Genetic Structure Analysis And Larvae Rearing Parameters Comparison Of Macrobrachium Rosenbergii

This study was carried out to analyse the genetic structure of parent shrimps and investigate the factors that influence the larvae rearing effect and growth performance of freshwater prawn Macrobrachium rosenbergii, several experiments were conducted, such as comparing genetic diversity and growth performance among different cultured populations, water quality monitoring, acute toxicity test of ammonia nitrogen and nitrite nitrogen, comparison of critical parameters of larvae rearing technology, all for further optimizing the parameters of artificial larvae rearing technology, provide evidance and scientific guidance for postlarvae production and germplasm improvement of Macrobrachium Rosenbergii. The main research contents were as follows:1. Microsatellite molecular markers were applied to analyse the genetic diversity and structure of five different cultivated populations of Macrobrachium Rosenbergii. Six pairs of primers were used to amplify microsatellite DNA from five cultivated populations. The results showed that the detected six microsatellite loci possessed high polymorphism [Polymorphism Information Content (PIC)= 0.8448～0.9374]. Genetic diversity of five populations reached high level [Expected Heterozygosity (He)= 0.865～0.889]. Genetic differentiation index (Fst) and AMOVA analysis showed that 98.13% genetic was derived from intra-population, only 1.87% variation was derived from inter-populations, which indicated that the genetic differentiation within populations belongs to low level (Fst<0.05). The results from analyzing genetic distance showed that the standard genetic distance between ZJ and NTH population was lowest (Ds= 0.0579), while that between ZJ and SH population was the highest (Ds=0.3535). The UPGMA phylogenetic tree based on genetic distance indicated that these five Macrobrachium Rosenbergii populations could be divided into two groups, ZJ and NTH population were gathered together to a genetic branch firstly, then clustered with another branch than include GX and ML population, and SH population form another relatively independent branch. The results demonstrated that although five Macrobrachium Rosenbergii populations exhibited high genetic diversity, the relationships among them were relatively close.2. One thousand and two hundred and eighty juveniles were selected from four different cultivated populations to conduct a 70-day feeding experiment, aim to compare growth performance of different cultivated populations of Macrobrachium Rosenbergii. The results showed:1) Among four populations, SH population obtained the highest survival rate (81.88%), while its WGR(Weight Gain Ratio) was the lowest. Survival rate of NTH population was the lowest(55.00%), significantly lower than that in other groups(P<0.05), but the WGR was the highest.2) The final body weight, WGR and SGR(Specific Growth Rate) of NTH population were significantly higher than that in other groups(P<0.05).3) Although the differences among four populations in fatness were not significant(P<0.05), NTH population get the highest fatness. In conclusion, there were significant differences in the growth performance of the offspring of different culture groups, NTH population, which had been selected and bred, have better growth performance to achieve higher economic benefit.3. Three nursery ponds with the same condition were selected to monitor water quality factors during larvae rearing period and analysis its changing pattern. Results show that with the increase in the number of days, the DO decreased slowly, pH was relatively stable, only decreased in low amplitude. The concentration of ammonia nitrogen and nitrite nitrogen was increased in a sawtooth shape, reach a periodical peak before changing water.4. Three nursery ponds that on Z3, Z5, Z8 development stage was selected to minitor water quality factors and analyse the changing pattern in a day, monitoring factors including pH, DO, ammonia nitrogen, nitrite nitrogen and COD. Results showed:1) The changing pattern of factors of rearing water on different stage is basically the same, the major fluctuations were mainly appeared after feeding or dirt suction.2) In one day, pH remained relatively stable; DO decreased slowly and then rebounded, the lowest value appeared between 11:00 and 12:00; 3) The fluctuation of ammonia nitrogen, nitrite nitrogen and COD was large, the whole showed an upward trend, and there was a strong correlation among these factors, the time interval between adjacent changes ranges from 30 minutes to 60minutes. In conclusion, during the larvae rearing period, the concentration of ammonia nitrogen and nitrite nitrogen, which have a important influence in larvae emergence rate, changes sharply. It is necessary to strengthen monitoring and take timely measures to reduce the toxic effects on the larvae, set a reasonable scheme of feeding and dirt suction to prevent water quality factors fluctuating widely, provide a stable environment for Macrobrachium Rosenbergii larvae.5. This experiment was carried out to investigate the toxic effects of total ammonia nitrogen (NH3-Nt), non-ionic ammonia nitrogen(NH3-Nm) and nitrite nitrogen (NO2-N) on Macrobrachium rosenbergii larva at different developmental stages. Different gradient concentrations of either NH3-N or NO2-N were formulated to determine the 96h acute toxicity effect on Z5、Z8、Z11 larva respectively. The results showed that the safe concentration (SC) of NH3-N(NH3-Nm) for Z5, Z8 and Z11 were 2.108 (0.115) mg/L,2.747 (0.151) mg/L and 2.762 (0.152) mg/L respectively, the SC of NO2-N for Z5, Zg and Z11 were 1.078 mg/L,1.238 mg/L and 2.048 mg/L respectively. We can suggest from this experiment that the concentration of NH3-Nm and NO2-N in larva-culturing water should be below 0.10 mg/L and 1.00 mg/L respectively during the postlarvae production process of giant fresh prawn, Macrobrachium rosenbergii.6. Gradients were set to study the effects of larvae density on rearing water quality and survival rate in post-larvae of Macrobrachium Rosenbergii. The results showed that within a certain range, the survival rate was significantly effected by larvae density. When larvae density increased from 120 ind/L to 160 ind/L, the average DO decreased by 8.50%, the average concentration of ammonia nitrogen and nitrite nitrogen increased from 1.539mg/L to 2.460mg/L and 0.256mg/L to 0.388mg/L, survival rate decreased from 63.75% to 43.88%. However, from the perspective of economic efficiency, increase larvae stocking density reasonable can bring maximum benefit. The results indicated that moderate rearing density could reduce the difficulty of water quality management and improve the emergence amount of per unit water and economic efficiency on artificial larvae rearing of Macrobrachium Rosenbergii.7. Quadratic orthogonal rotation combination design was applied to study the effects of Ca2+, Mg2+ and K+ contents in artificial seawater on postlarvae survival rate of the Macrobrachium Rosenbergii. Results showed that within the range of this experiment, the optimized concentration of Ca2+, Mg2+ and K+ was 165mg/L、375mg/L and 150mg/L. Under this optimal formula, the average metamorphosis rate was 60%. Good result was also obtained in the productive test, in which the survival rate was 61.8%, significantly higher than that of the original formula.8.In order to study the effects of different antibiotics on rearing water quality,bacteria amount,survival rate and growth performance of Macrobrachium Rosenbergii,4 nursery ponds were selected for 4 treatments (control group, ceftiofur sodium group; levofloxacin mesylate group; oxytetracycline group) to conduct comparison experiment of rearing and feeding, determination index include regular water quality indices, amount of bacteria and emergence rate. The results showed:1) All the three antibiotics can reduce the total bacteria count and Aeromonas count, levofloxacin mesylate reduce the number of Escherichia coli significantly and ceftiofur sodium followed, vibrio was not detected in all treatments.2) The effect of all three antibiotics on improving regular water qualities was not obvious.3) From the perspective of the emergence rate, Pefloxacin mesylate group was the best, Ceftiofur sodium group followed, oxytetracycline group and control group were similar and lower than the former two groups.4) The data of growth test show that the growth performance of oxytetracycline group was the worst, significantly worse than that of the other three groups (P<0.05), and there was no significant difference among control group, ceftiofur sodium group and levofloxacin mesylate group (P>0.05).Although antibiotic treatments have obvious influence on bacteria amount of rearing water and emergence rate of post-larvae, the effects of improving water quality were very limited. Using oxytetracycline may even degrade growth performance of larvae. It is recommended to use less or no antibiotics in postlarvae production of Macrobrachium Rosenbergii.