Important Fish Species Research Articles

Aeromonas hydrophila causes ferroptotic damage via its secreted effectors targeting splenic macrophages in teleost

Aeromonas hydrophila (A. hydrophila) is a well-known pathogen leading to huge economic losses in aquaculture. Using grass carp, a commercially important fish species, as a model, we found that A. hydrophila decreased fish survival, caused ferrugination and induced lipid peroxidation damage especially in spleen. Further investigations revealed that the bacteria particularly utilized secretory effectors to trigger ferroptosis by specially targeting splenic macrophages in which A. hydrophila effectors significantly elevated intracellular Fe2+ levels, initiated lipid peroxidation, and dampened mitochondrial membrane potential. Mechanistically, bacterial effectors could degrade ferritin and ferroportin1 via autophagy and proteasome pathways respectively, leading intracellular iron accumulation. Moreover, the effectors promoted glutathione (GSH) depletion via their stimulatory effects on ROS generation in splenic macrophages, suggesting that A. hydrophila effectors might suppress GSH-dependent cellular antioxidant system. Finally, an in vivo study uncovered that ferroptosis inhibitors significantly improve fish survival, ameliorated oxidative damage, and reduced bacterial load in spleen. Our data highlight the ferroptotic damage of A. hydrophila via its effectors in teleost and suggest ferroptosis is a potential target for fish against A. hydrophila infection.

Black Soldier Fly (Hermetia illucens) Meal as Direct Replacement of Complex Fish Feed for Rainbow Trout (Oncorhynchus mykiss) and African Catfish (Clarias gariepinus).

In the experiments, defatted black soldier fly meal reared on vegetable byproducts was used in the fry rearing of two economically important fish species, African catfish and rainbow trout. Both fish species were reared in a recirculation system and 0-33-66-100% of the complex fry feed was replaced by a defatted prepupae meal of black soldier flies during a 28-day feeding experiment. African catfish was reared at 25 ± 1 °C while rainbow trout was reared at 12 ± 1 °C. The results showed that the growth of African catfish was not significantly reduced when 66% of the feed was replaced by soldier fly meal (mean weight in the control fish group at the end of the experiment was 0.4632 ± 0.2469 g, while the 66% group resulted mean weights of 0.4150 ± 0.1886 g) and the survival did not show any statistically different results (mean survival in control group was 57.48 ± 13.76% while it was 56.6 ± 7.763% in the 66% group). In the case of rainbow trout, replacing the feed entirely with insect meal did not cause a decrease in weight gain (final mean weight in the control group was measured at 1.9640 ± 0.4154 g, while in the group consuming only insect meal, it was 1.9410 ± 0.4248 g) or in survival (in the control group 98.5%, while in the group consuming only insect meal 99.5%). All these preliminary results indicate that black soldier fly meal can be used directly as a nursery feed in fish farming as a partial or total replacement of complete feeds. The results showed that black soldier fly meal could replace 66% of the complex brood feed of African catfish and up to 100% of rainbow trout feed without deterioration of production results. Our experiments have therefore opened the way for further experiments on insect meal in larval rearing.

Extinction risks and threats facing the freshwater fishes of Britain

Abstract Extinctions occur naturally in all environments, but rates have accelerated rapidly during the Anthropocene, especially in fresh water. Despite supporting many fish species of conservation importance, there has never been a formal assessment of their extinction risks in Britain, which has impeded their inclusion in relevant legislation and policy. This study therefore used the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species™ Categories and Criteria to conduct the first systematic assessment of the extinction risks and threats facing the native freshwater and diadromous fishes of Britain. In addition, national assessments were produced for England, Scotland and Wales, reflecting the level at which environmental policy decisions are taken in Britain. Seven species were categorized as being threatened with extinction at the regional level, with European eel Anguilla anguilla and allis shad Alosa alosa classified as Critically Endangered, Atlantic salmon Salmo salar, vendace Coregonus albula and European whitefish Coregonus lavaretus classified as Endangered, and Arctic charr Salvelinus alpinus and twaite shad Alosa fallax classified as Vulnerable. In addition, burbot Lota lota was classified as Regionally Extinct, ferox trout Salmo ferox was categorized as Data Deficient, and 25 species were categorized as Least Concern. European sturgeon Acipenser sturio and houting Coregonus oxyrinchus, although probably native, qualified as only vagrants in fresh water, so were categorized as Not Applicable. The assessments provide objective baselines against which future changes can be determined, and a key evidence base to support policy and management decisions for the conservation of freshwater and diadromous fish species and their habitats in Britain. It is recommended that the assessments are repeated every 10 years, which would enable changes in conservation status, the effectiveness of policies and where targeted interventions may be required to be examined using the Red List Index.

Climate variability hypothesis is partially supported in thermal limits of juvenile Northwest Atlantic coastal fishes.

As ocean warming continues to impact marine species globally, there is a need to understand the mechanisms underlying shifts in abundance and distribution. There is growing evidence that upper and lower temperature tolerances rather than mean preferences explain range shifts, but the full thermal niche is unknown for many marine species and observational data are often ill-suited to estimate the upper and lower thermal tolerances. We quantified critical thermal maximum (CTmax ) and critical thermal minimum (CTmin ) using standard methods to quantify temperature limits and thermal ranges of 14 economically and ecologically important juvenile fish species on the US Atlantic coast. We then tested the climate variability hypothesis (CVH), which states that higher-latitude species should have a wider temperature tolerance due to higher climatic variability closer to the poles. Our findings generally support the CVH in the juvenile fishes that we evaluated. However, low-latitude species were not uniformly stenothermal. Rather, species with median occurrences across a wide range of latitudes had wide temperature tolerances, but only the tropical species we tested had more narrow ranges. These findings suggest that quantifying temperature tolerances may be used to predict which low-latitude species are most likely to shift in response to warming water and those that may be more sensitive to climate change in this region.

Edwardsiella tarda in Tambaqui (Colossoma macropomum): A Pathogenicity, Antimicrobial Susceptibility, and Genetic Analysis of Brazilian Isolates.

Edwardsiella tarda is a crucial pathogenic bacterium in tropical aquaculture. This bacterium was recently isolated from tambaqui (Colossoma macropomum), a commercially important fish species in Brazil. This study assessed the antimicrobial susceptibility, pathogenicity, and genetic diversity of the tambaqui-derived E. tarda isolates. Fourteen bacterial isolates isolated from tambaqui were identified as E. tarda by using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry and dnaJ gene sequencing. Antimicrobial susceptibility tests were conducted against seven drugs using the disc diffusion assay. The pathogenicity test conducted by intraperitoneal injection of 2.4 × 107 colony-forming units (CFU) fish-1 of E. tarda (ED38-17) into tambaqui juveniles eventually revealed that neither clinical signs nor death were present. However, splenomegaly and whitish areas in the spleen and kidneys were observed. The histological investigation also revealed granulomatous splenitis, nephritis, and hepatitis occurring internally. Repetitive extragenic palindromic-PCR fingerprinting separated the 14 isolates into three genetic groups. The antibiogram revealed that all E. tarda isolates were wild-type (WT) to florfenicol (FLO), norfloxacin (NOR), neomycin (NEO), erythromycin (ERY), and oxytetracycline (OXY); however, some were non-wild-type to sulfamethoxazole/trimethoprim (7.1%) and amoxicillin (21.4%). Therefore, through experimental infection, E. tarda ED38-17 could induce pathogenic effects in C. macropomum. Additionally, three distinct genetic types were found, and the E. tarda isolates were WT to FLO, NOR, NEO, ERY, and OXY. These findings raise awareness of a bacteria causing unseen lesions, a pathogen that will potentially impact tambaqui aquaculture in the future.

Effect of feed enriched by products formulated from coconut water, palm sap sugar, and mushroom on the chemical composition of feed and carcass, growth performance, body indices, and gut micromorphology of giant gourami, Osphronemus goramy (Lacepède, 1801), juveniles.

Background: Giant gourami, Osphronemus goramy is the most important freshwater fish species produced by aquaculture in Indonesia. This study aimed to the effects of various newly formulated products on the amino acid composition of the diet and whole-body carcass, and to analyse the growth coefficient, body indices, and gut micromorphology. Methods: One hundred gram of palm sap sugar was cooked in 1.1 litre of fresh water for fifteen minutes, to create 1 litre of 11% palm sap sugar solution (after some of it had been boiled off). Two litres of coconut water were then mixed with the litre of palm sugar solution. One litre of this product was added in turn to 2 g of Aspergillus niger (CP2), 2 g of Rhizopus oligosporus (CP3), and 2 g of Saccharomyces cerevisiae (CP4), while freshwater was used as a control (labeled CP1). Aquafeed was added to CP1, CP2, CP3, and CP4, to make diets labeled KP1, KP2, KP3, and KP4. The dosage was 150 ml/kg of feed. Juvenile giant gourami (initial weight 50±0.25 g and length 13.2±0.07 cm) were reared in triplicate net frames (2×1×1 m; water volume 1.5 m 3) in a freshwater concrete pond with a stocking density of 30 juveniles/net. Results: The results supported our hypothesis that different product formulations have a significant effect (P < 0.05) on aquafeed nutrition and the whole-body carcass, growth coefficient, feed utilization, body indices, and gut micromorphology of giant gourami juveniles. The thermal growth coefficient strongly correlated with the daily growth coefficient (r 2 = 92%), condition factor (r 2 = 77%), protein efficiency ratio (r 2 = 75%), while a moderate relationship with the feed intake ( r 2 = 69%). Conclusions: Diet KP3 contains higher total amino acids in diets and carcasses and leads to feed efficiency and better growth for giant gourami.

A Comparative Study of the Nutritional Composition, Fatty Acid Profiles and Organoleptic Evaluation of Clarias gariepinus (African Catfish) and Oreochromis nilotius (Nile Tilapia) Raised under Wild and Pond-Cultured Systems

Clarias gariepinus and Oreochromis niloticus are two important fish species that are widely consumed in many parts of the world. This study investigated the nutritional composition, fatty acid profiles and organoleptic evaluation of these two fish species raised under wild and pond-cultured systems. Five samples each of the species were randomly collected from Ashaka Town, Delta State, Nigeria. The proximate composition was determined using standard AOAC methods. Fatty acid profiles were analyzed using gas chromatography, while organoleptic evaluation was conducted using twenty panelists. C. gariepinus exhibited significantly lower (p&lt;0.05) moisture content (77.76±0.45 and 79.06±0.36) and higher crude fat content (1.75±0.14 and 1.32±0.33) respectively in both wild and pond-cultured species compared to O. niloticus. C. gariepinus had higher protein content than O. niloticus in both wild and pond-cultured species. The carbohydrate content of O. niloticus was significantly higher (p&lt;0.05) than in C. gariepinus, while the ash content of C. gariepinus and O. niloticus was not significantly different (p&gt;0.05). Both species exhibited variations in their fatty acid profiles, with significant differences (p&lt;0.05) observed in the levels of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs). All wild and pond- cultured fish species had the same pattern of fatty acid composition SFAs &gt; PUFAs &gt; MUFAs except wild C. gariepinus with SFAs &gt; MUFAs &gt; PUFAs pattern. Pond-cultured O. niloticus and C. gariepinus had higher total n-3 PUFAs and lower n-6 PUFAs values while wild O. niloticus and C. gariepinus had lower n-3 PUFAs and higher n-6 PUFAs values. This difference was statistically significant (p&lt;0.05). The results indicated significant organoleptic differences (p&lt;0.05) in consumer preference between wild and pond-cultured C. gariepinus, however, O. niloticus was found to be liked similarly regardless of its source (p&gt;0.05). These findings suggest that the type of habitat, fish species and diets have significant impacts on the proximate composition, fatty acid profiles and organoleptic attributes of fishes.

Intermittent hypoxia differentially affects metabolic and oxidative stress responses in two species of cyprinid fish.

Oxygen fluctuations are common in freshwater habitats and aquaculture and can impact ecologically and economically important species of fish like cyprinids. To gain insight into the physiological responses to oxygen fluctuations in two common cyprinid species, we evaluated the impact of short-term intermittent hypoxia on oxidative stress and metabolic parameters (including levels of prooxidants and oxidative lesions, antioxidants, mitochondrial enzyme activities, mitochondrial swelling, markers of apoptosis, autophagy and cytotoxicity) in silver carp Hypophthalmichthys molitrix and gibel carp Carassius gibelio. During hypoxia, gibel carp showed higher baseline levels of antioxidants and less pronounced changes in oxidative and metabolic biomarkers in the tissues than silver carp. Reoxygenation led to a strong shift in metabolic and redox-related parameters and tissue damage, indicating high cost of post-hypoxic recovery in both species. Species-specific differences were more strongly associated with oxidative stress status, whereas metabolic indices and nitrosative stress parameters were more relevant to the response to hypoxia-reoxygenation. Overall, regulation of energy metabolism appears more critical than the regulation of antioxidants in the response to oxygen deprivation in the studied species. Further research is needed to establish whether prioritizing metabolic over redox regulation during hypoxia-reoxygenation stress is common in freshwater cyprinids.

Are fishes selecting the trash they eat? Influence of feeding mode and habitat on microplastic uptake in an artificial reef complex (ARC)

Every year, coastal countries generate ∼275 million tons of plastic, and the oceans receive from 4.8 to 12.7 million tons3. Pollution by synthetic polymers is even more problematic for the environment when this material is fragmented into small portions, forming microplastics (MPs). In the present study, we analyze the selection of MPs by the ichthyofauna based on the availability of the morphotypes and polymeric composition of microplastic in the environment and compare the amount of MP in surface water, water column, sediments and fish in different organs, trophic categories, habitats and areas with and without artificial reefs. In order to achieve this goal, the shape, color, abundance and chemical composition of MPs in the digestive tract and gills of 18 fish species in artificial reefs area and control area, were evaluated. A total of 216 fish were analyzed, and 149 (60 %) had MPs in at least one organ and showed a mean concentration of 1.55 ± 3.31 MPs/g. Of the 18 fish species collected in the reef complex area, 17 (94 %) included individuals with at least one MP in digestive tract or gills. Four species showed the higher selectivity of MP types, colors, and polymers. More MPs were found in the fish, surface water, water column and sediment in the artificial reef area compared to the control areas. This is the first evidence of MP selection by commercially important fish species in artificial marine structures worldwide. These results provide useful information on MP pollution in RAs and highlight yet another issue that must be considered in the management of fisheries resources in the region and in other reef complexes around the world.

Length-weight relationship of six freshwater fish species from Wular Lake - A Ramsar site in Kashmir Himalaya, India

Aim: This study was undertaken to understand the length weight relation of six freshwater fish species from Wular Lake. Methodology: A total of 303 specimen belonging to two families (Cyprinidae and Nemacheilidae) and four genera (Schizothorax, Triplophysa, Crossocheilus, Puntius) from Wular Lake were collected from five different sites with the help of local skilled fishermen using cast nets and traditional nets. Total length and weight were measured to the closest 0.1 mm and 0.01 g employing a digital caliper and weighing balance, respectively. Results: The values of the exponent b in length-weight relationship was recorded as 2.05 for Triplophysa marmorata, 0.31 for Crossocheilus diplochilus, 0.12 for Pethia conchonius, 4.14 for Schizothorax niger, 2.58 for Schizothorax esocinus and 4.93 for Schizothorax curvifrons respectively. These results provide the primary basic information on length-weight parameters of these commercially important fish species from Wular Lake. Interpretation: Length-weight relationship can form a baseline data that can be further employed to study the growth pattern of fish species in the lake. This would help in the development of a strategy for conservation of natural stocks of these endemic fish species in Wular Lake. Key words: Ecological, Freshwater, Ramsar, Schizothorax, Wular Lake

Comprehensive transcripts analysis based on single-molecule real-time sequencing and Illumina sequencing provides insights into the mining of Toll-like receptor family in Schizothorax lissolabiatus.

Schizothorax lissolabiatus is an economically important cold-water fish species in southwestern China. Because of water pollution and habitat destruction, the number of wild populations has dramatically decreased. In this study, we used PacBio single-molecule real-time (SMRT) sequencing and Illumina sequencing to generate the first full-length transcriptome and transcriptome, respectively. A total of 19310 polished consensus reads (PC) were obtained, with an average length of 1379 bp and an N50 length of 1485 bp. Meanwhile, 12253 transcripts were successfully annotated as known homologous genes. The pathway annotation indicated that the enrichment and expression of most genes were mainly related to membrane, signal transduction and binding, and immune response. Furthermore, we identified 16 Toll-like receptors (TLRs) by mining the data from the transcripts. Phylogeny analysis showed that S. lissolabiatus TLR genes (slTLRs) supported the classification of TLRs into six families as in other vertebrates. Selection pressure analyses showed that 16 slTLRs revealed purification selection at the overall evolutionary selection. Further, positive selection signals were still detected in eight slTLRs, and most of the positive selection sites were located in the leucine-rich repeat region (LRR domain) associated with the recognition of pathogenic microorganisms, indicating that the function of these slTLR genes may be affected. Tissue specific expression analysis showed all slTLRs are present in kidney, spleen and liver but the relative expression varied among tissues. In conclusion, this study not only provided a valuable resource of transcripts for further research on S. lissolabiatus, but also contributed to improve the current understanding of the evolutionary history of immune-related genes and the TLR gene family in S. lissolabiatus.

Identification, characterization, and agglutinating activity of a novel C-type lectin domain family 3 member B (CLEC3B) discovered in golden pompano, Trachinotus ovatus.

The lectins are a large family of carbohydrate-binding proteins that play important roles in the innate immune response of various organisms. Although C-type lectin domain family 3 member B (CLEC3B), an important member of C-type lectin, has been well documented in humans and several other higher vertebrates, little is currently known about this molecule in economically important marine fish species. In this study, through transcriptomic and BLAST screening, a novel CLEC3B gene was identified in the golden pompano (Trachinotus ovatus). The T. ovatus CLEC3B (ToCLEC3B) was subsequently characterized by bioinformatic analysis and compared with those reported in other species. In addition, the expression patterns of ToCLEC3B in different tissues under normal condition and at different times post pathogen challenge were assessed. Furthermore, the agglutinating activity of ToCLEC3B with and without Ca2+ against different bacteria and blood cells of donor species were verified using the recombinant T. ovatus CLEC3B (rToCLEC3B). Our results demonstrated that ToCLEC3B is a Ca2+-dependent galactose-binding lectin with a single copy of carbohydrate recognition domain (CRD). Similar to CLEC3B reported in other species, the CRD domain of ToCLEC3B consists of two α-helices, six β-sheets, and four loops, forming two Ca2+- and a galactose-binding sites. According to the phylogenetic analysis, the ToCLEC3B was highly similar (similarity at 95.00%) to that of its relative, the greater amberjack (Seriola dumerili). The expression of ToCLEC3B was detected in all tissues examined under normal condition and was significantly up-regulated by injection of pathogenic microbes. In addition, the rToCLEC3B exhibited strong agglutinating activity against different bacteria and blood cells of donor species in the presence of Ca2+. Our results indicate that ToCLEC3B is a constitutive and inducible acute-phase immune factor in the host's innate immune response of T. ovatus.

Patterns and Trends in Chlorophyll‐a Concentration and Phytoplankton Phenology in the Biogeographical Regions of Southwestern Atlantic

AbstractThe Southwestern Atlantic Ocean (SWA), is considered one of the most productive areas of the world, with a high abundance of ecologically and economically important fish species. Yet, the biological responses of this complex region to climate variability are still uncertain. Here, using 24 years of satellite‐derived Chl‐a data, we classified the SWA into 9 spatially coherent regions based on the temporal variability of Chl‐a concentration, as revealed by SOM (Self‐Organizing Maps) analysis. These biogeographical regions were the basis of a regional trend analysis in phytoplankton biomass, phenological indices, and environmental forcing variations. A general positive trend in phytoplankton concentration was observed, especially in the highly productive areas of the northern shelf‐break, where phytoplankton biomass has increased at a rate of up to 0.42 ± 0.04 mg m−3 per decade. Significant positive trends in sea surface temperature were observed in 4 of the 9 regions (0.08–0.26 °C decade−1) and shoaling of the mixing layer depth in 5 of the 9 regions (−1.50 to −3.36 m decade−1). In addition to the generally positive trend in Chl‐a, the most conspicuous change in the phytoplankton temporal patterns in the SWA is a delay in the autumn bloom (between 15 ± 3 and 24 ± 6 days decade−1, depending on the region). The observed variations in phytoplankton phenology could be attributed to climate‐induced ocean warming and extended stratification period. Our results provided further evidence of the impact of climate change on these highly productive waters.

English

Genetic integrity of commercially important fish species is being compromised due to ongoing anthropogenic interventions. Hitherto, there are limited number of studies addressing the questions related to population structure of dwindling fish populations. Studies were undertaken to assess the genetic status of Bagarius bagarius populations from Indus River System by using five microsatellite DNA markers. DNA was extracted by PCI method and genotypic data was generated by PCR amplification of targeted loci. Results showed low-to-moderate level of genetic diversity in terms of number of alleles (Na), allelic richness (Ar), effective number of alleles (Nae) and heterozygosity (Ho and He). The observed heterozygosity (Ho) declined in comparison to the expected heterozygosity (He) in the wild stocks, with mean values ranging from 0.667 to 0.718 and 0.786 to 0.853, respectively. Significant deviation from H-W test was observed in 6 out of 25 tests. The population differentiation (FST) estimates were low (0.0013 to 0.0367) and insignificant. AMOVA showed that 62.38% genetic variation existed within individuals while 4.93% between populations. All of the populations were divided into two clusters by the UPGMA dendrogram constructed for genetic relatedness analysis. The study will be helpful in understanding the impact of genetic integrity on fish populations and, for sustainable management of fish genetic resources

March2 negatively regulates antiviral immune response by targeting tbk1 in grass carp (Ctenopharyngodon idella).

Grass carp is one of the most economically important fish species. Hemorrhagic diseases caused by grass carp reovirus (GCRV) can seriously damage the economic yield of grass carp. Therefore, antiviral research on grass carp is urgently needed. Membrane-associated RING-CH2 (MARCH2) negatively regulates the innate immune response in mice. However, little is known about the role of march2 in the antiviral innate immune response in teleost fish. Our present study showed that march2 has high homology in grass carp, its orthologs, and mammals, and has the same amino acid sequence in grass carp and crucian carp. Overexpression of Cimarch2 (Ctenopharyngodon idella march2) significantly inhibited interferon (IFN) activation induced by Polyinosinic-polycytidylic acid (poly I: C), spring viremia of carp virus (SVCV), and GCRV. However, knocking down Cimarch2 enhanced the activation of IFN induced by poly I: C, SVCV, and GCRV. Overexpression of Cimarch2 can promotes viral replication. Mechanistically, Cimarch2 tightly bound to TANK-binding kinase 1 (tbk1) and downregulated tbk1 through the proteasome pathway. Our results demonstrated the potential role of Cimarch2 in the antiviral breeding of grass carp.

Population connectivity and dynamics in early-life stages of Atlantic fish communities

IntroductionMany hypotheses have been suggested to explain recruitment variability in fish populations. These can generally be divided into three groups, either related to: larval food limitation, predation, or transport. Transport mechanisms are central for reproduction in pelagic species and three physical processes, concentration, enrichment, and retention are commonly referred as the fundamental “ocean triads” sustaining larval survival and thus success of reproductive effort. The aim of this study is to investigate linkages between primary production and transport processes of eggs and larvae for the most important commercial fish species in the Atlantic Ocean.MethodsWe simulated eggs and larvae dispersion using an individualbased model and integrating information on the fish ecology of the major fish stocks. Our work included a review on spawning ground locations, spawning time, eggs and larvae duration. Simulations were performed over a 10-year time period for 113 stocks (17 species) in order to assess variability in dispersion and common trends and factors affecting transport.ResultsThe level of primary production from initial to final position, i.e. from spawning to larval settlement, increased for some stocks (n=31), for others it declined (n=64), and for a smaller group (n=18) there was no substantial changes in level of primary production.DiscussionThis result implies that larval transport will not necessarily introduce larvae into areas of enhanced food availability expressed by the primary production at the site. These findings thus suggest marked differences in how physical and biological processes interact in the early life of major fish groups in the Atlantic Ocean. The results provide a further insight into fish larval drift and the potential role of primary production in emergence of spawning strategies.

Molecular characterization and expression profiling of foxl2 in zig-zag eel (Mastacembelus armatus)

Zig-zag eel (Mastacembelus armatus) is an important aquaculture fish species that is very popular as a table fish. However, the genetic regulation of gonad development and differentiation is not well understood. Foxl2 has been demonstrated to play a critical role in gonad development and differentiation in fish. In our study, foxl2 was first cloned and characterized from the gonads of zig-zag eel. The complete open reading frame sequence of foxl2 was 918 bp, encoding 305 amino acids. Multiple sequence alignments revealed that foxl2 gene was highly conserved in fish, especially in forkhead domain. Tissue distribution analysis revealed that foxl2 expressed mainly in ovary, gill, eye and brain. At five different embryonic stages, foxl2 mainly expressed at the gastrula stage. Besides, gonad expression pattern revealed the expression of foxl2 increased to peak in stage V of the ovary, while the expression level was highest in stage III of the testis. These results indicated that the foxl2 might play an important role in gonadal development of zig-zag eel.

DNA barcoding of five economically important freshwater fish species from the Nile River, Sudan

The study was conducted to barcode five freshwater fish species obtained from Nile River tributaries (the Atbara River and the Blue Nile), in March 2019, using analysis of partial CO1 gene sequences. Fish samples were identified morphologically as Nile perch Lates niloticus, Nile labeo Labeo vulgaris, North African catfish Clarias gariepinus, Cornish jack Mormyrops anguilloides and bebe mormyrid Hyperopisus bebe. Following DNA extraction, universal primers were used for amplification of the CO1 barcode region. The PCR products were sequenced and used for molecular identification. Each sequence was matched to corresponding GenBank sequences using the BLAST technique. Sequences of all specimens were aligned along with the GenBank published sequences and polymorphic sites were identified. The analysed sequences were uploaded to GenBank under the accession numbers OL804282– OL804286. The analysed partial CO1 barcode gene showed a readable length of ∼548–669 base pairs. Sequence comparison of CO1 gene sequences with sequences published in GenBank revealed 99.27–100% identities at the species level. Therefore, the CO1 barcodes accurately identified all the studied freshwater fishes. This is the first molecular DNA barcode characterisation of freshwater fish species found in Sudan. The fish CO1 gene sequences revealed in this study will serve as barcode references for future characterisations of Nile River fishes.

Per- and Polyfluoroalkyl Substances and Mercury in Arctic Alaska Coastal Fish of Subsistence Importance.

Per- and polyfluoroalkyl substances (PFAS) and mercury (Hg) are harmful compounds that are widely present in the environment, partly due to spills and atmospheric pollution. The presence of PFAS and Hg in the tissues of animals that are harvested by rural and Indigenous Alaskans is of great concern, yet fish in Arctic Alaska have not previously been assessed for concentrations of PFAS. Fish species of subsistence and recreational importance were collected from nearshore Beaufort and Chukchi Sea, Alaska habitats and assessed for PFAS and total mercury concentrations [THg]. We found multiple PFAS compounds present at low levels (<3 μg/kg) in the muscle tissue of inconnu, broad whitefish, Dolly Varden char, Arctic flounder, saffron cod, humpback whitefish, and least cisco. In addition, [THg] levels in these fish were well below levels triggering local fish consumption guidelines (<170 μg/kg). These initial results indicate no evidence of the Alaska Arctic nearshore fish species examined as an avenue of PFAS or Hg exposure to people who harvest them. However, sources and trends of these contaminants in the Arctic require further investigation. Environ Toxicol Chem 2023;00:1-7. © 2023 SETAC.

Heavy metals accumulation in some important fish species cultured in commercial fish farm of Natore, Bangladesh and possible health risk evaluation

Heavy metal contamination in aquatic environment is a serious concern throughout the world. Metal contamination are responsible for the accumulation of metals within the fish body. And, consumption of these contaminated fish possess serious threat to the associated consumers. In this current study, five commonly cultured freshwater fishes (rui, Labeo rohita; mrigal, Cirrhinus mrigala; silver carp, Hypophthalmicthys molitrix; bata, Labeo bata, and sarpunti, Puntius sarana) were collected from a commercial fish farm of Natore district, Bangladesh to analyze metals levels in edible portion (flesh), and to assess the associated human health risk. Several heavy metals such as zinc (Zn); cadmium (Cd); chromium (Cr); arsenic (As); lead (Pb); and nickel (Ni) were analyzed by a flame atomic absorption spectrophotometer. Besides, the target hazard quotient (THQ), hazard index (HI) and lifetime cancer risk (TR) were also estimated for assessing the associated human health risk. In this study, concentrations of Zn, Cd, Cr, As, Pb and Ni in different fish species were found 6.36 ± 1.48 to 13.31 ± 1.33; 0.017 ± 0.01 to 0.049 ± 0.02; 0.654 ± 0.04; 0.015 ± 0.01 to 0.033 ± 0.01; 0.534 ± 0.11 and 0.08 ± 0.05, respectively. All the analyzed values were within the recommended level except Cr in C. mrigala. The THQ, HI and TR values of all the analyzed metals in the fishes indicated that no associated cancer risk resulting from the consumption of those fishes. Therefore, the current study revealed that fishes of the target area might be free from associated metals contamination and hence, might be safe for human consumption.