Ovarian and spawning reference, size at first maturity and fecundity of Glossogobius giuris caught along Vietnamese Mekong Delta.

This study investigates the ovarian development, spawning patterns, maturity size and fecundity of the goby Glossogobius giuris-a commercial fish in the Vietnamese Mekong Delta-based on the data analysis of 659 individuals. Specimens were caught using trawl nets from four sites representing freshwater (Cai Rang, Can Tho) to salinized regions in the dry season (Long Phu, Soc Trang), and brackish water regions (Hoa Binh, Bac Lieu and Dam Doi, Ca Mau) over the 12 months of 2020. Histological analysis showed that it was a multi-spawner as different stages of oocytes appeared in mature ovaries. The fish could spawn throughout the year, with a peak in April at the freshwater region and in September at salinized and brackish areas as mature ovaries appeared monthly during the studied period and gonadosomatic index displayed the highest value in April and in September, respectively. This goby's primary egg releasing time tended to be regulated by salinity changes over the four sampling sites. Likewise, size at first maturity of this species could be related to the salinity variation as this value was the longest in freshwater (6.14 ± 0.17) and the shortest in the salinization region (4.82 ± 0.66). Batch fecundity is measured at 5,118-100,003 eggs/female and related to fish length and weight (r2  > 0.76). Findings can be useful for the development of fish conservation strategies and artificial reproducing studies.

The mismatch between morphological and molecular attribution of three Glossogobius species in the Mekong Delta.

BACKGROUND: The Vietnamese Mekong Delta (VMD) is the granary for the whole country, providing animal and plant resources, especially fish. Among the fish species, the genus Glossogobius are the majority. Until now, research for this species has been solely relied on fish morphology for identification. Hence, the present study aimed to describe the morphological variations of the morphologically identified gobies and to validate them at the molecular level through the sequencing of the barcode region, the mitochondrial cytochrome C oxidase subunit I (COI) gene to preliminary provide fundamental information for conservation. RESULTS: The mitochondrial cytochrome C oxidase subunit I genes were amplified successfully with an approximate size of 650-680 bp. Their morphometries were quite different, and the genetic distance (p-value) among groups and within groups ranged from 0.00 to 0.12. The similarity of the COI gene sequences between the analyzed samples and in the NCBI database was from 87.01 to 100%. The specimens of G. aureus, G. giuris and G. sparsipapillus were interspersed in small branches of the phylogenetic tree with a low genetic distance highlighting that the genetic diversity of COI gene was low among species. Therefore, it is recommended that a combination of morphological method and mtCOI DNA barcoding is required for accurate classification. CONCLUSION: This study helps determine three distinct lineages of Glossogobius species, so an appropriate strategy can be proposed for exploitation and conservation.

First reference on reproductive biology of Butis koilomatodon in Mekong Delta, Vietnam.

BACKGROUND: The key to fishery management is knowing the appropriate reproductive strategies of the targeted fish. For most gobiid species, the iteroparous pattern is dominant compared to semelparity. Albeit Butis koilomatodon plays an important role in the Mekong Delta's food supply, its reproductive biological data have not been known. Hence, this study was conducted to provide new fundamental knowledge of reproductive traits of Butis koilomatodon in the Mekong Delta. RESULTS: A total of 1314 individuals (903 males and 411 females) were monthly collected by bottom gill nets from July 2019 to June 2020 at six sampling sites along estuarial and coastal regions, from Tra Vinh to Ca Mau provinces, southern of Vietnam. pH and salinity of these six sampling sites are 7.72-7.93 pH and 11.17-26.17‰, respectively. The pH varies with sites, but not seasons; whereas a reverse case is found in salinity. Different types of oocytes are found in histological specimens of ovaries prove that B. koilomatodon is a multi-spawner. The gonadosomatic index value, together with the monthly presence of mature ovaries reveal that this species spawns throughout the year. The length at first mature male Butis koilomatodon (5.1-8.6 cm) is higher than that of females (4.8-6.7 cm), except in Hoa Binh and Dong Hai. Batch fecundity (3085 to 32,087 eggs/female) increases with fish weight (1.48-12.30 g) and length (4.8-9.0 cm) due to high determination values (r2 > 0.6). CONCLUSION: Knowledge of reproductive traits gained from this study was a reference source for future studies and helped manage this species' resources.