Search Results (5)

Background: The family Cyprinidae is predominantly restricted to freshwater habitats, making the evolution of diadromy and seawater adaptation exceptionally rare within this group. Pseudaspius hakonensis, a rare anadromous cyprinid, and its strictly freshwater congener P. leptocephalus, provide an ideal comparative model to investigate the molecular mechanisms underlying salinity adaptation. This study aimed to elucidate the tissue-specific transcriptional reprogramming, identify candidate genes and key pathways, and explore their association with seawater acclimation in P. hakonensis. Methods: We performed comparative transcriptomic analyses of gill, liver, and kidney tissues from both species using RNA-Seq. Sequencing reads were aligned to a high-quality reference genome of P. hakonensis. Differential expression analysis was conducted using DESeq2, followed by functional enrichment analyses (GO and KEGG) to identify significant biological processes and pathways. Results: A total of 8784, 5965, and 5719 differentially expressed genes (DEGs) were identified in gill, kidney, and liver tissues, respectively, with the gill showing the highest differences. Functional enrichment revealed tissue-specific roles: gill DEGs were associated with protein synthesis and energy metabolism; kidney DEGs with transport and detoxification; and liver DEGs with metabolic regulation and stress signaling. Cross-tissue analysis highlighted three core pathways consistently enriched: MAPK signaling, ABC transporters, and glutathione metabolism. Key candidate genes, including DUSP10, SLC38A2, ATP8B1, GSTA4, and MGST1, were significantly upregulated in P. hakonensis. Conclusions: This first multi-tissue transcriptomic comparison of an anadromous and a freshwater cyprinid reveals pervasive, tissue-specific molecular reprogramming underlying seawater adaptation in P. hakonensis. The coordinated activation of MAPK signaling, glutathione metabolism, and transporter pathways suggests an integrated regulatory network for osmoregulation and stress resistance. These findings provide novel insights into the genetic basis of salinity adaptation in cyprinids and identify candidate genes for future functional validation. Full article

Bonefishes are a nearshore species targeted by non-commercial anglers and subsistence fishers in the Central and South Pacific islands. Among the bonefish species in the Indo-Pacific region, Albula glossodonta are known to have one of the widest geographic ranges, from the Red Sea to the Central Pacific, but it is unknown how dispersive A. glossodonta are between geographically isolated islands. Volunteer anglers collected A. glossodonta fin clips from the main Hawaiian Islands in the North Pacific, Anaa Atoll in the South Pacific, and intermediate Kiritimati Island (Line Islands) to assess the scale of dispersal and population structure within the Pacific Ocean. Population genomics was conducted based on 208 individuals and 7225 SNPs. Although adult A. glossodonta exhibit strong site fidelity, genomic results show no population differentiation between Oahu and Maui in Hawai‘i. Bonefishes exhibit significant population structure between Anaa and Hawai‘i (F_ST = 0.096), with intermediate Kiritimati comprising admixed fishes. A lengthy larval duration likely promotes connectivity between Pacific islands. Regional management regimes may be most appropriate for a species with this level of dispersal. Full article

The daggertooth pike conger, Muraenesox cinereus, is an important demersal fish species in East Asia but the catch amount has declined in recent years. Spawning areas of M. cinereus have not yet been determined; identifying these have serious implications for resource management. Ichthyoplankton surveys are an effective method of distinguishing fish spawning areas and periods. Fish eggs were sampled from the waters adjacent to South Korea in August 2020 and 2022 using a Multiple Opening/Closing Net and Environmental Sensing System or a bongo net. In 2021, M. cinereus eggs were not collected. Three unidentified eggs (2.0–2.2 mm in diameter) were collected from the southeastern sea of Jeju Island at a seawater depth of 20–30 m and temperature of 20–22 °C. Muraenesox cinereus preleptocephali were gathered at 10–20 m depths from Jeju Island’s southernmost and eastern sea areas. The eggs and preleptocephali were identified as M. cinereus by their mitochondrial DNA 16S rRNA sequences. This is a new finding of eggs and leptocephalus of Muraenesox cinereus off Jeju Island, South Korea, which increases our understanding of the recruitment process of M. cinereus to facilitate resource management and species conservation. Full article

The freshwater eel Anguilla japonica is rapidly decreasing in number and has not yet been successfully mass produced. This may be at least partially attributable to the unique and long early life history of the eel. Therefore, we investigated its ontogeny of morphometry and growth pattern in larval stages to provide baseline information for understanding the early life history and improving seed rearing technology. This study was conducted for 200 days after hatching (DAH) and analyzed morphometry and allometry for eel larvae. The following cultured eel larval stages were identified: the yolk sac larvae stage (0–6 DAH, 3.23–6.85 mm total length (TL)), the pre-leptocephalus stage (7–30 DAH, 6.85–15.31 mm TL), and the leptocephalus stage (50–200 DAH, 15.31–60.06 mm TL). Cultured and wild eel larvae could be divided into characteristic larval stages at similar sizes. However, compared to wild eels, cultured eels had a slower growth rate and fewer preanal myomeres. Meanwhile, cultured eel larvae rarely had a mixed feeding period as the absorption of endogenous reserves was completed by 7 DAH. The lower jaw of eel larvae was significantly longer than the upper jaw from 50 DAH. In the pre-leptocephalus and leptocephalus stages, eel larvae showed continuous positive allometric growth at trunk height and tail muscle height with change to the willow leaf-like form. These growth characteristics may be the result of adaptation to the migration over long distances and to a diel vertical migration. The inflection point in the body parts growth patterns showed only before 30 DAH, and mass mortality appeared at this period. Therefore, to improve the growth and survival rates of cultured eel seed, it is necessary to focus on improving the feeding and rearing protocol until 30 DAH. Full article

The Japanese eel Anguilla japonica is an important aquaculture fish species in the East Asian countries of Japan, China, Korea, and Taiwan. All glass eel fry are captured from the wild and understanding the recruitment patterns of the glass eel is important. The larvae of A. japonica are passively transported to the East Asian Continental Shelf by the North Equatorial Current, the Kuroshio, the Kuroshio intrusion currents, and coastal currents. In each location, recruitment time is diverse: It is November in Taiwan and April in the Yalu River. How the glass eels reach recruitment areas remains poorly understood. Here, we combine information from larval ages based on otolith increments, simulated drifting paths on the East Asian Continental Shelf, and main fishing seasons in each location of East Asia. We identify five main recruitment blocks: (1) The main Kuroshio, (2) The Taiwan Strait Warm Current, (3) The Taiwan Warm Current, (4) The Yellow Sea Warm Current and (5) The branch of Yellow Sea Warm Current. The counted age of the glass eels is significantly underestimated for the later recruits, possibly due to the cessation of the otolith edge growth under low water temperatures. This study clarifies the eel’s larval characteristics and transport mechanisms in the East Asia Continental Shelf, providing important information for its recruitment dynamics in the marine stage. Full article