Seahorse TLR5 gene responses to Vibrio vulnificus infection, which in combination with scuticociliates causes heavy reductions in seahorse aquaculture

Transcriptional responses of liver and spleen in Lota lota to polyriboinosinic polyribocytidylic acid

Introduction

The cultured Lota lota can meet the market demand in the context of the decline of wild resources, but the disease in the high-density culture process also deserves attention. Therefore, understanding the immune regulation mechanisms of L. lota will be the basis for obtaining high benefits in artificial culture.

Methods

To explore the viral response mechanism of L. lota, RNA-seq was applied to identify the transcriptomic changes of the liver and spleen in L. lota by poly (I:C) stress.

Results

The DEGs (liver: 2186 to 3123; spleen 1542 to 2622) and up-regulated genes (liver: 1231 to 1776; spleen 769 to 1502) in the liver and spleen increased with the prolongation (12h to 48h) of poly (I:C)-stimulation time. This means L. lota needs to mobilize more functional genes in response to longer periods of poly (I:C)-stimulation. Despite the responses of L. lota to poly (I:C) showed tissue-specificity, we hypothesized that both liver and spleen of L. lota can respond to poly (I:C) challenge may be through promoting apoptosis of DNA-damaged cells, increasing the activity of immune-enhancing enzymes, and increasing energy supply based on DEGs annotation information.

Conclusions

Our results demonstrate the transcriptional responses of L. lota to poly (I:C)-stimulation, and these data provide the first resource on the genetic regulation mechanisms of L. lota against viruses. Furthermore, the present study can provide basic information for the prevention of viral diseases in L. lota artificial culture process.

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.

Dual RNA-Seq Unveils the Role of the Pseudomonas plecoglossicida fliA Gene in Pathogen-Host Interaction with Larimichthys crocea

In the present study, Larimichthys crocea and Pseudomonas plecoglossicida were selected as a host-pathogen interaction model for teleosts and prokaryotic pathogens. Five shRNAs were designed and synthesized to silence the fliA gene, all of which resulted in pronounced reductions in fliA mRNA; the mutant strain with the best silencing efficiency of 92.16% was chosen for subsequent analysis. A significant decrease in motility, intracellular survival and escape was observed for the fliA-RNAi strain of P. plecoglossicida, whereby silencing of the fliA gene led to a 30% decrease in mortality and a four-day delay in the onset of infection in L. crocea. Moreover, silencing of P. plecoglossicida fliA resulted in a significant change in both the pathogen and host transcriptome in the spleens of infected L. crocea. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of pathogen transcriptome data showed that silencing fliA resulted in downregulation of 18 flagellum-related genes; KEGG analysis of host transcriptome data revealed that infection with the fliA-RNAi strain caused upregulation of 47 and downregulation of 106 immune-related genes. These pathogen-host interactions might facilitate clearance of P. plecoglossicida by L. crocea, with a significant decrease in fliA-RNAi P. plecoglossicida strain virulence in L. crocea.