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Abstract Lanternfish not only boast the most abundant biomass among marine fish species but also play a vital role in marine ecosystems. As one of the lanternfish species with the highest global catch, the skinnycheek lanternfish (Benthosema pterotum) is widely distributed in the Indo-Pacific region, playing a pivotal role in the marine biological pump. This study constructed the first chromosome-level genome of B. pterotum using a combination of short-read sequencing, PacBio, and Hi-C sequencing technologies. The genome size of B. pterotum is 1,272.53 Mb, with a contig N50 of 810 Kb and a scaffold N50 of 54.49 M. More than 99.65% of contigs were successfully anchored onto 24 pseudochromosomes, and 95.7% of BUSCO genes were identified within the genome, demonstrating the high level of completeness in genome assembly. A total of 24,934 protein-coding genes were predicted, of which 99.02% were functionally annotated. The successful assembly of a high-quality genome for B. pterotum provides valuable genetic resources for better understanding its biological characteristics and potentially those of all lanternfish species.

Acanthopagrus latus and Rhabdosargus sarba are economically important marine species along the coast of China, with similar external morphological characteristics and living habits, with wide distribution and strong adaptability. To investigate the molecular mechanisms underlying the adaptive evolution of these two species, we conducted whole-genome resequencing of 10 individuals of both species from the coastal waters of Wuyu Island, Fujian, China, using high-throughput sequencing technology. We obtained SNP, InDel, CNV, and SV variation information and annotated these variations, constructing a genomic variation database for both species. By comparing the resequencing data with reference genomes, we identified 9,829,511 SNP loci in the population of A. latus and 34,051,056 SNP loci in the population of R. sarba. Using whole-genome SNP data, we employed Fst and ROD methods to identify candidate genomic regions under selection. Functional annotation and enrichment analysis using GO and KEGG databases revealed potential adaptive evolution in R. sarba associated with immune response, feeding, growth and development, and locomotion, while A. latus showed potential adaptive evolution associated with immune response, nervous system, growth and development, and metabolism.

Environmental DNA methods have emerged as a promising tool in fish diversity studies and fishery management in various aquatic ecosystems. However, eDNA metabarcoding of fish communities in small hydropower dam reservoirs has received limited attention. In this study, we tested whether eDNA metabarcoding was an appropriate approach for the characterization of fish communities and fishery stock assessment by comparing its results with combined capture-based fishing methods and hydroacoustic surveys, which involved species detection and abundance/biomass evaluation. Our results indicated that the species detection performance of eDNA metabarcoding was basically similar to that of traditional capture-based fishing gear. However, it was also noteworthy that the eDNA method failed to cover all species detected by capture-based method, although some additional species were found. Besides, although we observed a significant correlation between site occurrence and sequence abundance for fishes, an effort to quantitatively establish a correlation between eDNA sequence counts and fish abundance/biomass was unsuccessful. Therefore, our study suggested that eDNA metabarcoding was an important supplementary tool to traditional capture-based fishing methods for the investigation and biomonitoring of fish diversity in small hydropower dam reservoirs. Further studies on the mechanisms of eDNA production, persistence, transportation and degradation in reservoirs might facilitate the interpretation of fish abundance and biomass from eDNA data.

Studies on the demersal fish composition of the East Antarctic nearshore region are very scarce due to the harsh physical geography of the East Antarctic region, which is covered in ice and snow year round, leading to a scarcity of scientific surveys. Based on the data from the bottom trawl survey conducted by the 37–38th Chinese National Antarctic Research Expedition (CHINARE) program in the Cosmonaut Sea, East Antarctica, the species of demersal fishes were identified, and the demersal fish composition and the characteristics of depth distribution were examined and analyzed. The basic biological information of highly abundant species was analyzed. The results from 97 individuals sampled within 30–60° E, south of −65° S, indicate that the fishes belong to 5 orders, 11 families, 19 genera, and 23 species. Most of the species are found in Myctophidae and Bathydraconidae, and the most common species is Macrourus whitsoni (Macrouridae). Macrourus whitsoni and Prionodraco evansii have a high abundance in the survey. Macrourus whitsoni has body lengths of 144–662 mm and body weights of 17.3–1425.1 g, and Prionodraco evansii has body lengths of 90.18–134.33 mm and body weights of 4.9–20.7 g. The length–weight relationships for Macrourus whitsoni and Prionodraco evansii are y=0.00002x2.748 and y=0.000006x3.353, respectively. All the Macrourus whitsoni samples were found in waters deeper than 1000 m, with the highest number of individuals captured at depths of 1500–2000 m. Prionodraco evansii was found only at stations less than 250 m deep. These results complement the demersal fish composition and distribution data of the Cosmonaut Sea, East Antarctica. These data can provide valuable basic information for characterizing regional assemblages and delineating zoogeographic boundaries.

Abstract The Pacific saury (Cololabis saira) is one of the most commercially important pelagic fishes in Asia–Pacific countries. The oceanographic environment, especially the Oyashio Current, significantly affects the distribution of Pacific saury, and may lead to variations in their migration route and the formation of fishing grounds in Japanese coastal region and the high seas. In this study, six oceanographic factors, sea surface temperature (SST), sea surface chlorophyll-a concentration (SSC), sea surface salinity (SSS), sea surface height (SSH), mixed layer depth (MLD), and eddy kinetic energy (EKE), were associated with the monthly catch per unit effort 1 (monthly CPUE1, ton/vessel) and the monthly CPUE2 (ton/day) of Pacific saury from Chinese fishing vessels during the optimal fishing periods (September–November) in 2014–2017. The gradient forest analysis showed that the performance of monthly CPUE1 was higher than monthly CPUE2 and SST was the most important oceanographic factor influencing monthly CPUE1, followed by EKE. The generalized additive model indicated that SST, SSH, and EKE negatively affected monthly CPUE1, whereas SSC, SSS, and MLD induced dome-shaped increases in monthly CPUE1. The distributions of fishing locations are likely to form along Offshore Oyashio current and meanders, especially in October and November. Synchronous trends in the relationship between the intrusion area of the Oyashio and relative abundance variation index suggest that an increase in the intrusion area of the Oyashio causes more Pacific saury to migrate to the Japanese coastal region, and vice versa. These findings extend our understanding of the effects of the oceanographic environment on Pacific saury.

In order to explore the changes in protein expression of large yellow croaker Larimichthys crocea under high temperature stress, isobaric tags for relative and absolute quantitation (iTRAQ) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to perform proteome analysis on the liver between thermal-tolerant and thermal-sensitive groups of large yellow croaker. A total of 23,269 peptides and 3,388 proteins were identified, and 442 differentially expressed proteins (DEPs) were screened, among which 171 proteins were up-regulated and 271 proteins were down-regulated with fold change ≥ 1.2 or

Dongshan Bay is located on the west side of the Taiwan Strait, which had abundant fishery resources in the past. With the increase in fishing pressure, resources have declined. To restore the fishery resources in Dongshan Bay and to increase fishing yield, much enhancement and release work has been carried out in Dongshan Bay. The yellowfin seabream, Acanthopagrus latus (Houttuyn, 1782), is an important enhancement species in Dongshan Bay that is also frequently captured. Due to yearly progress in enhancement and release, it is necessary to study the current status of the genetic diversity of yellowfin seabream in Dongshan Bay. The results show that all yellowfin seabream populations have high genetic diversity, which is mainly related to its breeding habits and growth rate, and this ensures a large recruitment stock in the natural seas. The current population has differentiated from the historical population due to a change in genetic structure, and many historical haplotypes have been lost. The results of this study provide a reference for fishery management departments to formulate management measures and conservation policies specifically for yellowfin seabream. In particular, yellowfin seabream is a hermaphroditic and protandrous species. Targeting an older age group as the main fishing subject is not conducive to its breeding protection and resource growth, and therefore, fishing of an older age group should be restricted in fishery production.

Sexual growth dimorphism is a common phenomenon in teleost fish and has led to many reproductive strategies. Growth- and sex-related gene research in teleost fish would broaden our understanding of the process. In this study, transcriptome sequencing of shortfin scad Decapterus macrosoma was performed for the first time, and a high-quality reference transcriptome was constructed. After identification and assembly, a total of 58,475 nonredundant unigenes were obtained with an N50 length of 2,266 bp, and 28,174 unigenes were successfully annotated with multiple public databases. BUSCO analysis determined a level of 92.9% completeness for the assembled transcriptome. Gene expression analysis revealed 2,345 differentially expressed genes (DEGs) in the female and male D. macrosoma, 1,150 of which were female-biased DEGs, and 1,195 unigenes were male-biased DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the DEGs were mainly involved in biological processes including protein synthesis, growth, rhythmic processes, immune defense, and vitellogenesis. Then, we identified many growth- and sex-related genes, including Igf, Fabps, EF-hand family genes, Zp3, Zp4 and Vg. In addition, a total of 19,573 simple sequence repeats (SSRs) were screened and identified from the transcriptome sequences. The results of this study can provide valuable information on growth- and sex-related genes and facilitate further exploration of the molecular mechanism of sexual growth dimorphism.

Climate change and overfishing have led to the degradation of the quality and stock of Pampus echinogaster. Exploring the genetic structure and local adaptive evolutionary mechanisms of P. echinogaster is crucial for the management of this species. This population genomic study of nine geographical populations of P. echinogaster in China was conducted by specific-locus amplified fragment sequencing (SLAF-seq). A total of 935,215 SLAF tags were obtained, and the average sequencing depth of the SLAF tags was 20.80×. After filtering, a total of 46,187 high-consistency genome-wide single nucleotide polymorphisms (SNPs) were detected. Based on all SNPs, the population size of the nine P. echinogaster geographical populations was large. The Shantou population had the lowest genetic diversity, and the Tianjin population had the highest. Moreover, the population genetic structure based on all SNPs revealed significant gene exchange and no significant genetic differentiation among the nine P. echinogaster geographical populations, probably because of the population expansion after the last glacial period, the lack of balance between migration and genetic drift, and the long-distance diffusion of eggs and larvae. We suspect that variation of material metabolism, ion transfer, breeding, stress response, and inflammatory reactions-related genes were critical for adaptation to spatially heterogeneous temperature selection in natural P. echinogaster populations.

Fisheries management policies (FMPs) have been implemented in coastal countries to ensure a sustainable supply of seafood and the recovery of species diversity. Because of the depletion of fishery stocks, China has introduced a series of FMPs since 1995, including a seasonal fishing moratorium (SFM), a zero-growth strategy, and a minimum mesh size for fishing nets. Here, we built two mass balance models for 1997–2000 (M1997) and 2018–2019 (M2018) using Ecopath with Ecosim 6.6 to illustrate the interannual changes over the past two decades in the East China Sea (ECS). We then simulated two dynamic scenarios from 1997 to 2018, SFM (M2018SFM) and no SFM (M2018no-SFM), to test the role of the SFM under fishing pressure in the ECS. Ecopath showed that the ECS ecosystem is becoming more mature, although it is still unstable, featuring lower total primary production/total respiration, longer cycles, faster organic material circulation speed, and a higher omnivorous degree. This suggests a slow recovery for the ECS ecosystem in the past two decades. The biomass of fish in the ECS—especially the planktivores, dominated by small-sized Benthosema pterotum—significantly increased in M2018 versus M1997, but there were fewer medium- and large-sized fish. The keystone species switched from the planktivores/piscivores dominated by Decapterus maruadsi in M1997 to planktivores in M2018. Ecosim illustrated that the SFM has positive effects on fishery resources recovery, especially for commercial fishes (i.e., large yellow croakers and hairtails), as reflected by the significantly higher predicted biomass of fish in M2018SFM compared to M2018no-SFM and M1997, although the bioaccumulation was consumed by the intense fishing pressure after the SFM. However, the M2018SFM prediction for nektons was still lower than the actual value, especially for planktivores, which display a sharp increase in biomass. This should be partly attributable to the policy of the minimum mesh size (

Decapterus macarellus and D. macrosoma are economically important pelagic fish species that are widely distributed in tropical and subtropical seas. The two species are often mistakenly identified due to their morphological similarities as described in the Chinese literature on fish identification. In this study, D. macarellus and D. macrosoma samples were collected in the Eastern Indian Ocean and the South China Sea and reidentified using morphological and DNA barcoding techniques. The characteristics that distinguish the two species primarily include the scute coverage of the straight portion of the lateral line (the most indicative characteristic for classification), the shape of the predorsal scaled area and its location relative to the middle axis of the eye, and the shapes of the posterior margin of the maxilla and the posterior margin of the operculum. The results revealed a large number of misidentified sequences among the homologous cytochrome oxidase (COI) sequences of the two species in the NCBI database and that the genus Decapterus may include cryptic species. In terms of genetic structure, the Sundaland has not blocked genetic exchange between D. macarellus populations in the South China Sea and the Eastern Indian Ocean, giving rise to a high level of genetic diversity. In this study, we made corrections to the Chinese classification standards for D. macarellus and D. macrosoma and the erroneous reference sequences in the NCBI database, thereby providing accurate reference points for the future exploration of cryptic species in the genus Decapterus.

The southern lesser pomfret (Pampus minor) is an economically important fish, and its numbers are declining because of overfishing and environmental pollution. In addition, owing to the similarities of its external morphological characteristics to other species in the genus Pampus, it is often mistaken for grey pomfret (P. cinereus) or silver pomfret (P. argenteus) juveniles. In this study, the genetic diversity and structure of 264 P. minor individuals from 11 populations in China and Malaysia coastal waters were evaluated for the first time, to the best of our knowledge, using mitochondrial cytochrome b fragments. The results showed that P. minor had moderate haplotype diversity and low nucleotide diversity. Furthermore, two divergent lineages were detected within the populations, but the phylogenetic structure corresponded imperfectly with geographical location; thus, the populations may have diverged in different glacial refugia during the Pleistocene low sea levels. Analysis of molecular variation (AMOVA) showed that genetic variation originated primarily from individuals within the population. Pairwise FST results showed significant differentiation between the Chinese and Malaysian populations. Except for the Xiamen population, which was classified as a marginal population, the genetic differentiation among the other Chinese populations was not significant. During the Late Pleistocene, P. minor experienced a population expansion event starting from the South China Sea refugium that expanded outward, and derivative populations quickly occupied and adapted to the new habitat. The results of this study will provide genetic information for the scientific conservation and management of P. minor resources.

In this study, we conducted two surveys in the central and southern parts of the South China Sea, in autumn 2012 and spring 2013. Six juvenile tuna species were caught in each survey. Gradient forest analysis (GFA) and a generalized additive model (GAM) were used to analyze the relationship between the catch per unit effort (CPUE) for the juvenile tuna species and six sea temperature indices for the South China Sea. In the GFA, the temperature difference between the sea surface and 50 m depth (D50) showed the highest importance to CPUE than other indices, which indicates that D50 was the best predictor of the abundance of juvenile tuna species. The GAM analysis showed that lower deep-water temperature, a shallow mixed layer depth, and a higher difference in temperature between the surface and deeper water were associated with increased CPUE. The results indicate that a relatively rapid decrease in vertical water temperature is favorable for the aggregation of juvenile tuna. These results contribute to understanding of the distribution mechanism of juvenile tuna species in the South China Sea and provide a scientific basis for the rational development and utilization of tuna resources.

The Antarctic krill (Euphausia superba) fishery is the largest fishery in the Southern Ocean, and it has been operating for over 45 years. In the past decade, the spatial distribution of the krill fishery has focused on the Bransfield Strait off the Antarctic Peninsula (subarea 48.1). However, the high fishing effort and climate change have placed great pressure on krill resources in this region, and conservation concerns have been raised. Because aging krill is difficult and uncertain, we developed an integrated size-structured model to estimate the fishing mortality, recruitment and spawning biomass of krill. The results indicated that in 1992–2011, the average spawning biomass of krill ranged from 1.14 × 106 to 1.45 × 106 tons, the estimated biomass of the maximum sustainable yield (BMSY) ranged from 3.96 × 105 to 4.90 × 105 tons and the estimated average recruitment ranged from 2.3 × 1012 to 5.03 × 1012 individuals in the research area. We explored the effect of different data weighting schemes for the length data on the assessment output. However, our estimates also have uncertainties. In addition, an attempt was made to analyze the correlation between model-estimated recruitment and mature biomass with climate change. Future stock assessments of krill resources should be comprehensive and multimethod, and the management of krill resources should be based on science that considers the demand of fishing communities and ecosystem protection.

Fish skin mucus serves as the first line of defense against pathogens and external stressors. To screen thermal-tolerant protein marker in the skin mucus of large yellow croaker Larimichthys crocea, this study conducted proteome analysis on skin mucus between thermal-tolerant and thermal-sensitive groups of large yellow croaker. A total of 396 differentially expressed proteins (DEPs) were identified, among which 215 proteins were upregulated and 181 proteins were downregulated. Ten selected random DEPs were validated using a parallel reaction monitoring (PRM) assay, and the results showed that the proteome analysis results were reliable (r = 0.805, P

The Ninety East Ridge is a submarine north–south oriented volcanic ridge in the eastern Indian Ocean. Surface-layer ichthyoplankton collected in this area from September to October were identified by combined morphological and molecular (DNA barcoding) techniques, and their species composition, diversity, and abundance, and correlations with environmental variables were described. Collections comprised 109 larvae and 507 eggs, which were identified to 37 taxa in 7 orders, 20 families, and 27 genera, and were dominated by the order Perciformes and species Vinciguerria sp., Oxyporhamphus micropterus, and Decapterus macarellus. Species abundances at each station and of each species were relatively low, suggesting that this area or the time of sampling were not of major importance for fish spawning. Waters above Ninety East Ridge had lower species diversity but higher species richness than waters further offshore. A generalized additive model revealed that high abundance of ichthyoplanktonic taxa occurred in areas with low sea surface height and high sea surface salinity, temperature, and chlorophyll a concentration. Of these, sea surface height was most correlated with ichthyoplankton abundance. We provided baseline data on surface-dwelling ichthyoplankton communities in this area to aid in development of pelagic fishery resources in waters around the Ninety East Ridge.

At present, the methods for monitoring the health status of fish mostly utilize blood biochemical indicators. As the blood collection process often causes damage to the fish body (sometimes causing death), the need to develop a noninvasive detection method is urgent. Previous studies have shown that stress indicators can be detected in fish skin mucus or the surrounding water. In this experiment, the level of cortisol in the blood, fish skin mucus, and surrounding water of large yellow croaker was determined at 0, 0.5, 1, 1.5, and 2 h after high-temperature stress induction. Moreover, the levels of malondialdehyde (MDA), immunoglobulin M (IgM), and alkaline phosphatase (AKP) in the serum and fish skin mucus were also measured. The results were as follows: with increasing stress duration, the cortisol levels in the serum, fish skin mucus, and surrounding water increased first and then decreased, all reaching a peak at 1.5 h. The Pearson correlation coefficients for the cortisol levels between the serum and skin mucus, serum and surrounding water, and skin mucus and surrounding water were 0.936, 0.955, and 0.915, respectively, all with a significance level of P < 0.01. The MDA and IgM levels in the serum and fish skin mucus both increased first and then decreased, while the AKP levels in the serum and skin mucus decreased first and then increased. For the MDA, IgM, and AKP levels, the Pearson correlation coefficients between the serum and skin mucus were 0.586, 0.762, and 0.792, respectively, all with a significance level of P < 0.01. According to the results mentioned above, we can use the surrounding water or skin mucus as media to monitor early stress responses in large yellow croaker under high-temperature stress.

A new identification of Gymnothorax minor (Temminck & Schlegel, 1846) is documented based on morphological characteristics and DNA barcoding. Sixty-one individuals of G. minor were collected from the East China Sea and the South China Sea. This species was previously reported as Gymnothorax reticularis Bloch, 1795 in China because of the similarity in external shape and color. Gymnothorax minor can be easily distinguished from G. reticularis by its color pattern of 18–20 irregular dark brown vertical bars and the body having scattered small brown spots. Additionally, the teeth are uniserial on both jaws, and the vertebrae number 137–139. By combining congener sequences of the cytochrome oxidase I (COI) gene from GenBank, two groups were detected among all the COI sequences of the currently named G. minor, which further indicated that two valid species were present based on genetic distance. A divergence also occurred on the number of vertebrae between the northern and southern populations. The phylogenetic and morphological analysis strongly supports that the northern and southern populations of G. minor are two different species. Furthermore, the distribution area of the northern G. minor has expanded southward to 5°15'N in the South China Sea. More specimens of G. minor and G. reticularis are crucial in order to define their geographical distribution boundaries and provide the correct DNA barcoding.

Pampus argenteus is an economically important fish that is often erroneously identified as Pampus echinogaster. No population genetic analyses have been performed on the true P. argenteus species. Here, the mitochondrial control region (CR) was used to evaluate the population genetics and elaborate the historical demography of the Silver pomfret collected from six geographical locations in China, Pakistan, and Kuwait. A high level of genetic diversity was demonstrated in this species. Analysis of molecular variance (AMOVA) revealed that the genetic divergence was mainly derived from within the populations (P < 0.05). A historical demographic analysis indicated that the Silver pomfret experienced a recent population expansion during the late Pleistocene. The phylogeographical structure revealed two obvious lineages that diverged in the late Pleistocene, during which the Silver pomfret populations historically experienced exotic divergence and mixed again with differentiated populations. Currently, Silver pomfret populations have insufficient time to attain migration-drift equilibrium. Population genetic data of the Silver pomfret can provide preliminary genetic knowledge for its fishery management.

Predicting conversion of photosynthetic electron transport to inorganic carbon uptake rates (the so-called electron requirement for carbon fixation, KC) is central to the broad scale deployment of Fast Repetition Rate fluorometry (FRRf) for primary productivity studies. However, reconciling variability of KC over space and time to produce robust algorithms remains challenging, given the large number of factors that influence KC. We have previously shown that light appears to be a proximal driver of Kc in several ocean regions and we therefore examined whether and how light similarly regulated KC variability in the Arctic Ocean, during a summer cruise in 2016. Sampling transited ice-free and ice-covered waters, with temperature, salinity and Chl-a concentrations all higher for the ice-free than ice covered surface waters. Micro- and pico-phytoplankton generally dominated the ice-free and ice-covered waters, respectively. Values of KC, determined from parallel measures of daily integrated electron transport rates and 14C-uptake, were overall lower for the ice-covered vs. ice-free stations. As in our previous studies, KC was strongly linearly correlated to daily PAR (r = 0.68, n = 46, p < 0.001) and this relationship could be further improved (r = 0.84, n = 46, p < 0.001) by separating samples into ice-free (micro-phytoplankton dominated) vs. ice-covered (Nano- and Pico-phytoplankton dominated water. We subsequently contrasted the PAR-KC relationship form the Arctic waters with the previous relationships from the Ariake Bay and East China Sea and revealed that these various PAR-KC relationships can be systematically explained across regions by phytoplankton community size structures. Specifically, the value of the linear slope describing PAR-KC decreases as water bodies have an increasing fraction of larger phytoplankton. We propose that this synoptic trend reflects how phytoplankton community structure integrates past and immediate environmental histories and hence may be a better broad-scale predictor of KC than specific environmental factors such as temperature and nutrients. We provide a novel algorithm that may enable broad-scale retrieval of CO2 uptake from FRRf with knowledge of light and phytoplankton community size information.

Lycodes polaris is one of the most widely distributed and abundant eelpout species on the Arctic continental shelves with full mitogenome information unavailable. In this paper, complete mitochondrial genome of L. Polaris was determined with 16,595 bp in length, containing 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and 2 non-coding regions (origin of light strand replication and control region). All the protein-coding genes choose ATG as start codon in addition to that COI using GTG. Most genes use TAA or TAG as the stop codon while three others ended with incomplete stop codons. Phylogenetic relationship of L. polaris was also reconstructed. Our result will provide important basis for further studies of L. polaris.

In this study, the complete mitochondrial genome (mitogenome) sequence of Thryssa dussumieri was determined by long polymerase chain reaction and primer walking methods. The mitogenome was a circular molecule of 16,883 base pairs (bp) in length and contained 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA), 22 transfer RNA (tRNA), and a control region similar to those found in other bony fishes. The overall nucleotide composition was estimated to be 32.1% A, 26.1% C, 23.7% T, and 18.1% G. The neighbor-joining tree was reconstructed based on the 13 PCGs sequences of T. dussumieri and other 10 Engraulidae species. The mitogenome data will provide useful information for further studies on the phylogenetic analysis and population genetics.

The complete mitochondrial genome was determined for Arctic staghorn sculpin Gymnocanthus tricuspis (Reinhardt, 1830), which is considered an important part of Arctic food webs. The mitogenome sequence is 16,570 bp in length containing 2 ribosomal RNA genes, 22 tRNA genes, 13 protein-coding genes, and 2 non-coding regions consist of control region (CR) and light-strand replication origin (OL). The overall base composition of the mitogenome was estimated to be A 23.2%, T 29.0%, C 28.8%, and G 19.0%. The complete mitochondrial genome data will provide useful genetic information for future genetic variation identification and genetic diversity evaluation of this important species in Arctic Ocean.

Lycodes brevipes is one of the representative species of zoarcid fishes with little genetic information. The complete mitochondrial genome sequence of L. brevipes was sequenced by long PCR and primer walking methods. The mitogenome is a circular molecule of 16,537 bp in length including the structure of 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and two non-coding regions (origin of light strand replication and control region). The present study also revealed the phylogenetic relationship of this species at the molecular level using NJ algorithm. The mitogenome of L. brevipes provides essential genetic data for further phylogenetic and evolutionary analyses.

Myoxocephalus scorpius (Linnaeus, 1758) is the second abundant fish species in coastal Arctic ecosystems with very less genetic information. In this study, the complete mitochondrial genome sequence of M. scorpius was sequenced with 16,626 bp in length, including the structure of 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and two non-coding regions (origin of light strand replication and control region). All the protein-coding genes use ATG as start codon except COI using GTG. Most of them have TAA or TAG as the stop codon while COII, ND4, and Cyt b use T–. Phylogenetic tree involving all the available Arctic fish was also reconstructed and can provide further genetic analysis for this species.

Pacific herring show an abrupt genetic discontinuity in the central North Pacific that represents secondary contact between refuge populations previously isolated during Pleistocene glaciations. Paradoxically, high levels of gene flow produce genetic homogeneity among ocean-type populations within each group. Here, we surveyed variability in mtDNA control-region sequences (463 bp) and nine microsatellite loci in Pacific herring from sites across the North Pacific to further explore the nature of the genetic discontinuity around the Alaska Peninsula. Consistent with previous studies, little divergence (Φ(ST) = 0.011) was detected between ocean-type populations of Pacific herring in the North West Pacific, except for a population in the Yellow Sea (Φ(ST) = 0.065). A moderate reduction in genetic diversity for both mtDNA and microsatellites in the Yellow Sea likely reflects founder effects during the last colonization of this sea. Reciprocal monophyly between divergent mtDNA lineages (Φ(ST) = 0.391) across the Alaska Peninsula defines the discontinuity across the North Pacific. However, microsatellites did not show a strong break, as eastern Bering Sea (EBS) herring were more closely related to NE Pacific than to NW Pacific herring. This discordance between mtDNA and microsatellites may be due to microsatellite allelic convergence or to sex-biased dispersal across the secondary contact zone. The sharp discontinuity between Pacific herring populations may be maintained by high-density blocking, competitive exclusion or hybrid inferiority.

Based on bottom trawl survey data collected in November 2009 (autumn), February 2010 (winter), May 2010 (spring), and August 2010 (summer), the seasonal variation in the trophic structure of the fish community in Dongshan Bay and adjacent waters was investigated. A total of 114 species of fish were caught in surveys throughout the year. According to their feeding habits, the fish species in the surveyed area were classified into six functional groups, including planktivores (FG1), planktivores/benthivores (FG2), benthivores (FG3), benthivores/piscivores (FG4), piscivores (FG5), and omnivores (FG6). FG3 was the most diverse group, with 43 species, followed by FG4, with 29 species. The biomass of FG3 was the highest among all functional groups throughout the year and in each individual season. FG1 and FG5 had higher biomass proportions in spring than in the other seasons, accounting for 8.02% and 16.72%, respectively. The functional group diversity (HFD) and species diversity (Hs) showed similar variations, reaching their lowest values in winter and highest values in summer. In 2009-2010, the mean trophic position of the fish community in Dongshan Bay and adjacent waters was 3.64. This value was 3.74 in winter (highest), 3.49 in summer (lowest), 3.71 in spring, and 3.63 in autumn. The relationship between the trophic position and the mean body mass indicated that the seasonal variation in the mean body mass of high-trophic-level fish species was the highest in winter, followed by autumn, spring, and summer. In general, with seasonal and temporal changes, large-bodied, high-trophic-level fishes were gradually replaced by small-bodied, low-trophic-level fishes in the fish community of Dongshan Bay and adjacent waters in 2009-2010, and the trophic structure tended to become simplified. [ABSTRACT FROM AUTHOR]