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.

As aquaculture expands globally, understanding immune responses in non-traditional farmed species like Octopus vulgaris under varying environmental conditions is increasingly important. This study investigated lysozyme activity, a key innate immune marker, in cell-free hemolymph of O. vulgaris following experimental challenge with four Gram-negative fish pathogens (Photobacterium damselae subsp. piscicida, P. damselae subsp. damselae, Vibrio alginolyticus, and V. anguillarum O1) at two temperatures (21 ± 0.5 °C and 24 ± 0.5 °C). These pathogens were selected because octopus farming frequently occurs near fish aquaculture facilities, raising the potential for pathogen crossover. A total of 216 wild octopuses were injected intramuscularly or intravenously and sampled on days 0, 3, and 7 post-challenge. Lysozyme activity varied by pathogen, injection route, sampling time, and temperature. A significant time- and temperature-dependent increase was observed, especially in IM-challenged groups exposed to Photobacterium species. Elevated temperatures supported a more prolonged immune response. These results highlight lysozyme as a responsive biomarker of innate immunity in O. vulgaris and emphasize the role of environmental factors in immune modulation. This work provides a foundation for disease monitoring and health management in cephalopod aquaculture. Future research should examine long-term lysozyme dynamics, broader pathogen exposure, molecular mechanisms, and additional environmental stressors such as salinity and pollution.

European seabass (Dicentrarchus labrax) hematology is widely used in nutrition, welfare, stress and health studies, yet results from different laboratories are often difficult to compare. This critical narrative review examines how preanalytical handling, analytical procedure and biological context affect that comparability. It is written for researchers, diagnostic laboratories and aquaculture health teams that collect or use D. labrax blood data. Primary European seabass studies are discussed directly where they provide quantitative operating conditions, method comparisons or measurable biological changes. Manual microscopy, automated analyzers and flow cytometry are considered separately because nucleated erythrocytes and thrombocytes create different sources of error in each approach. The review distinguishes practical quality-control checks from the fuller reporting required for reproducibility and separates published operating conditions from numerical limits that have not been validated for the species. Seasonal studies show large coordinated shifts in red blood cell count (RBC), hemoglobin concentration (Hb) and hematocrit (Hct), whereas white blood cell count (WBC) and thrombocyte results remain particularly dependent on cell definition and analytical method. Published pooled estimates are useful for broad comparison but not as universal diagnostic limits. The most defensible use of European seabass hematology is therefore within a defined population, a stated sampling protocol and a method whose performance is known for the intended measurement.