Hepcidin, a cysteine-rich antimicrobial peptide, has a highly conserved gene structure in teleosts, and it plays an essential role in host immune response against various pathogenic bacteria. Nonetheless, few studies on the antibacterial mechanism of hepcidin in golden pompano (Trachinotus ovatus) have been reported. In this study, we synthesized a derived peptide, TroHepc2-22, from the mature peptide of T. ovatus hepcidin2. Our results showed that TroHepc2-22 has superior antibacterial abilities against both Gram-negative (Vibrio harveyi and Edwardsiella piscicida) and Gram-positive (Staphylococcus aureus and Streptococcus agalactiae) bacteria. Based on the results of a bacterial membrane depolarization assay and propidium iodide (PI) staining assay in vitro, TroHepc2-22 displayed antimicrobial activity by inducing the bacterial membrane depolarization and changing the bacterial membrane permeability. Scanning electron microscopy (SEM) visualization illustrated that TroHepc2-22 brought about membrane rupturing and the leakage of the cytoplasm for the bacteria. In addition, TroHepc2-22 was verified to have hydrolytic activity on bacterial genomic DNA in view of the results of the gel retardation assay. In terms of the in vivo assay, the bacterial loads of V. harveyi in the tested immune tissues (liver, spleen, and head kidney) were significantly reduced in T. ovatus, revealing that TroHepc2-22 significantly enhanced the resistance against V. harveyi infection. Furthermore, the expressions of immune-related genes, including tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin 1-β (IL-1β), IL-6, Toll-like receptor 1 (TLR1), and myeloid differentiation factor 88 (MyD88) were significantly increased, indicating that TroHepc2-22 might regulate inflammatory cytokines and activate immune-related signaling pathways. To summarize, TroHepc2-22 possesses appreciable antimicrobial activity and plays a vital role in resisting bacterial infection. The observation of our present study unveils the excellent application prospect of hepcidin as a substitute for antibiotics to resist pathogenic microorganisms in teleosts.

MicroRNAs (miRNAs) could regulate various biological processes. Nervous necrosis virus (NNV) is one of the primary germs of the Humpback grouper (Cromileptes altivelis), a commercial fish of great importance for Asian aquaculture. However, there is limited available information on the host-virus interactions of C. altivelis. miRNAs have been shown to play key roles in the host response to infection by a variety of pathogens. To better understand the regulatory mechanism of miRNAs, we constructed miRNA transcriptomes and identified immune-related miRNAs of C. altivelis spleen in response to NNV infection. Reads from the three libraries were mapped onto the Danio rerio reference genome. As a result, a total of 942 mature miRNAs were determined, with 266 known miRNAs and 676 novel miRNAs. Among them, thirty-two differentially expressed miRNAs (DEmiRs) were identified compared to the PBS control. These DEmiRs were targeted on 895 genes, respectively, by using miRanda v3.3a. Then, 14 DEmiRs were validated by qRT-PCR and showed consistency with those obtained from high-throughput sequencing. In order to study the relationship between viral infection and host miRNA, a cell line from C. altivelis brain (CAB) was used to examine the expressions of five known DEmiRs (miR-132-3p, miR-194a, miR-155, miR-203b-5p, and miR-146) during NNV infection. The results showed that one miRNA, cal-miRNA-155, displayed significantly increased expression in response to the virus infection. Subsequently, it was proved that overexpression of cal-miR-155 enhanced cell apoptosis with or without NNV infection and inhibited virus replication in CAB cells. Oppositely, the cal-miRNA-155 inhibitor markedly suppressed apoptosis in CAB cells. The results of the apoptosis-related genes mRNA expression also showed the regulation of cal-miR-155 on the apoptosis process in CAB cells. These findings verify that miR-155 might exert a function as a pro-apoptotic factor in reply to NNV stimulation in CAB cells and help us further study the molecular mechanisms of the pathogenesis of NNV in C. altivelis.

Humpback grouper Chromileptes altivelis (HG), red-spotted grouper Epinephelus akaara (RG) and black seabream Acanthopagrus schlegelii (BS) are three popular perciform fishes with an increasingly important farming industry. The prices of BS are much lower than other grouper species; however, the differences in the nutritive values of these three perciform fishes with commercial specifications have not been reported. In this study, the biochemical composition and non-volatile taste active compounds of adult HG, RG and BS were investigated. Moisture contents in BS were significantly higher than in HG and RG (p < 0.05), and relatively lower crude protein contents in BS were observed. Lipid contents of back muscle were lower than that of abdomen muscle in the three fish species. C22:6n-3 (DHA) was the major poly-unsaturated fatty acid (PUFA) in HG and BS, while the main PUFA in RG was C18:2n-6. The total healthy omega-3 fatty acid (Σn-3) profiles in HG were the highest (24.08–24.59%), followed by RG (18.24–19.06%) and BS (13.63–15.91%) (p < 0.05). Glycine was the most abundant free amino acid (FAA) in HG and RG, while lysine was the major FAA in BS. Equivalent umami concentration (EUC) values in BS were the highest, followed by HG and RG (p < 0.05). Lactic acid and PO₄³⁻ were the major organic acids and inorganic ions, respectively. In conclusion, HG and RG provided more protein and healthy omega-3 fatty acids than BS, while BS had a stronger umami taste according to the EUC values.

The spread of invasive species (IS) has the potential to upset ecosystem balances. In extreme cases, this can hinder economical utilization of both aquatic (fisheries) and terrestrial (agricultural) systems. As a result, many countries regard risk assessment of IS as an important process for solving the problem of biological invasion. Yet, some IS are purposefully introduced for what is seen as their potential economic benefits. Thus, conducting IS risk assessments and then formulating policies based on scientific information will allow protocols to be developed that can reduce problems associated with IS incursions, whether occurring purposefully or not. However, the risk assessment methods currently adopted by most countries use qualitative or semiquantitative methodologies. Currently, there is a mismatch between qualitative and quantitative assessments. Moreover, most assessment systems are for terrestrial animals. What is needed is an assessment system for aquatic animals; however, those currently available are relatively rudimentary. To fill this gap, we used the analytic hierarchy process (AHP) to build a risk assessment model system for aquatic IS. Our AHP has four primary indexes, twelve secondary indexes, and sixty tertiary indexes. We used this AHP to conduct quantitative risk assessments on five aquatic animals that are typically introduced in China, which have distinct biological characteristics, specific introduction purposes, and can represent different types of aquatic animals. The assessment results show that the risk grade for Pterygoplichthys pardalis is high; the risk grade for Macrobrachium rosenbergii, Crassostrea gigas, and Trachemys scripta elegans is medium; and the grade risk for Ambystoma mexicanum is low. Risk assessment of the introduction of aquatic animals using our AHP is effective, and it provides support for the introduction and healthy breeding of aquatic animals. Thus, the AHP model can provide a basis for decision-making risk management concerning the introduction of species.