Microcapsuled Diet Developement And Its Application In The Pearl Oyster Pinctada Fucata Martensii

This study is to evaluate the effects of microcapsuled diet developed for the pearl oyster, Pinctada fucata martensii. This report was conducted in three phases.In the first phases, the particle size, dispersion, and stability of the microencapsulated diet were first measured. After feeding the survival rate, growth rate, physiological and biochemical indices were measured and compared after 45 days, in which the experimental group(FEG) was fed with microencapsulated diet, and the control group(FCG) was cultured at sea. The results showed D0 has a continuous dense coating, less adhesion, good dispersion and suspension properties; and the particle size of D0 is less than 48 μm; the nitrogen retention rates after soaked was high. The results showed the absolute and relative growth rates of shell length, shell width, shell height, and total weight in the FEG were significantly lower than those in the FCG(P < 0.05). The lipid component of the edible part and pancreas amylase activity of the hepatopancreas of pearl oysters was significantly larger in the FEG than that in the FCG(P < 0.05). No significant differences were observed in the carbohydrate, protein, ash components of the edible part or protease, and cellulase activities of the hepatopancreas of pearl oysters between the FEG and FCG.Then, the D0 was optimized and we have prepared microcapsules D1, D2 and D3. The effects of three artificial diets(D1, D2 and D3) on survival, growth, biochemical composition, activity of immune enzyme and expression of immune-related gene in the hepatopancreas were investigated. Six experimental groups(SEG1, SEG2, SEG3, SEG4, SEG5 and SEG6) and one control group(SCG) were set up. SEG1, SEG2 and SEG3 were solely fed on D1, D2, and D3, respectively. SEG4, SEG5 and SEG6 were fed on mixed diets, as follows: D1 and Platymonas subcordiformis; D2 and P. subcordiformis; and D3 and P. subcordiformis, respectively. SCG was fed on only P. subcordiformis. All groups were continuously fed for 60 d. The survival, growth and biochemical composition of soft bodies were compared across the groups. Results showed that survival rate and the absolute growth rate(AGR) and relative growth rate(RGR) of shell length did not differ significantly across the groups(P> 0.05). The AGR and RGR of total weight differed significantly among the groups(P< 0.05). AGR and RGR of shell length and total weight were the highest in SEG5 and the lowest in SEG1. Gross fat content showed insignificant differences among the groups(P>0.05). However, gross protein content and ash content showed significant differences across the groups(P<0.05). The gross protein of the groups solely fed on artificial diets were lower than those of the groups fed on mixtures of artificial diets and microalgae or single microalgae. The contents of other amino acids, total amino acids(TAA), and essential amino acids(EAA) showed significant differences across the groups(P<0.05). TAA, EAA, and delicious amino acids of the groups fed solely on artificial diets were lower than those of the groups fed on mixtures of artificial diets and microalgae or single microalgae. The activity of alkaline phosphatase(ALP) and relative expression of ALP mRNA differed significantly among the groups(P<0.05); The SEG5 got the highest activity of ALP among the treatments, and there were no significant differences in relative expression of ALP mRNA was seen between the SEG5 and SCG(P>0.05). The activitiy of total superoxide dismutase(SOD) and relative expression of SOD mRNA showed significant differences among the groups(P< 0.05); There were insignificant differences in the activitiy of SOD and the relative expression of SOD mRNA between SEG5 group and control group(P>0.05). The activity of peroxidase(POD) and relative expression of glutathione peroxidase(GPx) mRNA showed significant differences across the groups(P< 0.05); The SEG5 got the highest activity of POD and relative expression of GPx mRNA among the treatments.After that, the effects of microcapsule diet designated D1 and D2 on growth traits and expression of mineralization gene in the mantle is evaluated in this study. Five groups(SEG1, SEG2, SEG4, SEG5 and SCG) were set up in the experiment. SEG1 and SEG2 were fed were fed D1 and D2, respectively. SEG3 and SEG4 the mixed diets of P. subcordiformis and D1 and P. subcordiformis and D2, respectively. SCG was fed P. subcordiformis. Growth rate and relative expression of pif177 mRNA and nacrein mRNA in the mantle central(Mc) and mantle edge(Me) among the five treatments were compared after a 60-day farming indoors.The results were that there was significant different in both the absolute and relative growth rates of shell width and shell height among the treatments. The SEG1 and SEG2 only fed D1 or D2 had lower absolute and relative growth rates than the other treatments. The SEG5 got the highest absolute and relative growth rates of shell width and shell height among the treatments. The relative expression of nacrein mRNA among the five treatments had significant differences(P<0.05); There were no significant differences in relative expression of nacrein mRNA in the mantle central was seen between the SEG5 and SCG(P>0.05). The relative expression of nacrein mRNA of SEG5 in the mantle central was higher than the other groups(P< 0.05). There were no significant differences in relative expression of nacrein mRNA in the mantle edge was seen among the SEG2, SEG5 and SCG(P>0.05). The relative expression of nacrein mRNA in the mantle edge of SEG5 was higher than the SEG1 and SEG4(P< 0.05). The relative expression of pif177 mRNA among the five groups significantly differed(P< 0.05). The relative expression of pif177 mRNA in the mantle among the SEG2, SEG5 and SCG had no significant differences(P>0.05). On the contrary, the relative expression of SEG1 and SEG4 group were both significantly lower than SEG5 group(P<0.05). There was a positive relationship between growth rates of both shell width and shell height and expression of mineralization gene.The third phases, we continued to optimize the formulation, and prepared microcapsuled feed(D4). The influence of D4 on pearl production traits of pearl oyster P. fucata martensii. Four groups(TEG1, TEG2, TEG3 and TCG) were set up in the experiment. TEG1 and TEG3 were fed P. subcordiformis and D4, respectively. TEG2 was fed the mixed diets of P. subcordiformis and D4. And the TCG was cultured at sea. All groups were continuously fed for 90 d. The survival rate, retention rate, pearl thickness, commercial pearl rate was compared, and pearl production was estimated. The results showed that the survival rate of group TEG1, TEG2 and TEG3 was significant higher than the control group TCG(P<0.05), but there were no significant differences in the survival rate among TEG1, TEG2 and TEG3(P> 0.05). The retention rate, pearl thickness, commercial pearl rate and the average weight of pearl were no significant difference among the groups(P> 0.05). And pearl production of per ten thousand which from high to low was TEG1, TEG2, TEG3 and the TCG in turn.These results showed that this microencapsulated diet have appropriate particle size and stability, which can be absorbed and digested by pearl oyster, and can enhance the immunity, the expression of mineralization gene and production of pearl oyster P. fucata martensii. The results suggested that the microcapsule diet can replace part of microalgae, which is helpful for further studies on developing artificial feed of pearl oyster P. fucata martensii.