Primary Studies On Polyculture Of Pacific White Shrimp (Litopenaeus Vannamei) With Grass Carp (Ctenopharyngodon Idellus)

In order to explore a sustainable shrimp pond farming method, this dissertation investigated the production efficiency and water quality of polyculture of pacific white shrimp with grass carp, the feasibility of double-cycle polyculture and the effects on vibrios control are also analyzed. The results are as follow:1 Theory and application status of polyculture in shrimp pondsBased on literature published in domestic and overseas journals, this section compared and summarized the theory of mix-culture in prawn ponds, the status of study and application in domestic and overseas systems, and existing issue in practical culture and their potential overcoming methods, in view of offering some theoretical basis for mix-culture in prawn ponds.2 Comparison of production and water quality dynamic between pacific white shrimp and grass carp poly-culture and shrimp monoculture systemsBased on the pacific white shrimp and grass carp polyculture model tried by farmers in Pearl river Delta, polyculture of pacific white shrimp Litopenaeus vannamei with grass carp Ctenopharyngodon idellus, crucian carp Carassius auratus, silver carp Hypo -phthalmichthys molitrix and bighead carp Aristichthys nobilis were conducted and examined in three low salinity ponds. And three pacific white shrimp monoculture model ponds as control were also located in Pearl River Delta of China. Results showed that: Polyculture group(PG) took ten days less than monoculture group(MG) in the culture cycle, but the average body weight, survival rate and unit area yield were respectively 6.24%, 26.25% and 55.86% higher than those of MG, and food conversion ratio was 8% lower than that of MG. The unit net production of grass carp was 1467.27 (±115.82) kg·hm^-2, the total unit net yield was 447.78(±34.20) kg·hm^-2 of omnivore fish crucian carp, filter-feeding fish silver carp and bighead carp. Survival rate of fish were all above 98%. Although total unit feed consumption of PG was higher than MG, NO₂-N and COD were lower, inorganic nitrogen existed mostly in the forms of TAN and NO₃-N, which were low toxic for shrimp; NO₂-N and transparency were stable. However, morning DO in PG ponds were sometimes at low level and needed to be strengthened with aerators.3 Experiment of double-cycle polyculture of pacific white shrimp with grass carp in low salinity pondsDouble-cycle polyculture(PG) of pacific white shrimp with grass carp,crucian carp,silver carp and bighead carp were conducted in three low salinity ponds, and the data were compared with pacific white shrimp monoculture model(PG), and all the ponds were located in Pearl River Delta of China. Fish were remained un-caught in the ponds when shrimp were harvested at the end of first PG cycle, and shrimp larval were put into the ponds directly when the second cycle began. Results showed that the difference of pH,DO,TAN,NO₂-N,NO₃-N,PO₄-P and COD between PG and MG ponds were not remarkable with feeding control, but the survival rate and unit area yield were 55.72% and 5.26% higher in MG. However, because of excessive feeding control in PG ponds, the average body weight and special growth rate of shrimp of PG were 46.51% and 4.38% lower than those of MG, food conversion ratio was 56.76% higher than that of MG. The unit net production of grass carp was 2038.13(±193.55) kg/hm², the survival rate was 97.75%, food conversion ratio was 0.92. The unit net yield of omnivore fish crucian carp in PG was 163.88kg/hm², the average weight was 0.48kg, the survival rate was 99%; the unit net production of filter-feeding fish silver carp and bighead carp was 827.06(±40.93) kg·hm^-2. In general, the profit was apparently imporved by double-cycle polyculture of pacific white shrimp with grass carp, and this model may be more resistant to shrimp diseases. However, a better feeding strategy is needed.4 Comparison of vibrios fluctuation and its relativity to water quality in the second cycle of fish-shrimp polyculture and shrimp monoculture pondsThe vibrios fluctuation and its relativity to water quality were analyzed in two shrimp culture models with culture data during July to August, 2010, and the polyculture model used crucian carp, silver carp and bighead carp, while the monoculture model ponds used antisepsis during water quality treatment. Probiotics were used in all of the ponds, disinfectors were used on time in monoculture ponds, and florfonicol and enrofloxacin were mixed in the feed when feed the monoculture ponds, while the polyculture ponds did not use any disinfectors and drugs. Results showed that: In monoculture ponds, vibrios quantity were depressed by water antisepsis and avoided the rapid increment in the end. As comparsion, the vibrios quantity ascended abruptly in polyculture tanks and reached 4.75×10³ CFU ml^-1. Survival of shrimp in monoculture ponds were lower than in polyculture ponds because of disease, and they were 32.61% and 87.37% respectively. In the present study, no obvious relativity between vibrios quantity and water quality factors were detected.