This study evaluated the effects of harvest and slaughter method, stunning procedure, and rearing water temperature on physiological stress response, loss of behavioral responses (LBR) and post − mortem muscle quality changes in European seabass ( Dicentrarchus labrax ). Physiological outcomes comprised plasma cortisol, glucose, lactate, and osmolality, while post-mortem outcomes were assessed by measuring muscle pH and rigor mortis temporal changes. Laboratory results indicated that crowding and brailing were associated with higher plasma cortisol and osmolality than rapid netting or hook-and-line capture. Brain spiking generally produced the shortest time to loss of behavioural responses and the lowest physiological stress response, whereas air asphyxia was associated with the greatest disturbance. Ambient temperature showed a significant interaction with harvest and slaughter method in the applied assessment parameters, in a condition-dependent manner. Industrial scale results supported the laboratory data showing that harvest method elucidates a strong stress response in European seabass and that application of stunning procedure is effective in reducing time to LBR and rigor mortis development in fish subsequently immerged in ice-slurry.
Photobacterium damselae subsp. piscicida (PDP), the causative agent of photobacteriosis, causes substantial economic losses in marine aquaculture worldwide. Although bacteriophages (phages) have emerged as promising alternatives to antibiotics for controlling bacterial fish pathogens, phages infecting PDP remain poorly characterized. In this study, we isolated a novel lytic phage, vB_PdP-TS25, from shellfish collected from the west coast of Korea and characterized its biological, genomic, and antibiofilm properties. Transmission electron microscopy showed that vB_PdP-TS25 has an icosahedral capsid and a short non-contractile tail, consistent with a podovirus-like morphology. The phage exhibited efficient lytic activity against PDP, with a latent period of 60 min and a burst size of approximately 125 PFU per infected cell. It remained stable across a broad pH range of 5–10 and at temperatures up to 37 °C. Its genome comprises 69,954 bp of linear dsDNA encoding 88 predicted open reading frames and one tRNA gene. No genes associated with antimicrobial resistance, virulence, or lysogeny were identified. Comparative genomic, phylogenetic, and gene-sharing network analyses consistently showed that vB_PdP-TS25 belongs to a divergent lineage of unclassified Caudoviricetes , with less than 30% intergenomic similarity to its closest known relatives. The phage also significantly inhibited PDP biofilm formation and disrupted established mature biofilms, possibly through the activity of two predicted depolymerase-associated proteins. These findings expand current knowledge of PDP-infecting phages and provide a foundation for developing phage-based strategies to control photobacteriosis in aquaculture.
The use of juvenile lumpfish for sea-lice control in salmon aquaculture faces several challenges, including limited understanding of how environmental factors regulate reproduction. This study investigated the effects of photoperiod and temperature manipulation on sexual maturation in male lumpfish. Fish were exposed to natural (NP) and compressed (CP) annual photoperiods, with temperature elevation applied close to and during the spawning period. Although body weight appeared slightly higher under NP before temperature elevation, the differences were not significant. Following temperature elevation, growth was significantly higher at only two sampling points: in the elevated-NP compared to CP, and later within NP. Gonadosomatic index increased prior to temperature elevation and declined during the spawning period. Based on descriptive temporal patterns, spermatozoa were detected early in development and increased over time, with earlier and higher proportions observed under CP with elevated temperature. Although not all changes were statistically significant, plasma testosterone (T) and 11-ketotestosterone (11-KT) tended to increase towards and decline during the spawning period, particularly in CP. Only a few statistically significant differences between treatments were detected because of substantial individual variability and experimental constraints, limiting firm conclusions regarding treatment effects. Future studies would benefit from considering genetic variation, sex-specific experimental groups, optimized timing of temperature manipulations, improved sampling consistency and larger sample sizes. Nevertheless, the observed temporal patterns and the few significant differences between treatments suggest that photothermal manipulation may influence the timing of sexual maturation in male lumpfish. These findings provide insight into male lumpfish reproductive dynamics under photothermal manipulation and lay a foundation for future research aimed at improving broodstock management strategies.
Photobacterium damselae subsp. piscicida (PDP), the causative agent of photobacteriosis, causes substantial economic losses in marine aquaculture worldwide. Although bacteriophages (phages) have emerged as promising alternatives to antibiotics for controlling bacterial fish pathogens, phages infecting PDP remain poorly characterized. In this study, we isolated a novel lytic phage, vB_PdP-TS25, from shellfish collected from the west coast of Korea and characterized its biological, genomic, and antibiofilm properties. Transmission electron microscopy showed that vB_PdP-TS25 has an icosahedral capsid and a short non-contractile tail, consistent with a podovirus-like morphology. The phage exhibited efficient lytic activity against PDP, with a latent period of 60 min and a burst size of approximately 125 PFU per infected cell. It remained stable across a broad pH range of 5–10 and at temperatures up to 37 °C. Its genome comprises 69,954 bp of linear dsDNA encoding 88 predicted open reading frames and one tRNA gene. No genes associated with antimicrobial resistance, virulence, or lysogeny were identified. Comparative genomic, phylogenetic, and gene-sharing network analyses consistently showed that vB_PdP-TS25 belongs to a divergent lineage of unclassified Caudoviricetes, with less than 30% intergenomic similarity to its closest known relatives. The phage also significantly inhibited PDP biofilm formation and disrupted established mature biofilms, possibly through the activity of two predicted depolymerase-associated proteins. These findings expand current knowledge of PDP-infecting phages and provide a foundation for developing phage-based strategies to control photobacteriosis in aquaculture.
Sex-biased pesticide tolerance is increasingly recognized in arthropods, yet its implications for parasite management in aquaculture remain poorly understood. This study evaluated sex-specific antiparasitic tolerance in the sea louse Caligus rogercresseyi , a marine ectoparasite and a major challenge for salmon aquaculture. Here we analyzed 340 bioassays conducted between 2018 and 2026 across southern Chile, exposing male and female sea lice to four chemical actives plus one botanical formulation with differing modes of action and lipophilicity. Using generalized linear mixed models and dose-response analysis, we found that females consistently exhibited lower mortality than males, indicating marked sex-dependent differences in susceptibility. Significant sex effects were detected for azamethiphos, deltamethrin, and cypermethrin, whereas significant sex-by-concentration interactions were observed for both pyrethroids. Sex-specific log-logistic models further showed that females displayed higher EC 50 and LD 50 values across all treatments. Although EC 50 differences were compound-dependent, female LD 50 values were significantly higher for all compounds, ranging from 1.6 to 3.7-fold those of males. Interestingly, the strongest sex-dependent responses were observed for lipophilic compounds, whereas water-soluble antiparasitics showed smaller differences between sexes. Our findings highlight the importance of incorporating sex as a factor in resistance monitoring and treatment evaluation, which may improve management strategies against sea lice in salmon aquaculture.
