凡纳滨对虾和罗氏沼虾肠道微生物及抗生素抗性基因多样性分析

探究凡纳滨对虾和罗氏沼虾肠道微生物及抗生素抗性基因(antibiotic resistance genes, ARGs)种类的差异。通过高通量测序和变性梯度凝胶电泳(denaturing gradient gel electrophoresis, DGGE)技术分析2种虾肠道微生物群落结构差异和微生物多样性,并运用PCR方法检测了2种虾肠道细菌常见38种ARGs的携带情况。结果显示,获得凡纳滨对虾和罗氏沼虾肠道细菌有效序列分别为42 795和40 713条,物种注释单元(operational taxonomic unit, OTU)数目分别为124和82,分类地位明确的细菌种类分别隶属5个门、17个属和5个门、16个属。凡纳滨对虾肠道细菌的优势类群为变形菌门,所占比例为75.45%,优势菌属为副球菌属(25.83%)和不动杆菌属(25.24%);罗氏沼虾肠道细菌的优势类群是厚壁菌门(49.74%),优势菌属为乳球菌属(49.01%)和弧菌属(29.98%)。凡纳滨对虾肠道细菌(2.19)Shannon指数高于罗氏沼虾肠道细菌(1.78),表明前者肠道细菌多样性大于后者。DGGE图谱的分析结果与高通量测序一致,2种虾肠道细菌种类差异很大。PCR结果显示,凡纳滨对虾肠道细菌携带15种ARGs,罗氏沼虾肠道细菌携带14种ARGs。本实验表明凡纳滨对虾肠道细菌的群落种类多样性、OTU丰富度、物种总数和ARGs种类均高于罗氏沼虾肠道细菌,为后续肠道微生物资源的挖掘提供了理论依据。     

Probiotic effect of Bacillus NL110 and Vibrio NE17 on the survival,growth performance and immune response of Macrobrachium rosenbergii (de Man)

Eight hundred and eighty‐five strains of bacterial isolates from various samples associated with the natural habitat of Macrobrachium rosenbergii were screened for their probiotic potential. Two putative probionts namely Bacillus NL110 and Vibrio NE17 isolated from the larvae and egg samples, respectively, were selected for experimental studies and were introduced to the juveniles of M. rosenbergii (0.080±0.001 g) through different modes such as through feed, water and both. The probiotic potential of the above bacteria in terms of improvements in water quality, growth, survival, specific growth rate (SGR), feed conversion ratio and immune parameters was evaluated. The treatment groups showed a significant improvement in SGR and weight gain (P<0.001). Survival among different treatment groups was better than that in the control group. There were also significant improvements in the water quality parameters such as the concentration of nitrate and ammonia in the treatment groups (P<0.05). Improvements in immune parameters such as the total haemocyte count (P<0.05), phenoloxidase activity and respiratory burst were also significant (P<0.001). It is concluded that screening of the natural microflora of cultured fish and shellfish for putative probionts might yield probiotic strains of bacteria that could be utilized for an environment‐friendly and organic mode of aquaculture.     

Vibrios associated with Macrobrachium rosenbergii (De Man, 1879) larvae from three hatcheries on the Indian southwest coast

Surveys for bacteriological analysis of larval samples to isolate the associated vibrios were carried out during 1985–1992, 2001 and 2002 in three different hatcheries located on the southwest coast of India. Vibrio isolates were examined for their species diversity, virulence based on haemolysis in prawn blood agar, lipolysis, proteolysis and chitinolysis and antibiotic sensitivity. Vibrio cholerae was the predominant species in the apparently healthy larval samples, whereas V. alginolyticus and V. vulnificus dominated during disease and morbidity. No correlation was found between the hydrolytic properties and haemolytic activity of the vibrios associated with the larvae. All isolates were resistant to erythromycin and resistance to oxytetracycline, ampicillin and streptomycin sulphate was prevalent among the larger section of the Vibrio population. This suggested that antibiotic application may not be of much use to protect the larvae from vibriosis. This is the first report on the diversity of Vibrio species associated with Macrobrachium rosenbergii larvae and their virulence characteristics based on haemolysis in prawn blood agar.     

Determination and transferability of plasmid‐mediated antibiotic resistance genes of the bacteria isolated from rainbow trout

Antibiotic resistance and the presence of resistance genes (ARGs) were investigated in the bacteria isolated from rainbow trout (Oncorhynchus mykiss) from different trout farms located in Turkey. The most frequent types of antibiotic resistance were towards β‐lactams (cephalothin [70% of bacterial isolates], amoxicillin [63%], ampicillin [62%], ticarcillin [56%], aztreonam [51%]), macrolide [erythromycin, 68%] and sulphonamide [sulphamethoxazole, 51%]. Of bacterial isolates, 51% were multiple drug resistant (MDR), while 35% of the isolates were extensively drug resistant (XDR). None of isolates were pandrug resistant (PDR). The most common ARGs were ampC (36%) and sul1 (24%). The class 1 integron gene cassette was detected in 51% of the bacteria. There was a strong positive correlation between the antibiotic resistance rate and the presence of ARGs (r² = .932). Gene encodes bla_CTX‐M1, one of the extended spectrum beta‐lactamase enzymes, was first described in Aeromonas caviae, Photobacterium damselae, Pseudomonas luteola and Burkholderia cepacia. It was determined that 35% of the bacteria harboured at least one plasmid. Plasmid‐mediated ARGs were identified to be tetracyclines (tetA, tetB, tetC, tetD), sulphonamides (sul1, sul3) and β lactams (ampC, bla_pse). Thus, results suggest that ARG contamination situation deliberates resistance to tetracycline, aminoglycoside, chloramphenicol and sulphonamide. Therefore, the presence and activity of ARGs in fish and in environmental bacteria may play an important role in the spread of resistance genes among bacteria by transposition or integron gene cassettes.     

Identification of bacterial agents causing mortality in postlarvae of giant freshwater prawn (Macrobrachium rosenbergii) in south‐west coastal districts of Bangladesh

Following an incidence of freshwater prawn Macrobrachium rosenbergii postlarvae (PL) mortality in hatcheries in summer 2012, samples from dead PL, rearing water and prawn feed from two south‐west coastal districts of Bangladesh were collected to isolate, identify and characterize the agents causing PL mortality. Antibiogram profile of sixteen randomly selected bacteria, isolated from dead PL, that grew on TCBS, to 20 different antibiotics belonging to 12 major groups revealed that the drug resistance pattern varied from moderate (56% to the drugs: ciprofloxacin, cefotaxime, nitrofurantoin, kanamycin) to complete (to penicillin, ceftazidime and oxacillin) level. To identify the isolates, amplified rDNA restriction analysis (ARDRA) classified them in to four groups, and RAPD (randomly amplified polymorphic DNA) typing yielded nine different types of isolates within these four ARDRA groups. The 16S rDNA gene sequences identified that the groups were genotypically diverse belonging to the bacterial species: Enterobacter cloacae, Klebsiella pneumoniae, Exiguobacterium profundum and Enterococcus casseliflavus, respectively, that all demonstrated their killing potential to PLs in a simulated environment. The study therefore identified four different bacterial pathogens, one of which, Exiguobacterium profundum is reported for the first here in Bangladesh, that demand special consideration for disease management strategy.     

Prevalence,phenotypic and genotypic diversity,antibiotic resistance,and frequency of virulence genes in Pseudomonas aeruginosa isolated from shrimps

Preventive measures should be prioritized for the increased growth of bacterial contamination in aquatic organisms. This study is aimed at molecular investigation of the prevalence of Pseudomonas aeruginosa, antibiotic resistance, and virulence factor encoding genes. After confirmation of P. aeruginosa collected from shrimp samples (in the same size) in Isfahan and Chabahar (Iran) in summer and autumn, antibiotic resistance encoding genes, virulence factor encoding genes, and multi-drug resistance (MDR) patterns were assessed. Bacterial contamination from Isfahan was higher than Chabahar despite having a cooler climate on summer days. Antibiotic resistance to piperacillin in fresh shrimp samples in summer in Isfahan was contrary to its usage as a front-line antibiotic agent. Lowered MDR pattern in frozen shrimp viability of bacteria was related to the varied expression of antibiotic resistance, highlighting the importance of regulations for cold chain in storage, transportation, and distribution of marine samples compared to fresh shrimps. Foodborne pathogens are of clinical and environmental importance. Results of our study indicated a high rate of frequency for P. aeruginosa isolated from marine samples. Maintenance of cold chain has indispensable roles in preservation, and reduction of P. aeruginosa frequency in aquatic organisms.

     

Simultaneous occurrence of Vibrio salmonicida and antibiotic-resistant bacteria in sediments at abandoned aquaculture sites

Abstract. The present authors have examined the survival of the fish pathogenic bacterium Vibrio salmonidda and the occurrence of antibiotic resistant bacteria in sediments from abandoned aquaculture sites. Survival of V. salmonidda was determined by fluorescent monoclonal antibody labelling combined with 4',6-diamidino-2-phenylindole (DAPI) staining. Using this method, the authors were able to detect V. salmonidda in sediment samples from six out of 12 abandoned fish farm locations. One out of the six positive stations was abandoned in 1982. Vibrio salmonidda was not detected at the three stations not affected by aquaculture (control locations) or in sediment samples taken 200–250m away from aqua-culture sites. When applying high-performance liquid chromatography, oxytctracyclinc or furazolidonc residues were not detected in sediment samples from control or abandoned aquaculture sites. Nevertheless, the percentage of bacteria resistant to oxytctracycline was higher in aquaculture sediments, as compared to control sediments. The simultaneous occurrence of fish pathogens and high levels of resistant bacteria in sediments increases the risk of transfer of resistance to the pathogens.     

鲍消化道及其养殖水体异养菌的耐药性研究

采用纸片扩散法对分离自福建省皱纹盘鲍(Haliotis discus hannai)消化道及其养殖水体中的284株异养细菌(其中消化道菌131株,水体菌153株)进行药物敏感测试,以期了解其耐药性概况。结果显示,皱纹盘鲍消化道与养殖水体异养菌对多种抗菌药物的耐药率差异不明显,大部分菌株对青霉素、卡那霉素、庆大霉素、利福平产生耐药性,耐药率最高达83.95%,而对诺氟沙星、恩诺沙星、氯霉素耐药率较低,受试的水体异养菌对诺氟沙星耐药率为0;不同来源菌株的多重耐药(multiple antibiotic resistance,MAR)现象普遍,消化道及其养殖水体异养菌的多重耐药率均值分别为59.15%和51.31%。该研究同时发现相同分离源的菌株对青霉素、卡那霉素、庆大霉素和利福平的耐药率呈现一定的季节波动规律,消化道异养菌于9月耐药率最低,而水体异养菌耐药率在6月最低。结果表明,皱纹盘鲍消化道及水体异养菌的多重耐药率较高,耐药状况较严重。     

Prevalence and antimicrobial resistance of vibrios of human health significance in inland saline aquaculture areas

This study was conducted to evaluate the prevalence, potential pathogenicity and antimicrobial resistance of Vibrio isolates from 65 soil/water/fish samples collected from inland saline aquaculture areas. Depending on the sample type, presumptive Vibrio counts ranged from 2.50 to 6.16 log₁₀ CFU/ml (or/g). Among the 119 confirmed Vibrio isolates, Vibrio cholerae was found to most dominant (91.6%) and it was detected in all the samples from inland saline areas. Seven other Vibrio spp. including Vibrio parahaemolyticus and Vibrio vulnificus were also detected. Except one O139 serotype, rest of the V. cholerae isolates were found belonging to non‐O1/non‐O139 serogroups. None of the V. cholerae isolate was found positive for ctx gene. Antimicrobial susceptibility testing against 7 commonly used antibiotics revealed highest resistance (50.4%) against ampicillin. Very high intermediate resistance (87.4%) was also observed against erythromycin. Contrary to previous studies, high susceptibility (>70%) to chloramphenicol, nalidixic acid, tetracycline and trimethoprim was observed in Vibrio isolates obtained in present study. Almost 20% of Vibrio isolates were resistant to two or more antibiotic classes with multiple antibiotic resistance (MAR) index value of ≥0.28. Presence of V. cholerae isolates with very high MAR index value of 0.85 also suggested that these multidrug‐resistant environment isolates could serve as reservoir of antibiotic‐resistant genes in aquatic systems. The presence of multiple drug resistance vibrios in emerging inland saline aquaculture systems emphasizes the need for their routine monitoring for developing the risk assessment and mitigation strategies.     

Histopathological changes in giant freshwater prawn Macrobrachium rosenbergii (de Man 1879) fed with probiotic Bacillus licheniformis upon challenge with Vibrio alginolyticus

The effect of dietary supplementation of probiotic bacterium Bacillus licheniformis on the histopathological changes in Macrobrachium rosenbergii juveniles (4.0 ± 0.02 g) challenged with known pathogenic strain of Vibrio alginolyticus are reported. Two isocaloric basal diets supplemented with probiotic bacteria B. licheniformis (1.0 × 10⁹ cfu/g feed) and other without probiotic supplementation were fed to the M. rosenbergii juveniles for 45 days. The histological observations revealed no significant changes in the hepatopancreas and gut tissues of both the experimental and the control groups which indicate that the present bacterium is a safe candidate probiont for the host. Prawns were challenged with V. alginolyticus after 45 days of feeding with probiotic diet. The histopathological studies of the hepatopancreas revealed that M. rosenbergii fed with probiotic‐supplemented diet showed less changes as compared to the prawns fed with control diet on second and fourth day of post‐experimental challenge with V. alginolyticus. Histopathological observations revealed that the gills of the prawns fed with control diet were severely affected in comparison to the prawns fed with probiotic‐supplemented diet after challenging with V. alginolyticus. Results from this study revealed the improved protection by dietary incorporation of B. licheniformis in reducing the histopathological manifestations due to V. alginolyticus infection in freshwater prawn.     

Antibiotic resistance in potentially bacteriocinogenic probiotic bacteria in aquaculture environments

Bacteriocin‐producing bacteria in aquaculture may prevent spreading of potentially pathogenic microorganisms, and could be used as an alternative to the empirical use of antimicrobial drugs, especially for prophylaxis. Bacteriocinogenic bacteria inoculated as probiotics should not carry undesirable traits, such as antibiotic resistance. This study aimed to find potentially bacteriocinogenic bacteria in an aquaculture system and evaluate their antimicrobial susceptibility patterns. Selective cultures for enterobacteria, non‐fermenting Gram‐negative rods and Gram‐positive cocci were obtained from water samples before bacterial isolation and biochemical identification. Overall, 160 representative strains were recovered and for 57 antagonism was observed against selected strains such as Staphylococcus aureus, with antagonism being expressed better on Brain Heart Infusion medium. After exclusion of interfering factors, bacteriocin or bacteriocin‐like substances were suggested to be related to the antagonism observed. Higher drug‐resistant rates were observed among potentially bacteriocinogenic bacteria for different antimicrobials of clinical relevance. Although antibiotic resistance is a global health problem and bacteriocins are attractive alternatives to classical antibiotic even to multiresistant bacteria, the data obtained suggest that bacteriocin‐producing bacteria may harbour resistance genes available for transference in different environments. From the ecological and biotechnological perspective, antimicrobial susceptibility tests must be always performed when prospecting potentially bacteriocinogenic bacteria as probiotic candidates in the environment.     

Dietary supplementation of host‐associated lactic acid bacteria modulates growth,metabolic activities,and immune‐related gene expression in giant freshwater prawn,Macrobrachium rosenbergii

The present study was carried out to evaluate the dietary effects of host‐associated lactic acid bacteria on growth performance, metabolic enzyme activities, and immune response of Macrobrachium rosenbergii juveniles. To formulate the test diets, a control (Con) diet was supplemented with a commercial probiotic and three host‐derived bacteria Enterococcus faecalis (EC), Lactococcus lactis I (LC‐I), and L. lactis II (LC‐II), which were previously isolated from the gastrointestinal tract of adult individuals of M. rosenbergii. Juvenile M. rosenbergii (0.65 ± 0.008 g) were randomly stocked at 20 individuals/100 L of fiberglass tanks with three replications for each test diet. After 50 days, juveniles fed the diets LC‐I and LC‐II showed significantly higher (p < .05) weight gain, specific growth rate, and the lowest feed conversion ratio. The analyses of glutamic oxaloacetate transaminase and glutamic pyruvate transaminase in muscle and hepatopancreas revealed significantly (p < .05) reduced values in LC‐I fed juveniles. The total hemocyte count and phenoloxidase activity were significantly increased (p < .05) in LC‐I and LC‐II fed juveniles. The relative mRNA expression patterns of immune‐related α2‐M, LGBP, ProPO, Cu, Zn‐SOD, TG, PE, AKP, and ACP genes were significantly (p < .05) upregulated in juveniles fed with LC‐I followed by the diet LC‐II. Finally, the study suggests that the growth performance and immune response of M. rosenbergii can be improved through supplementation of host‐associated L. lactis bacteria for its higher production.     

罗氏沼虾抗病选育群体的抗病性能及其遗传多样性分析

为深入了解罗氏沼虾抗病选育群体的抗病力和遗传信息,通过人工注射溶藻弧菌感染16个罗氏沼虾选育群体,并利用微卫星分子标记对选育群体进行遗传结构分析。结果显示,16个选育群体抗溶藻弧菌感染能力存在明显差别,并从中鉴定出抗病力强的群体3个(SCR11-6、SCR11-11和SCR11-16),其在感染溶藻弧菌感染后的成活率达80%;抗病力比较强的群体7个;抗病力一般的群体4个,成活率为65%～70%;抗病力差的群体2个,成活率为35%～50%。8对微卫星引物共检测到53个等位基因,每对引物的等位基因数为5～9个,平均为6.625个,多态信息含量(PIC)为0.629 4～0.829 4,平均为0.732 3。16个群体的平均PIC为0.493 2～0.695 6,平均观测杂合度为0.506 2～0.651 3,平均期望杂合度为0.551 9～0.733 2,遗传相似系数平均为0.655 2,遗传距离平均为0.434 4。并对DP和SP两群体罗氏沼虾个体扩增出的差异条带进行统计,分析其与罗氏沼虾抗病性状的相关性。结果表明,5个微卫星位点SUGbp8-103b、SUGbp8-101c、MRMB11、SUGbp8-137和MRMC2分别在203、263、185、335和96 bp等位基因与罗氏沼虾抗病性状存在一定的相关性,其中,位点MRMB11在185 bp等位基因跟抗病性有极显著的正相关性,相关系数为0.282。研究表明,16个选育群体中有4个群体的抗病力较强,同时与其它12个选育群体相比,这4个群体遗传多样性也比较丰富,这些罗氏沼虾群体的筛选为罗氏沼虾抗病新品种的培育奠定了重要基础。     

Bacterial microflora associated with farmed freshwater prawn Macrobrachium rosenbergii (de Man) and the aquaculture environment

The initial counts of bacteria associated with farmed giant freshwater prawn (Macrobrachium rosenbergii de Man) as well as with the water and sediment from two farms located at Kottayam district in Kerala (India) were determined. A total of 367 randomly selected isolates were characterized and identified. Prawn samples yielded mean microbiological counts of 4.92 log CFU g^?1 of shell with muscle and 7.78 log CFU g^?1 of intestine at 30°C. Bacterial numbers in the intestine of prawn were much higher than those in the pond water. Motile and non‐motile aerobic Gram‐negative bacteria together with Enterobacteriaceae accounted for 60–70% of the mesophiles isolated from water and prawn. However, the microorganisms isolated in significant numbers from shell with muscle and intestine of prawn were not recovered from the growing waters. Among Gram‐positive bacteria, Micrococcus, Bacillus, coryneforms, and Arthrobacter were found. Faecal coliforms and enterococci were found in significant numbers in M. rosenbergii. The rearing practices such as feeding and pond fertilization could have influenced the microflora in prawn. The commensal microflora of freshwater prawn included opportunistic pathogens such as Aeromonas spp. and Streptococcus spp. Storage of prawn at elevated temperatures can permit their survival and growth leading to quality loss. Care should be exercised during handling and processing to prevent contamination of edible meat.     

Survival of Escherichia coli in the intestine of fish

Establishment and persistence of Escherichia coli in the intestine of rainbow trout. Oncorhynchus mykiss (Walbaum), was investigated. Infection was achieved by ingestion of contaminated feed but not by bath exposure. At 15°C. E. coli was found to increase in number in the intestine offish after an initial decline, and could still be detected after 4 days. At 6°C it was detected for 2 days but the numbers declined steadily. A similar trend was observed when extracted gut content was inoculated with E. coli in vitro; after an initial decline, bacterial growth recovered. Gut content in vitro also was a suitable environment for plasmid-mediated transfer of resistance. Oxytetracycline resistance was transferred successfully from Aeromonas salmoniclda to E. coli. This could not be reproduced in vivo, perhaps because the inoculum of A. salmoniclda achieved per fish was not high enough as it did not withstand drying well on the feed pellets. Introduction by gavage was also tried but failed to establish an A. salmonicida infection. These results show that at temperatures around 15°C, the presence of E. coli in fish need not be an indicator of recent passage through polluted waters. It may be a consequence of infection established many days before, and perhaps some distance away. Furthermore, although transfer of antibiotic resistance from a fish pathogen did take place in the environment of fish intestinal content, the likelihood of this being a high-risk route for acquisition of resistance by bacteria that can affect humans is low.     

河北省海水池塘底质生物修复菌的分离筛选

为了修复对虾养殖池塘的养殖环境。从昌黎、乐亭、黄骅等3地的对虾池塘中取底泥,共分离出215种细菌．通过其对对虾饵料和蛤蜊内降解能力的测定,筛选出9株虾池有机污染降解茵。这些菌株能以对虾饵料作为生长的唯一碳源和氮源。并且对对虾的配合饵料和蛤蜊肉具有较强的降解能力。通过7d的培养。有4株细菌对对虾的饵料的COD去除率约70％。对蛤蜊肉的COD去除率超过50％,其他5株细菌对对虾饵料及蛤蜊肉的COD去除率也在30％以上。结果表明。这些细菌能快速消除对虾池塘的有机污染,具有修复虾池环境的潜力。     

广东地区吉富罗非鱼无乳链球菌病的流行情况与耐药性

为了调查广东省惠州、肇庆、珠海、湛江4个吉富罗非鱼主养区链球菌病的流行情况和耐药性,并进一步分析β-内酰胺酶基因与青霉素类药物的耐药性关系。本实验通过传统的方法对菌株进行分离纯化,扩增特异性基因cfb以及16s r DNA对各菌株进行鉴定;采用k-b法测定分离菌株的药物敏感性;通过PCR检测β-内酰胺酶类基因在分离菌株中的分布情况,并用Statistic6.0统计分析各β-内酰胺酶基因与青霉素类药物的耐药关系。实验结果表明,吉富罗非鱼无乳链球菌的阳性率从高到低的顺序为惠州(46.46%)湛江(43.24%)肇庆(17.30%)珠海(4.17%);药敏结果显示各地区无乳链球菌分离株对青霉素(耐药率为94.29%)和磺胺二甲基嘧啶(耐药率为86.40%)普遍耐药,对恩诺沙星最为敏感(耐药率为3.99%);β-内酰胺酶基因分布与细菌耐药性统计结果显示,无乳链球菌基因组中的9个β-内酰胺酶基因在各分离菌株中的分布呈高度多态性,其中SAG0658基因与氨苄青霉素抗性显著相关,提示SAG0658基因在无乳链球菌耐氨苄青霉素过程中发挥主要作用;此外,9个β-内酰胺酶基因与青霉素抗性无相关性,说明其在菌株对青霉素耐药过程中并未发挥明显作用,提示分离菌株对青霉素的耐药性可能依赖其他途径。     

Colonization and probiotic effects of lactic acid bacteria in the gut of the abalone Haliotis gigantea

Strains of lactic acid bacteria (LAB) were isolated from several different sources and evaluated in vitro for potential probiotic effects in abalones. Two isolates (Lactobacillus sp. strain a3 and Enterococcus sp. strain s6) were highly resistant to bile salt and/or gastric juice and inhibited the growth of three abalone pathogens (Listonella anguillarum, Vibrio harveyi, and V. carchariae). Each of the LAB isolates was used to supplement diet of the abalone Haliotis gigantea for a period of 3 weeks. One group of animals received Lactobacillus sp. strain a3 added to commercial dry feed, one group received Enterococcus sp. strain s6 added to the feed, and a control group received only standard commercial feed. Culturable LAB counts of gut homogenates indicate the a3 colonized in the gut of abalones. Digestive enzyme activities and the concentrations of a number of volatile short-chain fatty acids (VSCFA) were elevated in the gut of abalones receiving feed supplemented with the two LAB strains. These results indicate that dietary supplementation can enable LAB colonization or persistence in the gut of abalone species and can potentially enhance probiotic effects.     

Genetic divergence in Indian populations of M. rosenbergii using microsatellite markers

Macrobrachium rosenbergii, known as the giant freshwater prawn or Malaysian prawn, is the sixth largest aquaculture species in Asia. Knowledge of genetic diversity of M. rosenbergii is important to support management and conservation programmes, which will subsequently help in sustainable production of this economically important species. This study aimed to analyse the genetic diversity and population structure of five M. rosenbergii populations using 11 microsatellite loci. In analysing 240 samples, the number of alleles, observed heterozygosity (H_O) and expected heterozygosity (H_E) ranged from 3 to 20, from 0.250 to 0.978 and from 0.556 to 0.944 respectively. The five stocks of M. rosenbergii displayed high level of genetic diversity. Both the F_ST and amova analyses showed that there was significant genetic differentiation among all populations. The UPGMA dendrogram based on Nei's genetic distance matrix revealed that the Narmada and Mahi populations were in one cluster and Mahanadi and Subarnarekha populations in another single major branch, whereas the Kerala population clearly showed a separate cluster. This information on genetic variation will be useful for genetic improvement and conservation of Indian populations of giant freshwater prawn M. rosenbergii.     

Effects of Diet and Organic Fertilization on Water Quality and Benthic Macroinvertebrate Populations in Ponds Used to Culture Freshwater Prawn,Macrobrachium rosenbergii

ABSTRACT

Effects of three diets: (1) complete diet; (2) supplemental diet (vitamin and mineral supplements not added); and (3) the supplemental diet with an adjunct organic fertilization regimen (using distiller's dried grains with solubles [DDGS]) on benthic macroinvertebrate populations and water quality in experimental ponds used to culture freshwater prawns, Macrobrachium rosenbergii were investigated. Benthic samples were taken from deep (1.5 m) and shallow (1.0 m) areas of each of nine 0.02-ha ponds every three weeks, using a 0.09-m² Ekman dredge. The abundance of gastro-pods, oligochaetes, total non-insects, chironomids, total dipterans, total insects, and total macroinvertebrates was significantly higher (P <0.05) in ponds receiving the complete diet, possibly due to lower predatory pressure by prawns or direct benefits of micronutri-ents. Total macroinvertebrate abundance was significantly decreased (P <0.05) in ponds receiving supplemental diet (with and without organic fertilization), possibly due to increased predation by prawns to supplement the nutrition not provided by the lower quality diet. Organic fertilization significantly increased (P <0.05) the abundance of oligochaetes and total macroinvertebrates. These data suggest that M. rosenbergii can adjust to reduced feed quality by increasing consumption of benthic fauna.