| The living space of the breeding biology and the carrier of matter and energycirculation space were composed of pond water quality and bottom sediment. At present,due to the pursuit of high yield and high benefit, water quality and bottom sediment ofthe pond were severely damaged by a large number of fertilization, bait casting and highdensity cultivation mode. Excessive grazing also leads to the deterioration of theaquaculture pond water quality and bottom sediment as well as the drying up of naturalbait resources. The artificial diet was feed more and more at present, this leads to thequestions of higher production cost, low utilization of artificial bait, easy to causeresidual deposits, bait disrupt fishery ecological environment. So, the cultivation of thenatural bait is more important. Using organic fertilizer to cultivate natural baitorganisms is the traditional cultivation mode of shrimp and crab in China. With theexpansion of the farming area, using the traditional organic cultivation only cultivate alittle of natural bait to meet the need of shrimp and crab feeding, and it also bring into alarge number of organic residue, cause water pollution. As a new natural bait medium,benthic bait biological medium has been used in the main aquaculture.To analysis the effects of different culture medium and the stocking density on thechemical indexes of water quality and bottom sediment in aquaculture pond, species andbiomass of plankton and zoobenthos. This experiment studied three kinds of culturemedium(Benthic bait biological culture medium, chicken manure culture medium, pigmanure and chicken manure mixed culture medium) and three stocking density ofProcambarus clarkii and Eriocheir sinensis (6000:1000、8000:800、10000:300ind./667m2), a total of nine groups and each group have three repeat. The testlast for eight months, and the samples were taken in the middle of every month. Itcompared effects and application values that using different culture medium in theprocess of shrimp and crab breeding, as well as the appropriate stocking density. The results provided the theory basis for the development of new natural bait medium forcrayfish, also provided reference data to form a reasonable crayfish aquaculture model.Results indicated that:1. The effects of culture medium and stocking density on water temperature,dissolved oxygen, salt and hydrogen sulfide content are not significant (p>0.05).Theeffects of culture medium on water transparency, pH, NH4+-N and NO2--N content aresignificant(p<0.05): benthic bait biological culture medium significantly improve watertransparency, keep pH of water stable, reduced significantly NH4+-N and NO2--Ncontent of water (p<0.05), the effects of chicken manure culture medium and mixedculture medium are not working. Effects of different stocking density on watertransparency and ammonia nitrogen content are significant(p<0.05): high stockingdensity result in water clarity declining, ammonia levels significantly higher than otherstocking densities.2. The influence of different culture medium and stocking density on species andbiomass of planktonic algae is significant (p<0.05).Margalef index andShannon-Weaver index of planktonic algae of benthic bait biological culture mediumwere higher than the other two culture media, and biomass of harmful planktonic algaedecreased significantly (p<0.05). The effect of stocking density on green algae,bacillariophyta, cyanophyta is significant (p<0.05), especially biomass of harmful algalis more than50%in the total biomass in high-density groups. With stocking densityincreasing, abundance index and diversity indices were lower. In the same stockingdensity, the effect of culture medium on biomass composition of zooplankton issignificant (p<0.05). The proportion of large zooplankton such as Daphnia and Cyclopsbenthic bait is high but the percentage of small zooplankton is very small of biologicalculture medium, by contrast, chicken manure culture medium and mixed medium, thereis more obvious in high stocking density. In the same medium, the influence of stockingdensities on biomass of zooplankton composition is significant (p<0.05). As thestocking density increased, the proportion of large zooplankton such as cladocera,calanus and cyclops declined, supported by small zooplankton such as protozoa, rotifersand nauplii. The experimental results show that abundance and diversity indices ofplankton were lower in chicken manure culture medium and mixed media, combinedwith residual bait and waste increased in the stocking density, water organic pollution,cyanobacteria, dinoflagellates and other harmful algal bloom, eco-less effective and eventually affect the economic benefits.3. In different media and stocking densities, TN, TP and TOC accumulation insediment are different. The accumulation of TN, TP and TOC of benthic bait biologicalculture medium are lower than other media (p<0.05). The differences of TN, TP andTOC accumulation between chicken manure culture medium and mixed medium groupsare not significant (p>0.05). Different media, there are differences in effects of stockingdensity on TN, TP and TOC accumulation: in benthic bait biological culture mediumgroup, with stocking density increased, TN, TP and TOC accumulation is increased, andin high density group is higher than medium and low density groups (p<0.05), there areno significant differences in medium density group and low density group (p>0.05). Inchicken manure medium group, with stocking density increased, TN and TPaccumulation also increased, but there are no significant differences in high density andmedium density (p>0.05), all higher significantly than low density group (p<0.05). Withstocking density increased, TOC accumulation also increased, high-density group higherthan medium and low density groups (p<0.05), there are no differences betweenmedium density group and low density group (p>0.05). In chicken manure and pigmanure mixed medium group, with stocking density increased, TN and TPaccumulation also increased, high-density group higher than medium and low densitygroups (p<0.05), there are no differences between medium density group and lowdensity group (p>0.05). With stocking density increased, TOC accumulation alsoincreased, but there are no significant differences in high density and medium density(p>0.05), all higher significantly than low density group (p<0.05).4. Species and biomass of benthic animals in benthic bait biological culturemedium group are higher than other media (p<0.05), but there were no significantdifferences between chicken manure culture medium and mixed culture medium groups(p>0.05).In same medium group, with stocking density increased, species of benthicanimals are declined, and there were no significant differences in different stockingdensities (p>0.05). Figure5-2showed that: there were no significant differencesbetween chicken manure culture medium group and mixed culture medium group(p>0.05), but there were significant differences in benthic bait biological culturemedium group(p<0.05). In same medium group, with stocking density increased,biomass of benthic animals are declined, and there were no significant differences inmedium stocking density and low stocking density (p>0.05), biomass of high-density group is smallest(p<0.05).In conclusion, to compare water quality index, changes in plankton community andsediment, species and biomass of benthic animals under three kinds of culture mediaand three stocking densities, the results of study indicated that the benthic baitbiological culture medium and medium stocking density were optimum so as to giveconsideration to the ecological benefit and economic benefit. |
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