Biodiversity assessment is an important part of conservation management that ideally can be accomplished with noninvasive methods without influencing the structure and functioning of ecosystems. Environmental DNA (eDNA) metabarcoding has provided a promising tool to enable fast and comprehensive monitoring of entire ecosystems, but widespread adoption of this technique requires performance evaluations that compare it with conventional surveys. We compared eDNA metabarcoding and trawling data to evaluate their efficiency to characterize demersal fish communities in the Estuary and Gulf of Saint‐Lawrence, Canada. Seawater and bottom trawling samples were collected in parallel at 84 stations. For a subset of 30 of these stations, water was also collected at three different depths (15, 50, and 250 m) across the water column. An eDNA metabarcoding assay based on the 12S mitochondrial gene using the MiFish‐U primers was applied to detect fish eDNA. We detected a total of 88 fish species with both methods combined, with 72 species being detected by eDNA, 64 species detected by trawl, and 47 species (53%) overlapped between both methods. eDNA was more efficient for quantifying species richness, mainly because it detected species known to be less vulnerable to trawling gear. Our results indicated that the relative abundance estimated by eDNA and trawl is significantly correlated for species detected by both methods, while the relationship was also influenced by environmental variables (temperature, depth, salinity, and oxygen). Integrating eDNA metabarcoding to bottom trawling surveys could provide additional information on vertical fish distribution in the water column. Environmental DNA metabarcoding thus appears to be a reliable and complementary approach to trawling surveys for documenting fish biodiversity, including for obtaining relative quantitative estimates in the marine environment.

Aim:Epizootic ulcerative syndrome (EUS) causes by aquatic oomycete fungus, Aphanomyces invadans is a dangerous fish disease of a wide range of fresh and brackish water, wild and farmed fish throughout the world. The objective of the present study was to determine the susceptibility of a number of tropical fish species to the EUS and compare the severity of infection between experimental groups.Materials and Methods:Snakehead, Channa striata (Bloch, 1793); snakeskin gourami, Trichopodus pectoralis (Regan, 1910); koi carp, Cyprinus carpio (Linnaeus, 1758); broadhead catfish, Clarias macrocephalus (Günther, 1864); goldfish, Carassius auratus (Linnaeus, 1758); climbing perch, Anabas testudineus (Bloch, 1792); and Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) were challenged by intramuscular injection using zoospores of Aphanomyces invadans (NJM9701). The infected fish skins and muscles were examined for EUS histopathological characteristics, and the results on the severity of lesions and mortality were analyzed using SPSS program.Results:All zoospore-injected fish were shown to be susceptible to the EUS infection except Nile tilapia. Although, the general histopathological pattern was similar in the zoospore-injected group, but there were some variation in granulomatous reaction, that is the presence or absence of giant cells, and time of mortality were detected. The result of statistical analysis showed that there was a significant difference between species, (c2=145.11 and p<0.01).Conclusion:Gourami, koi carp, and catfish were demonstrated to be highly susceptible while goldfish and climbing perch were found to be moderately susceptible to the EUS infection. These findings suggested that the cellular response of fish to mycotic infection and granulomatous reaction varied in different fish species, which could not be an indicator of susceptibility or resistant to the EUS itself, although it was shown that the granulation rate and the level of maturity or solidification (consolidation of granulomas) were higher in resistant fish.