Meat Quality of Chinese Mitten Crabs Fattened with Natural and Formulated Diets

After 42 days feeding on either a Huayi formulated diet (HY) or trash fish (TF), the meat quality of Chinese mitten crab, Eriocheir sinensis, was compared. The meat yield of males (25 vs. 22%) was higher, but the total edible yield was lower than that of the females (p < 0.05). The proximate composition of both genders fed two diets was similar (p > 0.05), and there was no significant difference in the total collagen content of the meat (0.2–0.30%) between both dietary treatments and genders (p > 0.05). The diets had no significant effects on free amino acid content of the meat, while gender significantly affected the contents of some amino acids, such as taurine and glycine. Crabs fed TF had significantly lower contents of 20:5n-3 as well as higher arachidonic acid (ARA)/eicosapentaenoic acid (EPA) value compared with those of same sex crabs fed HY (p < 0.05). There were no significant dietary effects on a range of sensory traits evaluated by panelists, neither in female nor in male crabs. These results suggested no negative effects of formulated diet HY on the meat quality compared to trash fish. Therefore, diet HY could be used to replace the trash fish for fattening mitten crabs.     

Effects of dietary fish oil substitution with blending vegetable oils on growth performance,antioxidant enzyme activities and tissue fatty acid composition of juvenile swimming crab,Portunus trituberculatus

An 8‐week feeding trial was conducted to evaluate the effects of replacement of fish oil (FO) with blending vegetable oils (VOs) on growth performance, antioxidant enzyme activities and fatty acid composition in tissue of swimming crab Portunustrituberculatus. Five isonitrogenous and isolipidic diets were formulated to contain VOs (colza oil: palm oil: linseed oil = 4:2:1) to replace 0 (the control diet), 250, 500, 750 and 1000 g/kg of FO (defined D0, D25, D50, D75, D100). Three hundred juvenile swimming crabs (initial weight 2.34 ± 0.08 g) were randomly stocked and sorted into 300 individual rectangle plastic baskets in three cement pools. Each treatment has three replicates, one replicate has 20 swimming crabs, and each diet fed 60 crabs distributed in 60 baskets. The results indicated that crabs fed the control diet showed significantly higher survival, final body weight, per cent weight gain (PWG), specific growth rate and moulting frequency, crude protein and crude lipid contents in muscles than those fed the D75 and D100 VO diets (p < .05). Crabs fed the D25 VO diet showed significantly higher concentration of triglyceride, low‐density lipoprotein cholesterol and total protein, activities of superoxide dismutase, catalase and glutathione peroxidase (GSH‐Px) in haemolymph than those fed the control diet (p < .05). Fatty acid composition in hepatopancreas was positively correlated with dietary composition. In summary, based on the PWG, the optimal replacement of FO with VOs was estimated to be 250 g/kg. These findings demonstrated that swimming crabs make better use of FO than VOs.     

Pectin plays a role in restricting the utilization of rapeseed meal by Chinese mitten crab,Eriocheir sinensis

The present study aims to assess the anti‐nutritional effect of pectin and to better understand rapeseed meal (RSM) as a feed ingredient for Chinese mitten crab, Eriocheir sinensis. A semipurified diet containing 280 g/kg fish meal was formulated as a control diet (D_F). A second diet (D_P) was supplemented with 26.7 g/kg pectin; the amount was estimated to be equal to that in the third diet (D_R), which was formulated to include 400 g/kg RSM. Another diet (D_RPase) was supplemented with 12 g/kg pectinase based on D_R in which pectin was degraded by pectinase. The diets were randomly fed to twelve tanks of the crab for 8 weeks. Compared with the crabs fed D_F, the specific growth rate, protein efficiency ratio, apparent digestibility coefficients (ADC) of dry matter and protein, activity of aspartate transaminase (AST) and trypsin (TP), and high‐density lipoprotein (HDL) in the serum decreased significantly in the crabs fed D_R; the ADC of dry matter, activity of AST and serum HDL decreased significantly in the crabs fed D_p, but they were higher than in the crabs fed D_R. Compared with the crabs fed D_R, the ADC of dry matter, activity of AST and TP, and serum HDL increased significantly in the crabs fed D_RPase. The mRNA expression activity of both Es‐pl44 and Es‐pp1 was D_F < D_P < D_RPase < D_R. These results indicate that pectin contributed to low utilization of RSM in Chinese mitten crab.     

Nutritional qualities of normal and precocious adult male Chinese mitten crabs (Eriocheir sinensis)

The nutritional values of edible gonad, hepatopancreas and muscle tissues from normal and precocious adult male Chinese mitten crabs (Eriocheir sinensis) were investigated herein. The results showed that the average weight and meat yield (MY) of normal crabs were significantly higher than those of precocious crabs, while the hepatopancreas indexes (HSI) and gonadosomatic indexes (GSI) had no significant differences. Precocious and normal crabs had greater protein and lipid contents, respectively, and the differences were mainly reflected in gonads and hepatopancreas. While assessing the amino acid profiles, both precocious and normal crabs could be high‐quality protein sources, particularly the precocious crabs which showed higher levels of essential amino acids. In fatty acid profiling experiments, precocious crabs revealed higher EPA, ∑n‐3 polyunsaturated fatty acids (PUFA) and ∑n‐3/∑n‐6 ratios than normal crabs; however, DHA and ∑n‐6 PUFA contents were considerably lower. Additionally, contents of nutritious minerals K and Ca in precocious crabs were significantly higher than those in normal crabs, while Zn and Fe were significantly lower. In short, our data indicated that precocious Chinese mitten crabs are also a nutritious food, and even in some respects their nutritional value is higher than normal crabs.     

Growth and immune response of Chinese mitten crab (Eriocheir sinensis) fed diets containing different lipid sources

A 10‐week feeding trial was conducted to evaluate the effects of dietary lipid sources on the growth and immune responses of Chinese mitten crab Eriocheir sinensis. Six isonitrogenous and isoenergetic diets were formulated with fish oil (FO), linseed oil (LO), soybean oil (SO), rapeseed oil (RO), coconut oil (CO) and beef tallow (BT) as the sources of lipid with five replicates each. Thirty crabs (2.35 ± 0.14 g) were stocked into each tank and fed twice daily. Weight gain and specific growth rate of crab fed the FO diet were significantly lower than those fed other diets (P < 0.05), except for crabs fed LO diet (P < 0.05). Crab fed the SO diet weighed more than those fed FO diets (P < 0.05). Serum superoxide dismutase and malondialdehyde of crab fed the FO diet were significantly higher than in other groups (P < 0.05). Crab fed the FO diet had the highest activities of serum phenoloxidase, acid phosphatase, alkaline phosphatase and lysozyme (P < 0.05). The fatty acid composition in the liver of crab reflected the change in test diets. Our results indicate that the use of dietary vegetable or animal oils can achieve similar growth performance to the use of dietary FO in Chinese mitten crab, but non‐FOs may impair crab immunity. Soybean oil is recommended as a suitable replacer for FO in Chinese mitten crab diet.     

Effects of dietary visceral protein hydrolysate of rainbow trout on growth performance,carcass composition,digestibility and antioxidant enzyme in juvenile Oncorhynchus mykiss

The purpose of this study was to investigate the effects of dietary visceral protein hydrolysate (VPH) of rainbow trout on performance of juvenile Oncorhynchus mykiss. The antioxidant property of VPH was 85% ± 1.6%. Four diets were prepared including VPH free as the control and three diets with 5, 10 and 20 g/kg of VPH inclusions. Juvenile rainbow trouts (n = 252, 9.74 ± 0.22 g) were randomly distributed to experimental tanks. Final results showed the maximum amounts of weight gain and SGR and the lowest FCR value in fish fed with 10 g/kg VPH (p < .05). The highest carcass protein and fat contents were observed in 10 g/kg VPH treatment and the control diet, respectively (p < .05). The largest fat and dry matter digestibility were recorded in fish fed by 5 g/kg VPH (p < .05), while the control and 10 g/kg VPH diets showed the highest levels of protein digestibility (p < .05). Dietary inclusion of VPH improved SOD enzyme activity (p < .05). The results indicate that a diet containing 10 g/kg of VPH inclusion can improve growth performance and some other examined factors in juvenile O. mykiss.     

Study on the nutritional quality of ecologically bred Chinese mitten crabs with different body weights

To provide basic nutritional data and theoretical support for the processing and comprehensive utilization of the Chinese mitten crab, we performed a systematic study of the nutritional components of three edible parts, namely the hepatopancreas, gonads and abdominal muscle, of three groups of animals differing in body mass: 75.55 ± 1.56 g, 100.24 ± 2.04 g and 162.27 ± 3.44 g. The results showed that with a greater body mass, the water content was higher, the protein and ash contents were first higher and then lower, and the fat content was first lower and then higher. Amino acids (AAs), essential AAs (EAAs) and the EAA/AA ratio were first higher and then lower, all reaching the standard for high‐quality protein. The most limiting AA was valine. The EAA index was greater than 97 for all three edible parts of the medium‐sized crabs, indicating that crabs in this size group had very high nutritional value. The numbers of detected fatty acids were the same among the edible parts and the three size groups of the river crabs. Among the mineral elements measured, Ca, K and Na were the most abundant and showed a trend of first being higher and then being lower with a larger crab size. Although heavy metals were detected, the Cr, Pb and Cd levels were all within the permissible limits. Therefore, the nutritional quality of the three edible parts was greater for medium‐sized river crabs than for small and large mitten crabs.     

发酵饲料对中华绒螯蟹幼蟹生长、抗氧化、免疫和蛋白代谢的影响

为研究发酵饲料配伍配合饲料投喂对中华绒螯蟹幼蟹生长性能、抗氧化、免疫机能和代谢的影响,实验分别制备了5组饲料:对照组以幼蟹配合饲料为基础饲料(F0),各实验组在配合饲料基础上额外添加日投喂量5%、10%、15%和20%发酵饲料,并依次命名为F5、F10、F15和F20。150只均重无显著差异的中华绒螯蟹随机分5组,每组设3个重复,每重复10只蟹,分别饲喂对应组饲料,每天饱食投喂1次,养殖周期59 d。在养殖结束后采集血淋巴和肝胰腺以测定抗氧化指标、免疫指标和蛋白代谢酶活性。结果发现,额外投喂发酵饲料后,各组幼蟹的增重率和特定生长率均较对照组显著升高。随着额外投喂发酵饲料量的增加,血淋巴中过氧化氢酶含量先上升后下降,其中F5、F10和F15组较对照组显著升高。各处理组酸性磷酸酶活性高于对照组,但差异不显著。各组总蛋白和球蛋白含量随着发酵饲料额外投喂量提高呈现先升高后降低的趋势,但是各组间差异不显著。此外,额外添加日投喂量20%比例以下的发酵饲料,可以提升肝胰腺中胰蛋白酶、胃蛋白酶、谷草转氨酶、谷丙转氨酶活性。研究表明,额外投喂发酵饲料可以促进中华绒螯蟹幼蟹的生长,还可以提高其抗氧化能力、免疫机能和蛋白代谢能力。     

Effects of dietary starch levels on the growth,plasma metabolites and expression of genes involved in glucose transport and metabolism in Pelodiscus sinensis juveniles

A 10‐week feeding trial was conducted to evaluate the growth performance, glucose transport and metabolism of Chinese soft‐shelled turtles (Pelodiscus sinensis) exposure to graded levels of dietary starch (0.52%, 7.43%, 14.74%, 22.99% and 31.38%). The 360 turtles (initial body weight, 12.94 ± 0.50 g) with 12 replicates were randomly assigned to five experimental diets. The highest weight gain and specific growth rate (SGR) were observed in 7.43% group and the lowest in 31.38% group. The protein efficiency ratio, whole‐body lipid contents, hepatic glycogen contents and the 4‐hr postprandial plasma glucose levels were significantly increased with the increment of starch levels (p < .05). In contrast, the daily feed intake and feed conversion ration were significantly declined (p < .05). The mRNA levels of glucose transporter 2, glucokinase, pyruvate kinase, malic enzyme and acetyl‐CoA carboxylase alpha genes in the liver significantly increased as the increase in starch levels at 4‐hr and 24‐hr post feeding (p < .05). No significant differences were observed in the expression of gluconeogenesis genes at each time point (p > .05). These results suggested that dietary addition of starch up‐regulated hepatic glycolysis, glycogenesis and lipogenesis genes expression, but the deficient response of gluconeogenesis to dietary starch might be part of the causes limited the starch utilization. Based on the secondary polynomial regression of SGR, y = ?0.0011x² + 0.028x + 1.63 (R² = 0.9292), the 12.73% inclusion level of dietary starch was recommended in juvenile turtles.     

低聚壳聚糖对中华绒螯蟹生长性能、体成分、非特异性免疫及抗氧化能力的影响

为研究低聚壳聚糖对中华绒螯蟹生长性能、体成分、非特异性免疫及抗氧化能力的影响,实验选用个体均匀、初始均重为(16.20±1.30) g的中华绒螯蟹288只,随机分为4组,每组6个重复,每个重复12只,分别饲喂在基础日粮中添加0 (对照组)、25、50和100 mg/kg低聚壳聚糖的实验日粮,正式实验为期56 d。结果显示,与对照组相比,50和100 mg/kg低聚壳聚糖组中华绒螯蟹的饲料系数显著降低,可食内脏指数显著提高;50 mg/kg低聚壳聚糖组降低了中华绒螯蟹肌肉和可食内脏中粗脂肪含量,提高了蟹肌肉和可食内脏中超氧化物歧化酶和过氧化氢酶的活性;与对照组相比,50 mg/kg低聚壳聚糖组中华绒螯蟹碱性磷酸酶和酚氧化酶的活性显著提高。研究表明,添加低聚壳聚糖能够提高中华绒螯蟹生长性能、非特异性免疫和抗氧化能力,降低机体脂肪沉积,且添加量为50 mg/kg时效果较好。     

Effects of different stocking densities on the growth performance and antioxidant capacity of Chinese mitten crab (Eriocheir sinensis) in rice crab culture system

This study assessed the effects of stocking density (D02, 0.2 individuals/m²; D03. 0.3 individuals/m²; D04, 0.4 individuals/m²; D05, 0.5 individuals/m²; D06, 0.6 individuals/m²) on Chinese mitten crab (Eriocheir sinensis; 6.25?±?0.11 g) growth performance, tissue indices, antioxidant enzyme activity (total superoxide, catalase, glutathione peroxidase, total antioxidant capacity, and malondialdehyde), and mRNA expression of antioxidant-related genes (SOD, CAT, GPx) in rice crab culture systems. Our results demonstrated that increasing stocking densities decreased the final weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed conversion efficiency (FCR), and protein efficiency ratio (PER) of the crabs. The hepatosomatic index (HSI) of female crabs in D04 group was higher than that of other groups. The gonadosomatic index (GSI) of the male crabs in the D04 group was significantly higher than that of the other groups(P?<?0.05). The meat yield (MY), total edible yield (TEY), and condition factor (CF) of the female and male crabs in the D04 group were higher than those of the other groups. The antioxidant enzyme activity (T-SOD, CAT, GSH-Px, and T-AOC) of male and female crabs in the D04 group was significantly higher than that of the other groups, and the MDA content of the D04 group was significantly lower than that of the other groups (P?<?0.05). The stocking density of 0.4 individuals/m² effectively promoted the efficient mRNA expression of SOD, CAT, and GPx genes in the hepatopancreas of male and female crabs. In summary, the optimal stocking density of E. sinensis in the rice crab culture system is 0.4 individuals/m².

     

Effects of xylan and cottonseed meal on growth performance,digestion, intestinal morphology and the expression of two peritrophin genes of Chinese mitten crab,Eriocheir sinensis

Xylan is one of the main non‐starch polysaccharides (NSPs) in cottonseed meal. This study aimed to evaluate the anti‐nutrition effect of xylan and to better understand cottonseed meal as a feed ingredient for the Chinese mitten crab, Eriocheir sinensis. A diet containing 280 g/kg fishmeal without cottonseed meal or xylan was formulated as a control (FM diet). A second diet (XYL diet) was supplemented with 53.3 g/kg xylan according to its amount in the third diet, the cottonseed meal diet (CSM diet), which was formulated to include 400 g/kg cottonseed meal. The last diet (CSM + XYLase diet) included 400 g/kg xylanase hydrolysed cottonseed meal, in which most xylan was hydrolysed. Diets were isonitrogenous (370 g/kg crude protein) and isoenergetic (17.58 KJ/g) and were randomly fed to 12 tanks of crabs for 8 weeks. Results showed that no difference was detected among groups in growth performance, serum biochemical index, or digestive and metabolism enzyme activity (p > 0.05). The apparent digestibility coefficient (ADC) of dry matter was FM > XYL > CSM + XYLase > CSM (p < 0.05). The ADC of protein in crab fed diet FM and XYL was significantly higher than CSM and CSM + XYLase (p < 0.05). Cottonseed meal decreased the fold height of the hindgut, upregulated the expression of peritrophin genes of Es‐PL44 and Es‐PP1 (p < 0.05), while xylan decreased the fold height of the hindgut and upregulated the expression of Es‐PP1 (p < 0.05). These results indicated that the negative effect of cottonseed meal and xylan on digestibility partly compensated by enhanced absorption of the hindgut innerly and by supplementation of xylanase externally, and cottonseed meal is an attractive alternative protein source in general for Chinese mitten crab.     

Effect of poly‐β‐hydroxybutyrate on growth,enzyme activity and intestinal microbial community of Chinese mitten crab,Eriocheir sinensis (Milne‐Edwards) juveniles

Poly‐β‐hydroxybutyrate (PHB) is microbial carbon and energy storage polymer, which can be degraded into water‐soluble β‐hydroxybutyric acid in the gastrointestinal tract of aquatic animals. A 60‐day culture experiment was performed using Chinese mitten crab, Eriocheir sinensis (Milne‐Edwards) juveniles with an average initial body weight of 0.74 ± 0.06 g which were fed a diet supplemented with 0%, 0.5%, 1%, 3% or 5% PHB. A PHB dietary supplementation of 1% and 3% significantly improved the body weight gain, moulting frequency and concomitantly reduced 2nd–3rd moulting intervals of the crabs (P < 0.05). The dietary PHB level positively related to hepatopancreatic pepsin, trypsin and lipase activity (P < 0.05). Increasing the dietary PHB also improved total superoxide dismutase activity, but reduced alkaline phosphatase and acid phosphatase activity in the serum of hemolymph (P < 0.05). A 16S rRNA gene analysis by denaturing gradient gel electrophoresis indicated that PHB supplementation led to a significantly higher range‐weighted richness, diversity and evenness of the gut bacterial community when dosed at 3% in the feed. The beneficial effects of PHB are discussed in terms of immune defense, metabolism and gut microbiota of the crabs.     

Effects of gelatin or carboxymethyl cellulose supplementation during pelleting processing on feed quality,intestinal ultrastructure and growth performance in gibel carp (Carassius gibelio)

Gelatin and carboxymethyl cellulose (CMC) were often used as binders due to their binding ability. To investigate the effects of gelatin and CMC supplementation on feed quality, intestinal ultrastructure and growth performance of gibel carp, six pelleted feed were formulated: control; supplemented with gelatin (10 g/kg, 30 g/kg and 50 g/kg); and supplemented with CMC (10 g/kg and 30 g/kg). Increased gelatin supplementation levels reduced feed solubility and pellet softening (p < .05) and decreased chemical oxygen demand in the surrounding water after pellets were immersed (p < .05). Increased levels of gelatin supplementation enhanced digesta viscosity and reduced intestinal microvilli length and digestive enzymes activities (chymotrypsin and amylase; p < .05) of fish. Fish‐fed diets supplemented with 30 g/kg gelatin had higher levels of plasma total free amino acids and glucose (p < .05) than fish fed 10 g/kg and 50 g/kg gelatin. Feed supplemented with 10 g/kg CMC were softer than those supplemented with 30 g/kg CMC (p < .05); fish‐fed diets supplemented with 10 g/kg CMC had longer intestinal microvilli (p < .05) than fish fed 30 g/kg CMC. Thus, our results indicated that either gelatin or CMC is applicable to supplement in the feed for improving feed quality and without negative effect on growth performance of gibel carp.     

Effect of dietary soybean lecithin on growth parameters,digestive enzyme activity,antioxidative status and mucosal immune responses of common carp (Cyprinus carpio)

Common carp, Cyprinus carpio (13.54 ± 0.48 g), were fed soybean lecithin‐incorporated diets for 8 weeks. After the feeding trials, the different groups of fishes were assessed by survival, growth parameters, digestive enzymes, antioxidant enzyme activities, mucosal immune parameters, etc. The lecithin‐incorporated diets (10–30 g kg^–1) helped to increase the weight gain significantly (p < .05) compared with control groups; activity of digestive enzymes was also significantly (p < .05) higher compared with experimental groups. The antioxidant enzymes including catalase and serum superoxide dismutase were significantly (p < .05) higher in the C. carpio fed lecithin‐incorporated feed than the ones fed the control feed. The serum thiobarbituric acid‐reactive substances and serum glutathione peroxidase activity did not differ significantly (p > .05) between control and experimental groups. The positive correlation supported that antibacterial activity was significantly (p < .05) increased with increasing concentration of lecithin in the diets. Among the different mucosal immune parameters, lysozyme, protease and esterase activities were significantly (p < .05) increased with lecithin‐incorporated diets. The results of this study confirm that 20 and 30 g kg^–1 lecithin inclusion in diets helped to enhance the activities of digestive enzymes, antioxidant enzymes, antibacterial factors and mucosal immune parameters in C. carpio.     

Effect of dietary lipid levels on growth performance,fatty acid profile and enzymatic activity of juvenile swimming crab,Portunus trituberculatus

The main objective of this investigation was to study the lipid requirements of the early juvenile (C1) swimming crab (Portunus trituberculatus) based on growth performance, survival, moulting and fatty acid profile. Four test diets were formulated with graded lipid levels (3.63%, 6.70%, 10.72% and 13.91%). Each diet was fed to 4 replicates of crabs (30 crabs per replicate initial weight (8.4 ± 0.1 mg). In this study, crabs fed diets with 13.91% lipid had significantly (p < 0.05) higher survival than crabs fed with 3.63% lipid, but no significant (p > 0.05) improvement of survival was observed when dietary lipid increase from 6.70% to 13.91%. Crabs fed diets with 10.72% and 13.91% lipid had significant higher weight gain(WG) than crabs fed with 3.63% lipid. While crabs fed with diets containing 6.70%, 10.72% and 13.91% lipid showed no significant (p > 0.05) difference in weight gain(WG). Moreover, the lowest moulting number was observed in crabs fed diets with 3.63% lipid, but there was no significant difference (p > 0.05) among other groups. The content of LC‐PUFA and DHA in the crabs fed diets with 3.63% lipid was significant (p < 0.05) lower compared to other groups. But there was no significant (p > 0.05) difference in EPA and ARA content among all groups. The activity of lipase increased as dietary lipid level increased (from 6.70% to 10.72%). However, beyond 10.72%, a significant (p < 0.05) decreased in lipase activity was observed. The regression analysis of weight gain data indicated that crab fed diet containing 10.47% lipid level is considered as optimum lipid level for its maximum growth and moulting process.     

Effects of different dietary lipid sources on tissue fatty acid composition,serum biochemical parameters and fatty acid synthase of juvenile mud crab Scylla paramamosain (Estampador 1949)

A 6‐week study was conducted to determine the effects of different lipid sources in pelleted diets on juvenile mud crab Scylla paramamosain. Five isonitrogenous and isolipidic diets containing 8% level of fish oil (FO), lard (LD), safflower oil (SO), perilla seed oil (PO) or mixture oil (MO; V_FO:V_SO:V_PO = 1:1:1), and a live food of marine bivalve Potamocorbula rubromuscula as the control diet (CF), were fed to groups of 25 juvenile crabs (average initial weight 7.4 g, carapace width 3.5 cm) in triplicate. The results showed that crabs fed MO had the highest survival (P < 0.05). The moisture content was significantly higher in crabs fed LD, SO and PO (P < 0.05). Crabs fed SO exhibited the lowest crude protein and lipid (P < 0.05). Ash contents were obviously lower in LD group (P < 0.05). Highest total lipid in the hepatopancreas and muscle was in LD and FO group respectively. Glucose, total cholesterol and low‐density lipoprotein were higher while high‐density lipoprotein was lower (P < 0.05) in LD group. Tissue fatty acid compositions were consistent with those in diets. FO and MO diets had the same depression effect like CF on fatty acid synthase activity and mRNA expression in the hepatopancreas. The results of this study indicated that FO and mixed oil are suitable for preparation of pelleted diets with better effects for juvenile S. paramamosain compared with live food, and the ratio of n‐6/n‐3 fatty acids in pelleted diets must be <1.     

Responses of metabolism and haemolymph ions of swimming crab Portunus trituberculatus to thermal stresses: a comparative study between air and water

Two approaches (i.e. water and dry or semi‐dry transport) have been developed for the transport of swimming crabs Portunus trituberculatus in recent years. To evaluate their differential effects on physiological responses of crabs, we measured haemolymph components (metabolic substrates, metabolites and ions) and hepatopancreas glycogen level at different time intervals after exposure of crabs to thermal stresses in water and air. The immersed crabs exhibited no significant change in all metabolic substrates except the glucose level in the hypothermal stressed treatment (P > 0.05), whereas there was a great variation in haemolymph glucose and lipid level of air exposed crabs under both thermal stresses (P < 0.05). With respect to metabolites in immersed crabs, only urea concentration in hypothermal stressed crabs and lactate concentration in hyperthermal stressed crabs changed significantly during the experiment; by contrast, the air exposed crabs responded significantly in all metabolites to thermal stresses (P < 0.05). The immersed crabs decreased the concentration of Na⁺ and Mg²⁺, but increased the concentration of K⁺ and Ca²⁺. The change in Na⁺ and Ca²⁺ were not significant in the hyperthermal stressed crabs (P > 0.05). Nevertheless, all ions except K⁺ accumulated significantly in the air exposed crabs after thermal stresses (P < 0.05). Crabs in the two different media responded similar to thermal stresses in metabolism but differed greatly in ions regulation. The effects of thermal stresses on crabs could be magnified by exposure to air, leading to animals relying more on anaerobic metabolism and therefore limiting the usage of dry or semi‐dry transport approach especially at high temperature.