How host ecology influences the parasite communities of three Australian flathead fishes, Platycephalus spp. (Scorpaeniformes: Platycephalidae).

This study investigated the role of host traits, habitat, and sampling season on the prevalence and intensity of parasites in three species of platycephalid fishes. Three host species sampled were dusky flathead (Platycephalus fuscus, n = 3), blue-spotted flathead (Platycephalus caeruleopunctatus, n = 38), and tiger flathead (Platycephalus richardsoni, n = 59). A total of 14 metazoan parasite species were collected over 15 months, between July 2020 and September 2021. The parasites found included a chondracanthid copepod, adult hemiuroidean trematodes, cestode plerocercoids, larval and adult acanthocephalans, larval and adult nematodes, and an unknown species of helminth. General linear models were used to assess the relationship between host traits and sampling season with parasite infection intensity. The infection intensity of an unidentified plerocercoid species in P. caeruleopunctatus was found to be significantly associated with both sampling season and the interaction of host mass with sex. In P. richardsoni the infection intensity of the acanthocephalan, Corynosoma sp. was found to correlate with sampling season. The highest richness of parasite taxa was recorded from P. richardsoni, which may be due to the wide depth range of P. richardsoni, coupled with its generalist diet.

Investigating dynamics, etiology, pathology, and therapeutic interventions of Caligus clemensi and Vibrio alginolyticus co-infection in farmed marine fish.

This study investigated a disease outbreak characterized by caligid copepod infestations and subsequent secondary bacterial infections in European seabass (Dicentrarchus labrax) and flathead grey mullet (Mugil cephalus) cultivated at a private facility in the Deeba Triangle region of Egypt. Moribund fish displayed brown spots on the skin, tongue, and gills, along with lethargy and excess mucus. The fish suffered severe infections, exhibiting external hemorrhages, ulcers, and ascites. The fish had pale, enlarged livers with hemorrhaging. Comprehensive parasitological, bacteriological, molecular, immunity and histopathological analyses were conducted to identify the etiological agents and pathological changes. Caligid copepod infestation was observed in wet mounts from the buccal and branchial cavities of all examined fish, and the caligids were identified as Caligus clemensi through COI gene sequencing and phylogenetic analysis. Vibrio alginolyticus was confirmed as a secondary bacterial infection through biochemical tests, recA gene sequencing, and phylogenetic analyses. Antibiotic susceptibility testing revealed resistance to ß-lactams, aminoglycosides, and trimethoprim-sulfamethoxazole in V. alginolyticus isolates. Upregulation of the inflammatory marker IL-1ß in gill and skin tissues indicated a robust cell-mediated immune response against the pathogens. Histopathological examination revealed severe tissue damage, hyperplasia, hemorrhage, and congestion in the gills, along with hepatocellular degeneration and steatosis in the liver, providing initial insights into this outbreak. A comprehensive therapeutic regimen was implemented, comprising prolonged hydrogen peroxide immersion baths, followed by the application of the nature-identical plant-based compound Lice-less and probiotic Sanolife Pro-W supplementation. This integrated approach effectively eliminated C. clemensi infestations, controlled secondary bacterial infections, and restored fish health, reducing morbidity and mortality rates to minimal levels.

Estimating the copepod biomass in the North West African upwelling system using a bi-frequency acoustic approach.

The Canary Current Large Marine Ecosystem (CCLME) is one of the most productive Large Marine Ecosystems worldwide. Assessing the abundance, biomass and distribution of zooplankton in the southern part of this system, off the coast of West Africa, remains challenging due to limited sampling efforts and data availability. However, zooplankton is of primary importance for pelagic ecosystem functioning. We applied an inversion method with combined analysis of acoustic and biological data for copepod discrimination using a bi-frequency (38 and 120 kHz) approach. Large copepods with equivalent spherical radii > 0.5 mm were identified using differences in the mean volume backscattering strength (MVBS). Regarding abundance measured by net sampling, copepods strongly dominated the zooplankton community and the large fraction account for 18%. This estimate correlated significantly with MVBS values that were obtained using an inverse algorithm. We confirmed the utility of using 38 kHz for large copepod detection. An epipelagic biomass of large copepod was estimated at 120-850 mg m-2 in March during upwelling season. It is worth noting that this estimation likely underestimates the true biomass due to inherent uncertainties associated with the measurement method. We recommend future investigations in the interest of using only nighttime data to improve the sampling pattern, particularly on the upper part of the water column (< 10 m) as well as on the shallow part of the continental shelf (< 20 m depth) not covered by fisheries vessel. Nevertheless, such high copepod biomass supports high fish production underlining the key role of copepod in the CCLME. Our results open the way to the analysis of the fluctuation and trend of copepod biomass, along with three decades of fisheries acoustics data available in the region. This helps to determine ecosystem changes, particularly under climate change, and to investigate the role of copepods in the southern CCLME carbon pump at the fine scale.

Zooplankton responses to simulated marine heatwave in the Mediterranean Sea using in situ mesocosms.

Globally, marine heatwave frequency, intensity, and duration are on the rise, posing a significant threat to plankton communities, the foundational elements of the marine food web. This study investigates the ecological and physiological responses of a temperate plankton community in the Thau lagoon, north-western Mediterranean, to a simulated +3°C ten-day heatwave followed by a ten-day post-heatwave period in in-situ mesocosms. Our analyses encompassed zooplankton grazing, production, community composition in water and sediment traps, as well as oxidative stress and anti-oxidant biomarkers. The results revealed increased abundances of harpacticoid copepods and polychaete larvae during the simulated heatwave and post-heatwave event. Sediment trap data indicated elevated mortality, particularly dominated by polychaete larvae during the post-heatwave period. Oxidative stress biomarker (lipid peroxidation LPX) levels in the plankton community correlated with temperature, signaling cellular damage during the heatwave. LPX increased and proteins decreased with increasing salinity during the experiment. Offspring production peaked during the post-heatwave phase. Notably, the calanoid copepod Acartia clausi exhibited a preference for ciliates as its primary prey, constituting 20% of the overall available prey. Our findings suggest a potential shift in coastal zooplankton communities during future marine heatwaves, transitioning from calanoid mesozooplankton dominance to a system featuring meroplankton and/or harpacticoid copepods. Although species preying on microzooplankton may gain advantages in such conditions, the study underscores the damaging impact of heatwaves on organismal lipids, with potential consequences for reproduction, growth, and survival within marine ecosystems.

Effect of alternative natural diet on microplastic ingestion, functional responses and trophic transfer in a tri-trophic coastal pelagic food web.

The patchy distribution of microplastics (MP) and their size range similar to planktonic organisms, are likely to have major ecological consequences, through MP ingestion, food dilution, and transfer across trophic levels. Our study applied a community module using tritrophic food chain with zooplankton as prey, and a planktivorous seabass fry as predator. We conducted a series of feeding experiments and recorded the direct uptake of MP under six different concentrations ranging from 25 to 800 particles L-1. We also estimated the indirect transfer of MP via trophic link. The ingestion rates for Brachionus plicatilis, Mesocyclops isabellae, and Lates calcarifer, were 3.7 ± 0.3 MP ind-1 min-1, 1.69 ± 0.1 MP ind-1 min-1, and 3.51 ± 0.52 MP ind-1 h-1, respectively. In the presence of a natural diet, rotifers and copepods ingested significantly lower number, whereas, fish fry ingested a higher number of MP, suggesting further vulnerability to the consumers of MP-contaminated fish and potential biomagnification at higher trophic levels. Overall, the MP uptake rate increased with increasing concentration, and finally leveled off, indicating a type II functional response to MP concentration. The presence of natural diet led to a lower Km value. In the indirect transfer experiment, 74 % of B. plicatilis and 78 % of M. isabellae individuals were contaminated with MP, when offered as prey. Brachionid mastax and MP particles were observed in the gut of copepods. The fish fry gut content also recorded brachionid mastax, MP-contaminated copepods, and MP particles, showing direct evidence of trophic transfer pointing to a cascading effect on higher trophic levels including humans via piscivory.

Interactive effects of temperature and salinity on metabolism and activity of the copepod Tigriopus californicus.

In natural environments, two or more abiotic parameters often vary simultaneously, and interactions between co-varying parameters frequently result in unpredictable, non-additive biological responses. To better understand the mechanisms and consequences of interactions between multiple stressors, it is important to study their effects on not only fitness (survival and reproduction) but also performance and intermediary physiological processes. The splash-pool copepod Tigriopus californicus tolerates extremely variable abiotic conditions and exhibits a non-additive, antagonistic interaction resulting in higher survival when simultaneously exposed to high salinity and acute heat stress. Here, we investigated the response of T. californicus in activity and oxygen consumption under simultaneous manipulation of salinity and temperature to identify whether this interaction also arises in these sublethal measures of performance. Oxygen consumption and activity rates decreased with increasing assay salinity. Oxygen consumption also sharply increased in response to acute transfer to lower salinities, an effect that was absent upon transfer to higher salinities. Elevated temperature led to reduced rates of activity overall, resulting in no discernible impact of increased temperature on routine metabolic rates. This suggests that swimming activity has a non-negligible effect on the metabolic rates of copepods and must be accounted for in metabolic studies. Temperature also interacted with assay salinity to affect activity, and with acclimation salinity to affect routine metabolic rates upon acute salinity transfer, implying that the sublethal impacts of these co-varying factors are also not predictable from experiments that study them in isolation.

Morphological and Molecular Evidence of an Intergeneric Host-Range in Clavisodalis sentifer (Crustacea: Copepoda: Taeniacanthidae) Associated with Diadematid Sea Urchins from the Western Pacific.

Sea urchins have a wide variety of symbionts on their body surfaces and inside their bodies. Copepods of the genus Clavisodalis (Taeniacanthidae) collected from the esophagus of sea urchins of the genera Diadema and Echinothrix in southern Japan were identified based on their morphological characteristics, and molecular analysis was conducted to determine whether genetic variation occurs in copepods from different localities and hosts. Morphological observations identified individuals from southern Japan as Clavisodalis sentifer Dojiri and Humes, 1982, making this the first record of this species in the northern hemisphere and the first record of its genus in Japan. Morphological and molecular analysis suggested that the copepod specimens collected from multiple hosts across two genera would be the same species. Considering the typically observed high level of host specificity among taeniacanthid copepods, the utilization of hosts from two genera by C. sentifer is noteworthy.

A siliceous arms race in pelagic plankton.

Coevolution between predator and prey plays a central role in shaping the pelagic realm and may have significant implications for marine ecosystems and nutrient cycling dynamics. The siliceous diatom frustule is often assumed to have coevolved with the silica-lined teeth of copepods, but empirical evidence of how this relationship drives natural selection and evolution is still lacking. Here, we show that feeding on diatoms causes significant wear and tear on copepod teeth and that this leads to copepods becoming selective feeders. Teeth from copepods feeding on thick-shelled diatoms were more likely to be broken or cracked than those feeding on a dinoflagellate. When fed a large diatom, all analyzed teeth had visible wear. Our results underscore the importance of the predator-prey arms race as a driving force in planktonic evolution and diversity.

Wild salmon migration routes influence sea lice infestations: An agent-based model predicting farm-related infestations on juvenile salmon.

This study presents an Agent-Based Model (ABM) simulation to assess the impact of varying migration routes on sea lice (Caligus clemensi) infestation levels in juvenile wild sockeye salmon (Oncorhynchus nerka) in the Discovery Islands, British Columbia, Canada. This research highlights the importance of migratory routes in determining the extent of exposure to sea lice originating from nearby salmon farms. Three northward out-migration routes were modelled, each exposing the fish to different levels of infestation pressure based on proximity to salmon farms. The ABM incorporates spatially explicit migration patterns of juvenile sockeye salmon using a detailed raster map of the Discovery Islands. Key variables such as swimming speed, progression rate, and infestation levels were integrated into the model, offering a comprehensive analysis of migration and infestation dynamics. The study revealed that infestation rate is highly variable, depending on migration routes. Specifically, salmon traveling longer migration routes with lower infestation pressure may experience higher sea lice loads compared to those on shorter routes with higher infestation pressure. This underscores the role of low infestation pressures and the critical influence of swimming speed, which affects exposure time, and thus infestation rates. Additionally, the study conducted a sensitivity analysis to understand the influence of various parameters on infestation rates. This analysis highlighted the importance of swimming speed and progression rate, particularly in routes closer to the farms. The findings suggest that slower swimming speeds and meandering routes increase exposure to lice, thereby elevating infestation levels. The research contributes to understanding the dynamics of sea lice transmission and its relationship with salmon migration patterns. It underscores the necessity of considering migratory routes and farm proximity in managing and mitigating the impact of sea lice infestation on wild salmon populations. This study's insights are crucial for developing strategies to balance aquaculture practices with the conservation of wild salmon.

The effects of the toxic dinoflagellate Alexandrium on feeding, reproduction and mortality of the copepod Acartia: A systematic review employing weighted linear models.

The study of interactions between copepods of the genus Acartia and toxic dinoflagellates of the genus Alexandrium has been an important topic during the last four decades. Feeding behavior and physiological responses of copepods have been studied in laboratory and field experiments, sometimes with contradictory results. More recently, an evolutionary adaptive mechanism leading to enhanced tolerance of Alexandrium toxins in a population of Acartia experiencing chronic exposure to these dinoflagellates has been reported. In the present work, we collected data from the existing studies on the effects of Alexandrium on feeding, reproduction and mortality of Acartia. With these data, we performed a systematic review consisting of a secondary analysis employing general or generalized linear models, weighting data from different studies by the reciprocal of their standard deviation. Our first aim was to overcome shortcomings of individual studies: limited ranges of the variables and overlooked variables (experiment length, population adaptation). These shortcomings could have led to inconsistent conclusions by missing heterogeneous patterns in copepod responses and in the interactions between variables. Our second aim was to test the enhanced physiological performance of chronically exposed relative to naïve copepod populations over a wide geographic range. We found that the feeding rate is enhanced by increased food biomass, irrespective of the food type. Toxins do not have a clear effect on egg production and have a bi-phasic effect on egg hatching success, which was negative above a specific threshold. Toxins also increased mortality. Experiment length had a positive effect on egg production and negative on egg hatching. Naïve copepod populations showed consistently lower ingestion of Alexandrium and egg hatching rates, thereby supporting the spread of the aforementioned mechanism across populations over a wide geographic range.

Biodiversity patterns of epipelagic copepods in the South Pacific Ocean: Strengths and limitations of current data bases.

Basin-scale patterns of biodiversity for zooplankton in the ocean may provide valuable insights for understanding the impact of climate change and global warming on the marine ecosystem. However, studies on this topic remain scarce or unavailable in vast regions of the world ocean, particularly in large regions where the amount and quality of available data are limited. In this study, we used a 27-year (1993-2019) database on species occurrence of planktonic copepods in the South Pacific, along with associated oceanographic variables, to examine their spatial patterns of biodiversity in the upper 200 m of the ocean. The aim of this study was to identify ecological regions and the environmental predictors explaining such patterns. It was found that hot and cold spots of diversity, and distinctive species assemblages were linked to major ocean currents and large regions over the basin, with increasing species richness over the subtropical areas on the East and West sides of the South Pacific. While applying the spatial models, we showed that the best environmental predictors for diversity and species composition were temperature, salinity, chlorophyll-a concentration, oxygen concentration, and the residual autocorrelation. Nonetheless, the observed spatial patterns and derived environmental effects were found to be strongly influenced by sampling coverage over space and time, revealing a highly under-sampled basin. Our findings provide an assessment of copepods diversity patterns and their potential drivers for the South Pacific Ocean, but they also stress the need for strengthening the data bases of planktonic organisms, as they can act as suitable indicators of ecosystem response to climate change at basin scale.

METAZOAN PARASITE COMMUNITY OF THE YELLOW SNAPPER LUTJANUS ARGENTIVENTRIS: FACTORS THAT INFLUENCING SPECIES COMPOSITION AND RICHNESS.

A total of 366 individuals of Lutjanus argentiventris (Peters, 1869) were collected over a 5-yr period (October 2018 to June 2022) from Acapulco Bay, Mexico. Parasite communities in Lutjanus argentiventris were quantified and analyzed to determine the main factors that generate changes in species richness and/or species composition over time. The digeneans and copepods were the best-represented parasite groups. The parasite communities were characterized by a high numerical dominance of ectoparasites, mainly isopod larvae. Species richness at the component community level (9-23 species) was similar to the reported richness in other Lutjanus spp. The parasite communities of Lutjanus argentiventris exhibited high variability in species composition, suggesting that each parasite species may respond differently to environmental changes. However, the species richness and diversity were fairly stable over time; therefore, a clear pattern of interannual variation was not observed. Variations in the community structure probably were due to factors such as host traits (e.g., feeding behavior and body size), and possible interannual differences in environmental factors amplified by the occurrence of the anomalous event of La Niña.

Keratinocytes drive the epithelial hyperplasia key to sea lice resistance in coho salmon.

BACKGROUND: Salmonid species have followed markedly divergent evolutionary trajectories in their interactions with sea lice. While sea lice parasitism poses significant economic, environmental, and animal welfare challenges for Atlantic salmon (Salmo salar) aquaculture, coho salmon (Oncorhynchus kisutch) exhibit near-complete resistance to sea lice, achieved through a potent epithelial hyperplasia response leading to rapid louse detachment. The molecular mechanisms underlying these divergent responses to sea lice are unknown. RESULTS: We characterized the cellular and molecular responses of Atlantic salmon and coho salmon to sea lice using single-nuclei RNA sequencing. Juvenile fish were exposed to copepodid sea lice (Lepeophtheirus salmonis), and lice-attached pelvic fin and skin samples were collected 12 h, 24 h, 36 h, 48 h, and 60 h after exposure, along with control samples. Comparative analysis of control and treatment samples revealed an immune and wound-healing response that was common to both species, but attenuated in Atlantic salmon, potentially reflecting greater sea louse immunomodulation. Our results revealed unique but complementary roles of three layers of keratinocytes in the epithelial hyperplasia response leading to rapid sea lice rejection in coho salmon. Our results suggest that basal keratinocytes direct the expansion and mobility of intermediate and, especially, superficial keratinocytes, which eventually encapsulate the parasite. CONCLUSIONS: Our results highlight the key role of keratinocytes in coho salmon's sea lice resistance and the diverged biological response of the two salmonid host species when interacting with this parasite. This study has identified key pathways and candidate genes that could be manipulated using various biotechnological solutions to improve Atlantic salmon sea lice resistance.

First evidence of the induction of domoic acid production in Pseudo-nitzschia australis by the copepod Temora longicornis from the French coast.

Diatoms of the genus Pseudo-nitzschia are widespread in marine waters. Some of them can produce the toxin domoic acid (DA) which can be responsible for amnesic shellfish poisoning (ASP) when transferred into the food web. These ASP events are of major concern, due to their ecological and socio-economic repercussions, particularly on the shellfish industry. Many studies have focused on the influence of abiotic factors on DA induction, less on the role of biotic interactions. Recently, the presence of predators has been shown to increase DA production in several Pseudo-nitzschia species, in particular in Arctic areas. In order to investigate the relationship between Pseudo-nitzschia species and grazers from the French coast, exposures between one strain of three species (P. australis, P. pungens, P. fraudulenta) and the copepod Temora longicornis were conducted for 5 days. Cellular and dissolved DA content were enhanced by 1,203 % and 1,556 % respectively after the 5-days exposure of P.australis whereas no DA induction was observed in P. pungens and P. fraudulenta. T. longicornis consumed all three Pseudo-nitzschia species. The copepod survival was not related to DA content. This study is an essential first step to better understanding the interactions between planktonic species from the French coast and highlights the potential key role of copepods in the Pseudo-nitzschia bloom events in the temperate ecosystems.

Margalefidinium polykrikoides dinoflagellate blooms increase mortality of Acartia tonsa copepods.

Previous research on phytoplankton blooms has often focused on the initiation of blooms, while studies on the mechanisms underlying bloom decline and termination have been more limited. This study aimed to explore the extent of which Acartia tonsa (copepod) grazing does or does not contribute to Margalefidinium polykrikoides (dinoflagellate) bloom decline. M. polykrikoides is a prominent harmful algal bloom (HAB) species that forms dense blooms in coastal and estuarine systems around the world with known ichthyotoxic effects. Sampling occurred in the lower York River Estuary, Virginia, USA in 2021 and 2022 during two M. polykrikoides blooms. Prey removal experiments were conducted using organisms collected from the field to estimate A. tonsa ingestion rates on M. polykrikoides. While A. tonsa was capable of ingesting M. polykrikoides at low abundance, when M. polykrikoides abundance exceeded 2000 cells mL-1, A. tonsa experienced nearly 100% mortality in the 24-hour prey removal experiments. This suggests that A. tonsa likely cannot exert any top-down control on M. polykrikoides blooms, rather, at high concentrations, M. polykrikoides may act as its own grazing deterrent. Extensive M. polykrikoides blooms could therefore continue to persist due to a reduction in grazing pressure, rather than an increase. This would suggest that the decline of M. polykrikoides blooms is likely caused by another factor. As the frequency, duration, and magnitude of HABs are expected to increase in the future, these findings provide key insights to the trophic interactions that may be influencing the duration of M. polykrikoides blooms.

Deep-Sea Benthic Response to the Deepwater Horizon Oil Spill: Harpacticoid Families as Sentinels of Impact Through Space and Time.

The Deepwater Horizon (DWH) oil spill in the northern Gulf of Mexico, occurred in 2010 at 1525 meters depth, releasing approximately 507 M liters of oil. Research cruises in 2010 and 2011 were conducted to assess the initial and subsequent effects of the oil spill on deep-sea infauna. The spatial-temporal response of the deep-sea meiofaunal harpacticoid community composition to the DWH oil spill was investigated at 34 stations ranging from < 1 km to nearly 200 km from the wellhead in 2010 and 2011. The pattern of reduced harpacticoid diversity in impacted zones compared to non-impacted zones in 2010 persisted in 2011. However, an increase in Hill's diversity index (N1) and the family richness across the two years in some of the impacted stations could suggest a first signal of a tentative recovery and an improvement of environmental conditions. The multivariate analysis of harpacticoid family composition revealed the persistence of an impact in 2011 with moderately high values of turnover diversity in the harpacticoid communities through time (37%) and space (38-39%). The consistent presence in all years and stations of long-term tolerant families (e.g., Ameiridae), the sharp decrease of fast-responding opportunistic families (e.g., Tisbidae), and the increase of more sensitive ones (e.g., Ectinosomatidae, Canthocamptidae, Cletopsyllidae, and Laophontidae) lead to the preliminary conclusion that some initial signals of recovery are evident. However, as impacts were still evident in 2011, and because recruitment and succession rates can be extremely slow in the deep sea, full community recovery had not yet occurred one year after the DWH disaster. This study confirmed that harpacticoid copepod family diversity can offer an accurate assessment of oil-spill impacts on deep-sea benthic communities over space and time as well as a better understanding of the recovery mode of the system after an oil spill event.

Revealing the profound influence of diapause on gene expression: Insights from the annual transcriptome of the copepod Calanus finmarchicus.

Annual rhythms are observed in living organisms with numerous ecological implications. In the zooplanktonic copepod Calanus finmarchicus, such rhythms are crucial regarding its phenology, body lipid accumulation, and global carbon storage. Climate change drives annual biological rhythms out of phase with the prevailing environmental conditions with yet unknown but potentially catastrophic consequences. However, the molecular dynamics underlying phenology are still poorly described. In a rhythmic analysis of C. finmarchicus annual gene expression, results reveal that more than 90% of the transcriptome shows significant annual rhythms, with abrupt and dramatic upheaval between the active and diapause life cycle states. This work explores the implication of the circadian clock in the annual timing, which may control epigenetic mechanisms to profoundly modulate gene expression in response to calendar time. Results also suggest an increased light sensitivity during diapause that would ensure the photoperiodic entrainment of the endogenous annual clock.

Pennella balaenoptera actively select injured cetacean skin as attachment sites, making them potentially useful forensic tags.

Cetaceans harbor multiple epibionts on their external surface, and these attach to particular microhabitats. Understanding what drives the selection of attachment sites is relevant for refining the use of epibionts as indicators of their hosts. We report on about 100 females of the mesoparasitic copepod Pennella balaenoptera attached to a dead Cuvier's beaked whale Ziphius cavirostris stranded in Tunisia (western Mediterranean); the first report of P. balaenoptera in this country. The copepods were exclusively attached to numerous incisive, likely anthropogenic, wounds found on the host's skin. This finding suggests that newly recruited females may actively seek skin areas where physical penetration is facilitated; a factor that may help explain patterns of microhabitat selection by Pennella spp., and perhaps other pennellids, on their hosts. The estimated age of parasitization by P. balaenoptera (supported by age estimations of the co-occurring epibiotic barnacle Conchoderma virgatum) also suggests that the cetacean host likely survived these injuries, at least initially, and the presumed cause of death was starvation due to entanglement in a fishing net.

Environmental influence on the Atlantic salmon transcriptome and methylome during sea lice infestations.

The fish's immune response is affected by different factors, including a wide range of environmental conditions that can also disrupt or promote changes in the host-pathogen interactions. How environmental conditions modulate the salmon genome during parasitism is poorly understood here. This study aimed to explore the environmental influence on the Salmo salar transcriptome and methylome infected with the sea louse Caligus rogercresseyi. Atlantic salmon were experimentally infected with lice at two temperatures (8 and 16 °C) and salinity conditions (32 and 26PSU). Fish tissues were collected from the infected Atlantic salmon for reduced representation bisulfite sequencing (RRBS) and whole transcriptome sequencing (RNA-seq) analysis. The parasitic load was highly divergent in the evaluated environmental conditions, where the lowest lice abundance was observed in fish infected at 8 °C/26PSU. Notably, transcriptome profile differences were statistically associated with the number of alternative splicing events in fish exposed to low temperature/salinity conditions. Furthermore, the temperature significantly affected the methylation level, where high values of differential methylation regions were observed at 16 °C. Also, the association between expression levels of spliced transcripts and their methylation levels was determined, revealing significant correlations with Ferroptosis and TLR KEEG pathways. This study supports the relevance of the environmental conditions during host-parasite interactions in marine ecosystems. The discovery of alternative splicing transcripts associated with DMRs is also discussed as a novel player in fish biology.

Field evaluation of hydrogen peroxide bath technique for controlling sea lice (Lepeoptheirus spinifer) infestation in snubnose pompano (Trachinotus blochii).

Sea lice infestations can pose significant challenges in the aquaculture sector, affecting fish health and overall production. In the search for effective and eco-friendly solutions, hydrogen peroxide bath treatment has been considered as one of the promising methods. This is the first study to evaluate the field efficacy of hydrogen peroxide bath technique against sea lice infestation on cage-cultured snubnose pompano (Trachinotus blochii). Sea lice was identified as Lepeophtheirus spinifer using morphological description. Naturally-infested snubnose pompano stocked in 2 ×3×2 m3 net cages at 15 fish/cage at the Igang Marine Station of SEAFDEC/AQD, in Guimaras, Philippines were treated in triplicates with two hydrogen peroxide concentrations (1500 and 2000 ppm) in comparison to a control (seawater only) for 20 minutes at 32.8 ± 0.7 ppt and 28.9 ± 0.3 °C and were monitored at 3rd and 7th day post-treatment. The total mean intensity of sea lice, mean intensity per life stages (copepodid, chalimus I, chalimus II, pre-adult I, pre-adult II, adult male and adult female), and the 12-h viability of scraped male and adult female L. spinifer from the treatment groups were evaluated. The total mean intensity of sea lice in the treated groups at 3 day post-treatment was significantly lower than the control group (p<0.001). A possible re-infection of sea lice was observed 7 days post-treatment as explained by the slight increase in the mean intensity in the treated groups. However, no mortalities of pompano were recorded throughout the experiment. In addition, adult female lice were absent in the treated group while adult male lice were only detected in the 1500 ppm treatment group at a very low mean intensity. The viability test also showed that all sea lice were not able to recover after 12 h whereas a 100 % recovery rate was noted in the control group. Results suggest that the 1500 and 2000 ppm hydrogen peroxide concentrations are effective in reducing sea lice infestation on cage-cultured snubnose pompano. However, a long-term effect of hydrogen peroxide treatment on sea lice needs further investigation.