Brackish Ponds Research Articles

Application of a novel two-stage biofiltration system for simulated brackish aquaculture wastewater treatment.

Biofiltration is one kind of common technology used for treating micro-polluted brackish aquaculture wastewater. Based on the characteristics of actual water quality, a novel two-stage biofiltration system was set up to reduce potential nutrient pollution brought by the frequent exchange of water in brackish pond aquaculture. Zeolite was selected as filtration media for the first stage and pyrite mixed with a small amount of sulfur for the second stage. Apart from the adsorption of nutrients exerted by these natural minerals, biofilm played a leading role in nutrient removal. The surface and internal pore of zeolite-sheltered nitrifiers and sulfur-containing compounds enhanced autotrophic denitrification. It was found that ammonia adsorption capacity of zeolite was reduced by nearly 58% when salinity was increased to 1.5%, while phosphate adsorption capacity of pyrite was hardly influenced and systematic hydraulic retention time (HRT) of 24h was proven appropriate, 9.6h and 14.4h for the two stages, respectively. Meanwhile, removal efficiency of 96.5% for NH4+-N and 92.1% for total inorganic nitrogen (TIN) was achieved under this condition. The analysis of microbial community of biofilm indicated that dominant genera responsible for nitritation and nitration on the surface of zeolite were Nitrosomonas and Nitrospira, respectively. Dominant genera responsible for autotrophic denitrification on the surface of pyrite and sulfur were both Thiobacillus. In addition, Ferritrophicum, related to the iron-oxidizing bacterium, also coexisted due to biological oxidation of pyrite. Long-term operation verified applicability and stability of this two-stage biofiltration system for brackish aquaculture wastewater purification.

Technology engineering of rearing red tilapia saline (oreochromis niloticus) fed on artificial diet enriched with protease enzymes in an eroded brackish water pond

Technology engineering of red tilapia saline (O niloticus) was reared in brackish water pond fed on artificial diet enriched with protease enzymes in an eroded brackish water pond. The purpose of this study was to know of technology engineering of red tilapia saline reared in brackish pond that is exposed to effect eroded brackish water pond and the effect of adding protease enzymes in artificial feed to accelerate the growth and survival of red tilapia saline fish. The fish samples in this study used red tilapia saline with and average weight of 1.25 ± 0.09 g / fish with stocking 10 fish / m2. This research used experimental method with Completely Randomized Design, 4 treatments and 3 replications. The treatments in this study were the addition of papain protease enzyme in the artificial feed with different dose ie A (0 mg / kg of feed), B (350 mg / kg of feed), C (700 mg / kg feed), D (1050 mg / kg feed ). The parameters to be determed include relative growth rate (RGR), feed utilization efficiency (EPP), protein efficiency ratio (PER), feed conversion ratio (FCR), survival rate (SR), and water quality.

Tolerance to salinity and dehydration in the Sahara Desert blue-eyed turtle, Mauremys leprosa saharica (Testudines: Geoemydidae) from a brackish pond in the Lower Draa basin, southern Morocco

ABSTRACTThe marginal populations of the Sahara blue-eyed pond turtle, Mauremys leprosa saharica, in the southern-most species distribution range in the pre-Saharan areas of north-west Africa, are faced with extreme environmental conditions of arid climate and anthropogenic and climate change mediated water and land salinisation. In the current study, we investigated a small and isolated population of M. l. saharica at Sidi El Mehdaoui oasis in the Lower Draa River, southern Morocco, in order to assess its osmo- and iono-regulatory abilities and tolerance to salinity and dehydration. Upon capture, turtles were weighed and measured for shell dimensions and blood and voided urine were taken. Tests of exposure to different levels of water salinity (0%, 35%, and 50% seawater) and maintenance out of water (estivation simulation) were carried out. Osmolalities and Na+, Cl−, K+, and urea concentrations were determined in plasma and voided urine, and glycaemia was measured in blood, before and after tests. Turtles were able to survive in brackish waters with a salinity as high as 24% seawater (8.4 ppt). Their voided urine was hypotonic to plasma, which indicated that they could use their bladder water reserves for osmo- and iono-regulation until the iso-osmocity level beyond which osmotic and ionic anhomeostasy can occur. Experimental tests showed that the osmo- and iono-regulatory capacities of these turtles are relatively limited, and not enough effective to allow them to survive for long-term periods in brackish/saline waters or out of water, because of dehydration indicated by progressive weight loss to a critical threshold. The increased drought, water salinisation and habitat fragmentation related to anthropogenic activities and climate change, represent great threats that can create habitats exceeding the species’ threshold for a long-term persistence of the vulnerable small marginal populations of the Saharan pond turtle. So, conservation measures of these populations and their habitats are urgently needed.

Evidencing the cost of sexual reproduction in the rotifer Brachionus plicatilis

Sex poses an immediate cost for monogonont rotifers, which combine exclusively asexual reproduction with periods of co-occurrence between asexual and sexual reproduction in their life cycle. Because sex is linked to dormancy, sexual daughters do not contribute to the current growth of a clonal genotype, as they only produce males or diapausing eggs. Therefore, the expectation under the all-else equal assumption (i.e., sexual and asexual females having equivalent life-history traits) is that female genotypes investing more in sexual daughters during the planktonic growing season will have slower rates of clonal growth. Here, we tested if these genotypes compensate for this greater investment in sex with higher fecundity and/or survival. We studied 45 genotypes (clones) of Brachionus plicatilis established from diapausing eggs isolated from sediments of ten brackish ponds in Spain. Using a life-table experiment, we estimated the investment in sexual reproduction of these genotypes and several life-history traits (lifespan, lifetime reproductive success, generation time and intrinsic growth rate). Results showed that there was a lack of correlation between sex-investment and any other life-history trait. Neither fecundity nor survival compensated the investment in sexual reproduction, so we conclude that the all-else-equal assumption holds and sex is costly in B. plicatilis.

Plankton Taxonomic and Size Diversity of Mediterranean Brackish Ponds in Spring: Influence of Abiotic and Biotic Factors

In this study, performed in Mediterranean brackish ponds during spring season, we assessed the effects of biotic interactions and abiotic factors on the size and taxonomic structure of the phytoplankton and zooplankton. We used a taxonomic and a size diversity index as a descriptor of the community structure. We predicted that the size diversity of each trophic level would be mainly related to biotic interactions, such as size-based fish predation (in the case of zooplankton) and food resource availability (in the case of phytoplankton), whereas taxonomic diversity would be more affected by abiotic variables (e.g., conductivity, pond morphology). Our results showed a negative relationship between phytoplankton size diversity and food resource availability leading to low size diversities under food scarcity due to dominance of small species. Conductivity also negatively affected the phytoplankton size diversity, although slightly. Regarding zooplankton size diversity, none of predictors tested seemed to influence this index. Similar fish size diversities among ponds may prevent a significant effect of fish predation on size diversity of zooplankton. As expected, taxonomic diversity of phytoplankton and zooplankton was related to abiotic variables (specifically pond morphometry) rather than biotic interactions, which are usually body size dependent, especially in these species-poor brackish environments.

Germination capability of four charophyte populations (Characeae) from Mediterranean brackish ponds under warm experimental conditions

ABSTRACTThe diaspore banks from two brackish ponds within the Albufera de Valencia Natural Park (Spain) containing oospores of Chara hispida, C. aspera, C. canescens and Nitella hyalina were analys...

DETEKSI BAKTERI GENUS VIBRIO SEBAGAI CAUSATIVE AGENT PADA IKAN LELE SANGKURIANG (CLARIAS GARIEPINUS VAR. SANGKURIANG) DI KOTA TASIKMALAYA

Sangkuriang catfish (Clarias gariepinus var Sangkuriang) is the main commodity that widely cultivated in Tasikmalaya City. However, farmers have difficulty because of the disease which causes death in fish. High mortality is suspected as a vibriosis disease by genus Vibrio because redness wounds on dead fish. The purpose of this study is to know the genus Vibrio which causes of disease in Sangkuriang catfish. 10 samples of fish were taken from Sangkuriang catfish pond culture in Kelurahan Kersanagara Tasikmalaya City which were potentially suspected of vibriosis disease. Isolation of bacteria were done on TCBS medium. Bacterial isolates were collected from fish lesion on the body surface, liver, and kidneys of catfish. Isolation were able to gained 21 isolates and then 5 isolates (VK1, VK5, VK7, VK17, and VK21) were selected based on colony morphology and Postulates Koch’s were tested. The results showed that the clinical symptoms of catfish infected by vibriosis were redness lesions/ulcers on the body surface, hemorrhagic, fluid inside stomach, and fin eroded with redness wound. Bacterial identification through biochemical test revealed the causative agent of catfish disease at brackish pond area were bacteria of the genus Vibrio (VK 1, VK 5, and VK 7), Vibrio vulnificus (VK 17 and VK 21).

Givetian-Frasnian arid palaeoenvironments from the northern Gondwana: a case study from the Moesian platform (Bulgaria)

Palaeozoic deposits in the Moesian platform (northern Bulgaria) are known only from deep wells drilled for oil and gas prospecting. Sixteen microfacies (MFT 1–16) have been distinguished and described in the Givetian to Frasnian carbonate and evaporite sequences, represented in thirteen wells from the eastern parts of the platform. They are respectively interpreted as arid peritidal deposits, formed in a variety of carbonate/evaporite environments (from shallow subtidal zones, adjacent to tidal flat, to supratidal sabkha). The shallow subtidal zone is characterised by wave-dominated (possible carbonate sand shoals, MFT 1–3) and protected lagoon (MFT 4–8) settings. The intertidal zone is distinguished by the development of microbial mats with typical lamination (MFT 9 and MFT 10) and “bird’s eyes” type fenestrae (MFT 11). Unfossiliferous laminated mudstones (MFT 12), lag deposits rich in intraclasts (MFT 13), brackish ponds with charophytes (MFT 14), unfossiliferous homogeneous mudstones/dolomudstones (MFT 15) and sabkha evaporites (MFT 16) were formed within the range of the upper intertidal and supratidal zones. These deposits presumably reflect the transition of the platform from carbonate ramp to rimmed shelf. Most of the studied Givetian–Frasnian microfacies are comparable with Wilson’s Standard Microfacies Types and/or with other microfacies described from shallow-marine Middle–Upper Devonian carbonate and evaporite successions in Europe. It seems likely that during the Givetian–Frasnian time the Moesian carbonate platform was located in the arid climate zone on the northern shallow shelf of the Gondwana.

Persistence of submerged macrophytes in a drying world: Unravelling the timing and the environmental drivers to produce drought‐resistant propagules

Abstract Under a warming scenario many permanent inland water bodies in the Mediterranean region have become temporary ones, so the persistence of submerged macrophytes depends on the timely production of drought‐resistant propagules. Phenological research measures the timing of ecological processes and allows the consequences of disturbances such as climate change to be evaluated. Among macrophytes, the charophytes are widely distributed benthic macroalgae and are particularly sensitive to environmental variations. The systems in which they live constitute valuable, threatened, and protected habitats (European Habitats Directive code 3140). This study established a methodological basis for determining which environmental drivers trigger the sexual reproductive phenology of charophytes. For the first time, circular statistics were applied to describe and compare seasonal patterns for submerged macrophytes. Over a period of 2 years, three charophyte species growing in two Mediterranean brackish ponds were monitored. Most of the sexual reproduction occurred during spring and summer, including the production of drought‐resistant propagules, before the harshest conditions arrived. Each species showed a distinctive phenological pattern, according to specific breeding systems, life cycles, and environmental tolerances and requirements. Deeper conditions and higher salinities delayed reproduction. Different rainfall intensities in autumn produced distinctions between years, as stronger rainfall reduced the salinity stress and stimulated the reproduction of plants. Interacting factors act as cues for charophyte reproduction and cause antagonistic effects on propagule production. Among them, the heat required for each phenophase peak is essential for understanding the phenology of a population and for predicting its long‐term persistence. Charophytes appear to be good candidates for tracking climate change in shallow ecosystems. Further phenological studies should consider more species, populations, and long‐term observations in order to predict climate‐change effects on water bodies, and to develop effective plans for management and conservation. Circular statistics is a potential tool for analysing phenology in the context of global warming, as well as for many other conservation issues.

The life cycle of a parthenogenetic population of Chara canescens from an interdunal Mediterranean pond

Chara canescens lives in shallow brackish waters in the northern hemisphere. It has been described as an annual species that mostly reproduces by parthenogenesis, being the only species of Chara able to do so. However, much is still unknown about its life cycle and the differences between the sexual and the parthenogenetic populations. We monitored the life cycle of a parthenogenetic population growing in a brackish interdunal pond in the Albufera de València Natural Park (Spain). Approximately 30 specimens were harvested every 15–30 days throughout 2015. The longest polar axis and the largest equatorial diameter were measured, and the isopolarity index was calculated for the oogonia and the oospores. The non-swollen and the swollen oogonia were distinguished by size. This population had a short life cycle, but two types of shoots with different life history traits were found. A few small individuals overwintered underneath the emergent vegetation. In early March, new shoots appeared from the germinating oospores, growing fast and colonizing more open waters. The first oogonia appeared in April, enlarging and ripening along the first five whorls of the shoots. The oospores were produced in less than 15 days after the first oogonia emergence. The ripe oospores were small (average size ± SD: 392 ± 34 × 219 ± 24 μm; isopolarity index: 181 ± 22). Parthenogenetic reproduction lasted 5 months. No new fructifications were produced from September onwards. Although the oospores were smaller than those described in the literature for the species, they were clearly viable and enabled the persistence of the population through the winter.

Bays and Saline Pond Classification Generated from the Nhecolândia Pantanal Aerial Photograph Vegetation Indexes

The Pantanal is an extensive flooded plain, rich in biodiversity and considered a Biosphere Reserve and World Heritage Site. It has great complexity and can be divided into regions due to its each distinct characteristic. Nhecolândia is a very peculiar region because it is made up of thousands of freshwater and brackish ponds. The study objective was to evaluate the physical-chemical parameters of the Nhecolândia ponds and to analyze the vegetation indexes generated from UAV aerial photographs in order to identify what best distinguishes freshwater and brackish ponds and to differentiate study area features. The in-field and image data collection were performed on June 20, 2015. The aerial photographs were processed to obtain mosaic which served as a vegetation index basis. The indexes and wavelengths in the visible region analyses were performed for each of the area’s ponds. It was observed that bays and salines have a differentiated spectral behavior. The excess green and normalized excess green vegetation indexes presented results enough to separate freshwater from brackish ponds, plus to differentiate many study area features.

CHLORINE DEMAND AND BACTERIAL ABUNDANCE OF SHRIMP POND WATER UNDER DIFFERENT SUSPENDED SOLID CONCENTRATIONS

An experiment has been conducted to evaluate the chlorine demand and efficacy of 6 chlorine concentrations in brackish pond water, to control indigenous bacteria in shrimps pond.

Effects of invasion at two trophic levels on diet, body condition, and population size structure of Hawaiian red shrimp

AbstractWe examined the degree to which invasion by non‐native, nitrogen (N)‐fixing riparian trees and poeciliid fish alters diet of a common grazer/detritivore in brackish ponds on the dry coast of Hawai‛i Island. Because this shrimp, Halocaridina rubra (ʻōpaeʻula), displays a preference for autotrophic components of epilithon, we hypothesized that tree canopy would reduce their body condition and abundance, but that this would be moderated by nutrient quality of leaf litter (high‐quality, non‐native, nitrogen‐fixing tree vs. low‐quality, endemic non‐nitrogen‐fixing tree). We hypothesized that poeciliid invasion would reduce population size and body condition of H. rubra by direct predation and by inducing reductions in feeding rate. Analysis of stable isotopes (δD, δ13C, and δ15N) showed that direct consumption of leaf litter detritus supplemented H. rubra diet in ponds with canopy cover. In addition, epilithon in ponds with canopy cover was isotopically more similar to leaf litter than epilithon in ponds without canopy cover, and our evidence suggests this may be due to contributions of allochthonous nutrient sources to epilithon assemblages. However, canopy cover, whether native or invasive, did not decrease epilithon growth rates and had little effect on shrimp body condition or population size. In contrast, poeciliid invasion reduced daylight grazing on the benthos, and caused a reduction in body condition among larger shrimp. Our results indicate that primary succession by invasive trees may shift food web linkages in these ponds from autotrophic to heterotrophic support, without negative impacts on native grazer/detritivore communities. We suggest that poeciliid invasions have sub‐lethal effects on H. rubra as well as their direct predation effects, with potential long‐term implications for the ecosystem function of anchialine ponds and other coastal systems.

Egg hatching phenology and success of Lestes macrostigma in two temporary brackish ponds

Although a full life cycle approach is optimally needed to make conservation decisions, the egg stage is often neglected for insect species of special conservation interest. Water management and related abiotic factors are relevant factors to consider in aquatic species. Lestes macrostigma is a threatened damselfly restricted to temporary brackish waters. Here we provide detailed information on its hatching success and phenology in two natural field populations. Shoots containing fresh egg clutches of L. macrostigma were sampled in late June, just after the oviposition period. In the fall, shoots were separately placed in plastic boxes in two ponds in southern France. Examination of eggs indicated L. macrostigma overwinters at an early embryonic stage. The following spring we monitored hatching in detail. Hatching began on 15 March in both ponds and ended on 27 April. Hatching was synchronized, with half of the eggs hatching within five days in the first pond and 14 days in the second pond. Lower water te...

Rotifers and lower crustaceans from South-western Iceland.

Iceland is one of the countries with the highest freshwater availability according to UNEP's Vital water graphics (http://www.eoearth.org/view/article/152861/). Additionally, being an island, it is rich in coastal brackish and saline aquatic habitats. However, little is known about the microcrustaceans and rotifers inhabiting these numerous habitats. The freshwater fauna of Iceland is relatively understudied compared to the fauna of adjacent marine ecosystems. Exhaustive sampling of deep-sea fauna was conducted within the inter-Nordic BIOICE project. As a result, Apostolov (2011) recorded 32 copepod harpacticoids of which 20 are new for the fauna of Iceland. The first data on freshwater microinvertebrate fauna of Iceland date back to the 19th century (Guerne and Richard 1892a, Guerne and Richard 1892b). The first study on the rotifer fauna from the middle of the 20th century listed 59 species or subspecies (Bartos 1951). The majority of the available studies on inland water bodies focused on large lakes: Mývatn in the north-east (Ornolfsd and Einarsson 2004, Adalsteinsson 1979, Jonasson 1979, Lindegaard 1979); and Thingvallavatn (Antonsson 1992) and Kerið Lakes (Evtimova et al. 2014) in the south-west of the country. Recently scientists have become increasingly interested in the inland freshwater copepods and cladocerans from small freshwater bodies (Novichkova et al. 2014, Scher et al. 2000). Data on observed morphological variability and teratology of lower crustacean in subpolar environments, including Iceland, were presented by Sinev et al. (2012), Pandourski and Evtimova (2009), Pandourski and Evtimova (2006), Pandourski and Evtimova (2005). These aberrations affected the fifth pair of legs in calanoids, the posterior part of the body in cyclopoids, or the head and antennule in cladocerans. Our study presents data on taxa composition of Rotifera, Cladocera, and Copepoda in various aquatic habitats from South-western Iceland, including marine interstitial, wet bryophytes, springs, brackish and freshwater ponds and lakes.

Socio-Economic Considerations of the Aquaculture Industries in Cebu and Siquijor, Central Visayas, Philippines

Abstract Aquaculture industry has grown globally to fill in the shortage of fish supply from the sea. A study of aquaculture industries in ICRMP sites of Central Visayas was conducted to determine the socio-cultural and economic aspects of aquaculture. Results revealed that 79% of aquaculture systems are in freshwater and brackish ponds with 50% Oreochromis niloticus and 43% Chanos chanos as common cultured species. Ponds are operated by private individuals and conform to the standard culture systems of cultured species. The individuals that were employed in aquaculture industries are those that are living near the aquaculture sites which are mostly hired as caretakers and helpers and basically non-permanent and on-call basis. In spite of their employment in the aquaculture industries, communities near aquaculture sites are considered poor since majority of households are living below the poverty thresholds. There is a periodicity of consumption of aquaculture products in the community. The frequency of consumption is high during harvest time (50%) which usually happens every 3-4 months only, thus creating high demand in the community.

Application of endocrine disruptor screening program fish short-term reproduction assay: Reproduction and endocrine function in fathead minnow (Pimephales promelas) and killifish (Fundulus heteroclitus) exposed to Bermuda pond sediment.

A modified tier 1 Endocrine Disruptor Screening Program (EDSP) 21-d fish short-term reproduction assay (FSTRA) was used to evaluate the effects of sediment exposure from freshwater and brackish ponds in Bermuda on reproductive fecundity and endocrine function in fathead minnow (Pimephales promelas) and killifish (Fundulus heteroclitus). Reproductively active male and female fish were exposed to control sediment and sediment from 2 freshwater ponds (fathead minnow) and 2 marine ponds (killifish) contaminated with polyaromatic hydrocarbons and metals via flow-through exposure for 21 d. Reproductive fecundity was monitored daily. At termination, the status of the reproductive endocrine system was assessed by the gonadosomatic index, gonadal histology, plasma steroids (estrogen [E2], testosterone [T], and 11-ketotestosterone [11-KT]), steroidogenic enzymes (aromatase and combined 3β/17β -hydroxysteroid dehydrogenase [3β/17β-HSD]), and plasma vitellogenin (VTG). Decreased reproductive fecundity, lower male body weight, and altered endocrinological measures of reproductive status were observed in both species. Higher plasma T levels in female minnows and 11-KT levels in both male and female minnows and female killifish exposed to freshwater and brackish sediments, respectively. Decreased female E2 and VTG levels and gonadal cytochrome P19 (aromatase) activity were also found in sediment exposed females from both species. No effect on female 3β/17β-HSD activity was found in either species. The FSTRA provided a robust model capable of modification to evaluate reproductive effects of sediment exposure in fish.

Species diversity, spatial distribution, and virulence associated genes of culturable vibrios in a brackish coastal Mediterranean environment

The Vibrio genus is widespread in marine and brackish environments, and several species are human and animal pathogens of global importance. Vibrios adapt rapidly to many environmental stresses, so that brackish environments can be both a suitable niche and a possible reservoir for them. To test the occurrence of culturable vibrios and their possible correlation with environmental factors in a temperate brackish environment, a 1-year sampling study was performed in three brackish ponds located along the Central Thyrrenian coast in the Macchiatonda Nature Reserve (Santa Marinella, district of Rome, Italy). Molecular methods were used to detect Vibrio cholerae, V. parahaemolyticus, and V. vulnificus pathogenicity-associated genes among the Vibrio isolates. Out of 130 Vibrio isolates identified by sequencing a recA fragment, 70 harbored virulence-associated genes including ctx, ace, tcpA, tdh, trh, vvhA, vllY, and toxRS, so confirming the spread of virulence determinants across the environmental isolates. Ecological analysis showed that, although the water temperature is known to be a strong predictor of abundance and distribution of vibrios, its influence accounts for 27 % of the observed variance in the Macchiatonda samples, increasing to 40 % when combined with salinity.

Life-history traits, abiotic environment and coexistence: The case of two cryptic rotifer species

Trade-offs are important in life-history evolution and coexistence of competitors. However, how alternative life-history optima might promote competitor coexistence has received little attention. The rotifers Brachionus plicatilis and Brachionus manjavacas are two cryptic species with a considerable ecological overlap in relation to biotic factors. These species often co-occur in temporal brackish ponds characterised by environmental fluctuations. In these rotifers, sexual reproduction results in diapausing stages, which are able to survive through adverse conditions but constrain current population growth. In the present work, the differential responses of both cryptic rotifer species to varying salinities and temperatures in terms of population growth, sexual reproduction and diapause patterns (i.e., investment, viability and hatchability of diapausing eggs) were investigated to assess their possible roles in species coexistence. B. plicatilis and B. manjavacas showed differential responses to salinity and temperature and differed consistently in traits involved in diapause. The niche overlap between B. plicatilis and B. manjavacas decreased dramatically when the temperature and salinity response niche axes were added to a number of previously studied biotic niche axes. The results suggest that B. plicatilis exploits ephemeral and favourable conditions (low salinity) to invest in diapause, which would accelerate its exclusion from the water column but promote its long-term persistence. The findings show that cryptic species may evolve different compromises among life-history traits, allowing ecological divergence, and that ecological divergence may be uncoupled from morphological divergence for some factors in the abiotic environment.

Vibrio metoecus sp. nov., a close relative of Vibrio cholerae isolated from coastal brackish ponds and clinical specimens.

A Gram-staining-negative, curved-rod-shaped bacterium with close resemblance to Vibrio cholerae, the aetiological agent of cholera, was isolated over the course of several years from coastal brackish water (17 strains) and from clinical cases (two strains) in the United States. 16S rRNA gene identity with V. cholerae exceeded 98 % yet an average nucleotide identity based on genome data of around 86 % and multi locus sequence analysis of six housekeeping genes (mdh, adk, gyrB, recA, pgi and rpoB) clearly delineated these isolates as a distinct genotypic cluster within the V. cholerae-V. mimicus clade. Most standard identification techniques do not differentiate this cluster of isolates from V. cholerae. Only amplification of the ompW gene using V. cholerae-specific primers and a negative Voges-Proskauer test showed a difference between the two clusters. Additionally, all isolated strains differed phenotypically from V. cholerae in their ability to utilize N-acetyl-d-galactosamine and d-glucuronic acid as sole carbon sources. Furthermore, they were generally unable to infect the slime mould Dictyostelium discoideum, a widespread ability in V. cholerae. Based on these clear phenotypic differences that are not necessarily apparent in standard tests as well as average nucleotide identity and phylogeny of protein-coding genes, we propose the existence of a novel species, Vibrio metoecus sp. nov. with the type strain OP3H(T) ( = LMG 27764(T) = CIP 110643(T)). Due to its close resemblance to V. cholerae and the increasing number of strains isolated over the past several years, we suggest that V. metoecus sp. nov. is a relatively common species of the genus Vibrio, isolates of which have been identified as atypical isolates of V. cholerae in the past. Its isolation from clinical samples also indicates that strains of this species, like V. cholerae, are opportunistic pathogens.