| Pond fish culture is the most important fraction of aquaculture industry, and contributes to over 70% of the aquaculture production in China. However, technique retardation, environmental pollution and resources shortage severely restricted the sustainable development of aquaculture in ponds. The optimization of aquaculture mode could improve the structure and function of the culturing system, enhance the utilization efficiency of nutritional resources and reduce the risks caused by aquaculture pollution. Many works have carried out on optimizing the aquaculture mode domestic and overseas, however, scarce report refers to the aquaculture mode optimized by systematic establishment. In this article, we optimized the stocking structure and husbandry management in the integrated system associating with the economic species including grass carp (Ctenopharyngodon idellus), gibel carp (Carassius gibelio), silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis) and pearl mussel (Hyriopsis cumingii). We expected to provide some scientific data for the optimization of aquaculture in freshwater culture ponds in China. Results are showed as follows:(1) The environmental variables including water temperature, Secchi depth, dissolved oxygen, pH, conductivity, salinity, total ammonia (TAN), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), reactive phosphate (PO4-P), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (CODMn), chlorophyll a, composition and biomass of phytoplankton were monitored at two freshwater fish polyculture ponds at Huzhou city from May to November,2009 (experiment I). The Secchi depth, total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (CODMn were measured at 12 polyculture ponds near the above two ponds (including the above 2 ponds, experiment Ⅱ). Results showed that the TAN ranged form 1.372 to 1.664 mg/L, NO2-N ranged form 0.072 to 0.076 mg/L, NO3-N ranged form 0.139 to 0.144 mg/L, PO4-P ranged form 0.038 to 0.062 mg/L, TN ranged form 2.267 to 2.828 mg/L, TP ranged form 0.274 to 0.277 mg/L, CODMn ranged form 15.46 to 15.51 mg/L, the community structure of phytoplankton were dominated by blue-green algae and green algae with the size smaller than 10 um during the culturing period (experiment I). Secchi depth, TN, TP and CODMn in the twelve ponds in experiment II was 12 ～37 cm,2.85～5.87 mg/L,0.47～2.20 mg/L and 25.58-50.19 mg/L, respectively. According to the high concentrations of TN, TP and CODMn in the fish polyculture ponds, it is recommended that economic aquaculture species of filtering feeder should be introduced in these commercial ponds.(2) In this study, we investigated the species composition and biomass of phytoplankton and abiotic environmental factors in ten commercial Hyriopsis cumingii ponds located in Zhuji City, Zhejiang Province, from August 29 to September 1,2011. A total of 51 genus of phytoplankton were observed, and Merismopedia sp., Microcystis sp., Coelosphaerium sp. and Scenedesmus sp. were the dominant species during the investigation. The biomass of phytoplankton was 0.71-8.01 x 108 cell/L, and blue-green algae account for 71～97% of the phytoplankton biomass. Dissolved oxygen (4-12 mg/L) was relatively high, while Secchi depth (33 cm), total nitrogen (TN,1.933-4.062 mg/L), total phosphorus (TP,0.154-1.010 mg/L), chemical oxygen demand (6.49-10.06 mg/L) and TN/TP were low in the ponds. According to results of this investigation, it is recommended that the stocking density of omnivorous fishes and input of formulated fish feed should be increased, while the amount of duck manure input should be reduced, in these commercial ponds.According to the above results, the nutrition in the freshwater fish polyculture ponds could sufficiently maintain the development of pearl mussel H. cumingii.(3) An enclosure experiment was conducted to evaluate the effects of co-culturing freshwater pearl mussel H. cumingii in a fish polyculture system consisting of grass carp, gibel carp, silver carp and bighead carp on fish yield and water quality. Two treatments were examined. In treatment I, polyculture of grass carp, gibel carp, silver carp and bighead carp was used. In treatment II, the mussel was co-cultured in polyculture system of grass carp, gibel carp, silver carp and bighead carp used in treatment I at a mussel-fish ratio of 1:1. The experiment lasted 78 days, during which water samples were collected regularly, and species composition and biomass of phytoplankton, primary production (P), community respiration (R), dissolved oxygen (DO), pH, Secchi depth (SD), main ions (CO32-,HCO3-, Cl-, SO42-, Ca2+, Mg2+, Na++K+), total alkalinity, total hardness, ammonia (TAN), nitrite, nitrate, reactive phosphate, total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), chemical oxygen demand (CODMn), biological oxygen demand (BOD5) were monitored. The results showed that co-culturing H. cumingii significantly decreased the Ca2+ concentration in the enclosures, but did not significantly affect the other water quality parameters, such as species composition and biomass of phytoplankton, diversity of phytoplankton (Shannon-Weaver’s index, Margalef’s index, Pielou’s index), P, R, DO, pH, SD, CO32-, HCO3-, Cl-,SO42-, Ca2+, Mg2+, Na++K+, total alkalinity, total hardness, ammonia, nitrite, nitrate, reactive phosphate, TN, TP, TOC, CODMn and BOD5. Yields of grass carp, gibel carp and silver carp were relatively high, while production of bighead carp and accumulation of TN, TP, CODMn, BOD5 and TOC were low in treatment II, compared with treatment I. Therefore, co-culturing the mussel in a fish polyculture system of grass carp, gibel carp, silver carp and bighead carp not only enhance economic income of aquaculture practice, but also reduce the accumulation of nitrogen, phosphorus and organic matters.(4) There are increasing concerns about the adverse environmental impacts caused by effluent from aquaculture practices. One potential method of ameliorating this problem is to use filter-feeding bivalves to recapture the wasted nutrients in the water. In this study, we evaluated the impacts of introducing the pearl mussel H. cumingii on water quality and production performance into a freshwater fish polyculture system which contains grass carp, gibel carp, silver carp and bighead carp. Four treatments including three stocking densities of H. cumingii (90,60,30 mussel/enclosure, of which 5 were grafted with mantle epithelium pieces) and one control (no H. cumingii) were conducted by a 90-day land-based enclosures experiment. Results showed that the increased stocking density of H. cumingii could increasingly improve production performance of fishes (growth of grass carp and gibel carp, fish yield and FCR), phytoplankton (diversity, biomass and primary productivity), increment of Secchi depth and incremental concentrations of chemical variables (DO, pH, Ca2+, total alkalinity, total hardness, TAN, TN, TP, CODMn and BOD5), while decreasingly reduce the weight gain of H. cumingii and pearl yield. The impacts on environmental variables caused by seasonal alteration were higher than caused by alterative stocking density of mussel. The environmental variables including biomass of blue-green algae, Shannon-Weaver’s diversity index, total alkalinity and TAN proved to be the principal factors influencing the growth of grass carp, gibel carp, silver carp and bighead carp. It is suggested that the introduction of pearl mussel H. cumingii into the freshwater fish polyculture could enhance the ecological benefits and economic profits, and the effect associated with their stocking density. However, H. cumingii could not balance the accumulation of aquaculture wastes in the polyculture system. Hence, new technique should be developed to further decrease the aquaculture pollution.(5) A 90-day experiment was conducted in land-based enclosures to examine the effects of stocking density of freshwater pearl mussel H. cumingii and tilapia (Oreochromis mossambicus) on production performance and water quality in a fish polyculture system stocked with grass carp, gibel carp, silver carp and bighead carp. Four treatments including two stocking density of mussel (5 grafted mussel+85 non-grafted mussel VS 5 grafted mussel+55 non-grafted mussel) and two tilapia co-culturing regime (with or without tilapia addition) were designed. Fish in the enclosures were fed with formulated feed daily. No water was exchanged in the enclosures during the experiment. Tilapia significantly increased fish yield and concentrations of ammonia nitrogen, chemical oxygen demand and biochemical oxygen demand, but decreased the growth of non-grafted mussel and feed conversion ratio (P < 0.05). Meanwhile, H. cumingii relatively reduce the growth of grass carp, gibel carp, silver carp and bighead carp and pearl yield, impaired the diversity and function of phytoplankton. Increased the stocking density of H. cumingii could slightly enhance the nutrient utilization efficiency, maintain the diversity and improve the function of phytoplankton, and reduce the concentrations of N, P and organic matters in the water column. Results indicated increased the stocking density of H. cumingii could improve the production performance and cultured environment, thus should be recommended in the freshwater fish polyculture. Adding tilapia could significant enhance fish yield and nutrient utilization efficiency, but relatively restrict the growth of other fish species and pearl yield, and contribute to the deterioration of water quality, it is suggested that the stocking density of tilapia should be limited in the freshwater fish polyculture.(6) A 60-day experiment was conducted in land-based enclosures to examine the effects of co-culturing freshwater pearl mussel H. cumingii and adding a commercial microbial product (Novozymes pond plus) on production performance and water quality in a fish polyculture system stocked with grass carp, gibel carp, silver carp and bighead carp. Four treatments including two stocking structures (grass carp+gibel carp+silver carp+bighead carp VS grass carp+gibel carp+silver carp+bighead carp+H. cumingii) and two husbandry management (with or without Novozymes pond plus supplementation) were designed. Fish in the enclosures were fed with formulated feed daily and the commercial microbial product was added 12 g/enclosure every 7 day. The synergic effect of pearl mussel and microbial product could significantly enhance the fish yield (P< 0.05). Both the introduction of H. cumingii and adding Novozymes pond plus could relatively increase fish growth, fish yield and nutrient utilization efficiency, maintain the stability of phytoplankton, inhibit the growth of blue-green algae, enhance the primary productivity and decrease the water turbidity and concentrations of PO4-P, TN, CODMn and BOD5 though with no significant difference (P> 0.05). However, the supplementation of Novozymes pond plus impaired the mussel growth and pearl yield. Results indicated that the H. cumingii and microbial product could improve fish production performance and water quality at a certain extent in the polyculure system including grass carp, gibel carp, silver carp and bighead carp, and their synergic effect is better than either one. It is suggested that the economic benefits could be increased by increasing the formulated feed feeding fishes in the fish polyculture system with the supplementation of H. cumingii and microbial product.(7) The effects of stocking density of formulated feed feeding fishes and a microbial product supplementation on production performance and water quality in a mussel-fish integrated system including pearl mussel H. cumingii, grass carp, gibel carp, silver carp and bighead carp were examined through a 93-day land-based enclosures experiment. The stocking densities of formulated feed feeding fishes (grass carp:gibel carp= 2:1) were examined with either 20 grass carp and 10 gibel carp or 40 grass carp and 20 gibel carp. Each stocking density received a commercial effective microorganisms (EM) product or with no EM product supplementation. One half of the H. cumingii in each enclosure were given grafted operation with mantle epithelium pieces while the other half were not. The fish were fed with a formulated feed daily, and the EM product was added to the enclosures every 10 days. No water was exchanged throughout the experiment. Results showed that increasing stocking density of formulated feed feeding fishes substantially decreased the growth of grass carp, Secchi depth and TN/TP, and increased the concentrations of nitrite, orthophosphate, total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), chemical oxygen demand (CODMn), biochemical oxygen demand (BOD5), biomass of phytoplankton and proportion of blue-green algae in phytoplankton (P< 0.05), while slightly decreased the mussel growth and peal yield but increased fish yield and feed conversion ratio (P> 0.05). The EM supplementation significantly decreased the weight gain of grafted mussel (P< 0.05), relatively decreased the non-grafted mussel growth and pearl yield, reduced the concentrations of ammonia, TOC, COD, BOD5, biomass of phytoplankton and proportion of blue-green algae in phytoplankton, while enhanced the weight gain of formulated feed feeding fishes (grass carp and gibel carp), fish yield and nutrient utilization efficiency (P> 0.05). The results indicated that increasing stocking density of grass carp and gibel carp could impair the pearl yield and deteriorate the water quality, while the commercial EM product could not balance the pearl yield impairment and adverse environmental impacts caused by increasing input of exogenous nutrients though these two husbandry management could enhance the fish yield. It is suggested that caution should be taken into account by increasing the stocking density of formulated feed feeding fishes and using microbial products in the integrated culture containing pearl mussel, grass carp, gibel carp, silver carp and bighead carp.(8) The effects of stocking density of formulated feed feeding fishes and aeration on improving production performance and water quality by commercial microbial products in a fish-mussel integrated system including pearl mussel H. cumingii, grass carp, gibel carp, silver carp and bighead carp were evaluated through a 93-day enclosures experiment. The stocking densities of formulated feed feeding fishes (grass carp:gibel carp= 2:1) were examined with either 20 grass carp and 10 gibel carp or 40 grass carp and 20 gibel carp. Each stocking density were aerated with turbine aerators or not. One half of the H. cumingii in each enclosure were given grafted operation with mantle epithelium pieces while the other half were not. The fish were fed with a formulated feed daily, and the EM product was added to the enclosures every 10 days. No water was exchanged throughout the experiment. Results showed that increasing stocking density of grass carp and gibel carp substantially decreased the growth of grass carp, enhanced the community respiration of phytoplankton, increased TOC, TC, TN, TP, N/P, CODMn and BOD5 (P< 0.05). Aeration relatively enhanced fish yield and nutrient utilization efficiency, and reduced the concentrations of TN, TP, CODMn and BOD5 (P> 0.05). It is suggested aeration could enhance the effects of EM product on improving production performance and water quality in the integrated culture containing pearl mussel, grass carp, gibel carp, silver carp and bighead carp.(9) A 31-day experiment was conducted to examine the effects of three commercial microbial products (Novozymes pond plus, Zhongshui BIO-AQUA and Effective Microorganisms) on production performance and water quality in freshwater tanks stocked with grass carp, gibel carp and silver carp. Four treatments including blank control (BL), adding Novozymes pond plus (NO), adding BIO-AQUA (PB) or adding Effective Microorganisms (EM) were used. The fish were fed daily with a formulated feed, and each of the microbial products was added to the tanks every 10 days. No significant differences were found in survival, weight gain and feed conversion ratio of the fishes, Secchi depth, chemical water quality (dissolved oxygen, pH, ammonia, nitrite, nitrate, reactive phosphate, total nitrogen, total phosphorus and chemical oxygen demand) and phytoplankton (species, bio mass, chlorophyll a concentration and Shannon-Weaver’s diversity index) between the blank control and any other treatments (NO, PB and EM). This study indicates that the addition of these three microbial products every 10 days has limited function to improve production performance and water quality in freshwater polyculture of grass carp, gibel carp and silver carp within the first 31 days of application.In conclusion, our results showed that:(1) the freshwater fish polyculture ponds could provide sufficient nutrition for the growth of pearl mussel H. cumingii; (2) the introduction of H. cumingii could help to improve the economic and ecological benefits in the polyculture system including grass carp, gibel carp, silver carp and bighead carp, and the improvement associated with their stocking density; (3) the introduction of tilapia significantly increased the fish yield and nutrient utilization efficiency, but restricted the growth of other fish species and pearl yield, and led to the serious eutriphication in the polyculture system; (4) the microbial products could improve the fish yield and water quality, but could not balance the accumulation of aquaculture wastes in the fish-mussel integrated system, besides, the microbial products had a negative effect on the pearl yield; (5) the aeration could enhance the the effects of microbial products on improving production performance and water quality in fish-mussel integrated culture; (6) the addition of microbial products every 10 days has limited function to improve production performance and water quality in freshwater polyculture of grass carp, gibel carp and silver carp within the first 31 days of application. |
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