The Comparison Of Histological Structure And Lipid Profile Of Gills In Three Crabs Living In Different Habitats And The Effect Of Hypoxia And Lipids Profile In Diets On The Gills Of The Chinese Mitten Crab (Eriocheir Sinensis)

The swimming crab(Portunus trituberculatus), under portunidae family and portunus class is an important economic marine crab, and mainly present in China, Japan, Korea and Malaysia et al. Because of its grow-fast, big and taste well it has became an important species for fishing and marine culture. The Chinese mitten crab(Eriocheir sinensis) attach to grapsidae family, are also an important economic freshwater crab, inhabiting freshwater pools and rivers, although breeding in brackish water estuary. Sesarma dehaani is belonged to grapsidae family and Sesarma class, which is a species of macrofauna in Yangtze estuary coastal shoaly land ecosystem. They have small size, high density, inhabits area evident. These three species live in three different habitats. Its main rearing model is pond culture. In summer with high temperature, there is so many of unconsumed organism and fluid mud in the bottom of the ponds, which will consume dissolved oxygen, the juvenile Chinese mitten crabs will face a common threat from hypoxia.This paper compared the histological, ultrastructure and lipid profile of gills in three crabs living in different habitat using the method of tissue sectioning, electron microscope and biochemistry. Beside, the hypoxic conditions can certainly threaten crabs'respiration and osmoregulation. So our experiment fed the juvenile Chinese mitten crab with varying levels of dietary docosahexaenoic acid (DHA), arachidonic acid (ARA) and docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) ratios, then acclimated them in low dissolved oxygen water 24h. We measured the lipid profile in the gills of the juvenile crab in the normal and low dissolved oxygen respectively. For the aim was to determine the effect of the normal and low dissolved oxygen on the lipid profile of the juvenile crab's gills.1. The results indicated that the histological, ultrastructure in the different crabs were similar. The gill filament contained cuticle, epithelium, pillar cell, marginal vessel. There was a cavity between the cuticle and epithelial cell in Portunus trituberculatus, although there was no cavity in Sesarma dehaani and Eriocheir sinensis. The amount of the pillar cells was different. There was less pillar cell in the gill of Portunus trituberculatus. There were mocrovilli between epithelial cell and cuticle. Some long and thin, lining regularly; the other short and small, lining erratically. The shape of mitochondrion varied, round, elliptical or concentric circle. The amount of mitochondrion in anterior gills of Chinese mitten crab was significant higher than the other two, but those in posterior gills of Portunus trituberculatus was significantly lower. In addition, comparing to other two crabs, P. trituberculatus has lower density of microvilli. The microvilli in Sesarma dehaani and Eriocheir sinensis were lining compact and dense. It suggested that the difference structure and their varied habitats were for the purpose of acclimatization better, aimed to protect their physiological functions of respiration and osmoregulation to work normally.2.The total lipids comprised triglyceride(TG), free fatty acids(FFA), cholesterol(Cho), and phospholipids(PL). The content of TG in the anterior of P. trituberculatus was higher than the others(more than 3 times), the content of cholesterol(Cho) in the gills of Sesarma dehaani was significantly higher than that in the other two crabs, while the contents of the phospholipids appeared no significantly differences between the three kinds crabs. Besides, the saturated fatty acids(SFA) mainly comprised C16:0 and C18:0; monounsaturated fatty acids(MUFA) mainly include C16:1n7, C16:1n5, C18:1n9, C18:1n7 etc; highly unsaturated fatty acids(HUFA) covered C20:4n6(ARA), C20:5n3(EPA) and C22:6n3(DHA). The gills of S.dehaani was shown to have a significantly higher arachidonic acid(ARA) and the ratio of ARA/EPA than Eriocheir sinensis or P. trituberculatus, while the contents of DHA and EPA higher significantly in P. trituberculatus. The composition and the contents of the total lipids and fatty acids appeared a significantly differences between the three kinds crabs which living in difference environments, which suggested that the composition and content of fatty acids have related to the physiological functions of the gills.3. The juveniles of Chinese mitten crab (Eriocheir sinensis) were raised with diets including different contents of the essential fatty acids (EFA): docosahexaenoic acid (DHA, C22:6n-3), arachidonic acid (ARA, C20:4n-6) and docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) for about 1.5 and 2 months, and then transfer to Shanghai cultured another 2 months with the same diet. During the last 2 months, their contents of fatty acids in gills after acclimated to hypoxia 24 h and normal DO (dissolved oxygen) level were evaluated with biochemical method. The results indicated that ARA diet have significantly effect on the fatty acids in gills of juvenile crab, but the other two EFA diet were also promoted the absorption of EFA. It implicated that EFA enriched diet could increasing the contents of EFA in the gills of juvenile crab effectively, and it's good to their fuctions of respiration and osmoregulation.