The Comparison Of Physiology And Ecology Of Litopenaeus Vannamei Under Seawater And Freshwater Conditions In Relation To The Molt Stages

A series of indoor trials were conducted to investigate the comparison of body composition, nonspecific immunity, respiratory metabolism, digestive physiology and osmoregulation in juvenile Litopenaeus vannamei cultured in seawater and freshwater conditions in relation to molt stages. The primary results were listed below.1 Comparision of body and hemolymph composition of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stagesThis experiment was conducted to investigate the changes of body and hemolymph compsitions of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stages. The results showed that the crude protein contents in muscle of test shrimp were the lowest and the highest at A stage and C stage, respectively, under both seawater and freshwater conditions. The crude lipid contents in muscle showed no significant differences in a molt cycle under two conditions. Compared with the seawater conditions, the whole level of crude protein contents in muscle increased significantly under freshwater conditions, meanwhile, the whole level of crude lipid and moisture contents decreased significantly. The crude protein contents in hepatopancreas were lower at A stage and were higher at C stage under seawater conditions. The crude lipid contents in hepatopancreas at C stage were significantly lower than those at other stages. Under freshwater conditions, the crude protein contents in hepatopancreas showed lower level at post- and inter-molt stages and exhibited higher at pre-molt stage, while the crude lipid contents showed no significant differences among all stages. The whole level of crude protein, crude lipid and moisture contents exhibited no significant differences between two conditions. Methionine and alanine contents in muscle showed significant differences among all stages under seawater conditions, while valine and serine contents in muscle exhibited significant differences among all stages under freshwater conditions. Compared with the seawater conditions, the whole level of glycine, alanine, cysteine, valine, methionone, tyrosine, phenylalanine and histidine contents in muscle changed significantly under freshwater conditions. Under both conditions, the protein concentration in hemolymph increased gradually from post-molt stage to pre-molt stage, whereas the glucose concentration in hemolymph showed higher at post-molt stage, decreased at inter-molt stage, and increased at D3 stage. Compared with the seawater conditions, the whole level of protein and glucose concentration in hemolymph decreased significantly under freshwater conditions. The calcium and magnesium contents in hemolymph decreased during molt cycle under seawater conditions. The lowest phosphorus contents in hemolymph occurred at C stage, whereas it exhibited high level at premolt and postmolt stages. Under freshwater conditions, the calcium and magnesium contents in hemolymph showed lower at A stage, increased at B stage and decreased gradually after C stage. Kalium contents in hemolymph showed the same trend as calcium and magnesium. The higher contents of Phosphor exhibited at Do stage. Compared with the seawater conditions, the whole level of kalium and calcium contents in hemolymph increased significantly under freshwater conditions, whereas the whole level of phosphor contents in hemolymph decreased significantly, but no significantly changed was found in magnesium contents.2 Comparision of nonspecific immunity of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stagesThis experiment was conducted to compare total hemocytes counts (THC), phenol oxidase (PO) activities, respiratory burst (RB), nitric oxide synthase (NOS) activities and Lysozyme (LY) activities of Litopenaeus vannamei under seawater and freshwater conditions in relation to the the molt stages. It was found that:1) THC of experimental shrimp increased from post-molt stage to pre-molt stage in both seawater and freshwater conditions. THC of D3 stage was significantly higher than that of A stage under seawater conditions (P<0.05), whereas no significant differences were found among all stages under freshwater conditions (P>0.05).2) PO activity of experimental shrimp breeding in seawater and freshwater conditions reached peak at inter-molt stage and was 87.5 U/min and 45.0 U/min, respectively, and the lower levels of PO activity occurred at post-molt and pre-molt stages. The whole level of PO activity of experimental shrimp breeding in freshwater conditions was significantly lower than that in seawater conditions (P<0.05).3) The change trend of RB was similar to that of THC under seawater and freshwater conditions, and increased to the peak at pre-molt stage, especially D3 stage. The whole level of RB of experimental shrimp breeding in freshwater conditions was significantly lower than that in seawater conditions (P<0.05).4) NOS activities of experimental shrimp breeding in both seawater and freshwater conditions were higher level at pre-molt stage, whereas lower level occurred at inter-molt and pre-molt stage. The whole level of NOS activity of experimental shrimp breeding in freshwater conditions was significantly lower than that in seawater conditions (P<0.05).5) LY activity of experimental shrimp breeding in seawater and freshwater conditions changed an extent, and the highest levels were found at inter-molt stage. The whole level of LY activity in seawater was significantly higher than in freshwater conditions (P<0.05).3 Comparision of respiratory metabolism of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stagesThis experiment was conducted to compare the oxygen consumption rates (OCR), ammonia excretion rates (AER), urea excretion rates (UER), pyruvate kinase activities (PK) and lactate dehydrogenase activities (LDH) of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stages. It was found that:1) Under seawater condition, the high level of the OCR occurred around the ecdysis. The OCR of D3 stage and post-molt stage (A and B stages) increased and was 0.667 mg·g-1·h-1,0.696 mg·g-1·h-1 and 0.727 mg·g-1·h-1, respectively, the level of OCR of C, Do and D1 stages were between 0.567-0.581 mg·g-1·h-1, and the lowest level of OCR occurred at D2 stage (0.488 mg·g-1·h-1). Under freshwater conditions, the fluctuation trend of OCR was similar to that one under seawater conditions. The OCR of A and B stages was 0.651 mg·g-1·h-1 and 0.650 mg·g-1·h-1, respectively, and significantly higher than those at other stages (P<0.05). The whole level of OCR of shrimp cultured in seawater conditions was higher than that in freshwater conditions (P<0.05).2) Under seawater conditions, AER of shrimp at A and B stages (was 12.273μg·g-1·h-1 and 10.644μg·g-1·h-1, respectively) and these were significantly higher than that at C stage (4.574μg·g-1·h-1) (P<0.05), and AER increased with a certain extent at Do-D2 stages, then decreased to the lowest level at D3 stage (2.969μg·g-1·h-1). Under freshwater conditions, the highest level (40.501μg·g-1·h-1 and 31.164μg·g-1·h-1) of AER was occurred at post-molt stage, and significantly higher than those at other stages (P<0.05). The whole level of AER of shrimp cultured in seawater conditions was lower than that in freshwater conditions (P<0.05).3) Under seawater conditions, the UER of shrimp decreased around the ecdysis, reached the highest level at DO stage, and there were significant differences between them (P<0.05). Oppositely, under freshwater conditions, the UER of shrimp increased at pre- and post-molt stages, decreased at inter-molt stage and significant differences were found between them (P<0.05). The whole level of UER of shrimp cultured in seawater conditions was significantly higher than that in freshwater conditions (P<0.05).4) Under seawater conditions, PK activity of shrimp at A and B stages was 150.67 U/gprot and 164.50 U/gprot, respectively, decreased at C stage, and then reached the higher level at D1 and D2 stages (219.19 U/gprot and 233.30 U/gprot), finally decreased to the lowest level at D3 stage. Under freshwater conditions, PK activity of shrimp was highest at B stage (116.77 U/gprot), then decreased gradually with the passage of time, the lowest level occurred at pre-molt stage. Compared with the seawater conditions, the whole level of PK of shrimp cultured in freshwater conditions decreased significantly (P<0.05).5) Under seawater conditions, LDH activity of shrimp reached the peak at B stage (2587.99 U/gprot) and decreased gradually, while the lowest level occurred at D3 stage (1851.02 U/gprot). The fluctuation trend under freshwater condition was similar to that under seawater conditions. The highest level occurred at DO stage (4376.15 U/gprot), while the lowest level was showed at D3 stage (1159.55 U/gprot). There were no significant differences of the whole level of LDH activities between the two conditions.4 Comparision of digestive physiology of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stagesThis experiment was conducted to compare pepsin activities, tryptase activities, lipase activities and amylase activities of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stages. It was found that:1) the changing tendency of pepsin activities of experimental shrimp cultured in seawater and freshwater conditions was similar in a molt cycle. The higher level of pepsin activities occurred in post-molt stage, and then decreased at inter-molt stage, while the lowest level of that was found at pre-molt stage. There were no significant differences of the whole level of pepsin activities between the two conditions (P>0.05).2) Under seawater conditions, tryptase activity of experimental shrimp was the highest at A stage (4.556 U/mg prot), and tryptase activities were 3.462-3.820 U/mg prot at pre-molt stage. Under freshwater condition, tryptase activity at inter-molt stage was 1.950 U/mg prot and was significantly higher than those at other stages (P<0.05). The whole level of tryptase activity of experimental shrimp cultured in seawater conditions was higher than that in freshwater conditions (P<0.05).3) Under seawater conditions, lipase activities of experimental shrimp kept higher level at post-molt stage (A and B stages) and were 6.919 U/mg prot and 7.531 U/mg prot, respectively, and then decreased at inter-molt stage, and the lower level of lipase activities were found at pre-molt stage which were 4.646-5.258 U/mg prot. Under freshwater conditions, lipase activities of experimental shrimp were higher at post-molt stage, and the highest level was found at inter-molt stage (8.720 U/mg prot), and then decreased to 3.523-5.813 U/mg prot at pre-molt stage. No significant differences of the whole level of lipase activities were found between the two conditions (P>0.05).4) Under seawater conditions, amylase activity of experimental shrimp at A and B stages was 1.525 U/mg prot and 1.398 U/mg prot, respectively,and significantly higher than those at other stages (P<0.05). Under freshwater conditions, lipase activity of experimental shrimp reached the peak at inter-molt stage (2.954 U/mg prot), and was significantly higher than those at other stages (P<0.05). The whole level of amylase activity of experimental shrimp breeding in seawater conditions was 1.124 U/mg prot, and significantly higher than that in freshwater conditions.5 Comparision of osmoregulation of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stagesThis experiment was conducted to investigate the changes of osmolarity, hemocyanin concentration, Na+-K+-ATPase activity and carbonic anhydrase activity of of Litopenaeus vannamei under seawater and freshwater conditions in relation to the molt stages. The results showed that the changing trends of osmolarity were different under seawater and freshwater conditions. Under seawater conditions, the osmolarity of test shrimp kept higher level at pre-molt stage (D2 and D3 stages) and post-molt stage (A and B stages), whereas lower level occurred at inter-molt stage. Under freshwater conditions, the osmolarity of test shrimp kept lower level at post-molt stage (A and B stages), increased from inter-molt stage. The whole level of osmolarity of L. vannamei cultured in seawater conditions was significantly higher than that in freshwater conditions. There were two different changing trends of hemocyanin concentration of test shrimp under two conditions. Under seawater conditions, the hemocyanin concentration was lower at post-molt stage and increased gradually after that. There were no significant differences of hemocyanin concentration among all molt stages under freshwater conditions. The whole level of hemocyanin concentration of L. vannamei cultured in seawater conditions was also significantly higher than that in freshwater conditions. Under seawater conditions, Na+-K+-ATPase activity in gills kept lower at pre-molt stage (D2 and D3 stages) and post-molt stage (A and B stages), whereas higher level occurred at inter-molt stage. Under freshwater conditions, Na+-K+-ATPase activity in gills was the highest at A stage, and then decreased gradually, and reached the lowest at D3 stage. The trend of Na+-K+-ATPase activity was opposite to the one of osmolarity during the molt cycle under both seawater and freshwater conditions. The changing trends of carbonic anhydrase activity during the molt cycle were similar under two conditions. Carbonic anhydrase activity was higher at post-molt stage, and lower level occurred at other stages and narrowly increased at D3 stage. The whole level of two ion transport enzymes did not show significant differences between seawater and freshwater conditions.