Marine Teleost Research Articles

Rhipidocotyle husi n. sp. and three known species of Bucephalidae Poche, 1907 from the East Asian Region: morphological and molecular data.

AbstractMorphological data and the first molecular data are provided for four species of the trematode family Bucephalidae Poche, 1907 from marine and freshwater teleost fish species of East Asia. A new species, Rhipidocotyle husi n. sp., was isolated from Huso dauricus from the Amur River, Russia. Adult worms of this species were distinguished from their congeners Rhipidocotyle illense and Rhipidocotyle kovalai by morphological analysis. Three other known species were identified: Bucephalus skrjabini and Prosorhynchus cf. squamatus were detected in Siniperca chuatsi from the Amur River and in Myoxocephalus spp. from the Okhotsk Sea, Russia, respectively, while Prosorynchoides karvei was extracted from Strongylura strongylura from Halong Bay, Vietnam. The 28S ribosomal DNA (rDNA)-based phylogenetic analysis showed that the new species formed a shared polytomy clade with Rhipidocotyle fennica. Phylogenetic analysis of all available molecular data showed that four genera, namely Rhipidocotyle, Bucephalus, Prosorynchoides and Prosorhynchus, are para- or polyphyletic. Molecular-based phylogenetic analysis of morphologically validated bucephalid species indicated that three genera – Rhipidocotyle, Bucephalus and Prosorynchoides – were monophyletic. The genus Prosorhynchus maintained paraphyly, and P. cf. squamatus was more closely related to Dollfustrema spp. than to other Prosorhynchus spp. These findings do not exclude the possibility that representatives of Dollfustrema and P. cf. squamatus belong to the same genus.

Key Life History Attributes and Removal Efforts of Invasive Lionfish (Pterois volitans) in the Flower Garden Banks National Marine Sanctuary, Northwestern Gulf of Mexico

Indo-Pacific lionfish (Pterois volitans and P. miles) are the first marine teleost to have successfully invaded and become established in the Western Atlantic Ocean of the United States, Gulf of Mexico (GoM), and Caribbean Sea. Pterois volitans were first reported in the Flower Garden Banks National Marine Sanctuary (FGBNMS), a protected coral reef system in the northwestern GoM, in 2011. Little is understood about the life history characteristics of lionfish in this ecosystem. This study assessed population characteristics (size, density, age and growth) and removal efforts of lionfish (n = 1,665) at two coral reef sites within FGBNMS for 2015, 2016, and 2018. The annual increment formation in sagittal otoliths was examined to assess the age and growth of lionfish collected in 2018 (n = 100). Lionfish ranged in size from 75 to 444 mm total length (TL) and 4–1,153 g in total weight (TW). Six hundred and ten fish were randomly dissected for sex determination (females = 256, males = 354), females ranged in size from 137 to 348 mm TL and 21–586 g, while males ranged from 118 to 444 mm TL and 18–1,153 g. Interannual variation in mean lionfish density ranged from 26.7 individuals per hectare (ind ha–1) in 2016 to 81.1 ind ha–1 in 2018, while removal effort significantly increased ranging from 1.92 to 5.42 kg diver h–1. Lionfish age ranged from 0 to 10 years, with a mean age of 3.9 years. The observed values of the asymptotic maximum total length (L∞) and Brody’s growth coefficient (K) were 345 mm and 0.30 for females and 415 mm and 0.18 for males. Results suggest lionfish from FGBNMS exhibit markedly lower mean densities, a lower L∞ and growth rate, but attain older ages than lionfish in the Caribbean Sea, Western Atlantic Ocean, and other ecoregions in the northern GoM. This study describes the first key life history parameters and removal efforts for lionfish in a protected, healthy coral reef system in the northwestern GoM that may provide insight into environmental population controls (e.g., ecological resilience). Metrics from this study could be integrated into mechanistic ecological models to determine if FGBNMS is in fact exhibiting natural resilience to the lionfish invasion.

Calcium and strontium stable isotopes reveal similar behaviors of essential Ca and nonessential Sr in stream food webs

AbstractRecent studies showed the potential of stable isotopes of the macronutrient calcium (δ44/40Ca) and nonessential strontium (δ88/86Sr) as new trophic level indicators in terrestrial vertebrates and marine teleost fishes. In this study, we tested whether similar Ca and Sr isotopic fractionation trends existed in macroinvertebrate‐dominated stream food webs compared to vertebrates despite their physiological differences. We have determined the δ44/40Ca and δ88/86Sr values as well as the 87Sr/86Sr ratios of stream macroinvertebrates and small gobies and their potential metal sources (stream water, periphyton, and terrestrial plant litter) in upper and lower reaches of two streams in the Lake Biwa catchment, central Japan. The 87Sr/86Sr ratios revealed that stonefly nymphs, crustacea, and gobies mostly relied on aquatic Sr sources. Higher 87Sr/86Sr ratios of some crane fly and caddisfly larvae, mayfly, dobsonfly, and dragonfly nymphs indicated greater terrestrial contributions via plant litter. Positive correlations between the δ44/40Ca and δ88/86Sr values implied that similar Ca and Sr sources existed, and that Ca and Sr stable isotopes underwent similar fractionation trends although Sr was not essential. The δ44/40Ca and partly the δ88/86Sr values were positively correlated with Sr/Ca ratios and negatively with δ15N values indicating trophic effects on Ca and Sr stable isotopes. The enrichment of 44Ca and 88Sr in large filter‐feeding caddisfly larvae was a notable exception from these trophic trends. Our data confirm that the trophic 44Ca and 88Sr depletion observed for marine teleost fishes and terrestrial vertebrates also applied to macroinvertebrate‐dominated stream food webs despite their different physiologies indicating that shared mechanisms of Ca and Sr isotopic fractionation may exist at the cellular or molecular level between these taxa.

Intensive masculinization caused by chronic heat stress in juvenile Cynoglossus semilaevis: Growth performance, gonadal histology and gene responses

The sea temperature has been observed to chronically increase during the past decades, leaving unpredictable influences to the marine biological resources. Thus, it is of vital significance to study the biological responses of ocean inhabited organisms with the artificially stimulated heat stress environment. Cynoglossus semilaevis provides us with an ideal model to study the influence of chronic heat stress on the sexual differentiation in marine teleosts for its genetic sex determination (GSD) + environmental effected (EE) sex determination system. In this study, the comparative experiment was conducted employing heated seawater (HT group) and ambient seawater (CT group) to cultivate juvenile C. semilaevis respectively. Significant differences were exhibited in growth performance and a delayed germ cell development effect was found in pseudomales formed under chronic heat stress. Using transcriptome analysis, the transcription profile of 55 days post fertilization (dpf) and 100 dpf juveniles’ gonads were studied. A total of 47 libraries were constructed with an average mapping rate of 94.63% after assembling. GO and KEGG enrichment were proceeded using DEGs screened out between (1) pseudomale gonads at 55 dpf and 100 dpf in HT and CT group (2) pseudomale and female gonads at 55 dpf and 100 dpf in HT and CT group. Terms and pathways involved in steroid stimulation, reproduction ability, germ cell proliferation et al. were shed light on. The expression pattern of 29 DEGs including amh, hsp90b1, pgr et al. were also provided to supplement the results of functional enrichment. Weighted gene co-expression networks analysis (WGCNA) was constructed and hspb8-like, histone H2A.V were exhibited to play vital roles in the heat-induced masculinization. Our findings facilitate the understanding for transcriptional variations in intensive masculinization cause by chronic heat stress of C. semilaevis and provide referable study of the influences on the teleosts in elevated sea temperature.

Differential expression analyses reveal extensive transcriptional plasticity induced by temperature in New Zealand silver trevally (Pseudocaranx georgianus).

Ectotherm species, such as marine fishes, depend on environmental temperature to regulate their vital functions. In finfish aquaculture production, being able to predict physiological responses in growth and other economic traits to temperature is crucial to address challenges inherent in the selection of grow‐out locations. This will become an even more significant issue under the various predicted future climate change scenarios. In this study, we used the marine teleost silver trevally (Pseudocaranx georgianus), a species currently being explored as a candidate for aquaculture in New Zealand, as a model to study plasticity in gene expression patterns and growth in response to different temperatures. Using a captive study population, temperature conditions were experimentally manipulated for 1 month to mimic seasonal extremes. Phenotypic differences in growth were measured in 400 individuals, and gene expression patterns of pituitary gland and liver were determined in a subset of 100 individuals. Results showed that growth increased 50% in the warmer compared with the colder condition, suggesting that temperature has a large impact on metabolic activities associated with growth. A total of 265,116,678 single‐end RNA sequence reads were aligned to the trevally genome, and 28,416 transcript models were developed (27,887 of these had GenBank accessions, and 17,980 unique gene symbols). Further filtering reduced this set to 8597 gene models. 39 and 238 differentially expressed genes (DEGs) were found in the pituitary gland and the liver, respectively (|log2FC| > 0.26, p‐value < 0.05). Of these, 6 DEGs showed a common expression pattern between both tissues, all involved in housekeeping functions. Temperature‐modulated growth responses were linked to major pathways affecting metabolism, cell regulation and signalling, previously shown to be important for temperature tolerance in other fish species. An interesting finding of this study was that genes linked to the reproductive system were up‐regulated in both tissues in the high treatment, indicating the onset of sexual maturation. Few studies have investigated the thermal plasticity of the gene expression in the main organs of the somatotropic axis simultaneously. Our findings indicate that trevally exhibit substantial growth differences and predictable plastic regulatory responses to different temperature conditions. We identified a set of genes that provide a list of candidates for further investigations for selective breeding objectives and how populations may adapt to increasing temperatures.

Molecular Characterization, Tissue Distribution and Differential Nutritional Regulation of Three n-3 LC-PUFA Biosynthesis-Related Genes in Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂).

Elongases of very long-chain fatty acids (Elovls) and fatty acid desaturases (Fads) are crucial enzymes involved in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). In this paper, we report the molecular cloning and characterization of three genes from the marine teleost Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂, and analyzed tissue distribution and their expression in response to dietary n-3 LC-PUFA levels after a 42-day feeding experiment. The elovl5, elovl8 and fads2 genes encoded 294, 263 and 445 amino acids, respectively, which exhibited all the characteristics of the Elovl and Fads family. Tissue distribution analysis revealed that elovl5, elovl8 and fads2 were widely transcribed in various tissues, with the highest level in the brain, as described in other carnivorous marine teleosts. The transcript levels of elovl5, elovl8 and fads2 in the liver were significantly affected by dietary n-3 LC-PUFA, and higher LC-PUFA levels repressed their expression. These results demonstrated, for the first time, the presence and nutritional modulation of elovl5, elovl8 and fads2 cDNA in the juvenile hybrid grouper. Further studies are needed to determine the functional characterization of these genes and explore the mechanism of these genes when regulated by dietary fatty lipid profiles in this species.

Digenean Metacercariae Parasitic in a Staurozoan Cnidarian.

I report digenean metacercariae from Staurozoa, which were not previously known as digenean hosts. The host species, Haliclystus tenuis Kishinouye, 1910, was collected from algae in Oshoro Bay, Hokkaido, Japan, and contained metacercariae in the mesoglea. The metacercariae were encysted; cysts were oval, 93 µm long by 64 µm wide in one live individual. For the digenean, I generated partial sequences for the 18S rRNA (1585 bp) and 28S rRNA (1672 bp) genes, and the region spanning the 3' end of the cytochrome c oxidase subunit gene and the 5' end of the 16S rRNA gene, including the threonine tRNA gene (868 bp in total). Phylogenetic reconstructions based on combined 18S + 28S datasets showed the digenean to belong in Opecoelidae, members of which utilize marine or freshwater teleost fishes as definitive hosts, and placed it in Plagioporinae (sensu lato) clade C within Opecoelidae.

Evidence that host ecology drives first intermediate host use in the Didymozoidae (Trematoda: Hemiuroidea): an asexual infection in a vermetid (Gastropoda).

The Didymozoidae (Trematoda: Hemiuroidea) is among the most speciose trematode families, known from a wide range of marine teleost fishes. Despite their richness, however, didymozoid life cycles are unusually poorly known; only two first intermediate hosts are known, a marine bivalve (Anadara trapezia) and a pelagic gastropod (Firoloida desmarestia). This study uses multi-locus molecular sequence data to identify a novel first intermediate host for the family, a sessile gastropod of the genus Thylacodes Guettard (Vermetidae). The didymozoid infection is not identified to species but, based on molecular phylogenetic analyses, it is close to Saccularina magnacetabula Louvard et al., 2022, which uses a bivalve as a first intermediate host. The distribution of known first intermediate hosts of didymozoids (a bivalve, a holoplanktonic gastropod and a sessile gastropod that feeds with the use of mucus nets) suggests that first intermediate host use within the Didymozoidae has been opportunistically driven by the trophic ecology of potential mollusc hosts and has involved significant host-switching events.

Selection of reference genes suitable for normalization of qRT‐PCR data in spotted sea bass ( Lateolabrax maculatus ) under conditions of pathogen infections

The aim of this study was to select the most suitable reference genes for qRT-PCR of spotted sea bass (Lateolabrax maculatus) under different pathogen infection conditions. A total of 10 candidate reference genes were selected; they included RPL19, RPL7, RPL13, TUGB, 18S rRNA, CYTB5, eIF5A, ACTB, GAB2 and GAPDH. Transcript levels of these candidate reference genes were examined using qRT-PCR analysis in 11 tissues (heart, liver, stomach, pectoral fin, intestine, muscle, brain, skin, gill, head kidney and spleen). Four algorithms, geNorm, NormFinder, BestKeeper and comparative ΔCt method, were used to evaluate the expression stability of the candidate reference genes. RPL19 was the most stable gene in different tissues in L. maculatus under normal conditions according to the overall ranking of the four algorithms. GAPDH was the most unstable gene in different tissues. GAB2 was the most stable gene in both head kidney and liver in L. maculatus under V. harveyi infection; RPL19 and RPL13 were the most stable genes in head kidney and liver in L. maculatus under S. iniae infection respectively; RPL19 and GAB2 were the most stable genes in head kidney and liver in L. maculatus under RGV infection respectively; RPL7 and RPL19 were the most stable genes in head kidney and spleen in L. maculatus under ISKNV infection respectively. GAPDH was the most unstable gene in immune tissues in L. maculatus under pathogen infections. The present study provides the first validated reference genes for accurate data normalization in transcript profiling in L. maculatus infected by bacteria (V. harveyi and S. iniae) and virus (ISKNV and RGV), which will be indispensable for further gene expression in this economically valuable marine teleost.

Morphological and molecular characterization of the marine-teleost parasitizing acanthocephalan Echinorhynchus hexagrammi (Syndermata: Palaeacanthocephala) from a new host, Liparis sp. (Actinopterygii: Scorpaeniformes).

Originally described from the masked greenling Hexagrammos octogrammus (Pallas, 1814), the palaeacanthocephalan Echinorhynchus hexagrammi Baeva, 1965 has so far been known from seven species in six families of marine teleosts distributed in the Sea of Okhotsk off Sakhalin and in the Northwestern Pacific off Hokkaido, Japan. In this study, we examined the phylogenetic position of E. hexagrammi based on material obtained from the intestine of an unidentified snailfish, Liparis sp., dredged in Akkeshi Bay, Hokkaido, Japan. We performed an analysis using two gene markers, the mitochondrial cytochrome c oxidase subunit I and the nuclear 28S rRNA, along with other sequences available in public databases. In the resulting tree, E. hexagrammi was more closely related to two species complexes, the E. bothniensis Zdzitowiecki and Valtonen, 1987 complex and the E. gadi Zoega in Müller, 1776 complex, rather than to E. brayi Wayland, Sommerville, and Gibson, 1999, E. cinctulus (Porta, 1905), E. salmonis Müller, 1784, and E. truttae Schrank, 1788. The morphology of the examined material herein identified as E. hexagrammi is briefly described. This study represents the first host record of E. hexagrammi from the snailfish family Liparidae.

Divergent Processes Drive Parallel Evolution in Marine and Freshwater Fishes.

Evolutionary comparisons between major environmental divides, such as between marine and freshwater systems, can reveal the fundamental processes governing diversification dynamics. Although processes may differ due to the different scales of their biogeographic barriers, freshwater and marine environments nevertheless offer similar opportunities for diversification in benthic, demersal, and pelagic habitats. Here, we compare the evolutionary patterns and processes shaping teleost diversity in each of these three habitats and between marine and freshwater systems. Using specimens from the National Museum of Natural History, we developed a data set of linear measurements capturing body shape in 2266 freshwater and 3344 marine teleost species. With a novel comparative approach, we contrast the primary axis of morphological diversification in each habitat with the major axis defined by phylogenetic signal. By comparing angles between these axes, we find that fish in corresponding habitats have more similar primary axes of morphological diversity than would be expected by chance, but that different historical processes underlie these parallel patterns in freshwater and marine environments. Marine diversification is more strongly aligned with phylogenetic signal and shows a trend toward lineages occupying separate regions of morphospace. In contrast, ecological signal appears to be a strong driver of diversification in freshwater lineages through repeated morphological evolution in densely packed regions of morphospace. In spite of these divergent histories, our findings reveal that habitat has driven convergent patterns of evolutionary diversification on a global scale. [Benthic-pelagic axis; body shape; convergent evolution; morphological diversification; phylogenetic signal.].

Establishment of myoblast cell line and identification of key genes regulating myoblast differentiation in a marine teleost, Sebastes schlegelii.

Skeletal myoblasts are activated satellite cells capable of proliferation and differentiation. Studies on mammalian myoblast differentiation and myogenesis could be carried out in vitro thanks to the availability of mouse myoblast cell line C2C12. Lacking of muscle cell line hinders the studies of teleost fish myogenesis. Here, we established a continuous skeletal muscle cell line from juvenile rockfish (Sebastes schlegelii) muscle using explant method and subcultured more than 50 passages for over 150days. Stable expression of myoblast-specific marker, MyoD (myoblast determination protein) and the potential of differentiation into multi-nucleated skeletal myotubes upon induction suggested the cell line were predominately composed of myoblasts. Transcriptome analysis revealed a total of 4375 genes differentially expressed at four time points after the switch to differentiation medium, which were mainly involved in proliferation and differentiation of myoblasts. KIF22 (kinesin family member 22) and POLA1 (DNA polymerase alpha 1) were identified as the key genes involved in fish myoblast proliferation whereas MYL3 (myosin light chain 3) and TNNT2 (troponin T2) were determined as the crucial genes responsible for differentiation. In all, the continuous myoblasts cultured in this study provided a cell platform for future studies on marine fish myoblast differentiation and myogenesis. The molecular process of myoblast differentiation revealed in this study will open a window into the understanding of indeterminate muscle growth of large teleost.

Genomic Signatures of Domestication Selection in the Australasian Snapper (Chrysophrys auratus).

Domestication of teleost fish is a recent development, and in most cases started less than 50 years ago. Shedding light on the genomic changes in key economic traits during the domestication process can provide crucial insights into the evolutionary processes involved and help inform selective breeding programmes. Here we report on the recent domestication of a native marine teleost species in New Zealand, the Australasian snapper (Chrysophrys auratus). Specifically, we use genome-wide data from a three-generation pedigree of this species to uncover genetic signatures of domestication selection for growth. Genotyping-By-Sequencing (GBS) was used to generate genome-wide SNP data from a three-generation pedigree to calculate generation-wide averages of FST between every generation pair. The level of differentiation between generations was further investigated using ADMIXTURE analysis and Principal Component Analysis (PCA). After that, genome scans using Bayescan, LFMM and XP-EHH were applied to identify SNP variants under putative selection following selection for growth. Finally, genes near candidate SNP variants were annotated to gain functional insights. Analysis showed that between generations FST values slightly increased as generational time increased. The extent of these changes was small, and both ADMIXTURE analysis and PCA were unable to form clear clusters. Genome scans revealed a number of SNP outliers, indicative of selection, of which a small number overlapped across analyses methods and populations. Genes of interest within proximity of putative selective SNPs were related to biological functions, and revealed an association with growth, immunity, neural development and behaviour, and tumour repression. Even though few genes overlapped between outlier SNP methods, gene functionalities showed greater overlap between methods. While the genetic changes observed were small in most cases, a number of outlier SNPs could be identified, of which some were found by more than one method. Multiple outlier SNPs appeared to be predominately linked to gene functionalities that modulate growth and survival. Ultimately, the results help to shed light on the genomic changes occurring during the early stages of domestication selection in teleost fish species such as snapper, and will provide useful candidates for the ongoing selective breeding in the future of this and related species.

Two non-mammalian toll-like receptors (TLR21 and TLR22) from golden pompano (Trachinotus ovatus): Molecular cloning, gene characterization and expression analysis

Toll-like receptors (TLRs), important pattern recognition receptors (PRRs), involve in recognizing pathogen-associated molecular patterns (PAMPs) and play crucial roles in the host innate immunity. In the present study, two non-mammalian TLRs, troTLR21 and troTLR22, were identified and characterized from golden pompano (Trachinotus ovatus), a marine teleost with great economic values. The two TLRs were typical TLRs, containing several motifs conserved in TLRs family including leucine-rich repeat (LRR) motifs, a transmembrane domain, and a toll/interleukin-1 receptor (TIR) domain. The two TLRs shared high sequence identity with their counterparts in other teleosts. Phylogenetic tree analysis showed that troTLR21 and troTLR22 were well clustered with other fish TLR21 and TLR22, respectively. Quantitative real-time PCR (qPCR) revealed that the two TLRs were ubiquitously expressed in all investigated tissues, with higher transcription levels in the immune-related tissues (spleen and head kidney (HK)). Further, the expressions of troTLR21 and troTLR22 were significantly up-regulated in HK and spleen following Vibrio alginolyticus, lipopolysaccharide (LPS), and polyinosinic: polycytidylic acid (polyI:C) stimulation. Our results suggested that the two TLRs involve in the immune response against pathogen invasion in golden pompano, providing solid basis for further study the functions of fish-specific TLRs.

Ultraviolet light and ozone controls Cryptocaryon irritans infection in factory aquaculture

Cryptocaryon irritans is a pathogenic ectoparasitic ciliate that infects marine teleosts, causing massive mortality and economic losses in aquaculture. Ultraviolet light (UV) and ozone (O3) are commonly used for disinfection in factory aquaculture; however, the efficacy of neither method against C. irritans had been evaluated. This study aimed to evaluate the efficacy of UV and ozone in destroying C. irritans. UV or ozone treatment changed or ruptured the shape of C. irritans theronts, although C. irritans tomonts showed some resistance. The minimum in vitro lethal doses of UV and ozone against theronts were 2.88× 105 μWs/cm2 and 0.15 mg/L, respectively. In vivo, UV and ozone-treated theronts lost their ability to infect pompano (Trachinotus ovatus) when exposed to doses above 1.84 × 105 μWs/cm2 and 0.10 mg/L, respectively. Unexpectedly, exposure to low ozone levels (< 0.04 mg/L) enhanced theronts infecting ability. These results provide a reference for C. irritans theronts disinfection in factory aquaculture and further studies on C. irritans.

Oxidative stress in tissues of gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) juveniles exposed to ultraviolet-B radiation

Ultraviolet-B (UVB) radiation generates reactive oxygen species (ROS), which damage DNA, proteins, and lipids in aquatic organisms, including fish. This study evaluated UVB-induced oxidative stress in several tissues of two marine teleosts, gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). Juveniles of both species were exposed to four treatments simulating underwater UVB (no, low, moderate, and high UVB) doses for 6 weeks. Oxidative stress (the activities of several antioxidant enzymes (catalase, CAT; glutathione-S-transferase, GST; superoxide dismutase, SOD, and lipid peroxidation, LPO) were analyzed in the skin, liver, head kidney, gills, muscle, brain, intestine, spleen, and kidney samples obtained at increasing exposure times (3–43 days). UVB exposure induced significant lipid damage and antioxidant responses in several tissues, with the skin showing more pronounced effects in S. aurata than in D. labrax. In the skin of both species and in the liver of D. labrax, LPO levels significantly increased with increasing UVB intensity and exposure time. CAT activity was inhibited in both species (i.e., in liver, skin, head kidney, gills, spleen, and brain) of UVB exposed fish. SOD activity significantly decreased in the skin and head kidney of D. labrax; however, prolonged exposure time was required for significant effects in the skin and gills of S. aurata. GST activity reduced early in the skin of S. aurata, whereas significant effects were noted in the head kidney and brain at the end of experiment. An interactive effect between UVB intensity and exposure time was observed in the skin (seabream and seabass) and liver (seabass). Our results indicated that oxidative stress is induced in the skin as well as indirectly exposed tissues in S. aurata and D. labrax after UVB exposure at the subsurface of transparent seas.

Ecological and behavioural drivers of offspring size in marine teleost fishes

AbstractAimOur aim was to evaluate the role of ecological and life‐history factors in shaping global variation in offspring size in a marine clade with a diverse range of parental care behaviours.LocationGlobal.Time periodData sourced from literature published from 1953 until 2019.Major taxa studiedMarine teleost fishes.MethodsWe compiled a species‐level dataset of egg and hatch size for 1,639 species of marine fish across 45 orders. We used Bayesian phylogenetic mixed models to evaluate the relationship between offspring size and environmental factors (i.e., mean temperature, chlorophyll‐a and dissolved oxygen content together with their annual variation), as well as latitude, reproductive strategy, parental body size and fecundity. We also tested long‐standing hypotheses about the co‐evolution of offspring size and the presence of parental care in BayesTraits.ResultsAfter controlling for parental body size and phylogenetic history, we find that increased egg size is associated with colder and oxygen‐rich waters, while hatch size further depends on food supply and the reproductive strategy exhibited by the species. Irrespective of the initial investment in egg size, species with parental care or demersal egg development yield larger hatchlings compared to pelagic spawners. We also demonstrate that hatch size has co‐evolved with advanced forms of care in association with parental body but fail to find a relationship with other types of care.Main conclusionsOur study shows that parental care behaviours, together with environmental context, influence the evolution of classic life‐history trade‐offs on a global scale. While the initial investment in eggs is driven primarily by temperature and oxygen content, hatch size also reflects the impact of care an offspring has received throughout development. In support of the ‘offspring‐first’ hypothesis, we find that an increase in hatch size drives the evolution of advanced care provision.

Reproduction and Maturation of Sea Bass, Lateolabrax japonicus, after Transportation from Net-Cages to Indoor Tanks.

To determine whether the reproductive processes of sea bass, Lateolabrax japonicus, proceed normally after transportation from an outdoor net-cage into indoor tanks, we examined changes in the gonadosomatic index (GSI), histological gonadal tissue, and plasma levels of sex hormones (testosterone and estradiol-17ß) during their annual reproductive cycle. We also measured maturation and spawning across two sea water salinity levels (full and low salinity). Fecundity was estimated by the relationship between egg number and body size in female sea bass. Monthly changes in the GSI, histological gonadal tissues, and oocyte size showed both male and female sea bass reach final maturation in January and February, respectively, indicating that the spermiation of males occurs earlier than the spawning of females. The histological results indicated that the sea bass is a multiple spawner, similar to many marine teleosts, exhibiting group-synchronous oocyte development. Female maturation and spawning were enhanced in lower salinity seawater (29.6-31.0 psu) compared to that of normal salinity (34.5-35.1 psu). These results confirm that sea bass reproduction can occur successfully in captivity and imply that fertilized eggs can be collected from February to March. Additionally, our results show that lower salinity enhances oocyte maturation and spawning of female sea bass.

Insights from a Survey of Texas Gulf Coast Residents on the Social Factors Contributing to Willingness to Consume and Purchase Lionfish

Indo-Pacific lionfish (Pterois volitans and P. miles) are the first marine teleost to become established in the Western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Lionfish have been labeled a global conservation issue and pose major threats to local economies. To test whether commercial harvest of lionfish is a socially accepted management approach in Texas, we measured the components of an environmental behavior intention model with survey responses of Texas Gulf Coast residents (n = 420). Regression analyses of survey responses indicate that individuals were significantly more willing to consume lionfish if they had a high level of concern for the environmental problems posed by the invasive species and were more knowledgeable about the fish. Participation in an educational program that addresses lionfish was also found to be associated with greater willingness to consume lionfish among those who are moderately to highly concerned about the issue. The originality of this study is related to its contribution in identifying social factors that contribute to an individual’s willingness to consume lionfish. Insights from this study demonstrate the attitudinal and behavioral mechanisms that can be addressed to increase acceptance of using consumption as a sustainable management strategy to combat marine fish invasions.

Genome-wide association study identifies genomic loci of sex determination, gonadal weight and gonadosomatic index traits in Takifugu bimaculatus

Takifugu bimaculatus is a cultured marine teleost fish, distributed ranging from the southern Yellow Sea to the South China Sea. Understanding the mechanism of sex determination is essential for sex control breeding biotechnologies of T. bimaculatus. However, there lacks a rapid and accurate sex specific marker for the T. bimaculatus. In this study, whole genome resequencing was conducted on 71 individuals (including 49 females and 22 males), 331,190 high-quality polymorphic loci (34,435 INDEL, 296,755 single-nucleotide polymorphisms (SNPs)) were obtained through genome-wide association analysis (GWAS) by GEMMA (Genome-wide Efficient Mixed Model Association algorithm). 1403 loci on chromosome 7 were identified as sex significantly associated loci (P < 1.51 × 10−7), and a 12 Mb sex-associated region on Chr7 was narrowed down by Fst scanning. It was worth noting that the SNP, SNP1100879 on Chr7 at position 8,764,381 was identified to be sex determination in T. bimaculatus. 13 pairs of primers for sex identification Marker-F/R were designed and it was validated by PCR. However, only one pair of primers (SNP-7F/R) was sex-linked, in which 95% of female genotypes are homozygous CC and 88% of male genotypes are heterozygous CT, suggesting a XX/XY sex determination system in T. bimaculatus. In addition, 12 sex-related candidate genes were identified around 306 SNPs, including amhr2, dzip1, patz1, brdt, hmga2, gli1, inhbb, mmp19, wnt2b, taf4 and so on. Because of the significant difference of gonadal weight (GW) and gonadosomatic index (GSI) between females and males of T. bimaculatus, GWAS on GW and GSI of different genders were also conducted independently. Besides, we identified 11 SNPs, located on Chr7, Chr18, Chr21, and Chr2, showing genome-wide significant association with GW and GSI and five genes including cyp27b1, hexb, inhba, cgba and shbg, involved in oogenesis, ovarian follicle development, and regulation of estradiol secretion. Then, we performed the gene ontology (GO) and KEGG signaling pathway (KEGG) and Protein-protein interaction (PPI) network analyses of the candidate genes. amhr2, gli1, ihbb and dzip1 genes were identified as hub genes. In the present study, a sex-linked marker of T. bimaculatus was identified for the first time using whole-genome resequencing technology, and its limited versatility provided important clues for deciphering the sex determination mechanism in T. bimaculatus.