Isolation, identification, and histopathological analysis of Vibrio tubiashii from lined seahorse Hippocampus erectus

Identification and whole-genome sequencing analysis of Vibrio vulnificus strains causing pearl gentian grouper disease in China

Vibrio vulnificus is a pathogenic bacterium that causes disease in marine fish, affecting fish farming and human health worldwide. In May 2021, in the Bohai Bay region, a disease broke out in commercially farmed pearl gentian grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus), causing huge economic losses. The diseased fish had skin lesions, water accumulation in their abdomens, and showed tissue and organ damage. V. vulnificus biotype 2 has been reported in eels and other marine fish, but it is less reported in pearl gentian grouper. In this study, the pathogenic strain isolated from diseased fish was identified as V. vulnificus EPL 0201 biotype 2 on the basis of physiological and biochemical characteristics and the results of 16S rRNA gene and gyrB sequencing, virulence gene detection, and recursive infection experiments. To gain a comprehensive understanding of the pathogenicity and drug resistance of this strain, whole-genome sequencing was performed. Whole-genome analysis showed that the gene map of this strain was complete. The Virulence Factor Database annotation results showed that this strain had the key virulence factor genes vvhA and rtxA, which cause host disease. In addition, this strain had genes conferring resistance against cephalosporins, aminoglycosides, tetracyclines, and sulfonamides. Antimicrobial susceptibility testing confirmed the presence of these resistance genes identified in the genome. The results of this study show that V. vulnificus EPL 0201 biotype 2 is a multi-drug resistant strain with high pathogenicity.

Diversity of Seahorse Species (Hippocampus spp.) in the International Aquarium Trade

Seahorses (Hippocampus spp.) are threatened as a result of habitat degradation and overfishing. They have commercial value as traditional medicine, curio objects, and pets in the aquarium industry. There are 48 valid species, 27 of which are represented in the international aquarium trade. Most species in the aquarium industry are relatively large and were described early in the history of seahorse taxonomy. In 2002, seahorses became the first marine fishes for which the international trade became regulated by CITES (Convention for the International Trade in Endangered Species of Wild Fauna and Flora), with implementation in 2004. Since then, aquaculture has been developed to improve the sustainability of the seahorse trade. This review provides analyses of the roles of wild-caught and cultured individuals in the international aquarium trade of various Hippocampus species for the period 1997–2018. For all species, trade numbers declined after 2011. The proportion of cultured seahorses in the aquarium trade increased rapidly after their listing in CITES, although the industry is still struggling to produce large numbers of young in a cost-effective way, and its economic viability is technically challenging in terms of diet and disease. Whether seahorse aquaculture can benefit wild populations will largely depend on its capacity to provide an alternative livelihood for subsistence fishers in the source countries. For most species, CITES trade records of live animals in the aquarium industry started a few years earlier than those of dead bodies in the traditional medicine trade, despite the latter being 15 times higher in number. The use of DNA analysis in the species identification of seahorses has predominantly been applied to animals in the traditional medicine market, but not to the aquarium trade. Genetic tools have already been used in the description of new species and will also help to discover new species and in various other kinds of applications.

Edwardsiella tarda induces enteritis in farmed seahorses (Hippocampus erectus): An experimental model and its evaluation

Bacterial enteritis is an important deadly threat to farmed seahorses. However, its pathogenesis is obscure because of the paucity of reproducible experimental intestinal inflammation models. Herein, a strain of Edwardsiella tarda YT1 from farmed seahorse Hippocampus erectus was isolated and identified by morphological, phylogenetic, and biochemical analysis, and confirmed as a pathogen of enteritis for the first time by challenge experiment. Two E. tarda concentrations (1 × 10⁵ and 1 × 10⁷ colony forming units [cfu] ml^-1) were confirmed suitable for an enteritis model by intraperitoneal injection. To develop and evaluate the experimental model, we challenged seahorses with E. tarda and found that (1) the infection inhibited body length increase, significantly decreased body weight (P < 0.05), and induced typical pathological features including anorexia, anal inflammation, and intestinal fluid retention; (2) 19 external (weight, height, anal inflammation, feeding status, and intestinal fluid retention), histological (goblet and inflammatory cell numbers and thickening of lamina propria and muscularis mucosae), and molecular (hepcidin, liver-expressed antimicrobial peptide, lysozyme, piscidin, interleukin [IL]-1β, IL-1β receptor, IL-2, IL-10, interferon1, tumor necrosis factor [TNF]-α, and toll-like receptor 5 [TLR5]) indicators were suitable for model evaluation, as they could sensitively respond and varied similarly throughout the experiment, indicating the high sensitivity of seahorses against pathogen invasion; (3) TLR5 may play an essential role in triggering host immune responses during E. tarda-induced chronic enteritis, and (4) the evaluating system could reflect the pattern and intensity of disease progression. Thus, we developed an experimental model and an evaluating system of bacterial enteritis in farmed seahorses, helping us to reveal the pathogenesis of bacterial enteritis, identify potential therapeutic drugs, and search suitable genetic markers for seahorse molecular breeding.