Lymphocystis disease viruses (LCDVs) are viruses that infect bony fish which has been found in different locations across the globe. Four virus species have been classified by the International Committee on Taxonomy of Viruses (ICTV), despite remarkable discrepancies in genome size. Whole genome sequencing and phylogenetic analysis of LCDVs from wild fish from the North Sea and partial sequences from gilthead sea bream of an aquafarm located in the Aegean Sea in Turkey confirm that the LCDV1 genome at 100 kb is approximately half the size of the genomes of LCDV2-4. Since the fish species, of which LCDV1 was isolated, differ taxonomically at the order level, co-speciation can be excluded as the driver of the adaptation of the genome of this nucleocytoplasmic large DNA virus, but may represent an adaptation to the lifestyle of this demersal fish in the northeast Atlantic.

Antibiotics are extensively used in aquaculture to treat and prevent bacterial diseases, but their application can lead to negative side effects such as immunosuppression. Oxytetracycline (OTC) is a widely used antibiotic in aquaculture for treating bacterial diseases due to its broad‐spectrum activity and economic advantage. This study appraises the effects of OTC treatment on the immune response of European sea bass ( Dicentrarchus labrax , L. 1758) by assessing immune‐related gene expression, serological parameters, hematological parameters, and histological findings. Fish were divided into three groups: control (fed with nonsupplemented OTC), 75 mg OTC kg ⁻¹ day ⁻¹ feed, and 100 mg OTC kg ⁻¹ day ⁻¹ feed for 21 days. Blood and tissue samples were collected for analysis on the 4th, 7th, 10th, 14th, and 21st day of OTC feeding. The results showed a decrease in immune response parameters such as nitro blue tetrazolium (NBT) positive cell, total white blood cells (WBCs), serum lysozyme activity, serum Ig‐M levels, and serum complement activity for OTC‐fed fish, while immune‐related genes ( Lys-g , Ig-M , interleukin ( IL )‐ 1β , C3 , and major histocompatibility complex [ MHC ] –IIα ) were significantly downregulated in kidney and spleen tissues, especially with prolonged exposure. The study hypothesized that long‐term use of antibiotics in fish disrupts the functioning of the immune system. As a result of the study, the hypothesis was confirmed, and using OTC for longer than the normal treatment period or in high doses caused negative changes in the immune system parameters and made fish more susceptible to other pathogens.

This study evaluated the effects of three feeding regimens—commercial feed (CF), minced trash fish (MTF), and a 50:50 mixture (MIX)—on the growth performance and tissue composition of the blue crab (Callinectes sapidus) reared in a recirculating aquaculture system (RAS). A total of 96 crabs (8 per tank, four tanks per group) were fed daily at 3% of body weight. Growth was assessed via weight gain, carapace width (CW), and carapace length (CL), while biochemical analyses focused on lipid, fatty acid, and amino acid profiles. The CF and MIX groups exhibited significantly higher final body weights (115.64 ± 3.03 g and 113.53 ± 2.53 g, respectively) and CW (97.88 ± 1.02 mm and 97.16 ± 0.43 mm) compared to the MTF group (p < 0.05), suggesting more frequent or complete molting. The MTF group showed limited growth (102.81 ± 2.25 g; 95.24 ± 1.19 mm), likely due to reduced ecdysis events. Tissue lipid and fatty acid profiles reflected dietary inputs, with significant differences in DHA/EPA and n-3/n-6 ratios among treatments (p < 0.05). Essential amino acid levels decreased across all groups, possibly due to the metabolic demands of molting. These findings highlight the critical role of diet in promoting molting and improving tissue quality in blue crab aquaculture under controlled RAS conditions.