Fish infectious diseases are one of the main constraints of the aquaculture sector. The use of medicinal plants provides a sustainable way of protection using safe, eco-friendly compounds in a more cost-effective way of treatment, compared to antibiotics. The aim of the present study is the assessment of Artemisia arborescens (AA) feed-supplementation effects on gilthead seabream (Sparus aurata). Fish with an average initial body weight of 109.43 ± 3.81 g, were divided into two groups based on AA feed composition (A25 and A50). Following two months of ad libitum feeding, the effect of diets on fish weight and length were measured. Fish serum and mucus were analyzed for non-specific immune parameters (nitric oxide, lysozyme, myeloperoxidase, protease-/anti-protease activity, and complement), antibody responses, oxidative stress (cytochrome P450 1A1, metallothionein), and metabolism markers (total protein, alkaline phosphatase, and glucose). Expression levels of antioxidants (sod1, gpx1), cytokines (il-1b, il-10, tfgb1, and tnfa), hepcidin, and heat shock protein grp75 genes were measured in spleen samples. A results analysis indicated that A. arborescens use as a feed supplement has a compromised positive effect on the growth performance, immune response, and blood parameters of gilthead seabream. Overall, the suitability of A. arborescens as an efficient food supplement for gilthead seabream health improvement was investigated, setting the basis for its application assessment in Mediterranean aquaculture.

Viral infections of teleost fish have great environmental and economic implications in aquaculture. Nervous necrosis virus (NNV) is a pathogen affecting more than 120 different species, causing high mortality and morbidity. Herein, we studied the course of NNV experimental infection of D. labrax, focusing on survivors which indicated viral carrier state. To determine the carrier state of D. labrax head kidney, we performed a gene expression analysis of selected immune-related genes and we profiled its transcriptome 14 days post infection (dpi). All tested genes showed clear differentiations in expression levels while most of them were up-regulated 14 dpi suggesting that their role is not limited in early antiviral responses, but they are also implicated in disease persistence. To gain a better understanding of the fish that survived the acute infection but still maintained a high viral load, we studied the differential expression of 124 up-regulated and 48 down-regulated genes in D. labrax head kidney, at 14 dpi. Concluding, the NNV virus persistent profile was assessed in D. labrax, where immune-related gene modification was intense (14 dpi) and the head kidney transcriptome profile at this time point offered a glimpse into host attempts to control the infection in asymptomatic carriers.

Fish viral infections have great environmental and economic implications in aquaculture. Nervous necrosis virus (NNV) is a pathogen affecting more than 120 different species, causing high mortality and morbidity. Herein, we study how NNV re-infection affects the European sea bass (Dicentrarchus labrax, L.) head kidney transcriptome in disease-resistant and -susceptible sea bass families. To determine how each family responds to re-infection, we performed the RNA-sequencing analysis of experimentally NNV-infected D. labrax. Fish were experimentally infected in a long-term study, and one month after the last recorded death, all surviving fish were re-infected by the same NNV strain. Fish tissues were sampled 7 days upon re-infection. The transcriptome profiles of infected vs. non-infected fish revealed 103 differentially expressed genes (DEGs) for the resistant family and 336 DEGs for the susceptible family. Only a few pathways were commonly enriched in the two families, further indicating that the resistant and susceptible families utilize completely different mechanisms to fight the NNV re-infection. Protein–protein interaction analysis identified a variety of hub genes for the resistant and the susceptible families, quite distinct in their function on NNV resistance. In conclusion, NNV-resistant and -sensitive sea bass transcriptomes were analyzed following NNV survivors’ viral re-infection, offering a glimpse into how host attempts to control the infection depending on its genetic background in relation with virus resistance.

Viral nervous necrosis, caused by the nervous necrosis virus (NNV), is an important threat to aquaculture, causing great economic losses and a high environmental burden. European sea bass (Dicentrarchus labrax) is highly affected by NNV, and selective breeding programs for disease resistance have been established in order to achieve a sustainable aquaculture and minimize the need for vaccines, drugs and antibiotics. Resistant and susceptible European sea bass were experimentally challenged with NNV and their head kidney transcriptomes were analyzed at three time points, i.e., 3 hpi, 2 dpi and 14 dpi. Numerous differentially expressed genes (DEGs) were identified in the head kidneys of resistant and susceptible infected vs. non-infected sea bass. Gene ontology enrichment, pathway, and protein–protein interaction analyses revealed that the NNV-resistant fish control their response to viral infection more efficiently, utilizing different mechanisms compared to the susceptible fish. Resistant fish displayed higher levels of interferon-related elements, cytokines, antigen presentation, T-cell activity, apoptosis, and programmed cell death combined with a controlled inflammatory response and more active proteasome and lysosome functions. The susceptible fish appeared to have high immune responses at the early infection stages, accompanied by high expressions of inflammatory, complement and coagulation pathways. Insulin metabolism was better regulated in the resistant fish and the control of lipid metabolism was less effective in the susceptible family. The cytoskeleton- and cell adhesion-related pathways were mostly down-regulated in the susceptible fish, and the intracellular transport and motor proteins were utilized more efficiently by the resistant fish. The present study represents a thorough transcriptomic analysis of NNV infection effects on a resistant and a susceptible European sea bass head kidney. The obtained results provide valuable information on the mechanisms that offers pathogen resistance to a host, with many aspects that can be exploited to develop more efficient approaches to fighting viral diseases in aquaculture.