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Mussels are a group of bivalves that includes the dominant species of shallow-sea, freshwater, and deep-sea chemosynthetic ecosystems. Mussels cling to various solid underwater surfaces using a proteinaceous thread, called the byssus, which is central to their ecology, physiology, and evolution. Mussels cluster using their byssi to form "mussel beds," thereby increasing their biomass per unit of habitat area, and also creating habitats for other organisms. Clustered mussels actively filter feed to obtain nutrients, but also ingest pollutants and suspended particles; thus, mussels are good subjects for pollution analyses, especially for microplastic pollution. The byssus also facilitates invasiveness, allowing mussels to hitchhike on ships, and to utilize other man-made structures, including quay walls and power plant inlets, which are less attractive to native species. Physiologically, mussels have adapted to environmental stressors associated with a sessile lifestyle. Osmotic adaptation is especially important for life in intertidal zones, and taurine is a major component of that adaptation. Taurine accumulation systems have also been modified to adapt to sulfide-rich environments near deep-sea hydrothermal vents. The byssus may have also enabled access to vent environments, allowing mussels to attach to "evolutionary stepping stones" and also to vent chimneys. [ABSTRACT FROM AUTHOR]

Correction to: Fisheries Science https://doi.org/10.1007/s12562-021-01550-5 In the Original Publication, an article note is missed and it should be "Published with support by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant no. The Article note is available in this correction. [Extracted from the article]

The meat quality of farmed yellowtail Seriola quinqueradiata fed on extruded pellets (EP) containing 0.5% (v/v) red pepper (experimental group) was compared with yellowtail of the same age fed on EP (control group). In 1-year-old yellowtail, the crude lipid content of the dorsal muscle of the experimental group tended to be lower than that of the control group. In contrast, there was no difference in the lipid content of the dorsal muscle between the control group and the experimental group in 2-year-old yellowtail. The muscle texture of the experimental group was significantly firmer than that of the control group, with the effect of red pepper unrelated to fish age and lipid content. Color change of red muscle of the experimental group was significantly lower than that of the control group, and the content of thiobarbituric acid-reactive substances in the red muscle was significantly lower in the experimental group than in the control group. These results are the first to demonstrate that the inclusion of red pepper in the diet is able to reduce the loss of muscle texture firmness and to slow down color change in red muscle of yellowtail. [ABSTRACT FROM AUTHOR]

To study the mechanism of faster growth of the sculpin Cottus kazika in seawater (SW) than in fresh water (FW), we transferred 120-day-old juveniles from FW to SW, 1/3 SW or FW, and survival, growth and levels of transcripts of growth hormone (GH) gene in the pituitary and insulin-like growth factor I (IGF-I) gene in the liver were examined 20 and 40 days after transfer. The survival rates of fish reared in SW and 1/3 SW were higher than the FW controls. The growth was fastest in SW and slowest in the controls. IGF-I gene transcripts increased in SW-reared fish 40 days after transfer compared with the controls, while GH gene transcripts did not. Juveniles of 1 year of age were transferred from FW to SW or 1/3 SW, and GH and IGF-I gene transcripts were compared after 48 h. In this short-term experiment, the level of GH gene transcripts was higher in fish reared in SW and 1/3 SW, while no difference was found in the IGF-I gene transcripts. Thus, the GH gene transcripts increased only transiently after SW transfer but the IGF-I gene transcripts increased gradually for 40 days, suggesting that the long-term increase in IGF-I gene expression is involved in the enhanced growth in SW and GH may play an initiation role for growth enhancement. [ABSTRACT FROM AUTHOR]

Nematodes belonging to the family Anisakidae including Anisakis simplex and Pseudoterranova decipiens are known to cause anisakiasis when their live larvae are ingested by humans. We estimated the possibility of anisakid infection to salmonids, farmed in sea net-pens at Onagawa Bay, Miyagi, Japan, in 1992, 1998 and 1999, by direct examination of the edible muscle and examination of the contents of the alimentary canal. From direct examination of the muscle, no nema-tode was found in the 249 farmed coho salmon Oncorhynchus kisutch and 40 farmed rainbow trout Oncorhynchus mykiss. In contrast, third-stage larvae of Anisakis simplex were found in seven of 14 wild coho salmon caught in Russia and all the 40 wild chum salmon Oncorhynchus keta caught at Nemuro and Kesennuma in 1998. The stomach and intestines of 521 farmed coho salmon and 40 farmed rainbow trout were examined carefully for the existence of possible carrier organisms such as crustaceans, fish or squid. Such carrier organisms were not found in the stomach and intestines of farmed fish. Thus, we conclude that the possibility of anisakid infection is very low in farmed salmonids. [ABSTRACT FROM AUTHOR]

In invertebrates inhabiting hydrothermal vent areas, hypotaurine, a precursor of taurine, is thought to mitigate the toxicity of hydrogen sulfide in vent fluids. Information about hypotaurine synthesis pathways in invertebrates is limited, although two pathways, the cysteamine [2-aminoethanethiol (AET)] pathway and the cysteine sulfinate (CSA) pathway are known in mammals. In this study, we cloned a cDNA encoding AET dioxygenase (ADO), the central enzyme of the AET pathway, from the vent mussel Bathymodiolus septemdierum. In the encoded protein (BsADO), functionally important residues, including metal-binding histidines, are conserved. In maximum likelihood phylogenetic analysis, BsADO clustered with ADOs of other invertebrates. By reverse transcription PCR, BsADO mRNA was detected in all tissues examined at similar levels, suggesting that its function is distinct from that of the CSA pathway, predominantly expressed in the gill. BsADO with a His tag, expressed in Escherichia coli in the presence of Fe2+, converted AET to hypotaurine, but BsADO expressed in the absence of iron exhibited lower activity. BsADO was active from pH 8 to 11, and from 0 °C to 37 °C, with a peak at 20 °C. This is the first functional characterization of ADO in marine invertebrates. [ABSTRACT FROM AUTHOR]

Cytochrome P450 1A (Cyp1a) catabolizes polycyclic organic compounds. In this study, we sequenced the cyp1a gene from two Javanese medaka Oryzias javanicus strains and examined gene expression in response to two organic pollutants, phenanthrene and pyrene. Sequence comparisons among the two strains identified several single-nucleotide polymorphisms (SNPs), two of which resulted in amino acid substitutions. Reverse transcription PCR analysis of major organs revealed that the cyp1a mRNA level is highest in the liver. After determining LC50s against phenanthrene and pyrene for 96 h (3.9 and 2.5 µM, respectively), cyp1a mRNA expression in the liver against sublethal concentrations of phenanthrene and pyrene was examined. Using quantitative real-time PCR, a positive correlation was discovered between the cyp1a mRNA levels and pyrene concentration, and similar tendency was observed for phenanthrene. cyp1a may serve as a quantitative indicator of a broad range of pollutants. [ABSTRACT FROM AUTHOR]

Taurine and hypotaurine are abundantly present in molluskan tissues; however, the pathways for their biosynthesis have not yet been well investigated. In this study, we established a method for simultaneous detection of taurine-related compounds, including taurine, hypotaurine, cysteic acid, cysteine sulfinic acid (CSA), cystathionine, γ-aminobutyric acid, and β-alanine along with 17 free amino acids, using phenylthiocarbamyl derivatization in ammonia-containing solution, followed by injection into reversed-phase high-performance liquid chromatography. Using this method, we analyzed the major tissues (gill, mantle, adductor muscle, foot, and digestive gland) of the hydrothermal-vent-specific mussel Bathymodiolus septemdierum. The gill and digestive gland were suggested to be the major organs for taurine/hypotaurine biosynthesis because taurine and hypotaurine levels tended to be high, and their precursors, i.e., cysteine, cysteic acid, and CSA (only in digestive gland), were detected in these two tissues. Cystathionine was detected at relatively high level in digestive gland and in other tissues at low levels, suggesting its role as storage material for taurine/hypotaurine biosynthesis. Adductor muscle was found to be rich in free amino acids, mainly due to abundance of non-sulfur-containing amino acids. [ABSTRACT FROM AUTHOR]

Various invertebrates inhabiting hydrothermal vents harbor thiotrophic endosymbionts that provide the host with nutrients and are possibly involved in the detoxification of harmful sulfides. In this study, we first determined the partial 16S rRNA gene sequence of the thiotrophic symbiont of the deep-sea mussel Bathymodiolus septemdierum, a dominant species at hydrothermal vents in the Izu-Ogasawara (Bonin) area. We then designed a new probe, Bsob692, for fluorescent in situ hybridization (FISH) using regions completely conserved among thiotrophic symbionts of all bathymodiolin mussels and established the protocol for FISH to compare the distribution and amount of the symbiont using an image analysis program that is commercially available. We compared fluorescent intensity in the gill of the mussels collected at different sites and found a higher intensity in specimens collected from a site with higher sulfide concentration. We also compared mussels reared in the presence and absence of sulfide and found that the former had a higher fluorescent intensity. [ABSTRACT FROM AUTHOR]

Seawater around deep-sea hydrothermal vents and cold seeps contain high levels of hydrogen sulfide, which is toxic to most animals. Invertebrates inhabiting these environments have been reported to accumulate high levels of thiotaurine, a sulfur-containing amino acid. Thiotaurine is likely to play an important role in sulfide detoxification, but its functions in the detoxification process are still unknown. We cloned methane-seep mussel Bathymodiolus platifrons cDNA encoding the taurine transporter (TAUT), which transports thiotaurine and its precursors across the cell membrane. Phylogenetic analyses revealed that the predicted peptide formed a clade with the TAUTs of shallow-water mussel Mytilus galloprovincialis and the hydrothermal vent mussel Bathymodiolus septemdierum that harbors thioautotrophic bacteria. We then reared B. platifrons in the presence or absence of Na2S and quantified TAUT mRNA using a real-time PCR system. The amount of TAUT mRNA in the gills of B. platifrons increased with rearing in the presence of Na2S for 69 days, but no change was observed in the absence of sulfide. These results suggest that TAUT plays an important role in sulfide detoxification, even in species that do not harbor thioautotrophic bacteria. The TAUT mRNA level was variable in the mantle and low in the foot throughout the entire rearing period, regardless of the presence/absence of sulfide, suggesting that TAUT gene expression is regulated differentially in each tissue. [ABSTRACT FROM AUTHOR]