Effects Of Formulated Diet And Culture Modes On Culture Performance And Nutritional Composition Of Swimming Crab Portunus Tritructus

The swimming crab（Portunus trituberculatus）is one of the important marine crabs in China.At present,the pond culture of P.trituberculatus mainly relies on feeding frozen trash fish and low-value shellfish.It is very urgent to develop formulated feed for pond culture of P.trituberculatus.This experiment is designed firstly to investigate the appropriate dietary protein content for pond-reared P.trituberculatus.Then,the further study was conducted to compare the effects of two feeding modes on the culture performance,physiological metabolism,biochemical composition and feed contribution of pond-reared P.trituberculatus.Finally,the effects of two pond culture modes on the performance and economic benefits of P.trituberculatus were studied.The results as follow:1.Effects of dietary protein levels on growth,ovarian development,physiological metabolism and biochemical composition of swimming crab（Portunus trituberculatus）The study was designed to investigate the effects of dietary protein levels on growth,ovarian development,physiological metabolism and biochemical composition of swimming crab Portunus trituberculatus.Four experimental diets were formulated to contain different protein levels（30%,34%,38%and 42%,defined as Diet 1#-Diet4#）,which are isoenergic and islipidic.These diets were fed to pond-reared female P.trituberculatus for 120-day culture experiment.The results showed as follows:（1）Dietary protein levels had no significant influence on the growth of pond-reared females P.trituberculatus,and the weight gain rate and specific growth rate of females in each diet decreased significantly during the whole culture period.（2）Diet 3#treatment had the highest gonadosomatic index（GSI）and total edible yield（TEY）,but no significant differences were found on hepatosomatic index（HSI）,meat yield（MY）and condition factor（CF）.（3）The activity of glutamic-oxalacetic transaminase（GOT）decreased with increasing protein level（P<0.05）,while the content of total free amino acid（TFAA）increased with increasing protein level（P<0.05）.Diet 3#treatment had the highest malondialdehyde（MDA）content in hemolymph among the four treatments（P<0.05）.Diet 2#treatment had the highest glutamic-pyruvic transaminase（GPT）activity and lowest glutamic-oxalacetic transaminase activity（P<0.05）.The blood urea nitrogen（BUN）content in Diet 3#hepatopancreas was significantly higher than that of other Diets（P<0.05）.The activity of superoxide dismutase（SOD）,glutathione peroxidase,（GSH-Px）,acid phosphatase（ACP）and alkaline phosphatase（AKP）in hepatopancreas decreased with increasing protein level.（4）The contents of crude protein in ovary and hepatopancreas increased significantly with increasing dietary protein（P<0.05）,while Diet 1#and 3#treatments had the higher crude protein content in muscle among the four treatments（P<0.05）.The increasing trend was found on the contents of total lipids in the ovary increased with increasing dietary protein（P<0.05）.Diet 1#treatment had the highest total lipids content in hepatopancreas and muscle,while the lowest total lipids content was found in Diet 2#treatment（P<0.05）.The contents of total essential amino acids（∑EAA）and non-essential amino acids（∑NEAA）in muscle of Diet 1#and 3#treatments were significantly higher than that of other two treatments（P<0.05）.These results indicated the appropriate protein level in diet was approximately 40%for adult female P.trituberculatus.The results showed that the appropriate protein level in diet could improve ovarian development,strengthen amino acid metabolism and decrease oxidative stress.2.Effects of the two feeding modes on ovary development,physio-biochemical and feed contribution of pond-reared P.trituberculatusSwimming crab（Portunus trituberculatus）is an important marine aquaculture species in China.At present,the diets of P.trituberculatus is mainly fed with traditional diets（trash fish）during the whole culture process.It is the development trend of swimming crab to feed formulated diets throughout the whole course culture.This study was conducted to investigate the effect of two feeding modes（formulated diets,traditional diets）on culture performance,physio-biochemical and food contribution of P.trituberculatus.（1）The two diets no significant influence on gonadosomatic index （GSI）and hepatosomatic index（HSI）,and the weight gain rate and specific growth rate of P.trituberculatus fed with formulated diets significantly higher than that of the traditional diets treatment（P<0.05）.（2）The activity of glutamic-oxalacetic transaminase（GOT）in hemolymph of traditional diets treatment were significantly higher than that in formulated diets treatment（P<0.05）,and the activity of GOT,glutamate-pyruvic transaminase（GPT）,superoxide dismutase（SOD）,glutathione peroxidase,（GSH-Px）and malondialdehyde（MDA）content in hepatopancreas of traditional diets treatment were significantly lower than those in formulated diets treatment（P<0.05）.（3）The contents of total lipids in ovary and hepatopancreas of formulated diets treatment was lower than that in traditional diets treatment,while crude protein,total lipids and carbohydrate in muscle of were higher than that in traditional diets treatment（P<0.05）.（4）The contents of saturated fatty acids and monounsaturated fatty acids in the three tissues were similar between the formulated diets and the traditional diets.The content of 18:2n6 and 20:5n3 in ovary and hepatopancreas of formulated diets treatment was significantly higher than that in traditional diets treatment,while the content of 22:6n3 and DHA/EPA in three tissues of formulated diets treatment was significantly lower than that in traditional diets treatment（P<0.05）.（5）The essential amino acids and non-essential amino acids in muscle of compound diet group were significantly lower than those of traditional diets treatment（P<0.05）.Essential amino scores（EAAs）in muscles of P.trituberculatus were evaluated under the two treatments.All EAAs were higher than 100 without restriction amino acids.（6）Theδ¹³C value in formulated diets was significantly higher than that in traditional diets（P<0.05）,but there was no significant difference in the trophic level.（7）The contribution of bait of the two feeding modes was the highest,which were 40.25%and 39.24%.The contribution proportion in zooplankton of formulated diets treatment was lower than that in traditional diets treatment,while the contribution proportion in background and zoobenthos were higher than those in traditional diets treatment（P<0.05）.In conclusion,the formulated diets can ensure normal growth and development of swimming crab throughout the whole culture-cycle in pond.There was no significant difference in the food contribution of formulated diet and trash fish to P.trituberculata,while the nutritional composition of the formulated diet was slightly worse than that of the traditional diet.3.Effects of culture models on the culture performance and economic benefits of swimming crabPond-culture is the major culture method for the swimming crab,Portunus trituberculatus,and this study was conducted to investigate the effects of P.trituberculatus monoculture and P.trituberculatus and ridgetail white prawn E.carinicauda polyculture on culture performance and economic benefits.The results showed that:（1）There were no significant difference in the average body weight between the monoculture and polyculture modes of P.trituberculatus（P>0.05）.In all modes,the weight gain and specific growth rate of P.trituberculatus showed a decreasing trend during the whole culture period.Although the survival rate,average body weight and yield of P.trituberculatus in polyculture were higher than those in monoculture,no significant difference was detected on these parameters（P<0.05）.（2）The feed conversion rate of monoculture model of P.trituberculatus was significantly higher than the other two culture modes（P<0.05）.However,there were no significant differences in tissue coefficient,total rate of edible and condition factor of swimming crabs between the two treatments.（3）Monoculture of P.trituberculatus had the lowest total income,net profit and return of investment,while the highest values were found in polyculture mode of P.trituberculatus and E.carinicauda.In conclusion,the polyculture of P.trituberculatus and E.carinicauda in ponds had the good culture performance and economic benefits,which could be extended in the future.