DNA-based species identification of shark fins traded in thai markets.

Shark fins are among the most highly prized seafood products in the world with massive consumption in Asia over the past several decades. The demand for shark fins is a major driver of the enormous population declines of elasmobranchs that are generally vulnerable to overexploitation. This study aims to better understand the species composition of shark fin products in Thailand and their conservation statuses by using DNA-based species identification. Various types and sizes of shark fins were collected from 4 locations in Thailand. DNA barcoding method based on a fragment of the cytochrome c oxidase subunit I (COI) gene was applied to species identification. Fins from at least 15 shark species were found from Thailand's markets. The spottail shark (Carcharhinus sorrah) and the night shark (Carcharhinus signatus) were the two dominant species presented in this study. 34% of identifiable samples are the species that have not been record in this region. 62% of species detected from the fin samples are categorized under the threatened categories of IUCN Red List. Species composition reported in shark fin products potentially helps indicate the appropriate conservation action and increases awareness from monitoring the trade in elasmobranch products. Supplementary Information: The online version contains supplementary material available at 10.1007/s10592-023-01519-0.

Screening for microplastics in marine fish of Thailand: the accumulation of microplastics in the gastrointestinal tract of different foraging preferences.

Microplastics in marine organisms are nowadays considered a worldwide phenomenon. An action plan needs to establish to solve this marine pollutant. It requires multidisciplinary information, including the accumulation of data on microplastics in marine biota. The research of microplastic ingestion in the marine environment and organisms of Thailand is limited. As a result, this study was conducted to evaluate the accumulation of microplastics in marine fish from Thailand and to investigate whether the different foraging mechanisms of fish impact the occurrence of microplastics in their gastrointestinal tract. A total number of 361 demersal fish and 131 pelagic fish were investigated. The collected microplastics were counted according to their shape and color. Their polymer type was identified by FT-IR for the first time in fish from Thailand. Moreover, microplastics ingestion sorted by fish size was noted. The number of ingested microplastics in this study was relatively low compared to other locations. There was no significant difference in the number of microplastics ingested between demersal and pelagic fish (p = 0.132). Microplastic fibers were the dominant shape found in both demersal (82.76%) and pelagic fish (57.14%). The most common polymer type was polyamide in both demersal (55.17%) and pelagic fish (50.00%). The dominant microplastics color in both demersal and pelagic fish was red (31.03% and 28.57%, respectively). Microplastics ingestion along different fish sizes fluctuated. This study provides evidence to fill a gap of research relating to microplastic ingestion by fish from Thailand.

Candidate gene identification of ovulation-inducing genes by RNA sequencing with an in vivo assay in zebrafish.

We previously reported the microarray-based selection of three ovulation-related genes in zebrafish. We used a different selection method in this study, RNA sequencing analysis. An additional eight up-regulated candidates were found as specifically up-regulated genes in ovulation-induced samples. Changes in gene expression were confirmed by qPCR analysis. Furthermore, up-regulation prior to ovulation during natural spawning was verified in samples from natural pairing. Gene knock-out zebrafish strains of one of the candidates, the starmaker gene (stm), were established by CRISPR genome editing techniques. Unexpectedly, homozygous mutants were fertile and could spawn eggs. However, a high percentage of unfertilized eggs and abnormal embryos were produced from these homozygous females. The results suggest that the stm gene is necessary for fertilization. In this study, we selected additional ovulation-inducing candidate genes, and a novel function of the stm gene was investigated.

Fine selection of up-regulated genes during ovulation by in vivo induction of oocyte maturation and ovulation in zebrafish.

BACKGROUND: Two essential processes, oocyte maturation and ovulation, are independently induced, but proceed cooperatively as the final step in oogenesis before oocytes become fertilizable. Although these two processes are induced by the same maturation-inducing steroid, 17α, 20ß-dihydroxy-4-pregnen-3-one (17, 20ß-DHP), in zebrafish, it has been suggested that the receptor, and thus the signal transduction pathway is different for each process. Although much progress has been made in understanding the molecular mechanisms underlying the induction of oocyte maturation, the mechanisms for inducing ovulation remain under investigation. In the present study, in vivo induction techniques that permit the induction of oocyte maturation and ovulation in living zebrafish (in vivo assays) were used to select highly up-regulated genes (genes associated with ovulation). Using an in vivo assay, ovarian tissues that induced only oocyte maturation could be obtained. This made it possible for the first time to distinguish maturation-inducing genes from ovulation-inducing genes. Using a genome-wide microarray of zebrafish sequences, the gene expression levels were compared among an ethanol (EtOH)-treated group (non-activated group), a diethylstilbestrol (DES)- or testosterone (Tes)-treated group (maturation-induced group), and a 17, 20ß-DHP-treated group (maturation- and ovulation-induced group). Ovulation-specific up-regulated genes were selected. The mRNA expression levels of the selected genes were measured by quantitative polymerase chain reaction (qPCR). RESULTS: Among 34 genes identified, three that showed ovulation-specific increases were selected as candidates potentially associated with ovulation. The ovulation-specific up-regulation of three candidates, slc37a4a, zgc:65811 and zgc:92184 was confirmed by qPCR. CONCLUSION: Our in vivo assay provides a new approach to precisely select genes associated with ovulation.

Generation of Transparent Zebrafish with Fluorescent Ovaries: A Living Visible Model for Reproductive Biology.

The transparent zebrafish enables researchers to study the morphology and distribution of cells and tissues in vivo. To capture the dynamic processes of germ cell proliferation and juvenile ovarian development in zebrafish in vivo, we established transgenic (TG) lines to allow us to monitor the changes in the ovaries of living fish. The original transgenic line with ovarian fluorescence was occasionally established. Although the cDNA integrated in the strain was constructed for the expression of enhanced green fluorescent protein (EGFP) driven by the medaka ß-actin promoter, expression of EGFP is restricted to the oocytes and gills in adult fish. Mutant strains with transparent bodies, roy and ruby, were isolated in zebrafish. In this study, we crossed the TG strain with fluorescent ovary with transparent strains and established the TG (ß-actin:EGFP);ruby strain. The strain is highly transparent, and the oocytes are easily observed in living fish. We identified a fluorescent tissue that might contain the undifferentiated germ cells close to the cloaca in the strain. This strain can be used for analysis of ovarian development in vivo.