Effect of Dietary Protein Concentration and Stocking Density on Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctatus

Diets containing 28% and 32% crude protein were compared for pond‐raised channel catfish Ictalurus punctatus stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48.5 g/fish were stocked into 30 0.04‐ha ponds. Five ponds were randomly allotted for each dietary protein ± stocking density combination. Fish were fed once daily to satiation for two growing seasons. There were no interactions between dietary protein concentration and stocking density for any variables. Dietary protein concentrations (28% or 32%) did not affect net production, feed consumption and weight gain per fish, feed conversion ratio, survival, processing yields, fillet moisture, protein and ash concentrations, or pond water ammonia and nitrite concentrations. Fish fed the 32% protein diet had slightly but significantly lower levels of visceral and fillet fat than fish fed the 28% protein diet. As stocking density increased, net production increased, while weight gain of individual fish, feed efficiency, and survival decreased. Stocking densities did not affect processing yield and fillet composition of the fish. Although highly variable among different ponds and weekly measurements, ponds stocked at the highest density exhibited higher average levels of total ammonia‐nitrogen (TAN) and nitrite‐nitrogen (NO₂‐N) than ponds stocked at lower densities. However, stocking density had no significant effect on un‐ionized ammonia‐nitrogen (NH₃‐N) concentrations, calculated based on water temperature, pH, and TAN. By comparing to the reported critical concentration, a threshold below which is considered not harmful to the fish, these potentially toxic nitrogenous compounds in the pond water were generally in the range acceptable for channel catfish. It appears that a 28% protein diet can provide equivalent net production, feed efficiency, and processing yields as a 32% protein diet for channel catfish raised in ponds from advanced fingerlings to marketable size at densities varying from 14,820 to 44,460 fish/ha under single‐batch cropping systems. Optimum dietary protein concentration for pond‐raised channel catfish does not appear to be affected by stocking density.     

Effect of different culture conditions on the structural diversity of prokaryote communities in the sediment of earth ponds stocked with gilthead seabream Sparus aurata (Linnaeus, 1758)

In this study, we evaluate the use of polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE) for monitoring the effect of different aquaculture practices on sediment prokaryote (Archaea and Bacteria) communities. The effect of initial fish (gilthead seabream Sparus aurata) stocking density on the structural diversity of prokaryote communities of earth ponds bottom sediments was evaluated using PCR‐DGGE after a 5 month grow‐out period. An identical approach was used to monitor the effect of supplying different fish feeds [commercial feed (CD) versus an ecofeed (ECO)]. One additional variable was the use of copper sulphate (CuSO₄) as an algicide in some of the experimental rearing tanks. The statistical analyses of prokaryote community profiles showed that the presence of fish in earth ponds significantly influenced the structure of sediment prokaryote communities, when compared with earth ponds without fish, independently of the stocking density. Our results also indicated that the structure of the prokaryote communities of earth ponds supplied with the ECO feed shared a strong similarity with that fed CD. Curiously, the use of CuSO₄ in ponds receiving the ECO feed promoted significant differences on the structural composition of the bacterial community, but not on the archaeal community. DGGE molecular fingerprints are suitable for fast evaluation of new management practices in food‐fish production on earth ponds by monitoring shifts on microbial communities in bottom sediments.     

强降雨对粤西凡纳滨对虾养殖池塘微生物群落的影响

于强台风"莫拉菲"环流云系带来的持续强降雨天气前后(2009年7月14日和7月28日),对广东省茂名市电白县凡纳滨对虾半集约化养殖土池的水样和泥样进行调查,研究施用微生态制剂和未施用微生态制剂的虾池水体及底泥中的异养细菌、弧菌和芽孢杆菌的变化情况,并利用BIOLOGECO微板对水体和底泥的微生物群落代谢变化进行探讨。结果发现,定期施用微生态制剂的虾池水体和底泥中的细菌数量和微生物群落功能在强降雨前后基本保持稳定;未施用微生态制剂的虾池在强降雨后,水体的弧菌数升高,Simpson指数和McIntosh指数显著降低(P0.05),水体和底泥微生物群落对碳源的利用率变化明显。研究结果表明,与施用微生态制剂的虾池相比较,未施用微生态制剂的虾池在强降雨后,水体及沉积物环境波动变化明显,强降雨对其水域环境产生很大的影响。因此建议在对虾养殖过程中定期施用微生态制剂,并针对恶劣天气采取有效措施,以稳定虾池水体及沉积物的微生物生态。     

Characterization of microbial communities in intensive GIFT tilapia (Oreochromis niloticus) pond systems during the peak period of breeding

Aquaculture pond is a complex ecosystem where the microorganisms in the sediments, in the animal intestinal tract and in water interact with each other to influence the water quality and health of aquatic animals. In order to understand the spatial distribution and relationship of microbial communities in intensively farmed genetically improved farmed tilapia (GIFT, Oreochromis niloticus), 454 high‐throughput pyrosequencing was applied to analyse the 16S rRNA gene of bacteria in intensive GIFT ponds in Wuxi City, Jiangsu Province, China. A total of 72 747 initial sequences were obtained from four depths of pond water, from tilapia large intestines and from pond sediment. The most common phylum in all samples was Proteobacteria, Actinobacteria and Cyanobacteria were the most abundant in water, Fusobacteria and Firmicutes in the large intestine and Chloroflexi in sediment samples. The sediment microbial community structure was comparatively similar to that of the tilapia large intestine. The microbial communities from different water depths were somewhat similar, especially the three most shallow samples, although the abundance of Actinobacteria gradually decreased with increased water depth. This data offer a preliminary exploration of the response mechanisms of the bacterial communities to aquafarming and contributes to the understanding of the status of bacterial communities of tilapia pond systems during the peak period of breeding from the aspect of their spatial distributions.     

奥尼罗非鱼养殖池沉积形成及其主要影响因子的初步研究

在半封闭式奥尼罗非鱼养殖池中投入饲料,探索养殖过程中鱼池沉积形成及其主要影响因子。试验结果表明:无论养鱼或未养鱼,投饲或不投饲,各池均发生不同程度的沉积;外源饲料输入量相同时,养鱼池新颗粒物生成量(干重)比未养鱼池大15.63%,而沉积量比未养鱼池小19.49%;无外源饲料输入时,养鱼池的沉积量比未养鱼池大75.76%;养殖系统内养殖对象与其所处环境的相互依存和相互制约对系统新颗粒物生成及沉积具有重要作用。     

微生物制剂对养殖池塘细菌群落影响的PCR-DGGE分析

为了解微生物制剂在水产养殖环境修复中的作用机制,采用聚合酶链式反应—变性梯度凝胶电泳(PCR-DGGE)方法,研究不同微生物制剂对养殖池塘上覆水和沉积物中细菌群落的影响。结果显示,施用微生物制剂前后,试验塘上覆水样品中细菌的DGGE优势条带无明显变化,细菌群落组成没有明显差异,提示微生物制剂对试验塘上覆水中的细菌群落组成影响很小。相对而言,施用过微生物制剂的池塘相对于对照池塘其细菌群落结构发生的变化较大;泼洒EM菌原粉3 000 g/hm2加芽孢杆菌原粉750 g/hm2的试验塘沉积物中细菌群落2 d内发生了较大变化,之后相对稳定,对照池塘和泼洒EM菌原粉3 000 g/hm2加光合细菌原粉1 500 g/hm2的试验塘沉积物中细菌群落组成变化很小。     

Bacterial composition,abundance and diversity in fish polyculture and mussel–fish integrated cultured ponds in China

Bacterial community and abiotic environmental parameters in twelve freshwater aquaculture ponds were analysed. According to the major component of stocked animals, the ponds were grouped into four types: black carp Mylopharyngodon piceus, largemouth bass Micropterus salmoides, yellow catfish Pelteobagrus fulvidraco and pearl mussel Hyriopsis cumingii ponds. Each type of pond was stocked with three species of Chinese carps (silver carp, bighead carp and gibel carp) to form a unique mode of fish polyculture or mussel–fish integrated culture. The bacterial composition was identified using 16S rDNA sequencing. Totally, 3701 and 11 150 operational taxonomic units (OTUs) were identified from the water and sediment samples respectively. The number of OTUs, abundance‐based coverage estimator, Chao1 index and Shannon diversity index were lower in the water column than in the sediment, suggesting that diversity and stability of bacterial community were higher in the sediment. In the water column, Proteobacteria, Actinobacteria and Bacteroidetes dominated at the phylum level, and 26 dominant genera were identified. In the sediment, Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria and Nitrospirae dominated at the phylum level, and 25 dominant genera were identified. Bacterial compositions between the ponds with different aquaculture modes were similar at the phylum levels, but varied at the genus levels. The bacterial composition in the ponds was correlated with hardness, ammonia and total nitrogen in the water column. This study indicates that the type of aquaculture mode is a factor regulating the microbial community, which provides an insight towards microbial management through probiotic manipulation in pond culture.     

Influence of sediment phosphorus on utilization efficiency of phosphate fertilizer: a mesocosm study

Influence of initial sediment phosphorus content of the pond sediment on P dose efficiency was examined in a laboratory experiment using four types of sediments collected from ponds located along a nutrient gradient in a sewage‐fed fish farm. Each sediment type (500 g) was dispensed in a glass jar with water and treated with single super phosphate (SSP) treatment at 1.25, 2.5, 5.0 and 10.0 mg L^?1 in triplicate. Determination of orthophosphate (OP) and soluble reactive phosphorus (SRP) in water and available and total P in sediment showed increased response in relation to dose and time. At a given dose, the rate of increase for all species of phosphate in sediment or water was maximum in the case of local pond (LP) soil followed by stocking pond (SP), facultative pond (FP) and anaerobic pond (AP) soil, suggesting that utililization of phosphate fertilizer was much better under oligotrophic conditions than under eutrophic states. The SSP‐induced OP peak at 10 mg L^?1 in LP sediment was similar to that of 5.0 mg L^?1 in AP sediment containing 59% enhanced initial phosphate, implying that fertilizer application can be profitably reduced by 18% in the former without limiting the OP level in the water phase. It is concluded that dosage selection of phosphorus fertilizer in aquaculture ponds should be based on an evaluation of the initial P status of the system.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

Fish feeds from grass clippings

The objective of this research was to develop a quality fish feed that could be produced from simple plant material by way of microbial processing. Silaged grass clippings, applied to shallow ponds, produced floating mats of microbial biomass containing 26% protein and 43% carbohydrate in 7–10 days. The final silage-microbe mat (SMM) showed increases of over 300% in biomass and 100% in protein content over the silage feedstock. Productivity and microbial succession patterns were similar in laboratory ponds and tropical field ponds located in the Dominican Republic. In laboratory experiments SMM-fed tilapia, Oreochromis niloticus, showed significant growth increases over controls (fed commercial catfish fish feed), if they were allowed to graze the SMM together with the gelatinous detrital deposited during SMM culture. SMM produced little fish growth if it was harvested and fed separately in clean-bottom ponds without detrital buildup. These data show that the microbial mat produced from processed grass clippings can produce a nutritious natural fish food in the pond. The detrital trophic level in the sediment (stimulated by SMM culture), is a critical component in this diet.     

影响斑点叉尾亲鱼自然产卵率的关键因素研究

斑点叉尾是重要的经济养殖鱼类,本文从斑点叉尾亲鱼年龄、放养密度、产卵槽类型、饲料类型、池塘局部气候条件、池塘底质类型等方面对影响斑点叉尾自然产卵的关键因素进行了研究。结果表明,挑选4～5龄的亲鱼,在冬季气温、水温适当偏低的山区风口处建培育池,培育池底质为黏土硬底质或鹅卵石带沙底质,每667 m^2放亲鱼10～30组,全部投喂动物性饲料,用特制的土瓦罐作产卵槽,获得较高的自然产卵率。     

Comparison of bacterial communities in channel catfish Ictalurus punctatus culture ponds of an industrial ecological purification recirculating aquaculture system

The industrial aquaculture pond system has gradually replaced the use of traditional earthen pond, as it causes less pollution and is more economical. In this study, an industrial ecological purification recirculating aquaculture system consisting of the water source pond, high‐density culture ponds, a deposit pond, and ecological purification ponds for channel catfish cultivation was established. Twelve water samples from different ponds were sequenced, and the bacterial communities were analysed. The abundances of Cyanobacteria and Merismopedia varied in different functional ponds of the system. The water quality was stable after two months of cultivation at 1.89 ± 0.22 mg/L total nitrogen, 1.1 ± 0.08 mg/L NH₄‐N and 0.43 ± 0.1 mg/L total phosphorus. The fish weight increased in a nearly linear manner, reaching 237.63 ± 23.8 per fish at day 120. An analysis of the environmental parameters, water quality and fish weight suggested that the system had an effective water purification process. Canonical correspondence analysis showed that the community was affected at the genus and phylum levels by different environmental parameters. We identified several dominant beneficial bacteria with nutrient removal abilities. Overall, our results demonstrated that the ecological purification recirculating aquaculture system had notable effects on water quality improvement and promoted changes in bacterial populations. These results provide important information on the microbial ecology of pond industrial eco‐aquaculture systems.     

Microbial communities in sea cucumber (Apostichopus japonicus) culture pond and the effects of environmental factors

This study investigated microbial community composition as well as their correlation with environmental factors of Apostichopus japonicus culture ponds in northern China by 16S rRNA gene amplicon sequencing. The results showed that microbiota richness varied consistently with diversity in the pond ecosystem. Microbiota richness and diversity were highest in sediment, followed by gut of A. japonicus and water. The dominant bacterial phylum in the pond ecosystem is Proteobacteria. Gammaproteobacteriaeria and Flavobacteria are two dominant bacterial classes in the ecosystem. There is significant difference (p < 0.05) between dominant bacterial communities at the levels of order, family and genus. There is also remarkable regional difference (p < 0.05) between microbial community composition in the pond ecosystems. Specifically, microbial community composition in Changhai and Yingkou show a high similarity, so do those of Laoting and Rushan. According to the redundancy analysis of the microbial community composition and pond environmental factors, chemical oxygen demand is the dominant environmental factor determining microbial community composition in pond water; sulphide has the greatest influence on the microbial community composition in pond sediment; the rest of environmental factors have varied influence on microbial community composition in pond ecosystems.     

Androgen-induced sex-inversion of Oreochromis (Trewavas) hybrid fry stocked into cages standing in an earthen pond

Gonadally undifferentiated Oreochromis niloticus × O. aureus hybrid fry (F₂ generation), were fed a single level of androgen-treated diet (60 mg/kg 17-α-ethynyltestosterone), in earthen pond cages, an indoor tank and outdoor concrete tanks. All fry fed androgen-treated diets had populations consisting of ≥ 96% males, whilst those populations fed control diets had sex ratios which were not significantly different from an expected 1:1. No all-male broods were obtained, but populations composed of 96% and 99% males were produced in earthen pond cages following 25- and 28-day treatment periods, respectively, at a mean temperature of 30°C. Fry in outdoor pond cage treatments appeared to grow faster than those inside. Additional, naturally occurring food in the ponds is considered partly responsible for this. Survival of fry during androgen treatments depended upon size and density at stocking. Larger and more vital fry survived better than newly hatched fry.     

Effects of Stocking Density on Growth of Tilapia nilotica Cultured in Cages in Ponds

Reported maximum carrying capacities of Tilapia nilotica reared in cages are Iow ranging from 10 to 70 kg/m³. This may be related to total numbers of caged fish reared in a body of water and not simply density per cage volume. An experiment was conducted to demonstrate such effects.
Sixteen cages in a 0.77 ha pond were stocked with T. nilotica at either 250, 500, 750, or 1,000 fish/cage for a total of 12,987 fish/ha. One cage in each of four 0.13 ha ponds was stocked with either 250 or 1,000 fish/cage for a total of 1,923 or 7,692 fish/hectare, respectively. Fish were fed a 32% protein diet at equal rates for 169 days. In the 0.77 ha pond, yield per cage was positively correlated with stocking density, while individual mean weights were negatively correlated with stocking density. However, among equal densities per cage between ponds, fish in the 0.13 ha ponds gained about 26% more than in the 0.77 ha pond. An interaction of the effects of density per cage volume and per pond area may have occurred.     

Pond‐raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus,Do Not Respond to Microbial Phytase Superdosing

Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to “superdosing” of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.     

Enhancing productivity of Labeo victorianus ponds using maize flour as a carbohydrate source

This study investigated the effects of manipulating carbon–nitrogen (C/N) ratio and fish stocking density on pond productivity: total heterotrophic bacteria counts, plankton biovolume and benthic macro‐invertebrates. Labeo victorianus juveniles were reared for 72 days in 18 hapas suspended in six ponds measuring 150 m² at densities of 10, 15 and 25 fish m^?2. Fish in hapas received a locally formulated and prepared feed containing 295 g kg^?1 crude protein, and ponds were treated with a C/N ratio of either 10 or 20. All treatments were carried out in triplicate. Increasing C/N ratio from 10 to 20 increased phytoplankton by 13% and zooplankton biovolume by 25% in the water column (P < 0.001). Total benthic macro‐invertebrates biovolumes were also 30% higher (P < 0.05) with a C/N ratio of 20 compared to 10. Total heterotrophic bacteria counts increased both in water and sediment by 29% while net yield increased by 15% from 1534 (C/N 10) to 1821 (C/N 20) kg ha^?1 72 day^?1. C/N ratio of 20 and a stocking density of 25 fish m^?2 led to the highest yield, survival, production and net benefits. It is suggested that polyculture may lead to better utilization of pond communities to further improve pond productivity.     

RESPONSES OF PLANKTONIC AND BENTHIC COMMUNITIES TO FERTILIZER AND FEED APPLICATIONS IN SHRIMP MARICULTURE PONDS

An experiment was performed to evaluate the responses of naturally occurring populations of plankton and benthos to applications of inorganic fertilizer and commercial marine ration in a shrimp grow-out facility near Angleton, Texas. Ten ponds were stocked with an average of 17,000 post-larval Penaeus stylirostris on July 8, 1980. Three of these ponds received fertilizer 19 days before stocking and again 7 days after stocking. Another 3 ponds were fed daily with Ralston Purina Experimental Marine Ration 20 beginning on the stocking day. Three other ponds received the 2 fertilizer applications and daily feed. One control pond was not given fertilizer or feed. Beginning 19 days before stocking and continuing for 14 weeks, samples were collected and quantitatively analyzed for chlorophyll, zoo-plankton and benthic organisms. Results indicated that fertilizer stimulates the production of chlorophyll and planktonic copepods. Planktonic rotifers varied independently of feed or fertilizer. Densities of planktonic polychaete larvae seemed to be related to changes in the populations of benthic adult polychaetes. The benthic community was dominated by polychaetes, harpacticoid copepods and nematodes. Polychaetes tended to be more abundant when feed was present. Harpacticoids and nematodes did not seem to be affected by experimental treatments. All benthos fell to very low densities after 50 days of the study. The best shrimp production occurred in feed and fertilized ponds, followed by feed only, fertilizer only and the control. Potential linkages between natural production and shrimp growth are discussed.     

强天气干扰条件下粤西凡纳滨对虾养殖池塘细菌群落动态特征

于暴雨频发的华南雨季（2009年5月-8月）对粤西凡纳滨对虾（Litopenaeus vannamei）养殖池塘水体和底泥进行调查,研究在强天气干扰条件下养殖池塘细菌数量动态及多样性指数变化情况。结果发现,水体异养细菌在104-106 cfu？mL-1间波动,弧菌数量在养殖初期高达105 cfu？mL-1, 虾池301# 和404# 自6月18日开始施用芽孢杆菌（Bacillus subtilis）等微生态制剂后,其弧菌（Vibrio sp.）数量维持在104 cfu？mL-1以下,403# 和305# 波动较大且多次超过105 cfu？mL-1;4口虾池水体弧菌与异养细菌的数量比值在养殖初期均超过20%,之后301# 和404# 保持在12%以下,403#和305# 在养殖后期分别达到21%和33%。底泥异养细菌先升高后稳定,弧菌数量除305# 较稳定外,其他虾池波动较大（103-107 cfu？g-1）。施用微生态制剂池塘301#和404#水体微生物群落多样性较前期降低,305#和403#较前期升高;底泥微生物群落多样性则呈现相同的变化规律,群落的丰富度、常见种的优势度和群落均度较前期有所降低。结果表明,施用微生态制剂的虾池可在气候多变的情况下保持养殖水体细菌群落的相对稳定,抑制弧菌滋生,降低微生态环境风险。