expression showed the same tendency in all tissues.Overall,these results indicate that temperature decreases in the range of 8 to 5°C may induce a stress response in S.maximus and that temperature should be kept above 8°C in the aquaculture setting to avoid damage to the fish.     

Concentrations and Distribution of Trace Metals of PM_(10) and TSP Particles Collected in the Qingdao Area

Aerosol samples of PM10 (particulate matter with aerodynamic diameters less than 10μm) and TSP (total suspended particles) were simultaneously collected from April 2001 to March 2002 at the top of Mount Baguan on the downtown campus of Ocean University of China, Qingdao, China. The concentrations of Al, Fe, Mn, Cu, Pb and Zn were determined by means of inductively coupled plasma atomic emission spectrometry (ICP-AES). The monthly variability of the mass concentrations of aerosol particles and the concentrations of trace metals are presented and discussed. The distribution pattern of these metals in PM10 and TSP is also discussed. During the observation period, the mass concentration of PM10 at this site ranged from 13.80 to 306.42μgm-3 , while that of TSP ranged from 31.02 to 568.82μgm-3. Both PM10 and TSP reached their highest concentrations in springtime, while the lowest values occurred in summertime. The concentrations of crustal metals followed the same variation pattern, while those of anthropo     

Comparative Study on the AUergenicity of DifferentLitopenaeus vannamei Extract Solutions

Allergen extracts are widely used for allergy diagnosis and treatment. The application of shrimp extract is hampered dueto the low protein concentration and the inconsistent allergenicity. Extracting solutions are considered to be the primary limitingfactor of protein extraction from crustaceans. This study aimed to select an optimal solution for shrimp protein extraction by com-paring the allergenicity of different shrimp extracts. The effect of 7 existing or modified extracting solutions were evaluated, includ-ing the glycerol-NaC1 solution, the glycerol Cocaine＇s solution, the buffered saline solution, the Cocaine＇s solution, the Glucoseleaching solution, 1 mol L-1 KC1 solution, and 0.01 mol L-1 phosphate buffered saline solution with and without dithiothreitolor （DTT）.The quantitative （protein concentration） and qualitative parameters （SDS-PAGE protein patterns and immuno-reactivity） were deter-mined using the sodium dodecyl sulfate polyacrylamide gel electrophoresis, enzyme linked immunosorbent assay and immunoblottingassay. Results showed that the 1 molL-1 KC1 solution with DTT was optimal for shrimp protein extraction, which yielded high con-centrafion and allergenicity in the protein extract, including major and minor allergens. The 1 tool L-l KC1 solution with DDT is pro-posed for preparation of shrimp extract and associated allergy diagnosis, as well as potential applications for other crustaceans.     

Influence of Ultrasonic Treatment on the Allergenic Properties of Shrimp （Penaeus vannamei ） Allergen

The present study was undertaken to determine whether high intensity ultrasound could reduce the allergic properties of shrimp allergens. Reducing the allergenic properties of these allergens will be beneficial to allergic individuals. Samples of shrimp protein extract and shrimp muscle were treated by high-intensity ultrasound with water bathing at 0 ℃ or 50 ℃ for different time periods. The treated and untreated samples were then analyzed by SDS-PAGE, Western blots and competitive inhibition ELISA （Ci-ELISA） to determine the shrimp allergenicity. The results show that high-intensity ultrasound has no effect on allergenicity when the extracts were treated at 0℃. However, a significant decrease was observed in the level of the major shrimp allergen, Pen a 1, when the samples were treated at 50 ℃. In the determination of allergenicity with CiELISA, a reduction in IgE binding was also observed.     

Supplementation of Yeast Extract to Practical Diet Improves the Growth,Anti-Oxidative Capacity and Intestinal Morphology of Shrimp Litopenaeus vannamei

Two control diets based on the commercial formula were designed to contain high(27%, D1) and low(22%, D2) levels of fish meal, respectively. Into D2, 500, 1000 and 1500 mg kg~(-1) of yeast extract were added, respectively, yielding three experimental diets(YE1 through YE3). Shrimp(initial body weight 0.30 g ± 0.02 g) were fed with the experimental diets, five tanks each diet and 30 shrimp individuals each tank, for 8 weeks, and then challenged with Vibrio parahaemolyticus. The results showed that the specific growth rate(SGR) of shrimp in D2 was significantly lower than that of shrimp in D1(P 0.05). The SGR of shrimp in YE3 was similar to that of shrimp in D1. The feed intake of shrimp was similar between D1 and D2. The feed conversion ratio and protein efficiency ratio of shrimp were similar among all diets(P 0.05). YE significantly improved the activity of glutathione S-transferase. The concentration of glutathione(GSH) and the total serum anti-oxidative capacity(T-AOC) of D1 were significantly higher than those of shrimp feeding other diets(P 0.05). The content of serum malondialdehyde of shrimp feeding YE2 and YE3 was significantly lower than that of shrimp feeding D2(P 0.05). The thickness of intestine muscular layer of shrimp feeding YE1 and YE2 was similar to that of shrimp feeding D1. The shrimp feeding YE1 showed the highest villus height of intestine among all groups. The cumulative mortality after challenging was similar among all groups(70.00%–86.67%)(P 0.05). In conclusion, 1000–1500 mg kg~(-1) of YE was suggested to be supplemented into the practical diets to improve the growth, anti-oxidative capacity and intestinal morphology of shrimp L. vannamei.     

Trophic Interaction in a Portunus rituberculatus Polyculture Ecosystem Based on Carbon and Nitrogen Stable Isotope Analysis

Trophic interaction among various biomass groups in a swimming crab Portunus trituberculatus polyculture pond was investigated using carbon and nitrogen stable isotope analysis. The polycultured animal species also included white shrimp Litopenaeus vannamei, short-necked clam Ruditapes philippinarum, and redlip mullet Liza haematochila. The mean δ~(13)C value for all the biomass groups in polyculture ecosystem ranged from -25.61‰ to -16.60‰, and the mean δ~(15)N value ranged from 6.80‰ to 13.09‰. Significant difference in the δ~(13)C value was found between particulate organic matter(POM) and sediment organic matter(SOM)(P 0.05), indicating that these two organic matter pools have different material sources. Assuming that a ~(13)C-enrichment factor of 1.00‰ and a ~(15)N-enrichment factor of 2.70‰ existed between consumer and prey, diets of the four cultured animals were estimated using a stable isotope mixing model. The estimated model results indicated that P. trituberculatus mainly feed on Aloidis laevis; L. vannamei mainly feed on shrimp feed; while A. laevis, R. philippinarum and L. haematochelia mainly feed on POM. Shrimp feed was also an important food source of R. philippinarum and L. haematochelia. The diets of P. trituberculatus, L. vannamei, R. philippinarum, and L. haematochila showed complementary effects in this polyculture ecosystem. Our finding indicated that the polyculture of these four organisms with suitable farming density could make an effective use of most of the food sources, which can make a highly efficient polyculture ecosystem.     

PLASMA CORTISOL AND GLUCOSE CONCENTRATIONS IN THE STRIPED MULLET (MUGIL CEPHALUS L.) SUBJECTED TO INTENSE HANDLING STRESS

The plasma cortisol and glucose concentrations were determined in mature female striped mullet (Mugil cephalus L . ) subjected to short term intense handling stress . The results indicated that plasma cortisol levels reached a peak 20 min after stress and declined gradually afterwards . The highest concentration of plasma glucose was observed 30 min after stress . The present study showed that the rise of plasma glucose was associated with the plasma cortisol levels .     

A Comparative study on the nonspecific immunity of juvenile Litopenaeus vannamei ever inhabiting freshwater and seawater

A study on the nonspecific immunity of Litopenaeus vannamei ever inhabiting freshwater and seawater was carried out at different molt stages by comparing their total hemocyte count(THC) and respiratory burst(RB) and activity of phenol oxidase(PO), nitric oxide synthase(NOS) and lysozyme(LY). Two-way ANOVA showed that salinity and molt stage independently affected THC and RB and the activity of PO, NOS and LY of juvenile L. vannamei significantly(P 0.05). The THC and RB and the activity of NOS gradually increased from the post-molt stages(A and B) to the pre-molt stages(D0–D3), which were common in shrimps inhabiting freshwater and seawater. The activity of PO peaked at the inter-molt stage(C), and touched the lowest at the post-molt stage in freshwater and pre-molt stage in seawater. The activity of LY was stable over the molt cycle. The RB and the activity of PO, NOS and LY of juvenile L. vannamei were significantly lower in freshwater than in seawater; whereas THC was significantly higher in freshwater than in seawater(P 0.05). It was concluded that the post-molt stage(especially stage A) was critical to shrimp culture, which should be intensively attended when L. vannamei was cultured in freshwater.     

Glutamate dehydrogenase and Na+-K+ ATPase expression and growth response of Litopenaeus vannamei to different salinities and dietary protein levels

Improvement in the osmoregulation capacity via nutritional supplies is vitally important in shrimp aquaculture.The effects of dietary protein levels on the osmoregulation capacity of the Pacific white shrimp(L.vannamei) were investigated.This involved an examination of growth performance,glutamate dehydrogenase(GDH) and Na+-K+ ATPase mRNA expression,,and GDH activity in muscles and gills.Three experimental diets were formulated,containing 25%,40%,and 50% dietary protein,and fed to the shrimp at a salinity of 25.After 20 days,no significant difference was observed in weight gain,though GDH and Na+-K+ ATPase gene expression and GDH activity increased with higher dietary protein levels.Subsequently,shrimp fed diets with 25% and 50% dietary protein were transferred into tanks with salinities of 38 and 5,respectively,and sampled at weeks 1 and 2.Shrimp fed with 40% protein at 25 in salinity(optimal conditions) were used as a control.Regardless of the salinities,shrimp fed with 50% dietary protein had significantly higher growth performance than other diets;no significant differences were found in comparison with the control.Shrimp fed with 25% dietary protein and maintained at salinities of 38 and 5 had significantly lower weight gain values after 2 weeks.Ambient salinity change also stimulated the hepatosomatic index,which increased in the first week and then recovered to a relatively normal level,as in the control,after 2 weeks.These findings indicate that in white shrimp,the specific protein nutrient and energy demands related to ambient salinity change are associated with protein metabolism.Increased dietary protein level could improve the osmoregulation capacity of L.vannamei with more energy resources allocated to GDH activity and expression.     

Closed recirculating system for shrimp-mollusk polyculture

This paper deals with a new system of aquaculture, i.e., a closed recirculating system for shrimp-mollusk polyculture. The culture system consisted of several shrimp ponds, a mollusk water-purifying pond and a reservoir. During the production cycle, water circulated between the shrimp and mollusk ponds, and the reservoir compensated for water loss from seepage and evaporation. Constricted tagelus, Sinonovacula constricta, was selected as the cultured mollusk, and Pacific white shrimp, Litopenaeus vannamei, as the cultured shrimp. The main managing measures during the production cycle were： setting and using the aerators; introducing the probiotic products timely into the shrimp ponds; adopting a “pen-closing” method for controlling shrimp viral epidemics; setting the flow diversion barriers in the mollusk pond to keep the circulating water flowing through the pond along a sine-like curve and serve as substrate for biofilm; no direct feeding was necessary for the cultured mollusk until the co-cultured shrimp was harvested; natural foods in the water from the shrimp ponds was used for their foods. Two sets of the system were used in the experiment in 2002 and satisfactory results were achieved. The average yield of the shrimp was 11 943.5 kg/hm^2, and that of the mollusk was 16 965 kg/hm^2. After converting the mollusk yield into shrimp yield at their market price ratio, the food coefficient of the entire system averaged at as low as 0.81. The water quality in the ponds was maintained at a desirable level and no viral epidemics were discovered during the production cycle.     

Lack of Gender Effect on the Pharmacokinetics of Oxytetracycline in Fenneropenaeus chinensis After Intramuscular Administration

Fenneropenaeus chinensis, an economically important shrimp species, currently suffers from epizootic diseases due to high density stocking and bacterial infections. Oxytetracycline(OTC) has been widely used to treat various systemic bacterial infections in shrimp farming. In the present study, the effect of gender on pharmacokinetics of OTC in F. chinensis was investigated. The OTC concentrations in hemolymph of shrimp after single intramuscular administration(75 mg OTC per kg body weight) were analyzed by high performance liquid chromatography and best described with a two-compartment open model which is characterized by a short elimination half-life, low clearance, and a relatively large apparent volume of distribution. The pharmacokinetic equations were Ct = 58.54e-0.38 t + 11.67e-0.04 t for females; and Ct = 27.94e-0.28 t + 14.87e-0.04 t for males. The distribution and elimination half-lives of OTC were 1.82 and 19.58 h, respectively, in females and 2.50 and 16.11 h, respectively, in males at 22℃. The areas under the drug concentration curve were 480 mg L-1 h-1 in females and 430 mg L-1 h-1 in males. The total body clearance of the drug was 157.11 m Lkg-1 h-1 in females and 172.47 m L kg-1 h-1 in males. The apparent volume distribution was 4.44 in females and 4.01 L kg-1 in males. There was no significant difference in pharmacokinetic parameters between female and male shrimps, indicating that there is no need to consider the gender effect in clinical use of OTC in F. chinensis farming.     

Biochemical response of the mussel Mytilus coruscus (Mytiloida: Mytilidae) exposed to in vivo sub-lethal copper concentrations

Many aquatic organisms are negatively affected by exposure to high copper concentrations.We investigated the biochemical response of the mussel Mytilus coruscus(Mytiloida:Mytilidae) to copper exposure.In vivo bioassays using M.coruscus and different copper concentrations were conducted.The activity of six biomarkers,namely superoxide dismutase(SOD),catalase(CAT),acid phosphatase(ACP),alkaline phosphatase(AKP),glutamic-oxaloacetic transaminase(GOT) and glutamic-pyruvic transaminase(GPT) were measured.Survival rates decreased with increased copper concentrations and exposure times.The LC50 values at 48,72,and 96 h exposure were 0.48,0.37,and 0.32 mg/L,respectively.Within digestive glands,CAT activity increased with increasing Cu concentrations.The activity of AKP showed no significant change,while the remaining four enzymes showed decreasing activity with increasing Cu concentrations.Within the gills,AKP activity increased when the Cu concentration was 0.05 mg/L,but showed no significant changes at higher concentrations.Activity of CAT and ACP within gills tended to decrease with increasing Cu concentration.The activity of SOD and GPT decreased at an exposure concentration of 0.2 mg/L.GOT activity within gills decreased at 0.1 mg/L and increased at an exposure concentration of 0.2 mg/L.Within the adductor muscle,AKP activity increased at 0.05 mg/L but did not change at higher exposure concentrations.ACP activity within adductor muscle tissue showed no change,while activities of CAT,GOT and GPT decreased with increasing Cu concentrations.SOD activity within the adductor muscle tissue significantly decreased at the 0.02,0.05 and 0.2 mg/L exposure concentrations.Our results show tissue specific differences for the six biomarkers in for M.coruscus.Our findings provide the basis for the establishment of reference activity levels against which biomarker changes can be estimated,and are essential preliminary steps in development of in vivo bioassays.     

Production of Pacific White Shrimp Polycultured with Swimming Crab at Different Densities,and Nutrient Budget in the Enclosure System

This study was to evaluate the effect of stocking densities on the nitrogen and phosphorus budgets for a polyculture of the crab Portunus trituberculatus and the Pacific white shrimp Litopenaeus vannamei.The shrimps(initial weight,0.012 g)were cultured at a density of 45 shrimp m^-2,and juvenile crabs(initial weight,0.024 g)were cultured at five densities of 0,3,6,9,and 12 crabs m^-2.The treatments were grouped as C0S45,C3S45,C6S45,C9S45,and C12S45,respectively.Water quality parameters,growth of shrimp and crabs,and nitrogen and phosphorus budget were measured.The results indicated that the shrimp performances in polyculture treatments C3S45 and C6S45 were superior to those in the crab-free treatment(C0S45).The crab in treatments C3S45 and C6S45 exhibited a significantly higher final mean weight and carapace width/length than those in treatments C9S45 and C12S45.The final size and survival of crabs had a negative correlation with the increasing crab stocking density.The contents of total phos-phorus and total nitrogen and the comprehensive contamination index values were higher in the C9S45 and C12S45 treatments than in the other treatments.The conversion ratios of nitrogen for crab and shrimp growth in treatment C3S45 were significantly higher than those in the crab-free treatment.These findings indicate that polyculturing shrimp with crabs at suitable densities can improve productivity,profitability,nutrient utilization,and the environmental quality.From the 60-day treatments,the optimal culture densi-ties were 3-6 crabs m^-2 and 45 shrimps m^-2.