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In Vietnam, a great number of toxic substances, including carcinogens and procarcinogens, from industrial and agricultural activities, food production, and healthcare services are daily released into the environment. In the present study, we report the development of novel yeast-based biosensor systems to determine both genotoxic carcinogens and procarcinogens by cotransformation with two plasmids. One plasmid is carrying human CPR and CYP (CYP3A4, CYP2B6, or CYP2D6) genes, while the other contains the RAD54-GFP reporter construct. The three resulting coexpression systems bearing both CPR-CYP and RAD54-GFP expression cassettes were designated as CYP3A4/CYP2B6/CYP2D6 + RAD54 systems, respectively and used to detect and evaluate the genotoxic potential of carcinogens and procarcinogens by selective activation and induction of both CPR-CYP and RAD54-GFP expression cassettes in response to DNA damage. Procarcinogens were shown to be predominantly, moderately or not bioactivated by one of the CYP enzymes and thus selectively detected by the specific coexpression system. Aflatoxin B1 and benzo(a)pyrene were predominantly detected by the CYP3A4 + RAD54 system, while N-nitrosodimethylamine only moderately activated the CYP2B6 + RAD54 reporter system and none of them was identified by the CYP2D6 + RAD54 system. In contrast, the genotoxic carcinogen, methyl methanesulfonate, was detected by all systems. Our yeast-reporter system can be performed in 384-well microplates to provide efficient genotoxicity testing to identify various carcinogenic compounds and reduce chemical consumption to about 53% as compared with existing 96-well genotoxicity bioassays. In association with a liquid handling robot, this platform enables rapid, cost-effective, and high-throughput screening of numerous analytes in a fully automated and continuous manner without the need for user interaction.

Periophthalmodon septemradiatus (Hamilton, 1822) is a unique mudskipper living in the mudbanks from estuarine to riverine regions in the Vietnamese Mekong Delta (VMD), but there is no data on its growth patterns and condition factors that are helpful for fish resource assessment and adaptation understanding. This study was conducted at five sites, from the lower (Soc Trang province) to middle (Can Tho city) and upper (An Giang province) reaches of Bassac River in VMD, to provide knowledge on growth patterns and condition factors to this mudskippers. Fish samples were caught using traps and hands for 24 months, from July 2017 to June 2019, at these five sites. The total length and weight of 3,417 individuals (1,340 females and 2,077 males) varied by sex, season and site (p < 0.001 for all cases). This species exhibited a positive allometric type as the slope (b = 3.06 ± 0.01) of the length-weight relationship (LWR) was >3 (p < 0.001) for both sexes. The growth pattern changed with sex as mudskipper showed isometry in females but positive allometry in males. Maturity also affected fish growth type since it shifted from negative allometry in immature groups to positive allometry in mature groups. The growth pattern of fish changed from isometry in the dry season to positive allometry in the wet season. The mudskipper showed isometry at the lower reaches in Soc Trang but positive allometry at the middle and upper reaches in Can Tho and An Giang. The condition factor (CF) did not change according to sex, size and season, but with month and site variables. The present environmental condition in these studied sites tended to be not good enough for this fish as CF (0.95 ± 0.01) was less than 1 (p < 0.001). The findings provided basic information on the growth and adaptation of P. septemradiatus being helpful in fish adaptation understanding and resource conservation in VMD.

Growth pattern and condition factor (CF) are essential to fish resource assessment but limited to Periophthalmus gracilis—an amphibious fish living in the mudflats along the Indo-Pacific regions, including the Mekong Delta (MD), Vietnam. This study lasted from April 2020 to March 2021 to verify if their growth pattern and CF change with sex, size, season, month and site. The total length and weight of 486 individuals (236 females and 250 males) were 2.9–5.9 cm and 0.13–1.66 g, respectively. The mudskipper displayed negative allometry as the slope value (b = 2.69 ± 0.06) obtained from length and weight (LWR) was significantly less than 3 (p < 0.01), indicating that most fish specimens were caught in the immature stage. The fish growth pattern did not change with sex as both males and females displayed negative allometry but varied by size since the mudskipper showed negative allometry in the immature group and isometry in the mature group. Likewise, growth type changed with season since fish showed negative allometry in the dry season but isometry in the wet season. As the slope value (b) varied by site and month, the mudskipper displayed spatiotemporal growth patterns, ranging from negative to positive allometry. The CF was impacted by sex as this value of females (1.09 ± 0.02) was higher than that of males (0.96 ± 0.01, p < 0.01). Besides, CF was regulated by fish length since this value was higher in the mature group (1.12 ± 0.03) than in the immature group (1.01 ± 0.01, p < 0.01). Likewise, CF was affected by season as this value was higher in the wet season (1.05 ± 0.02) than in the dry season (0.99 ± 0.01, p < 0.01). Although the CF varied with site and month variables (p < 0.01), this value (1.02 ± 0.01) was generally higher than 1, showing fish adapted well to their habitat. The fish length at first capture should be increased to exploit this species sustainably.

Length-weight relationship (LWR), growth pattern and condition factor (CF) play a vital role in fish resource evaluation and management but data on this is limited for Periophthalmus variabilis. This is an amphibious fish that lives in the mudflats of the mangrove forests in the Western Pacific regions, including the Vietnamese Mekong Delta (VMD). This paper contributes to the understanding of the LWR, growth pattern and CF of P. variabilis. Fish specimens were collected by hand at four sites in the VMD from April 2020 to March 2021. The analysis of 495 individual fish (259 females and 236 males) showed that fish weight could be estimated from a given fish length due to high determination values (r2 = 0.70 − 0.97). Dusky-gilled mudskippers of the VMD exhibited positive allometry, as indicated by their larger than 3 b value (b = 3.094 ± 0.045, p = 0.04). However, the growth pattern of the mudskipper between the sex and maturation stage (immature versus mature) showed isometry. These fish displayed positive allometry in the dry season (b = 3.138 ± 0.065) (>3, p = 0.04) but isometry in the wet season (b = 3.058 ± 0.061) (≈3, p = 0.34). Fish growth ranged from isometry to positive allometry and varied by site (b = 2.850 ± 0.103–3.370 ± 0.114) and month (b = 2.668 ± 0.184–3.588 ± 0.299) based on the b value. The CF of P. variabilis was not affected by sex (p = 0.29), body size (p = 0.64) or season (p = 0.43), but was affected by site (p = 0.01) and month (p = 0.01). The CF of this species (1.05 ± 0.02) was higher than 1 (p

The food composition and feeding ecology of fishes living in the intertidal zone play an essential role in understanding the energetic connectivity between terrestrial and aquatic systems. Periophthalmus chrysospilos is an amphibious fish species occurring in the intertidal zone, but data on its diet and foraging ecology is still poorly known. This study on Ps. chrysospilos was carried out from April 2020 to March 2021 at four sites within the Mekong Delta estuary to define the influence of spatio-temporal factors on the diet of this species. The diet composition and relative gut lengths (RGLs) of Ps. chrysospilos were analysed in relation to four parameters—sex, size, site, and season. A total of 1,031 individuals were collected, and their digestive tract lengths were used to calculate the RGL. The digestive tracts of only 546 individuals were with food items (approximately 1:1 of empty vs full digestive tract) and were subsequently used for further analyses. The ranges in total length and weight in both adult and juvenile individuals were 3.4–10.6 cm and 0.38–14.13 g, respectively. The RGL values varied with season, fish size and site, but was always lower than 1, indicating a predominantly carnivorous diet. The variability of food items found within the digestive tracts demonstrated its adaptability in pursuing prey items within the limits of the littoral zone, and its importance as a conduit of terrestrial-marine connectivity. This species is characterised as an opportunistic mesopredator feeding primarily on Acetes spp., Uca spp., Dolichoderus sp., and rarely on Polychaeta and Actinopterygii. Other items found within the digestive tract are Mollusca, and detritus. The diet composition of Ps. chrysospilos did not vary with season and size, but changed with sex and site parameters. Uca spp. contributed to the sexual variation in dietary component, whereas Mollusca, Uca spp., Dolichoderus sp. and detritus, were drivers for spatial variation in the dietary component. The research provides fundamental information on diet composition and feeding strategy, as well as contributes towards knowledge on foraging ecology and resource use by intertidal animal communities.

Ellochelon vaigiensis is widely distributed and plays a vital role in the fisheries in the Mekong Delta (MD), but data on its population biological traits have not been known. Consequently, this study was conducted to provide data on its population biology used for fishing status assessment and fish resources management. Fish specimens were collected using trawl nets in two regions of the Hau River mouth, including northern in Ben Tre and Tra Vinh (BTTV) and southern in Soc Trang and Bac Lieu (STBL). Fish population biological parameters were estimated using FiSAT II software based on the fish length-frequency data. The male and female length-frequency data in each ecoregion were pooled together. Data analysis of 1,383 individual fish showed the sex ratio of the species was 1.00:1.30 at BTTV (309 females and 402 males) and 1.00:1.25 STBL (299 females and 373 males). Most fish specimens were caught at 12–22 cm total length (914 individuals), accounting for 66.09% of the fish collection. The difference in salinity between these two regions could affect the population biological parameters of E. vaigiensis. There were five cohorts (e.g., five growth curves) in the BTTV and STBL. The von Bertalanffy curves of fish populations at BTTV and STBL were L = 33.6 (1 −e−0.46(t + 0.34)) L = 31.5 (1 −e−0.56(t + 0.29)), respectively. The growth index (Φ′) of this species at STBL (2.74) was higher than that at BTTV (2.72), whereas its longevity at BTTV (6.52 yrs) was higher than at STBL (5.36 yrs). The biomass and relative yield parameters, including E0.1, E0.5 and Emax were 0.358, 0.265 and 0.436 at BTTV; and 0.418, 0.293, and 0.513 at STBL, respectively. The fishing (F), natural (M), and total (Z) mortalities were 0.35/yr, 1.06/yr, and 1.41/yr at BTTV; and 0.55/yr, 1.24/yr, and 1.78/yr at STBL, respectively. The BTTV and STBL population was not overexploited because the exploitation rate (EBTTV = 0.25, ESTBL = 0.31) was lower than E0.1 (0.358 in BTTV and 0.418 in STBL).

This present study provides an overview of the reproductive traits, including ovarian development, spawning season, size at maturity (Lm), and fecundity of Acentrogobius viridipunctatus – a high economic value fish in the Vietnamese Mekong Delta (VMD). A total of 432 females were collected using trawl nets from January to December 2020 at four sites, including Long Huu-Tra Vinh (LHTV), Trung Binh-Soc Trang (TBST), Dien Hai-Bac Lieu (DHBL), and Tan Thuan-Ca Mau (TTCM). The ovarian diameter was seen to increase from 2.09 (stage I) to 6.57 mm (stage V). Histological analysis showed that the goby was a multi-spawner due to the different oocyte stages found in stages IV and V of ovaries. It can release eggs all year-round due to the monthly appearance of ovarian stages IV and V during the study period, with the main peak in the 2–4 months of the wet season noted with the highest value of gonadosomatic index at that time. The Lm increased from 6.6 cm at TBST to 9.4 cm at TTCM. This species displayed relatively high fecundity, ranging from 5,481 to 130,683 eggs/female. The average fecundity of this fish was 27,698 ± 7,983 eggs/female at LHTV, 46,592 ± 7,264 eggs/female at TBST, 23,271 ± 4,985 eggs/female at DHBL, and 31,408 ± 2,515 eggs/female at TTCM. Egg diameter ranged from 0.45 ± 0.01 at DHBL to 0.50 ± 0.01 at TBST. For sustainable exploitation, local governments should ask the fishers to avoid catching fish during the main spawning period, and the fish length at first capture should be >Lm.

Periophthalmus chrysospilos is an amphibious fish living in mudflats from eastern India to Indonesia, including the Vietnamese Mekong Delta. Population biological traits play an important role in fishery assessment, but understanding is limited for this species. In total 1,031 specimens were caught in two regions covering four provinces, including the TVST (Duyen Hai, Tra Vinh and Tran De, Soc Trang) and BLCM (Dong Hai, Bac Lieu and Dam Doi, Ca Mau). Results found that the sex ratio was close to 1:1. The parameters of the von Bertalanffy in TVST were L∞ = 12.8 cm, K = 0.41 yr−1, t0 = −0.10 yr and in BLCM were 12.7 cm, 0.38 yr−1 and −0.08 yr, respectively. Although the growth coefficient (Φ′) in BLCM (1.79), was lower than that in TVST (1.83), the species shared a similar size at first capture (7.9 cm in TVST and 7.9 cm in BLCM). The species suffered from heavy pressure of fishing in TVST as fishing mortality in TVST (2.32 yr−1) was higher than that in BLCM (1.38 yr−1), leading to the higher total mortality (Z = 3.60 yr−1) in TVST compared to BLCM (Z = 2.59 yr−1). By contrast, the species showed similar natural mortality over both sites (1.20 yr−1 in TVST and 1.22 yr−1 in BLCM). The Periophthalmus chrysospilos population was reasonably exploited because E values (0.64 in TVST and 0.53 in BLCM) were lower than E10 (0.706 in BTTV and 0.705 in STBL). Nonetheless, to avoid the consequences of overfishing, some sustainable fisheries practices should be implemented, such as protecting mangrove forests, restricting fishing during the recruitment period, using appropriate fishing tools and increasing mesh size.