Study On Preparation Microencapsulated Diet And Effect On Digestive Physiology Of Larval Shrimp (Penaeus Japonicus Bate)

Live food is a key bottleneck to the culture of crustacean larvae and marine fish larvae. Live food poses many problems for the larviculture such as risk of pathogen transmission, expense of culture and problems with availability. The ultimate solution to the above problems is development of microdiet to partially or completely replace live food. Microdiets can provide a reliable and reproducible feed supply.The mian contents of this research are as follows:1. Different methods to prepare the microencapsulated diet. Gelatin and gelatin/maltodextrin as wall material were adopted to prepare the microencapsulated diet by spray-drying respectively. The frequency distributions of the microencapsulated diets were in normal distribution. The retention efficiency of coated Vitamin C was 20.51% during the spray drying process. SEM images showed the gelatin-walled microcapsules and gelatin/maltodextrin-walled microcapsules with a uniform film around the core. The lipid encapsulation efficiency of gelatin-walled, gelatin/maltodextrin-walled was 26.59%, 18.07% respectively , the nitrogen retention efficiency of the microencapsulate diet was 36.03%,24.93% respectively. The gelatin/gum-walled microencapsulated diet was prepared by coacervation. SEM images showed the diets were not with a uniform film and adhere each other. The lipid encapsulation efficiency and nitrogen retention efficiency of microencapsulated diets is 26.37%,27.47%. Coacervation is not adapted to prepare the microencapsulated diet. The calcium-alginate microencapsulated diet was prepared by pore-coagulation bath method. SEM images showed there are some depressions and many small cracks on the microcapsule coarse surface. The pore-coagulation bath method was not adapted to industrialized production. The basal diet as core material was made into pellets by extrusion-spheronization, then the pellets were put into the fluidized bed, adopting the mode of bottom spray coating to complete the coating process. SEM images showed that the appearance of the diet microencapsulated with ethyl cellulose with a uniform surface and a continuous film around the core. The inclusion efficiency, lipid encapsulation efficiency of the microencapsulated diet was 97.2±1.7%, 63.2±3.7% respectively. The nitrogen retention efficiency of the microencapsulated diet incubation in 35‰NaCl solution for 20 min, 40 min and 60 min was 73.6±2.6%, 65.8±3.5% and 53.7±4.2% respectively.2. The diets microencapsulated with gelatin and ethyl cellulose for larval shrimp (Penaeus japonicus) were produced using fluidized bed coating process. The two microencapsulated diets were within a broad size range. The size of the diet microencapsulated with ethyl cellulose was smaller than that of the diet microencapsulated with gelatin. SEM images showed the appearance of the microencapsulated diets was a dense film with a superior physical quality. The retention efficiency of vitamin C was 88.2% in the coating process. Despite the less amount of wall material used, the diet microencapsulated with ethyl cellulose had a better performance with regard to production efficiency, lipid encapsulation efficiency and free amino acid retention efficiency compared with the diet microencapsulated with gelatin. The pH value of the diet microencapsulated with gelatin and ethyl cellulose was 5.98, 6.24 respectively. The diet microencapsulated with ethyl cellulose had better performance with slow release characteristic in different solution (pH, temperature) compared with the diet microencapsulated with gelatin.3. The mysisⅡlarval shrimp (Penaeus japonicus) 10 days after hatch (DAH) were fed different diets respectively for 20 days. There were four treatments. Control: 50% shrimp flake+50% Artemia; GroupⅠ: 50% diet microencapsulated with gelatin + 25% shrimp flake +25% Artemia; GroupⅡ: 100% diet microencapsulated with gelatin; GroupⅢ: 100% diet microencapsulated with ethyl cellulose. The growth and survival of the larval shrimp confirmed the microencapsulated diets with good digestibility. There were significant differences in growth and survival, trypsin activity, and amylase activity of the larvae between the two microencapsulated diet groups and the control (P<0.05), but there was no significant difference in alkaline phosphatase activity in the larvae of each group (P>0.05). There were significant differences in total length and trypsin activity of the larvae between the two microencapsulated diet groups (P<0.05). The results showed that the larval digestive enzymes adapted to the feed composition, and the wall materials had no significant effect on the digestive enzymes activity of the larval shrimp.4. The microscopic structure of the intestine was classified as four layers, striated border, mucosa, submucosa and muscular layer. There were many goblet cells and columnar cells in the hepatopancreas. No available information about the differentiation of the intestine and hepatopancreas of the shrimp larvae from different treatments was detected under histological analysis. A large basal nucleus, abundant mitochondria, some zymogen granules and lipid droplets in intestine epithelium were visible. The big mitochondria with large number mainly scattered at the top of the cells. The pinocytotic activity of the gut enterocytes for their intracellular digestion.The nutrient components in intermediate intestine of shrimp larvae decreased gradually in the order of GroupⅢ, GroupⅡ, GroupⅠand the control. Wall material had no significant effect on the digestive system and the microencapsulated diets with slow and controlled release characteristic in the digestive tract of the larval shrimp.5. On the condition that the protein content is same, change the composition of amino acid in the feed formulation by changing the the content of casein and fish meal. The amino acid of the diet and the larval shrimp were compared. Increasing the content of casein and decreasing the content of fish meal in the feed formulation decreased the growth performace of the larval shrimp and digestive enzyme activity. On the condition that the fat content is same, fish oil substitute the Schizochytrium algal meal in the feed formulation. The composition and content of fatty acid of the diet and larval shrimp were compared. The fatty acid 18:2n-6 showed a dramatic proportional increase in larval tissue relative to its proportional composition in both the live and formulated diets. Fish oil substitute Schizochytrium algal meal in the feed formulation can improve growth performance and digestive enzyme activity of the larval shrimp.