Freshwater Counterparts Research Articles

Ecological stoichiometric of C, N and P of Coilia species

Fish of the Coilia genus play a crucial ecological role by serving as a vital link between marine and freshwater ecosystems. To gain a comprehensive understanding of the ecological patterns, intra-interspecific variations, and potential determinants of Coilia from an ecological stoichiometry perspective, analyzed the concentrations of C, N, and P elements in various types of Coilia, including C. nasus, C. mystus, C. grayii, C. brachygnathus, and C. nasus taihuensis, across the Yangtze River basin. The result shows that: 1) A broad spectrum of eco-stoichiometric patterns within Coilia species, facilitating their adaptation to diverse ecosystems, including seawater and freshwater. Specifically, the C content in Coilia species from 40% to 70%, while N% and P% range between 4%–12% and 0.5%–3%, respectively. 2) Intriguingly, interspecific variations in eco-stoichiometric patterns are predominantly driven by anadromous populations. The anadromous Coilia species, including C. nasus, C. mystus, and C. grayii, exhibit significantly higher C contents and C/N, C/P, and N/P ratios compared to their landlocked and freshwater counterparts (C. nasus taihuensis and C. brachygnathus). However, the trends in N and P content are reversed. 3) Intraspecific differences vary among Coilia species, notably observed in C. nasus taihuensis and C. brachygnathus, where there's minimal correlation with body size. Conversely, C. nasus and C. mystus demonstrate a substantial influence of body size, with increasing fish size associated with higher C content, C/N, C/P, and N/P ratios, while N and P content decrease. This suggests that larger fishes store more energy (C%) in preparation for reproductive migration. In conclusion, this study provides a scientific foundation for comprehending the ecological patterns and intra-interspecific variations in Coilia. Furthermore, it contributes to the application of ecological chemometrics in the study of migratory fish, enriching our understanding of the intricate dynamics within this ecologically significant species.

Habitat salinity and source-induced variation in body shape of euryhaline long whiskers catfish (Mystus gulio)

The study was carried out to investigate the body shape variation of the Mystus gulio collected from three different salinity gradient habitats (high-salinity brackish water, low-salinity brackish water, and freshwater) and two different sources (wild and hatchery) using linear morphometric distances, landmark-based truss-networking and geometric morphometrics. A total of 436 individuals of M. gulio were collected from the high-salinity (8–15 ppt), low-salinity (2–6 ppt), and freshwater bodies (0 ppt). For wild versus hatchery sources body shape variation, 430 individuals of M. gulio were collected from various coastal rivers and hatcheries. M. gulio from different salinity gradient habitats and sources exhibited negligible sexual dimorphism. Principal component analysis (PCA) indicated that high and low salinity populations appeared to form overlapping clusters with the freshwater populations, but other multivariate analyses discriminated both populations from brackishwater habitats from the freshwater counterparts. The geometric morphometrics displayed that the body shape variation of M. gulio from salinity gradient habitats was mainly visible in the width of the dorsal-ventral part, the snout shape, the tail shape, the head region, and the eye diameter. PCA demonstrated that multivariate spaces of both the wild and captive populations overlapped each other, although many individuals of the wild population were discriminated from the culture populations. Our results showed that truss networking and geometric morphometric methods provide consistent outcomes for body shape discrimination in the M. gulio populations.

Cracked and shucked: GC-APCI-IMS-HRMS facilitates identification of unknown halogenated organic chemicals in French marine bivalves

High resolution mass spectrometry (HRMS)-based non-target analysis coupled with ion mobility spectrometry (IMS) is gaining momentum due to its ability to provide complementary information which can be useful in the identification of unknown organic chemicals in support of efforts in unraveling the complexity of the chemical exposome. The chemical exposome in the marine environment, though not as well studied as its freshwater counterparts, is not foreign to chemical diversity specially when it comes to potentially bioaccumulative and bioactive polyhalogenated organic contaminants and natural products. In this work we present in detail how we utilized IMS-HRMS coupled with gas chromatographic separation and atmospheric pressure chemical ionization (APCI) to annotate polyhalogenated organic chemicals in French bivalves collected from 25 sites along the French coasts. We describe how we used open cheminformatic tools to exploit isotopologue patterns, isotope ratios, Kendrick mass defect (Cl scale), and collisional cross section (CCS), in order to annotate 157 halogenated features (level 1: 54, level 2: 47, level 3: 50, and level 4: 6). Grouping the features into 11 compound classes was facilitated by a KMD vs CCS plot which showed co-clustering of potentially structurally-related compounds. The features were semi-quantified to gain insight into the distribution of these halogenated features along the French coast, ultimately allowing us to differentiate between sites that are more anthropologically impacted versus sites that are potentially biodiverse.

Seawater sea-sand Engineered Geopolymer Composites (EGC) with high strength and high ductility

In this study, seawater sea-sand Engineered Geopolymer Composites (SS-EGC) were developed and investigated for the first time. The developed EGC achieved high compressive strength (over 140 MPa) and high tensile ductility (around 8%) simultaneously. Emphasis was placed on understanding the influence of seawater and sea-sand (compared to freshwater and washed sea-sand) on the matrix properties and tensile performance of EGC, with two fly ash-to-slag ratios (8:2 and 2:8) considered in the matrices. Results showed that the use of seawater hindered the reaction of EGC matrix and led to a slight reduction of compressive strength (compared to the freshwater counterpart). It was found that the content of hydrotalcite phases in SS-EGC matrix was higher than that of freshwater EGC. In addition, using seawater was found to increase the average modulus of matrix obtained from nanoindentation, leading to a higher fiber/matrix bond strength. The tensile strain capacity of SS-EGC was slightly lower than that of freshwater EGC. The developed SS-EGC showed superior crack resistance and better sustainability than the cement-based counterpart from the literature (with similar compressive strength). The findings of this study provided useful knowledge for the design and development of high-strength high-ductility SS-EGC towards sustainable and resilient marine infrastructures.

Concentration-response of six marine species to all-trans-retinoic acid and its ecological risk to the marine environment

Being a class of vitamin A’s main derivatives, retinoic acids (RAs) are important to animals’ growth and development. Previous studies demonstrated that exposure of excessive amounts of RAs would lead to malformation and abnormal development in aquatic animals such as amphibians and fishes. Currently, there are only limited toxicity data of RAs available for freshwater species, while those for marine species are seriously lacking. This study aimed to fill such data gap by conducting toxicity tests on six marine species (i.e., one microalga, four invertebrates and one fish) towards the exposure to all-trans-RA (at-RA), which is the most widely distributed RA in the environment. Results showed that the embryo of medaka fish Oryzias melastigma was the most sensitive towards the exposure of at-RA while the gastropod Monodonta labio was the least sensitive. A species sensitivity distribution (SSD) was constructed based on the experimental results generated from the present study. An interim marine-specific predicted no-effect concentration (PNEC) of at-RA was derived at 2300 ng/L. By computing the hazard quotients using the interim marine-specific PNEC and available measured and predicted concentrations of RAs, we found the current levels of RAs posed no immediate risks to the marine environment of Hong Kong. The interim marine-specific PNEC was more than 500-fold of freshwater-specific PNEC (i.e., 3.93 ng/L), indicating that marine species were generally less sensitive than their freshwater counterparts towards RAs. This was the first study to document the concentration-response of various marine species towards at-RA exposure and construct the marine-specific SSD for assessing the ecological risk of at-RA towards the marine environment. Since various forms of RAs and their metabolites often coexist in aquatic environments, further studies should investigate their combined toxicity to an array of marine species of different trophic levels with consideration of chronic exposure scenarios.

Lake snow as a mercury methylation micro-environment in the oxic water column of a deep peri-alpine lake

Hg methylation in the oxic water column of marine environments has been linked to the presence of suspended and settling particles known as marine snow, which acts as a micro-niche for MeHg production. While marine snow has been thoroughly studied, its freshwater counterpart, lake snow, received less attention, even though few works have highlighted its ability to be a micro environment for Hg methylation in freshwater systems. Here we present new data of MeHg and THg concentrations in the lake snow of a deep peri-alpine lake (Lake Geneva, Switzerland-France). Particles were sampled from the lake and from its main tributaries using continuous flow filtration and continuous flow centrifugation, respectively. MeHg concentrations ranged from 0.48 ± 0.09 ng/g to 9.61 ± 0.67 ng/g in the lake particles, and from 0.30 ± 0.08 ng/g to 2.41 ± 0.14 ng/g in tributary particles. Our results suggest that lake snow is a likely micro-niche for Hg methylation, like marine snow, and that this methylation takes place inside the particles with a subsequent diffusion to the water column. Moreover, we propose a conceptual model to explain the MeHg behavior related to the lake snow along Lake Geneva water column and a mass balance model to estimate the time required to reach the steady state of MeHg in the water column. Our calculation indicates that the steady-state is reached after 37 days. This result is compatible with particles residence times from the literature on Lake Geneva. These particles forming the lake snow are probably a major entry point into the lake's food chain.

Microfluidic analysis of seawater-based CO2 capture in an amine solution with nickel nanoparticle catalysts

Post-combustion CO2 capture methods like amine scrubbing are currently being utilized to reduce CO2 emissions from fossil fuel power plants. Aqueous monoethanolamine (MEA) solutions are typically used in these processes due to their high CO2 absorption capacity and rapid reaction rate, but these solutions also produce environmentally harmful toxic wastewater and consume large amounts of freshwater. This research analyzes the effectiveness of seawater-based MEA solutions containing nickel nanoparticles (NiNPs) as catalysts, with the goal to minimize the amount of MEA required in the amine scrubbing process and eliminate the use of freshwater. This study is the first to use natural seawater solutions as an alternative to freshwater solutions for CO2 capture. In a microfluidic environment, CO2 microbubbles were generated and their change in size with respect to time was observed to determine the CO2 absorption capacity and rate of the test solutions. Pure seawater demonstrated comparable CO2 absorption to deionized (DI) water. Seawater-based amine solutions absorbed merely 1.79 % less CO2 than DI water-based amine solutions. Seawater-based amine solutions demonstrated faster CO2 absorption rates than their freshwater counterparts. Lastly, to further optimize CO2 absorption, NiNPs were added to each test solution. Seawater with MEA and NiNPs absorbed only 1.15 % less than its DI water counterpart, confirming seawater’s potential as amine-based solvent for industrial CO2 capture applications.

Research biases create overrepresented “poster children” of marine invasion ecology

AbstractNonnative marine species are increasingly recognized as a threat to the world's oceans, yet are poorly understood relative to their terrestrial and freshwater counterparts. Here, we conducted a systematic review of 2,203 research articles on nonnative marine animals to determine whether the current literature reflects the known diversity of marine invaders, how much we know about these species, and how frequently their impacts are measured. We found that only 39% of nonnative animals listed in the World Register of Introduced Marine Species appeared in the peer‐reviewed English literature. Of those, fewer than half were the subject of more than one study. There is currently little focus on the consequences of marine introductions: only 9.9% of studies quantified the impact of nonnative species. Finally, our knowledge of nonnative marine species is heavily limited by strong taxonomic biases consistent across all phyla, resulting in one or two disproportionately well‐studied representatives for each phylum, which we refer to as the “poster children” of invasion. These gaps in the literature make it difficult to effectively triage the most detrimental invasive species for management and illustrate the challenges in achieving the global biodiversity goals of preventing and managing the introduction and establishment of invasive species.

Nutritional evaluation of some economically important marine and freshwater mollusc species of Bangladesh

Molluscs are the most important resources among all the seafood items in South-East Asian countries. However, very little information available on nutritional value of molluscs in these regions. In this study, we evaluated the 7 economically important species of molluscs in terms of proximate composition, amino acids profile, fatty acids profile, cholesterol and heavy metal contents in the bivalves (mussels, oysters, clams and cockles) and univalve (snail) collected from freshwater and marine environments of Bangladesh. The results of the proximate analyses revealed that significantly higher amount of crude protein contents were present in marine water oysters, clams and cockles (59.3 ± 0.3 to 75.4 ± 0.2%) than the freshwater mussels and snail (36.9 ± 0.4 to 49.6 ± 0.6%) on dry matter basis. However, carbohydrate contents were significantly higher in freshwater mussels and snail (30.2 ± 0.9 to 57.3 ± 0.2%) compared to the marine water bivalves (8.1 ± 0.4 to 20.2 ± 0.6%). Crude lipid contents were ranged from 2.5 ± 0.2 to 11.2 ± 0.1% and ash from 11.4 ± 0.1 to 16.8 ± 0.6% among the bivalves and snail species. The amino acid contents were comparatively higher in marine water bivalves than their freshwater counterparts. Saturated fatty acid contents were found to be higher in marine water bivalves than the freshwater mollusc species. The results also show that the omega-3 (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) fatty acids were comparatively higher in oysters, clams and cockles in marine water than those in freshwater mussels and snail. However, omega-6 fatty acids like linoleic acid (LA), α- linolenic acid (ALA) and arachidonic acid (ARA) were higher in freshwater mussels and snail than in the marine bivalves. The n-3/n-6 ratio were significantly higher in oysters and cockle species than the other groups of bivalves and snail. The index of atherogenicity and index of thrombogenicity of the mollusc species ranged from 0.74 ± 0.1 to 1.74 ± 0.2 and 0.5 ± 0.1 to 2.6 ± 0.2, respectively. The results show that marine water bivalves contained higher amount of potassium, sodium, iron, chlorine especially oyster species contained significantly higher iodine than the freshwater bivalves and snail. However, freshwater mussels and snail showed significantly higher amount of zinc contents than the marine bivalves. The heavy metal contents such as arsenic, chromium and mercury were absent or present in very tiny amounts among the mollusc species. Significantly higher amount of cholesterol was present in marine bivalves and freshwater snail species than the freshwater mussels. Overall, the results indicate that marine bivalves can be good sources of high quality protein and lipid especially EPA and DHA. On the other hand, freshwater mussels and snails also could be good sources of protein, LA and ARA but scarcity of EPA and DHA.

Microplastics in some fish species and their environs in Eastern Visayas, Philippines

Microplastics are a global concern, and yet, Philippine studies about it are still wanting. This study investigated microplastic ingestion among detritus-feeding mullet versus the herbivorous rabbitfish, and between freshwater and marine fishes. The first part aimed to compare microplastics in fishes’ guts differing in feeding guilds, individual sizes, and body weights. The second part compared MPs in fishes’ guts and their surrounding waters. Part one revealed that herbivores (58.57%) ingested more MPs than their detritivore-counterparts (30.0%). Pearson correlation, averaging 0.06, suggests a weak correlation between fish weight and MPs amount for both species. Part two showed marine fishes (66.0%) ingested more MPs than its freshwater counterparts (45.0%). A very weak correlation was observed between fish weight and amount of MPs ingested. Fish along the estuary ingested more MPs than those in other stations. No significant differences (p = 0.23) between the MPs in the water samples from each sampling stations was found.

Resequencing and SNP discovery of Amur ide (Leuciscus waleckii) provides insights into local adaptations to extreme environments

Amur ide (Leuciscus waleckii), a Cyprinid species, is broadly distributed in Northeast Asia. Different from its freshwater counterparts, the population in Lake Dali Nor has a strong alkalinity tolerance and can adapt to extremely alkali–saline water with bicarbonate over 50 mmol/L. To uncover the genetic basis of its alkaline adaptation, three populations, including one alkali form from Lake Dali Nor (DL), one freshwater form from its adjacent sister Lake Ganggeng Nor (GG), and one freshwater form from its historical origin, namely, the Songhua River (SH), were analyzed using genome resequencing technology. A total of 679.82 Gb clean data and 38,091,163 high-quality single-nucleotide polymorphism (SNP) loci were detected in the three populations. Nucleotide diversity and population structure analysis revealed that the DL and GG populations have lower nucleotide diversities and different genetic structures than those of the SH population. Selective sweeping showed 21 genes involved in osmoregulatory regulation (DLG1, VIPR1, AKT1, and GNAI1), inflammation and immune responses (DLG1, BRINP1, CTSL, TRAF6, AKT1, STAT3, GNAI1, SEC22b, and PSME4b), and cardiorespiratory development (TRAF6, PSME4b, STAT3, AKT1, and COL9A1) to be associated with alkaline adaption of the DL population. Interestingly, selective pressure (CodeML, MEME, and FEL) methods identified two functional codon sites of VIPR1 to be under positive selection in the DL population. The subsequent 3D protein modeling confirmed that these selected sites will incur changes in protein structure and function in the DL population. In brief, this study provides molecular evidence of population divergence and alkaline adaptation, which will be very useful for revealing the genetic basis of alkaline adaptation in Amur ide.

Aquaculture Applications of the Family Gobiidae


 
 
 
 
 
 
 Marine ornamental fish production is still in its infancy compared with its freshwater counterpart. About 1,800 wild-caught fish species are imported into the United States each year, clear proof of the need for the expansion of marine ornamental production to include new species and families of fish. The family Gobiidae is the fourth most imported family of marine ornamental fish. Gobies can be easily housed with a variety of other species of fish. Several have qualities that lend themselves to aquarium life. Some clean other fish and others sift the sand bed. Many naturally perch on the rockscape or corals, spending their time beautifying their surroundings with their bright colors and intriguing behavior. This 7-page fact sheet written by Jesse Von Linden, Joshua T. Patterson, Cortney L. Ohs, and Matthew A. DiMaggio and published by the UF/IFAS Program in Fisheries and Aquatic Sciences, School of Forest Resources and Conservation provides a brief overview of the family including description and taxonomy, natural history, culture techniques, a bit about disease challenges, and advice on marketing for ornamental Gobids. https://edis.ifas.ufl.edu/fa226
 
 
 
 
 
 

Metagenomics Uncovers a Core SAR11 Population in Brackish Surface Waters of the Baltic Sea

The Baltic Sea represents one of the largest brackish ecosystems where various environmental factors control dynamic seasonal shifts in the structure, diversity, and function of the planktonic microbial communities. In this study, despite seasonal fluctuations, several bacterial populations (<2% of the total OTUs) that are highly dominant (25% of relative abundance) and highly frequently occurring (>85% of occurrence) over four seasons were identified. Mathematical models using occurrence frequency and relative abundance data were able to describe community assembly persisting over time. Further, this work uncovered one of the core bacterial populations phylogenetically affiliated to SAR11 subclade IIIa. The analysis of the hypervariable region of 16S rRNA gene and single copy housekeeping genes recovered from metagenomic datasets suggested that the population was unexpectedly evolutionarily closely related to those inhabiting a mesosaline lacustrine ecosystem rather than other marine/coastal members. Our metagenomic results further revealed that the newly-identified population was the major driver facilitating the seasonal shifts in the overall community structure over the brackish waters of the Baltic Sea. The core community uncovered in this study supports the presence of a brackish water microbiome distinguishable from other marine and freshwater counterparts and will be a useful sentinel for monitoring local/global environmental changes posed on brackish surface waters.

Microbiome of the deep Lake Baikal, a unique oxic bathypelagic habitat

AbstractLake Baikal is the deepest lake in the world. Its depth provides the only bathypelagic (> 1000 m deep) freshwater habitat on Earth and its oxic, ultra‐oligotrophic features make it a freshwater counterpart of the deep ocean. Here we have analyzed metagenomes from 1250 and 1350 m deep samples and built 231 metagenome‐assembled genomes (MAGs). We detected high fractions of Thaumarchaeota (ca. 20% of 16S rRNA reads) and members of the candidate phyla radiation (CPR) (3–4.5%). Among the MAGs, we obtained ammonia‐oxidizing archaea (AOA, Nitrosopumilaceae) and bacteria (AOB, Nitrosomonadaceae), and nitrite‐oxidizers (Nitrospirae) indicating very active nitrification. A new clade of freshwater SAR202 Chloroflexi and methanotrophs (Methyloglobulus) were also remarkably abundant, the latter reflecting a possible role of methane oxidation as well. Novel species of streamlined and cosmopolitan bacteria such as Ca. Fonsibacter or acI Actinobacteria were more abundant at the surface but also present in deep waters. Conversely, CPRs, Myxococcales, Chloroflexi, DPANN (Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanoarchaeota and Nanohaloarchaeota) archaea, or Gammaproteobacteria were found only in bathypelagic samples. We noted various important taxonomic and metabolic differences between deep aphotic region of Lake Baikal and marine waters of similar depth: Betaproteobacteriales, CPR, and DPANN superphylum were only found in bathypelagic Baikal, while Deltaproteobacteria, Gammaproteobacteria, or Alphaproteobacteria prevailed in oceanic samples. The genes mediating ammonia and methane oxidation, aromatic compound degradation, or alkane/methanesulfonate monooxygenases were detected in higher numbers in deep Baikal compared to their oceanic counterparts or its own surface. Overall, depth seems to be less relevant than salinity in configuring the microbial community.

MICROSTRUCTURE INVESTIGATION OF SEAWATER VS. FRESHWATER CEMENT PASTES

Recently, seawater has emerged as viable mixing water for concrete, especially in the case of non-reinforced concrete applications or with the use of non-corrosive reinforcement. Previous studies concerning seawater-mixed concrete mostly revealed an initial slight increase in its strength performance (i.e., till Day 14 following mixing), followed by a strength reduction of 7–15% (i.e., after 28 days or longer) as compared to the conventional freshwater-mixed concrete. With an attempt to explain such observations, this paper aims at comparing the microstructure of freshwater-and seawater-mixed cement pastes. Scanning electron microscopy was utilized to observe the microstructure of freshwater and seawater pastes at Days 3 and 28 following mixing. At Day 3, seawater paste was observed to have more densified microstructure as compared to that of the freshwater counterpart, resulting in relatively higher strength performance. At Day 28, the microstructure was almost similar for the two cement pastes. However, seawater paste was observed to have salt impurities as a result of seawater ions, which possibly cause a slightly lower strength performance as compared to the freshwater paste.

Comparison of nutrient retention efficiency between vertical-flow and floating treatment wetland mesocosms with and without biodegradable plastic

Treatment wetlands are ecological systems that are engineered to improve polluted water quality through macrophyte, soil, and microbial remediation and are used commonly for urban and agricultural runoff treatment. However, constructed wetlands used for marine aquaculture effluent treatments are understudied when compared to their freshwater counterpart. We compared the nutrient retention and the microbial communities of two types of constructed wetland mesocosms, a vertical-flow treatment wetland (VFTW) and floating treatment wetland (FTW) in subtropical south Florida. To enhance nutrient retention efficiency, we implemented biodegradable plastic (polycaprolactone), as an external carbon source and monitored the performance of VFTW and FTW for the treatment of marine aquaculture effluent. Polycaprolactone surface were covered by various cyanobacterial genera including Oscillatoria, Leptolyngbya, Brasilonema, and Trichormus and some plastic-degrading bacteria such as Pseudomonas. The presence of a biodegradable plastic in FTW improved the overall performance of nitrogen removal (nitrite plus nitrate) by 14% through denitrification. The pattern of nutrient removal between two treatment wetland mesocosms were significantly different (p < 0.01), with over 87–91% retention of total nitrogen in VFTW and no retention in FTW, the latter due to poor retention of nitrite plus nitrate and production of organic nitrogen from the system not present in inflow waters. Total phosphorus was retained in both mesocosm types, with higher retention (74–81%) in the VFTW than in the FTW (17–40%). The nutrient retention in VFTW was higher overall compared with FTW mesocosms regardless of biodegradable plastic presence.

Persistence of phylogeographic footprints helps to understand cryptic diversity detected in two marine amphipods widespread in the Mediterranean basin

Amphipods of the genus Gammarus are a vital component of macrozoobenthic communities in European inland and coastal, marine and brackish waters of the Mediterranean and the Black Sea. Exceptional levels of cryptic diversity have been revealed for several widespread freshwater Gammarus species in Europe. No comprehensive assessment has yet been made for brackishwater counterparts, such as Gammarus aequicauda and G. insensibilis, which are among the most widely dispersed members of the so-called “G. locusta group” in the Mediterranean and in the Black Sea. Here we probe the diversity of these morphospecies examining the partitioning of mtDNA and nDNA across multiple populations along their distribution range and discuss it within the regional paleogeographic framework.We gathered molecular data from a collection of 166 individuals of G. aequicauda and G. insensibilis from 47 locations along their distribution range in the Mediterranean including the Black Sea. They were amplified for both mitochondrial COI and 16S rRNA as well as the nuclear 28S rRNA. All five MOTU delimitation methods (ABGD, BIN, bPTP, GMYC single and multiple threshold models) applied revealed deep divergence between Black Sea and Mediterranean populations in both G. aequicauda and G. insensibilis. There were eight distinct MOTUs delimited for G. aequicauda (6–18% K2P) and 4 MOTUs for G. insensibilis (4–14% K2P). No sympatric MOTUs were detected throughout their distribution range. Multimarker time-calibrated phylogeny indicated that divergence of both G. aequicauda and G. insensibilis species complexes started already in the late Oligocene/early Miocene with the split between clades inhabiting eastern and western part of the Mediterranean occurring in both species at the similar time.Our results indicate a high cryptic diversity within Mediterranean brackishwater Gammarus, similar to that observed for freshwater counterparts. Moreover, the phylogenetic history combined with the current geographic distribution indicate that the evolution of both studied Gammarus morphogroups has been strongly connected with the geological events in the Mediterranean Basin and it reflect the turbulent history of the area.

Genetic diversity in fishes is influenced by habitat type and life-history variation.

Populations of fishes are increasingly threatened by over‐exploitation, pollution, habitat destruction, and climate change. In order to better understand the factors that can explain the amount of genetic diversity in wild populations of fishes, we collected estimates of genetic diversity (mean heterozygosity and mean rarefied number of alleles per locus) along with habitat associations, conservation status, and life‐history information for 463 fish species. We ran a series of phylogenetic generalized least squares models to determine which factors influence genetic diversity in fishes after accounting for shared evolutionary history among related taxa. We found that marine fishes had significantly higher genetic diversity than freshwater fishes with marine fishes averaging 11.3 more alleles per locus than their freshwater counterparts. However, contrary to our expectations, genetic diversity was not found to be lower in threatened versus not‐threatened fishes. Finally, we found that both age at maturity and fecundity were negatively related to genetic variation in both marine and freshwater fishes. Our results demonstrate that both life‐history characteristics and habitat play a role in shaping patterns of genetic diversity in fishes and should be considered when prioritizing species for conservation.

Molecular characterization and expression patterns of Nanog gene validating its involvement in the embryonic development and maintenance of spermatogonial stem cells of farmed carp, Labeo rohita

BackgroundThe homeobox containing transcription factor Nanog plays crucial roles in embryonic development/proliferation and/or maintenance of spermatogonial stem cells (SSCs) via interacting with transcription factors such as Oct4 and Sox2 in mammals. However, knowledge of its exact mechanistic pathways remains unexploited. Very little is known about teleost Nanog. Information on the Nanog gene of farmed rohu carp (Labeo rohita) is lacking. We cloned and characterized the Nanog gene of rohu carp to understand the expression pattern in early developmental stages and also deduced the genomic organization including promoter elements.ResultsRohu Nanog (LrNanog) cDNA comprised an open reading frame of 1,161 nucleotides bearing a structural homeodomain; whereas, the genomic structure contained four exons and three introns suggesting that it is homologous to mammalian counterparts. Phylogenetically, it was closely related to freshwater counterparts. Protein sequence (386 AA of 42.65 kDa) comparison revealed its low similarity with other vertebrate counterparts except that of the conserved homeodomain. Tissue distribution analysis revealed the existence of LrNanog transcripts only in adult gonads. The heightened abundances in the ovary and proliferating spermatogonia suggested its participations in maternal inheritance and male germ cell development. The potentiating abundances from fertilized egg onwards peaking at blastula stage vis- à-vis decreasing levels from gastrula stage onwards demonstrated its role in embryonic stem cell development. We also provided evidence of its presence in SSCs by western blotting analysis. Further, the promoter region was characterized, predicting a basal core promoter and other consensus elements.ConclusionThe molecular characterization of LrNanog and its documented expression profiling at transcript and protein levels are indicative of its functional linkage with embryonic/spermatogonial stem cell maintenance. This is the first report of LrNanog genomic organization including its promoter sequence information with predicted regulatory elements of a large-bodied carp species. This will be useful for elucidating its mechanism expression in future. Nanog could be used as a potential biomarker for proliferating carp SSCs.

The development of cellular immune defence in marine medaka Oryzias melastigma

Environmentally induced alterations of the immune system during sensitive developmental stages may manifest as abnormalities in immune organ configuration and/or immune cell differentiation. These not only render the early life stages more vulnerable to pathogens, but may also affect the adult immune competence. Knowledge of these sensitive periods in fish would provide an important prognostic/diagnostic tool for aquatic risk assessment of immunotoxicants. The marine medaka Oryzias melastigma is an emerging seawater fish model for immunotoxicology. Here, the presence and onset of four potentially sensitive periods during the development of innate and adaptive cellular immune defence were revealed in O. melastigma: 1.) initiation of phagocyte differentiation, 2.) migration and expansion of lymphoid progenitor cells, 3.) colonization of immune organs through lymphocyte progenitors and 4.) establishment of immune competence in the thymus. By using an established bacterial resistance assay for O. melastigma, larval immune competence (from newly hatched 1dph to 14dph) was found concomitantly increased with advanced thymus development and the presence of mature T-lymphocytes. A comparison between the marine O. melastigma and the freshwater counterpart Oryzias latipes disclosed a disparity in the T-lymphocyte maturation pattern, resulting in differences in the length of T-lymphocyte maturation. The results shed light on a potential difference between seawater and freshwater medaka in their sensitivity to environmental immunotoxicants. Further, medaka immune system development was compared and contrasted to economically important fish. The present study has provided a strong scientific basis for advanced investigation of critical windows for immune system development in fish.