Effects of Microbial Fermented Feed on Growth and Development of Farmed Crayfish

Microbial fermented feed possesses a natural fermentation flavor and exhibits good palatability.It is not only easily digestible and absorbable by livestock but also non-toxic.Additionally,it has the capacity to inhibit the proliferation of pathogenic bacteria,facilitate the growth and development of animals,and enhance their immune response,disease resistance,and overall production performance.This paper summarizes the selection of common feed materials and microbial strains used in fermented feed,as well as their effects on the growth performance,muscle quality,antioxidant capacity,and immune function of crayfish.The aim of this study is to provide a reference for the further popularization and application ofmicrobialfermented feed in crayfishaquaculture.

Preliminary Results of Crayfish Distribution and Diseases in Latvia

A lot of water reservoirs offer good natural conditions for crayfish breeding. Today there are four crayfish species present in Latvia--the European species noble crayfish （Astacus astacus）, narrow-clawed crayfish （Astacus leptodactylus）, the North American signal crayfish （Pacifastacus leniusculus） and spiny-cheek crayfish （Orconectes limosus）. In general, crayfish were found in 258 localities--lakes （175）, rivers and streams （66）, reservoirs, ponds and gravel-pits （17）. A. astacus in Latvia is the dominant crayfish species distributed in all regions. Narrow-clawed crayfish was registered since 1960s. North American signal crayfish was introduced due to its resistance to diseases, but spiny-cheek crayfish arrived from Lithuania waters spontaneously. The main threat for crayfish population is crayfish plague, initiated by mucus Aphanomyces astaci. Astacus astacus was more susceptible species in comparison with Pacifastacus leniusculus and Orconectes limosus. Though the North American signal crayfish and spiny-cheek crayfish were not only resistant, they were the carriers of this disease. The physical habitat alterations, pollution and overfishing are significant during the first year breeding period. Crayfish might serve as bacteria carriers and can cause substantial fish diseases （such as aeromonosis, flavobacteriosis）.

Technical Standards for Lotus Root-Redswamp Crayfish Integrated Farming

Lotus root-redswamp crayfish integrated farming is a kind of ecologicalgrow mode on the basis of paddy field, which is an innovated mode for agricultural structure adjustment and special agriculture with high efficiency. In order to regulate producing technology of this mode, the essay puts forward some technical require- ments, stressing on cultivar selection, field works, farming technology and product quality, which aims at providing technical support for agricultural production.

Clinical characteristics of patients with Haff disease after eating crayfish

BACKGROUND: The study aimed to explore the clinical presentations, laboratory findings, treatments and prognosis of patients with Haff disease after eating crayfi sh. METHODS: Sixteen patients with Haff disease after eating crayfish were admitted to the Emergency Department of Beijing Chao-yang Hospital between June 2013 and August 2017. Clinical data was retrospectively analyzed. RESULTS: Alcohol consumption and exercise were found to be most commonly associated with the onset of rhabdomyolysis after consuming crayfi sh. Most patients were young adults and the symptoms mostly occurred within 24 hours of consumption of crayfi sh. Clinical symptoms included myalgia (100%), fatigue (87.5%), nausea (43.8%), dizziness (62.5%), chest distress (37.5%) and fever (18.8%). Also found after laboratory testing was elevations in the levels of creatine kinase (11,376±5,535 U/L), myoglobin (350±158 ng/mL), lactate dehydrogenase (6,539±3,180 U/L), alanine transaminase (174±71 U/L) and aspartate aminase (348±100 U/L). The incidence of renal dysfunction was low (6.25%), and all 16 patients had a good prognosis. CONCLUSION: Patients with Haff disease exhibited typical symptoms after consuming crayfish, and laboratory findings gave highly accurate diagnostic results. The development of rhabdomyolysis was considered to be associated with alcohol consumption and exercise, but further studies are needed to demonstrate its relationship with crayfi sh consumption. Compared with other causes of rhabdomyolysis, rhabdomyolysis after crayfi sh consumption has fewer complications and better prognosis.

Sustainability of the rice-crayfish farming model in waterlogged land:A case study in Qianjiang County, Hubei Province, China

The rice-crayfish farming model has been rapidly developed and become an economically viable method to supply food in China in recent years.However,its environmental and economic sustainability has not been thoroughly investigated.This study uses a survey in 2016 and a field experiment in 2017 in Qianjiang,Hubei Province,China to assess the relative economics of concurrent rice-wheat(RW),rice-crayfish(RC),and crayfish monoculture(CM)models in waterlogged land areas.Thefield survey indicated that the RC model had a higher benefit-cost ratio(3.5:1)than the RW(2.0:1)and CM(3.1:1)models and the RC model protected farmers’enthusiasm for grain production facing unfavourable weather conditions.The field experiment aimed to explore nitrogen management strategies in RC fields.In the experiment,four levels of nitrogen concentration gradient-0 kg N ha^(-1)(0 N),75 kg N ha^(-1)(75 N),150 kg N ha^(-1)(150 N)and 225 kg N ha^(-1)(225 N),were set in a 2-year-old rice-crayfish(RC2)field,an 8-year-old rice-crayfish(RC8)field,and a RWfield as a control.Thefield experiment results suggested that the peak rice yield in RW,RC2,and RC8 occurred when 225 N,150 N and 75 N were used,respectively.In RC2 and RC8,however,residual feed-nitrogen that was not used by crayfish was utilized by rice plants.Thus,an optimal amount of nitrogen in RCfields was proposed to improve the nitrogen use efficiency and reduce environmental pollution by nitrogen fertilizer.Farmers use less nitrogen but have higher net income in RC than in RW and CM.It is necessary to sustainably develop integrated farming technologies(i.e.,properfield configurations for ricefields)to effectively sustain rice production.The results also showed that the RC farming model was a viable diversification option for rice farmers in waterlogged land.

In vivo neutralization assays by monoclonal antibodies against white spot syndrome virus in crayfish (Cambarus proclarkii)

The neutralizing activities of eight monoclonal antibodies （MAbs） against white spot syndrome virus （WSSV） （2D2, 2B2,1D2, 1D5, 1C2, 4A1, 6A4 and 6B4） were analyzed by in vivo experiments. Gills from WSSV-infected shrimp were homogenized and ten-fold serially diluted by PBS, and then incubated with MAbs （hybridoma culture supernatant）, respectively. The mixture of WSSV and MAbs were injected into crayfish （Procambarus clarkii）. After challenge, the death rates of crayfish were counted to determine the neutralizing activities of MAbs. At the same time, the mixture of myeloma culture supernatant and WSSV or PBS was served as positive or negative control, respectively. The results showed that, at each virus dilution, the mean time to death of the crayfish injected with MAb-treated virus was significantly longer than that in the positive control, though they all showed 100% mortality within 25 d, and meanwhile, few crayfish died in the negative control. Among the eight MAbs, 2D2, 2B2, 1D2 and 1D5, especially the former two, delayed the mortality significantly, and 1 C2, 4A1 and 6A4 delayed the mortality as well but not so efficiently, while MAb 6IM was efficient only when the virus concentration increased. The results indicated that the anti-WSSV MAbs can neutralize WSSV in different virus dilutions.

Characterization of Specific Spoilage Bacteria and Volatile Flavor Compounds of Flavored Crayfish

It is a common issue in the processing industry of crayfish that flavored crayfish stored at room temperature is perishable.In order to establish an effective putrid prediction mechanism,high-throughput sequencing and solid phase microextraction gas chromatography-mass spectrometry(SPME-GCMS)were used to analyse the microbial community structure and volatile flavor compounds of normal and putrid crayfish.The results showed that Aeromonas(57%),Macrococcus(7.7%),Vibrio sp.(6.6%),Acinetobacter(5%),Citrobacter(4.9%)and Enterobacter(1.49%)were the main bacterial genus in the refrigerated fresh crayfish(HNA).And Staphylococcus(17.04%),Aeromonas(4.46%),Xanthomonas(4.16%),Streptococcus(4.62%)and Enterococcus(2.77%)were the main bacterial genus in the marinated and refrigerated crayfish(HND).With the spoilage of samples(HNE and HNC),the diversity of bacteria decreased,and the specific spoilage bacteria grew rapidly,mainly Enterococcus,Bacillus,Lactobacillus,Leuconostoc,Weissella.Meanwhile,the volatile compounds in non-spoilage sample(HNA and HND)were mainly alkane compounds,aldehydes compound and esters compounds;and the volatile compounds in spoilage samples were mainly alcohols,acids,benzene compounds,terpenoids,N-containing compounds,S-containing compounds and ethers.This indicated that the contents and types of volatile compounds changed with the sample spoilage and deterioration.Correlation analysis results showed that Enterococcus,Lactobacillus and Bacillus were significantly positively correlated with alcohols,acids,benzene,terpenoids,N-containing compounds,S-containing compounds and ether compounds,while Aeromonas,Megasphaera,Acinetobacter,Citrobacter and Vibrio were significantly positively correlated with alkane compounds and esters compounds,and Leuconostoc were significantly positively correlated with alcohol compounds.These results can provide a theoretical guidance for the storage of cooked flavor crayfish at room temperature.

Crayfish Shell Waste as Safe Biosorbent for Removal of Cu^(2+)and Pb^(2+)from Synthetic Wastewater

Crayfish shell is an abundant natural waste and is also a potential biosorbent for pollutants,especially,heavy metals.In this study,the safety of the use of crayfish shell as a biosorbent was first assessed by release experiments involving primary heavy metal ions,such as Cu^(2+),Zn^(2+),and Cr^(3+),in aqueous solution under different environmental conditions.The release concentrations of heavy metals were dependent on pH,ionic strength,and humic acid;and the maximum release concentrations of heavy metals were still lower than the national standard.Specifically,Cu^(2+) and Pb^(2+) removal by crayfish shell in synthetic wastewater was investigated.The removal process involved biosorption,precipitation,and complexation,and the results indicate that crayfish shell is an excellent biosorbent for Cu^(2+) and Pb^(2+) removal.The precipitation step is particularly dependent on Ca species,pH,and temperature.The maximum removal capacities of Pb^(2+) and Cu^(2+) were 676.20 and 119.98 mg/g,respectively.The related precipitates and the generated complex products include Cu_(2)CO_(3)(OH)_(2),Ca_(2)CuO_(3),CuCO_(3),Pb_(2)CO_(3)(OH)_(2),CaPb_(3)O_(4),and PbCO_(3).

Nutritional and Sensory Evaluation of Rice-Based <i>Masa</i>Enriched with Soybean and Crayfish

Masa is a cereal based snack made from rice, maize or millet. It is popularly consumed in the northern regions of Nigeria. The objective of this work was to assess the nutritional and sensory properties of the rice-Masa, enriched with soybean and crayfish. The enriched rice-Masa produced were labelled sample A (100% rice), sample B (rice: soybean blend (80:20), sample C (rice: crayfish blend (80:20) and sample D (rice: soybean: crayfish (80:10:10). The proximate and mineral composition was evaluated according to standard methods. Anti-nutrient content was also determined. Sensory evaluation was carried out to assess the acceptability of the enriched rice-Masa. The chemical analysis showed that protein, fibre, iron, zinc and vitamin A and beta carotene contents were highest in sample D with values 8.35 (±0.08) g/100g, 1.08 (±0.02) g/100g, 2.82 (±0.03) mg/100g, 4.20 (±0.03) mg/100g, 602.3 (±1.28) μg/100g and 420.2 (±0.98) μg/100g respectively, while calcium was highest in sample C with a value of 27.34 (±0.06) mg/100g. Moisture and ash contents increased from 47.4 (±0.50) g/100g to 50.9 (±0.80) g/100g and 0.40 (±0.01) g/100g to 1.15 (±0.01) g/100g respectively, while carbohydrate and energy contents decreased from 28.1 (±0.03) g/100g to 21.9 (±0.04) g/100g and 308.42 kcal/100g to 285.64 kcal/100g respectively. The sensory evaluation showed that with regards to taste, aroma, texture and overall acceptability, the sample enriched with soybean was more preferred to that enriched with crayfish, or a combination of both. Enrichment of Masa could contribute to improvement of nutritional status if promoted as a nutritious, healthy indigenous snack not only where Masa is already widely consumed, but also in other parts of Nigeria where it has not found wide acceptance.

Crayfish Robot That Generates Flow Field to Enhance Chemical Reception

This paper describes a wheeled underwater robot developed for locating chemical sources autonomously under stagnant flow conditions. In still water, the released chemical stays in the immediate vicinity of the source location. The search for chemical sources under such conditions is extremely laborious since the presence of a chemical source cannot be detected from a distant place. The chemical sensors on the robot show no response unless a chemical substance released from the source arrives at the sensors. Crayfish in search of food are known to actively generate water currents by waving their small appendages with a fan-like shape. It is considered that the generated water currents help their olfactory search. The smell of food is carried to their olfactory organs from the surroundings by the generated flow, and then is perceived. The robot presented in this paper employs arms mimicking the maxillipeds of a crayfish to generate water currents and to draw chemicals to its sensors. By waving the arms vertically, a three-dimensional flow field is generated and water samples are drawn from a wide angular range. The direction of a chemical source can be determined by comparing the responses of four laterally aligned electrochemical sensors. Experimental results show that the flow field generated by the maxilliped arms is more effective in collecting chemical samples onto the sensors than that generated by a pump. The robot equipped with the maxilliped arms can detect the presence of a chemical source even if the source is placed off the trajectory of the robot.

Heart and ventilatory measures in crayfish during copulation

Monitoring heart rate (HR) and ventilatory rate (VR) during defined sensory stimuli and during aggressive and submissive social interactions has provided additional information of a crayfish's physiological state which is not achieved by behavioral observations. In this study, the HR and VR of crayfish were monitored before, during and after the act of copulation in both heterosexual partners. The female crayfish abruptly reduces HR and VR during copulation but the male maintains HR and VR. After separation from copulation the female HR and VR are elevated, potentially paying back the O2 debt. The tight relationship with HR and VR in direction of change indicates a potential neural coupling. These physiological changes in cardiac and respiratory systems suggest an autonomic-like regulation of HR and VR. How these neuronal functions are driven and regulated remains to be determined. Olfactory cues from the female to the male during copulation may be reduced by the reduction in VR in the female. These studies offer experimental paradigms for future neuronal and pharmacological investigations into autonomic regulation of HR and VR as well as the neural circuitry involved.

Dietary Intake, Carcinogenic and Non-Carcinogenic Risk Potentials of Lead, Cadmium, Mercury and Arsenic Exposure via Consumption of Dried Crayfish in Calabar, Nigeria

Intense pressure from both onshore and offshore oil exploration and exploitation activities, together with the accompanying urbanization and industrialization has resulted in massive contamination of land and water resources in Niger Delta, Nigeria. Whereas crayfish is very sensitive to contaminant in the aquatic environment and constitute an important part of human diet, its quality and safety from environmental pollutant is of serious health concern. Evaluation of dietary intake, potential carcinogenic and non-carcinogenic risk of lead, cadmium, mercury and arsenic exposure via consumption of dried crayfish purchased from major markets in Calabar, Nigeria was carried out between June and August 2021. Thirty-six composite samples of dried crayfish purchased from 180 vendors were used for the study. Heavy metals concentrations were determined using Atomic Absorption Spectrophotometer (Model AA-6800, Japan) after wet digestion. Metals concentrations (Mg/kg) were of the ranges 0.02 - 0.24, 0.14 - 0.86, 0.32 - 0.72, 0.04 - 0.19 for Pb, Cd, Hg and As respectively. The mean content of cadmium and mercury exceeded FAO/ WHO and Commission of European Communities maximum levels for crustaceans. Average Estimated Daily Intake for each of the metals was found to be above the recommended daily intake level except for arsenic. The average estimated daily intake values for Cd and Hg were also above the tolerable upper intake level. Average Target Hazard Quotient of all the metals and Hazard Index of all the markets were below 1.00. The Incremental Lifetime Cancer Risk of the metals was greater than the standard tolerable regulatory risk (10-4) for carcinogens. Consumption of crayfish purchased from major markets in Calabar could pose a range of carcinogenic and non-carcinogenic human health risks.

Study on the Effect of "Crayfish-Rice Continuous Cropping" on Grain Production:A Case Study of Hubei Province

Taking Hubei Province as an example,starting with the present situation and existing problems of grain production,this paper expounds the great significance of"crayfish-rice continuous cropping"model in improving grain quality,and analyzes the beneficial influence of"crayfish-rice continuous cropping"on grain production and the difficulties it faces.This paper also puts forward some measures and suggestions for the further popularization of"crayfish-rice continuous cropping"in order to maintain food security.

Phenotypic plasticity in the monoclonal marbled crayfish is associated with very low genetic diversity but pronounced epigenetic diversity

Clonal organisms are particularly useful to investigate the contribution of epigenetics to phenotypic plasticity,because confounding effects of genetic variation are negligible.In the last decade,the apomictic parthenogenetic marbled crayfish,Procambarus virginalis,has been developed as a model to investigate the relationships between phenotypic plasticity and genetic and epigenetic diversity in detail.This crayfish originated about 30 years ago by autotriploidy from a single slough crayfish Procambarus fallax.As the result of human releases and active spreading,marbled crayfish has established numerous populations in very diverse habitats in 22 countries from the tropics to cold temperate regions.Studies in the laboratory and field revealed considerable plasticity in coloration,spination,morphometric parameters,growth,food preference,population structure,trophic position,and niche width.Illumina and PacBio whole-genome sequencing of marbled crayfish from representatives of 19 populations in Europe and Madagascar demonstrated extremely low genetic diversity within and among populations,indicating that the observed phenotypic diversity and ability to live in strikingly different environments are not due to adaptation by selection on genetic variation.In contrast,considerable differences were found between populations in the DNA methylation patterns of hundreds of genes,suggesting that the environmentally induced phenotypic plasticity is mediated by epigenetic mechanisms and corresponding changes in gene expression.Specific DNA methylation fingerprints persisted in local populations over successive years indicating the existence of epigenetic ecotypes,but there is presently no information as to whether these epigenetic signatures are transgenerationally inherited or established anew in each generation and whether the recorded phenotypic plasticity is adaptive or nonadaptive.

Effects of transport stress on immune response, physiological state, and WSSV concentration in the red swamp crayfish Procambarus clarkii

Transport is an essential part of the aquaculture and research of the main freshwater aquaculture crayfish Procambarus clarkii in China.However,transport is often accompanied by a low survival rate.Assessing the physiological state of P.clarkii before and after transport may discover the cause of this high mortality rate.In this study,ice-cold and exposed-to-air transport methods were compared using an array of parameters,including relative expression level of heat shock protein 70(HSP70),content of serum glucose and cortisol,immune parameters(enzyme and immune-related genes),and white spot syndrome virus(WSSV)concentration were investigated to understand the physiological state of P.clarkii before and after transport,as well as the cause of dying crayfish on days 5 and 7 after transport stress.Histological sections of hepatopancreas,gills,and intestines reflected pathological changes.The survival rate of crayfish with ice-cold transport was significantly higher than that with exposed-to-air transport,and mortality peaked at 3-9 days after transport stress.A prolonged response to oxidative stress and short-term immunosuppression was present after transport,and the trend of the WSSV concentration in the hepatopancreas was similar to the mortality rate of P.clarkii.The contents of serum glucose and cortisol,antioxidant enzymes and immune-related indexes,and the concentration of WSSV in hepatopancreas of dying crayfish were significantly higher than those of vibrant crayfish on the 5th and 7th days after transport.The hepatopancreas,intestines,and gills of dying crayfish had varying degrees of damage,and the hepatopancreas and intestines were severely damaged.The results suggested that the death of P.clarkii after transport stress is caused by oxidative stress,the imbalance of reactive oxygen species regulation,and decreased WSSV resistance,which eventually led to irreversible tissue damage.The increase of WSSV in the body of crayfish might be the direct cause of crayfish death.

Identification of quantitative trait loci for growth traits in red swamp crayfish(Procambarus clarkii)

Genetic breeding is an important approach to improve the economic traits of aquaculture animals.Unfortunately,the genetic basis for important economic traits of red swamp crayfish,including growth-related traits,has not yet been reported.In the present study,two full-sib families and two natural populations were employed to identify quantitative trait loci(QTLs)for growth-related traits of red swamp crayfish.In total,28 QTLs for five growth-related traits,including body weight,body length,carapace length,carapace width,and abdomen length,were repeatedly identified in more than two families/populations,by means of association analysis;nine of these displayed a heterosis effect.The phenotypic variations of the five investigated traits explained by the 28 QTLs ranged from 4.2%to 19.0%.Eight additive and three heterosis QTLs were further successfully validated using comparative analysis of favoured alleles between the small and big size crayfish groups in the natural population.In conclusion,this study investigated the genetic basis of growth-related traits in red swamp crayfish,which is of great significance for their application in the future molecular breeding of the species.

稻虾共作模式下克氏原螯虾对水稻土团聚体特征及有机碳分布的影响

为研究长期稻虾共作模式下克氏原螯虾对水稻土团聚体数量、稳定性以及土壤团聚体有机碳含量、分布的影响,本研究依托始于2014年的长期定位试验,设置冬泡无秸秆还田(W)、冬泡+秸秆还田(WS)和冬泡+秸秆还田+养虾(WSC)3个处理,采集各处理表层土壤样品,分析土壤团聚体及有机碳分布特征。结果表明:土壤水稳性团聚体以>1~2 mm粒级为主,在冬泡条件下秸秆还田处理显著提高了土壤中>2 mm团聚体比例、有机碳含量和有机碳贡献率,且增加了土壤团聚体平均质量直径;相对于冬泡+秸秆还田处理,冬泡+秸秆还田+养虾处理土壤>2 mm和>1~2 mm团聚体比例显著提高了19.8%和6.5%,而0.053~0.25 mm团聚体比例则显著下降了9.2%,且>0.25 mm的团聚体数量、平均质量直径和几何平均直径分别提高了7.8%、20.6%和37.5%。冬泡+秸秆还田+养虾处理的土壤总有机碳、微生物量碳和颗粒有机碳含量较冬泡+秸秆还田处理分别显著提高了6.2%、34.0%和23.1%,且显著提高了<0.25 mm团聚体中有机碳的含量。研究表明,稻虾共作模式下克氏原螯虾养殖促进了土壤大团聚体的形成,增强了团聚体稳定性,增加了土壤有机碳及活性组分含量,尤其提高了微团聚体中有机碳含量,提升了土壤固碳能力。

小龙虾扰动下水稻秸秆腐解及养分释放和表面结构变化特征

为探究持续泡水条件下小龙虾参与水稻秸秆腐解过程与特征,完善稻虾模式水稻秸秆还田技术、实现秸秆资源的高效利用及农田可持续发展,采用自制尼龙网箱法,在稻虾环沟模式的养殖沟内,以不养虾为对照,模拟研究小龙虾扰动下水稻秸秆的腐解特性、养分释放特征及其表面微观结构变化特点。结果显示,无论是否有小龙虾参与,水稻秸秆各时段平均腐解率表现出快—慢—快—慢—快的特点;150d及以前,有虾处理与无虾处理各时段腐解量、累计腐解率和各时段平均腐解率差异均不显著,180d及以后各指标均表现为有虾处理显著高于无虾处理,至210d时,有虾处理水稻秸秆累计腐解率达85.67%,比无虾处理高出12.35百分点。秸秆养分累积释放率均表现为K>P>N;150 d及以后,有虾处理N累积释放率表现出高于无虾处理的趋势,180 d及以上,有虾处理P累积释放率和总养分累积释放率表现出高于无虾处理的趋势,至210 d,有虾处理K累积释放率表现出高于无虾处理的趋势。120d及以后,有虾处理的秸秆表面结构受破坏程度明显大于无虾处理。结果表明,稻虾环沟模式下,小龙虾扰动能增加中后期水稻秸秆表面微观结构的受破坏程度,促进后期水稻秸秆腐解和养分释放。

水分优化管理对稻虾共作模式水稻产量及土壤还原性物质的影响

通过探索水分优化管理对稻虾共作模式水稻产量及土壤还原性物质的影响,为该模式下水稻水分管理和土壤改良提供科学依据。在水稻直播和机插两种种植方式下,分别设置以水稻分蘖后期和成熟期两次重晒田等措施为主的水分优化管理处理、以水稻分蘖后期和成熟期两次轻晒田等措施为主的水分常规管理处理,于湖北省潜江市采用田间定位试验开展研究。结果表明,在水稻直播和机插条件下,水分优化管理相对于常规管理平均增产率分别为8.5%和9.4%,增产效果均达到显著水平。相对于常规管理,水分优化管理对水稻有效穗数和每穗粒数的正效应大于结实率和千粒质量。水稻分蘖后期,水分优化管理相对于常规管理0~10 cm土层亚铁含量下降40.8%~41.8%,0~20 cm土层还原性物质总量下降45.1%~46.4%;与分蘖后期相比,水稻收获后0~20 cm土层亚铁和还原性物质总量总体呈下降趋势。由此表明,稻虾共作模式下分蘖后期和成熟期两次重晒田等水分优化管理措施能够显著增加水稻产量,缓解土壤潜育化程度。

红螯螯虾幼虾对4种水稻农药耐受性研究

为了解稻田常用的生物农药或杀虫剂对红螯螯虾大规格幼虾的毒性效应,测定了中生菌素、氯虫·噻虫嗪、噻唑锌和井冈霉素A对其的急性毒性反应。结果表明:4种农药对红螯螯虾大规格幼虾96 h半致死浓度分别为19.66、1.65、1132.83、2092.07 mg/L。安全浓度分别为5.65、1.27、260.40、248.11 mg/L,根据耐受性和行为特征观察发现,4种药物对于4 cm左右的红螯螯虾幼虾的毒性大小依次为氯虫·噻虫嗪>中生菌素>噻唑锌>井冈霉素A,根据国家标准(GB/T16310.5—1996),噻唑锌和井冈霉素A对于4 cm红螯螯虾幼苗属于无毒农药,中生菌素属于微毒农药,而氯虫·噻虫嗪为中毒农药。本试验明确了红螯螯虾幼虾对水稻常用农药的耐受性,为红螯螯虾-水稻综合种养过程中的病害防治工作提供参考。