OBJECTIVE:Phytogenics, which are plant-derived compounds, are increasingly gaining importance in aquaculture as sustainable and natural feed additives that support the performance and health of cultured fish. The current study evaluated the effects of dietary phytogenic supplementation in Nile Tilapia Oreochromis niloticus and the influence of phytogenics on growth, immunity, and resistance against Flavobacterium oreochromis. METHODS:Fish were fed six experimental diets, including a control diet and five commercial phytogenic treatments-Syrena Boost (SY), Actifor Pro, Actifor Power (APO), Enviro QS, and Fresta Protect-for 60 d in a -recirculating aquaculture system. These products included bioactive compounds, such as saponins, thymol, essential oils, and condensed tannins. At the end of the trial, fish were sampled and blood was collected for serum lysozyme and biochemistry analyses, while spleen and head kidney were collected for immune gene expression analysis. After sampling, fish were challenged with F. oreochromis to evaluate resistance. RESULTS:No significant differences in growth performance or nutrient utilization were observed among dietary treatments compared with the control. However, fish that were fed with phytogenic diets exhibited enhanced innate immune responses, as indicated by increased serum lysozyme activity in the APO treatment group (mean ± SE = 17.8 ± 0.76 μg/mL) and elevated serum albumin in the SY and Actifor Pro treatment groups. Although no significant differences were found in the expression of immune-related genes (interleukin-1 beta, interleukin-6, interleukin-8, and tumor necrosis factor alpha), multivariate analysis revealed tissue-specific and diet-dependent immune patterns. During the bacterial challenge with F. oreochromis, all phytogenic treatments resulted in a significantly higher survival compared with the control group, with fish in the SY (∼58%) and APO (∼51%) treatment groups showing the lowest cumulative mortality. CONCLUSIONS:These findings indicate that phytogenic compounds could enhance resistance to F. oreochromis in Nile Tilapia through modulating the innate immune response. Overall, among the five commercial phytogenics evaluated in this study, SY and APO showed the most potential as functional feed additives to improve Nile Tilapia immunity and resistance to columnaris disease.
OBJECTIVE:The aquaculture sector in Pakistan remains underdeveloped, as aquaculture has not yet received adequate attention. Studies focusing on the health status of fish in the natural water bodies within Pakistan are rare. METHODS:This study isolated and characterized bacteria from naturally infected cyprinid species across Khyber Pakhtunkhwa province. In total, 56 bacterial species were identified from 100 different naturally infected freshwater fish samples, with both internal and external organs examined. RESULTS:Molecular characterization showed that among the nine families characterized in total, the dominant families were Enterobacteriaceae and Aeromonadaceae, and the dominant species were Enterobacter spp., Aeromonas spp., Klebsiella spp., Symbiopectobacterium spp., and Citrobacter spp. This study also found bacterial species for the first time in Pakistan that are rarely reported in global aquaculture. These included Rahnella contaminans and species of Rahnella, Yokenella, and Morganella in the gills, liver, and muscle of Common Carp Cyprinus carpio, Rohu Labeo rohita, and Grass Carp Ctenopharyngodon idella. Additionally, human bacterial pathogens were also detected, which may indicate a potential health risk for fish consumers. CONCLUSIONS:Based on the level of bacterial infections observed, there is a critical need for continuous monitoring of fish populations to prevent potential disease outbreaks in aquaculture and thus avert economic losses.
OBJECTIVE:In this study, the pathogenicity of two genetically distinct Lactococcus petauri strains, one isolated from catfish Ictalurus spp. in Alabama, USA, belonging to sequence type 142, and one from Rainbow Trout Oncorhynchus mykiss in California, USA, belonging to sequence type 145, were evaluated in experimental challenges using a Nile Tilapia Oreochromis niloticus fingerling infection model. METHODS:Since tilapia can be cultured at a wide range of temperatures in vivo, experiments were conducted at 25 ± 2°C and 30 ± 2°C. The fish were challenged via intracoelomic injection of ∼107 CFU/fish or by immersion in 5 L of water containing ∼107 CFU/mL for 1 h. Morbidity and mortality were monitored twice daily for 3 weeks. Water samples from each tank were collected at 6 h and at 1, 9, and 15 d postchallenge to evaluate L. petauri DNA load using a species-specific quantitative PCR. RESULTS:No significant morbidity or mortality was observed in any of the treatment groups during the challenge. At the end of the 3 weeks, all of the fish were euthanized and brain samples from 10 fish per group were cultured on nutrient agar to evaluate the bacterial persistence in the survivors. None of the surviving fish yielded positive isolation of L. petauri. Additionally, no significant histopathological changes were observed between the control and challenged tilapia. Bacterial DNA in the water was detected only at 6 h and at 1 d postchallenge in some treatments. CONCLUSIONS:These findings suggest that under the conditions that were tested, the two strains of L. petauri that were evaluated appear of low virulence to Nile Tilapia.
OBJECTIVE:We compared differentially expressed genes in Chinook Salmon Oncorhynchus tshawytscha with three divergent Ichthyophonus statuses (undetected, subclinical infections, or clinical disease; n = 100) to investigate associated transcriptomic responses. Disease associated with the fish parasite Ichthyophonus sp. was first diagnosed in adult Chinook Salmon from the Yukon River in the late 1980s and has subsequently been implicated in premature host mortality. METHODS:Chinook Salmon tissue sample collections and Ichthyophonus infection data were leveraged from a multi-agency collaboration during summer 2022 at three locations along the main-stem Yukon River that spanned nearly 2,000 km of freshwater migration (lower, middle, and upper river). We sequenced the transcriptome and compared this to infection status based on routine diagnostic procedures. RESULTS:Among the 17,569 genes for which messenger RNA was detected, we identified a transcription signature in the skeletal muscle that was associated with Ichthyophonus infections and included 53 differentially expressed genes. The differentially expressed genes and their pathways included those known for involvement in immune functions, energy synthesis, cellular breakdown, and reproduction-all processes that are known to be influenced by senescence during spawning migrations. CONCLUSIONS:Results demonstrate a clear transcriptional difference between diseased fish (clinical disease group) and those in which Ichthyophonus was undetected, including identifying candidate markers for infection in this population. These results provide a foundation for development of nonlethal biomarkers to evaluate potential Ichthyophonus infections in Chinook Salmon based on gene transcription, protein products, or gene variants (e.g., polymorphisms).
OBJECTIVE:The highly lethal Vibrio disease (HLVD) caused by highly lethal Vibrio parahaemolyticus (VpHLVD) represents a significant threat to Pacific white shrimp Litopenaeus vannamei aquaculture. The existing disease control approaches often rely on antibiotics, leading to drug resistance and environmental pollution, thereby limiting the sustainable development of shrimp farming. Probiotics are recognized for their ability to enhance host disease resistance and to inhibit pathogenic bacteria with high safety and environmental friendliness. METHODS:We evaluated the potential of a probiotic bacterial dietary supplement for HLVD prevention. Bacillus altitudinis strain JSHY-074, isolated from coastal aquaculture environments in Jiangsu, China, was identified based on morphological characterization, 16S ribosomal DNA sequencing, and whole-genome analysis. Its antagonistic activity against V. parahaemolyticus strain SHY1669 was determined by co-culture inhibition tests, and the probiotic effect was verified through a VpHLVD challenge experiment on Pacific white shrimp fed with JSHY-074. RESULTS:The strain JSHY-074 exhibited potent antagonistic activity against V. parahaemolyticus strain SHY1669, with inhibition zones expanding from 12 ± 0.31 mm (mean ± SD) at 6 h of co-culture to 30 ± 0.84 mm at 96 h of co-culture. At an inoculum density of 1.0 × 108 CFU/mL, the inhibition rate reached 88.58% at 72 h. Whole--genome analysis revealed nine gene clusters associated with secondary metabolite production, with lichenysin preliminarily identified as the primary active compound. The VpHLVD challenge experiment demonstrated that feeding Pacific white shrimp with strain JSHY-074 achieved a 70% survival rate within 5 d and a 5,942-fold reduction in hepatopancreas pathogen load (from 6.12 × 107 to 1.03 × 104 copies/ng). CONCLUSIONS:This is the first report of B. altitudinis exhibiting antagonistic activity against VpHLVD. The high technological readiness level of B. altitudinis JSHY-074 makes it a versatile probiotic feed additive, and its safety and effectiveness make it well suited for fast deployment and use in shrimp farming, offering a nutritional approach to reducing antibiotic dependency and promoting sustainable aquaculture practices.
OBJECTIVES:Given the limited ocular pathology data for common cuttlefish Sepia officinalis and hummingbird bobtail squid Euprymna berryi despite their high visual dependency, the purpose of this study was to investigate and describe the ophthalmic lesions in a cohort of laboratory-housed common cuttlefish and hummingbird bobtail squid. METHODS:Cases were retrospectively selected from the International Zoo Veterinary Group Pathology database that reported confirmed clinical ophthalmic lesions or histopathological lesions. Twenty-five cases were identified that included clinical records and gross and histopathological examination of whole specimens. The cases included 19 common cuttlefish and six hummingbird bobtail squid, thus providing a sample of 50 eyes and orbital cavities. RESULTS:Thirty-two of 50 individual eyes (64%) and 30 of 50 white bodies (60%) were affected. The most frequent lesion that was observed was inflammation (n = 29/32, 91%), primarily manifesting as uveitis (n = 23/32, 72%) and phakitis (n = 10/32, 31%). Cataracts were also common (n = 14/32, 44%), often with cataract-associated inflammation (n = 9/14, 64%). Leukopoietic hyperplasia of the white body was bilaterally observed in 15 of 25 animals (60%) and was thought to be associated with exophthalmos. In the absence of notable intraocular or infraorbital lesions in some animals, this change was considered reactive, likely in response to nonocular lesions, such as ulcerative dermatitis and branchitis. Notable additional findings included hypopyon-like lesions (n = 3/32, 9%), a single case of congenital ocular malformation, and one case with mesenchymal proliferations that were reminiscent of florid fibroplasia. CONCLUSIONS:This study contributes to the expanding knowledge of cephalopod ocular pathology, with previously unreported findings in these cephalopods including congenital ocular malformation and cases of -hypopyon-like lesions with proteinaceous material exudation and hemocytes in the anterior chamber. Additionally, it offers specific insights into the ocular pathology of the hummingbird bobtail squid.
OBJECTIVE:This study evaluated the effect of commercial Bacillus spp. probiotics on growth performance, immunity, gut microbiota composition, and disease resistance to Vibrio parahaemolyticus in Pacific white shrimp Litopenaeus vannamei that were reared under biofloc conditions. METHODS:A 56-d feeding trial was conducted in a static biofloc system with postlarval shrimp (1.00 ± 0.03 g). A total of 1,080 shrimp were randomly assigned to three groups: two treatment levels (recommended dose [PRO × 1] and a doubled dose [PRO × 2]) of a commercial probiotic blend, PRO4000X, alongside a control group (CTL; no probiotics). At the trial end point, hepatopancreas and gut samples were collected for gene expression. Gut samples were also obtained for gut microbiota analysis via 16S ribosomal RNA sequencing, and hemolymph samples were withdrawn to measure the total hemocyte count. RESULTS:Probiotic applications did not significantly affect growth performance, including final biomass, mean weight, survival, and feed conversion ratio under the experimental conditions. The probiotic-treated shrimp exhibited enhanced survival during a V. parahaemolyticus (strain A3) challenge, with significantly lower mortality rates (P < 0.001; 42.5 ± 4.3% for PRO × 1 and 60 ± 6.5% for PRO × 2) relative to the CTL (100 ± 0.00%). Immune parameters, such as total hemocyte count, did not differ. Interestingly, the expression of the antioxidant gene sod (superoxide dismutase) in the shrimp gut was significantly downregulated in the PRO × 1 group relative to the control (P = 0.030), which suggests reduced oxidative stress under probiotic supplementation. The analysis of the gut microbiota revealed differences in alpha diversity, specifically in evenness and Shannon index, which were significantly higher in the PRO × 1 group. The analysis of the bacterial composition also revealed minor shifts in the dominant genera. Notably, Lysobacter was more abundant in the PRO × 1 group, which potentially reflects positive modulation of gut microbial communities in response to probiotic supplementation. CONCLUSIONS:Overall, the application of PRO4000X probiotics significantly reduced the V. parahaemolyticus infection in the shrimp that were reared in biofloc water and supported the regulation of immunity and microbial communities in the gut. These findings indicate that probiotics potentially help to improve shrimp health when shrimp are cultured in biofloc systems.
OBJECTIVE:The present study examined the effect of humic substance and butyric acid blend (HSB) supplementation, with and without yeast cell wall (YCW), on gut morphology, immunity, and resistance to Flavobacterium covae, Edwardsiella ictaluri, and their coinfection in juvenile Channel Catfish Ictalurus punctatus. METHODS:A feeding trial was conducted in a recirculating aquaculture system with Channel Catfish fingerlings (19.7 ± 0.2 g). Thirty-seven Channel Catfish were randomly assigned into four dietary groups with supplemented feed (g/kg): HSB (2.0 HSB), YCW (0.5 YCW), HSB + YCW (1.0 HSB, 0.25 YCW), and a control group (not supplemented), each consisting of eight replicates. After 45 d of feeding the diets, growth performance was assessed and head kidney, spleen, and gill tissues were sampled for gene expression, while serum was collected for lysozyme activity. Subsequently, fish were pooled by treatment and challenged by immersion with either E. ictaluri (S97-773; 7.4 × 106 CFU/mL), F. covae (ALG-00-530; 1.2 × 106 CFU/mL), or coinfection with simultaneous half-doses of both bacteria. RESULTS:No significant differences were observed in fish growth performance and survival across treatments. However, Fulton's K-factor was significantly higher in the HSB group compared with the control. Serum lysozyme activity was significantly higher in the HSB group, while a numerically higher body mucus lysozyme activity was observed in the HSB + YCW group. No diet-related cytokine gene expression differences were observed in the kidney and splenic tissues. However, differences were observed in the expression of lysozyme genes lysc and lysg in the gill, with the highest expression in the YCW group. Furthermore, expression of ctsd (cellular protease) and defb (antimicrobial peptide) were different across all groups. Specifically, ctsd was upregulated in the HSB group when compared with the control. The expression of defb was upregulated in all treated groups, including HSB, YCW, and HSB + YCW, compared with the control group. After a 14-d bacterial challenge with either F. covae, E. ictaluri, or simultaneous exposure to both, significant differences in survival probabilities were observed across the treatment groups in the single E. ictaluri and coinfection groups but not in the F. covae group. Survival following E. ictaluri challenge varied among groups, with higher survival observed in the HSB group (79%) compared with the control fish (52%). Similarly, the HSB group showed improved survival (72%) compared with YCW (30%), HSB + YCW (45%), and the control group (30%) within the coinfected groups. Furthermore, the survival rate of Channel Catfish was lower in the coinfected groups than in those solely infected with E. ictaluri. CONCLUSIONS:Feeding Channel Catfish with a dietary humic substance and buryate blend reduced the susceptibility of Channel Catfish to E. ictaluri and coinfection with F. covae. These research findings have potential practical implications for fish health and provide an alternative tool for the management of coinfections in the catfish industry.
OBJECTIVE:The present study assessed the added diagnostic value of histopathology in complementing molecular detection of World Organization for Animal Health-listed viral pathogens during Colombia's national shrimp health surveillance program. METHODS:Pooled samples of pleopods from 1,470 whiteleg shrimp Penaeus vannamei (5 animals/pool for a total of 294 pooled samples) were screened for white spot syndrome virus, Taura syndrome virus, and yellow head virus using standardized PCR/reverse transcription PCR assays in accordance with Instituto Colombiano Agropecuario protocols. A subset of 81 shrimp was taken for whole-body histopathology analysis following standardized protocols and a semiquantitative G0-G4 lesion grading scale. Lesions were classified by organ system, and histopathological findings were compared to molecular results. RESULTS:All PCR assays were negative, with internal and external controls performing as expected. Using histopathology, lesions were identified in 77% of the shrimp examined, and lesions were primarily mild. Frequent findings included integumentary and gill colonization by Zoothamnium spp.; hepatopancreatic tubular necrosis with hemocytic granuloma-like reactions compatible with bacterial infection; intranuclear inclusion-like bodies, possibly of parvoviral origin; and focal myofiber necrosis, with organisms consistent with microsporidia. Autolysis was common but did not preclude lesion interpretation. CONCLUSIONS:Histopathology provided diagnostic information that was not captured by targeted molecular assays, revealing subclinical, opportunistic, and nonviral processes relevant to shrimp health. Incorporating histopathology into routine surveillance programs enhances pathogen detection and strengthens health assessments to certify disease-free status of shrimp production systems, as recommended by the World Organization for Animal Health.
OBJECTIVE:The objective of this study was to evaluate the potential influence of skeletal muscle mercury (Hg) concentrations on the biometric parameters and the frequency of lesions in Smallmouth Bass Micropterus dolomieu that were captured from three streams in Great Smoky Mountains National Park. By investigating the correlations between lesions, parasitism, and Hg concentrations, this study details the potential sublethal Hg contamination in fish in protected stream ecosystems. METHODS:Postmortem examinations with comprehensive histopathological analysis were performed on Smallmouth Bass (n = 62) that were collected from three streams in Great Smoky Mountains National Park, Abrams Creek (nAC = 27), Little River (nLR = 19), and Middle Prong Little Pigeon River (nMP = 16), from June to October 2022. Postmortem and histopathological data were matched to existing data on the concentrations of Hg in skeletal muscle to determine relationships between Hg concentration and pathology. RESULTS:Smallmouth Bass from Abrams Creek had higher total Hg concentrations, higher proportions of gill lesions, lymphohistiocytic epicarditis, and increased percentages of splenic pigmented macrophage aggregates but lower proportions of myxozoan cysts relative to the fish from other streams. Smallmouth Bass with high concentrations of Hg exhibited increased total length and body mass and more frequently showed the presence of glycogen-like vacuolation and increased pigmented macrophage aggregates in kidney tissue. Myxozoan cysts were more common in fish with lower total Hg levels, signifying the possible role of environmental impacts on myxozoan infection pressure. CONCLUSIONS:These findings highlight the complex health profiles of Smallmouth Bass in a protected stream ecosystem, including high levels of Hg, parasitism, and lesions. Furthermore, this study underscores the importance of monitoring and mitigating heavy metal contaminants to safeguard wildlife health and recreational fishing resources.
OBJECTIVE:This study aimed to characterize the effects of Prochristianella sp. infection (Cestoda: Trypanorhyncha) in the Octopus maya, with focus on tissue pathology, immune response, and potential implications for host health. METHODS:Molecular analyses of 28S ribosomal DNA were performed to confirm the identity of collected parasites from the buccal mass of octopus hosts. Macro- and microscopic observations of O. maya tissues, hemocyte counts, and histological analyses were conducted to assess the damage caused by the infection. Comparisons were made between naturally infected octopuses from Río Lagartos, Yucatán (the affected group), and minimally infected octopuses from Campeche (the control group) to establish a reference baseline for health and tissue morphology. RESULTS:Prochristianella sp. 1 was the only parasitic species infecting the buccal mass of octopuses collected from Río Lagartos, contrasting with the absence of the parasite in octopuses from Campeche, which were used as a reference group to characterize the infection. The affected group exhibited an undescribed capsular structure on the superior mandibular muscle of the buccal mass, containing cestodes and mucus and associated with tissue alterations, such as fibrosis, hemocyte infiltration, and focal necrosis. These findings led to the provisional designation of this condition as "myocestodiasis in cephalopods." CONCLUSIONS:This work provides new findings on helminth-induced pathologies, generating hypotheses about the underlying mechanisms in infected cephalopods. The study highlights the importance of multidisciplinary approaches to understanding host-parasite interactions. Furthermore, it lays the groundwork for managing and conserving the O. maya, an important marine resource of the Yucatán Peninsula.
OBJECTIVE:This study presents a juvenile green sea turtle Chelonia mydas case of fishing line ingestion during artisanal fishing monitoring, highlighting the importance of imaging and complementary diagnostics in detecting clinical alterations and managing marine debris-related injuries. METHODS:During artisanal fishing monitoring in Rio Grande do Sul, Brazil, a juvenile green sea turtle with a protruding fishing line was captured. Clinical evaluation included physical examination, ultrasonography, radiography, and hematological-biochemical analyses (e.g., red blood cell count, hemoglobin, white blood cell count, urea). RESULTS:Radiography and ultrasonography revealed a fishing line extending consecutively through the oral cavity, esophagus, and stomach without associated hooks, enabling manual line removal. Hematological findings indicated systemic responses to gastrointestinal trauma-regenerative macrocytic anemia (red blood cell count = 0.18 × 10⁶/µL; hemoglobin = 8.3 g/dL; hematocrit = 25%; mean corpuscular volume = 1,388 fL), leukocytosis (white blood cell count = 10,600 cells/µL), and elevated urea (232.59 mg/dL), suggesting dehydration and catabolic stress. Coelomic fluid accumulation indicated localized inflammation, though intestinal motility remained intact. Successful manual extraction avoided surgical intervention. CONCLUSIONS:This case underscores the role of diagnostic tools (imaging, hematology) in assessing debris-related health impacts in aquatic species. The findings align with broader evidence of fishing gear as a pervasive stressor in marine ecosystems, contributing to anemia, metabolic dysregulation, and inflammatory sequelae. This work emphasizes the need to integrate clinical diagnostics into fisheries management and expand health-monitoring protocols to address anthropogenic threats across aquatic taxa.
OBJECTIVE:Captive animals are exposed to various stressors originating from their artificial environment. Although stress can initially be an adaptive physiological response, persistent stress generally decreases immune function and makes animals more susceptible to pathogens. Environmental enrichment is a strategy that has been widely used to mitigate excessive stress and enhance animal welfare, but the effectiveness of individual enrichment components remains controversial. Hence, this study aimed to reveal the effect of shelter enrichment on stress levels and parasite infections in Masu Salmon Oncorhynchus masou. By using a single component, the study will help to provide a better understanding of the underlying mechanism of the enrichment effect. METHODS:We explored whether shelter-enriched conditions relieved stress in Masu Salmon by evaluating plasma cortisol levels. Fish provided with shelters were expected to experience less aggression from conspecifics and less stress from human disturbance. Moreover, we conducted a parasite challenge test using Ichthyobodo sp. to determine whether the presence of shelters inhibited infection by mitigating stress levels. RESULTS:Fish in enriched tanks had significantly lower basal cortisol levels than those in control tanks, suggesting that they were less affected by stressors. Although the difference was not significant, fish in enriched tanks also tended to experience less infection by the parasites than fish in control tanks. CONCLUSIONS:Given these results, simple shelter enrichment appears to be an effective method for mitigating stress among captive fish and reducing stress intensity or frequency. In addition, shelter enrichment could be used to inhibit infectious diseases, although further work is needed to prove the effect. These findings confirm that shelter enrichment has measurable effects on the factors related to fish welfare, which should encourage the adoption of enrichment in fish farms.
OBJECTIVE:Myxosporean parasites are worldwide-distributed cnidarians that infect the organs and tissues of marine and freshwater organisms, primarily fish. Based on morphological peculiarities, two myxosporean species, Myxidium gadi and Ceratomyxa merlangi, from the gallbladder content of Whiting Merlangius merlangus inhabiting four sampling localities (Kocaeli, Sinop, Ordu, and Trabzon) along the Black Sea coast of Türkiye have been identified. METHODS:Concordant with the morphological data, the first phylogenetic analyses on the nucleotide sequences of 18S ribosomal DNA confirmed our Myxidium specimens to be M. gadi. This study also provided the first molecular data on C. merlangi, which appeared to be the closest species to C. cretensis and C. arcuata on the phylogenetic trees. The infection prevalence (%) and density values of each parasite species were calculated according to season and sampling localities of Whiting. RESULTS:Ceratomyxa merlangi had a higher overall prevalence value (39.6%) than M. gadi (25.7%). The density values of both parasite species ranged between 2+ and 3+ in all fish samples. When the infection indices in sampling localities were compared for both parasite species, C. merlangi and M. gadi had the highest infection prevalence values in Sinop samples (66.3%); the highest density of infection (3+) was recorded in Sinop samples for C. merlangi and in Ordu samples for M. gadi. CONCLUSIONS:This study provides the first molecular data on M. gadi and C. merlangi, revealing their phylogenetic positions. In addition, seasonal and regional infection data for these species in the southern Black Sea region are reported for the first time, and it has been determined that both species can occur together.
OBJECTIVE:We sought to establish a current understanding of the histopathology of bivalves following exposure to heavy metal and to standardize the related terminology and microscopic diagnostic techniques, highlight limitations that hinder understanding, and discuss future research perspectives. METHODS:We conducted a literature review, looking for studies that implemented histopathological analyses to describe the damage that is caused by heavy metal bioaccumulation. For further description, we categorized lesions as regressive, defensive, or progressive. RESULTS:We analyzed 49 articles that employed histopathological techniques to describe the morphological changes that are associated with heavy metal bioaccumulation in bivalves. Since the 1980s, a growing interest in understanding how heavy metals affect bivalves has been evident, given the increasing number of published articles. Most studies were descriptive, although some contained experimental methods. The descriptive studies described damage to the digestive gland, gonads, gills, and kidneys. Defensive lesions were the most common response in the literature, with inflammation events reported in most cases. Regressive and progressive lesions were also documented, with necrosis (regressive change) and fibrosis (progressive change) being the most commonly reported, although not always correctly identified using microscopy. CONCLUSIONS:Histopathological studies on the effects of heavy metals on bivalve health are abundant, and the resulting morphologic lesions have been described extensively. However, most studies on heavy metal accumulation in bivalves have not followed a microscopic approach, focusing instead on using bivalves solely as sentinel or bioindicator species. A histopathologic evaluation is a common and important facet of pathologic analyses; however, we identified inconsistencies among diagnoses and misleading use of pathological terms. Therefore, we highlight the need to establish a systematic and standardized characterization of lesions at the microscopical level and their subsequent categorization to reduce the ambiguity of pathological descriptions. Implementing other methodological approaches in combination with histopathological analysis will improve our understanding of how heavy metals affect the health of bivalves.
OBJECTIVE:Renibacterium salmoninarum, the causative agent of bacterial kidney disease, poses a major threat to both wild and aquaculture salmonid populations. Traditional detection methods typically involve lethal sampling to collect kidney tissues but are often impractical for species of conservation concern. This study evaluates nonlethal sampling techniques for detecting R. salmoninarum in Greenback Cutthroat Trout Oncorhynchus clarkii stomias by comparing mucus, blood, and ovarian fluid samples to conventional kidney tissue. METHODS:During the 2019 spawning season, we collected samples from 781 adult fish and tested for R. salmoninarum via direct fluorescent antibody test (DFAT) and quantitative polymerase chain reaction (qPCR). RESULTS:A total of 25 and 256 kidney tissues were positive by DFAT and qPCR, respectively. Of the three nonlethal samples tested, mucus swabs showed the highest percent correlation for detection with positive kidney tissues (DFAT = 47.6%, qPCR = 41.7%). Blood and ovarian fluid samples showed a lower percent correlation with positive kidney tissues (blood: DFAT = 12.0%, qPCR = 1.2%; ovarian fluid: DFAT = 12.5%, qPCR = 21.4%). CONCLUSIONS:Our results suggest that nonlethal mucus swabbing could serve as a practical alternative for monitoring R. salmoninarum, especially in conservation efforts where minimizing fish mortality is critical.
OBJECTIVE:We investigated viral hemorrhagic septicemia virus dynamics in wild fish populations of the St. Lawrence River to compare host competency among five abundant native species and the invasive Round Goby Neogobius melanostomus following two decades of host-pathogen coevolution. To examine species' responses to the virus and identify principal hosts as viral reservoir species, we used viral surveillance among Round Gobies, Yellow Perch Perca flavescens, Rock Bass Ambloplites rupestris, Pumpkinseed Lepomis gibbosus, Bluegill L. macrochirus, and Brown Bullhead Ameiurus nebulosus collected from the nearshore fish community in the upper St. Lawrence River during spring 2020-2021. METHODS:Reverse-transcription quantitative PCR was used to detect and quantify viral nucleoprotein gene genetic material in pooled organ (i.e., liver, kidney, and spleen) and brain tissues of wild fish belonging to several susceptible host species. RESULTS:Reverse-transcription quantitative PCR detected viral hemorrhagic septicemia virus genetic material in each species during both sampling years. There was significant variation between species in both infection prevalence and median viral titer. Invasive Round Gobies exhibited significantly higher prevalence and titers compared to any of the native species. However, some native fishes (e.g., Yellow Perch and sunfishes Lepomis spp.) presented higher infection prevalence and viral concentrations compared to the others (e.g., Rock Bass and Brown Bullhead). CONCLUSIONS:Multiple species remain susceptible to viral hemorrhagic septicemia virus under enzootic conditions; however, viral infections are distributed unevenly among host species. Invasive Round Gobies have amplified reservoir competence compared to native fish species.
OBJECTIVE:The Spotted Scat Scatophagus argus, particularly in aquaculture, is commonly affected by intestinal parasitic infections that impact its health and growth. Filisoma spp., an acanthocephalan parasite, and Cryptosporidium spp. cause intestinal inflammation in various marine fish; however, infections with Cryptosporidium spp. or co-infection with these parasites have not been identified in Spotted Scat. METHODS:Host-parasite interactions in fish, including the inflammatory responses of the intestine, were investigated in 32 cultured Spotted Scat from Songkhla, Thailand. The study used parasitological examination, including polymerase chain reaction and nucleotide sequencing of the ITS1 and ITS2 regions of the ribosomal RNA gene for acanthocephalans and the 18S ribosomal RNA gene for Cryptosporidium. Additionally, histopathology and immunohistochemistry for interleukin-4 expression were performed. RESULTS:Most of the infected fish showed no significant clinical signs, with postmortem findings of hemorrhagic, congested, and edematous intestines. Parasitological analysis revealed that 84.37% of the fish were infected, with 9.37% having a single helminth infection, 40.62% being infected with coccidia, 34.37% having mixed infections with both parasites, and 15.62% of the fish being free from intestinal parasites. Polymerase chain reaction and nucleotide sequencing indicated that F. argusum and C. bollandi were the parasites involved. Histopathology showed increased inflammatory cell infiltrations, particularly eosinophilic granule cells and mononuclear cells, as well as higher levels of histopathological changes (vascular congestion, tissue necrosis, and epithelial desquamation) in the single F. argusum infection and co-infection with F. argusum and C. bollandi compared with C. bollandi infection alone. Similarly, significantly elevated interleukin-4 expression in the intestines, indicating a strong proinflammatory immune response, was observed in these groups. CONCLUSIONS:This study highlights the detrimental effects of F. argusum, regardless of whether it is a single or concomitant infection, which may impact the health of fish.
OBJECTIVE:Piscine lactococcosis associated with Lactococcus petauri is a serious emerging threat to fish populations in the Americas. This bacterial disease commonly presents as a hemorrhagic septicemia, resulting in high mortality rates and substantial financial losses. There are no commercial vaccines in the United States, and treatment options are limited and understudied. Florfenicol (Aquaflor) is a broad-spectrum antibiotic approved for finfish aquaculture, and erythromycin (Aquamycin 100) is an investigational new animal drug. This study aimed to compare the effectiveness of florfenicol- and erythromycin-medicated feed against lactococcosis through cohabitation challenges in Rainbow Trout Oncorhynchus mykiss. METHODS:Shedder fish were intracoelomically injected with L. petauri (∼1.5 × 104 CFU) and introduced to naïve populations at 13°C or 18°C. Treatments were initiated immediately after observation of mortality, with fish receiving florfenicol at 15 mg/kg for 10 d, erythromycin at 100 mg/kg for 21 d, or the control diet. RESULTS:At 18°C, cohabitant survival was significantly higher in florfenicol-treated (100%) and erythromycin-treated (93%) tanks compared to untreated positive controls (60%). There were no mortalities at 13°C or in the negative control tanks. In sampled survivors, L. petauri was detected by quantitative PCR in 29% of positive control fish, 14% of erythromycin-treated fish, and 14% of florfenicol-treated fish at 18°C compared to 21, 7, and 0%, respectively, at 13°C. Culturable bacteria were only recovered from 14% of positive control fish at both temperatures. CONCLUSIONS:These results indicate that early intervention with florfenicol or erythromycin can limit the spread of L. petauri and that lower water temperatures reduce disease onset, improving options for managing lactococcosis in aquaculture.
OBJECTIVE:Fish disease in aquaculture is a major risk to food safety. The identification of infected fish and disease categories present in fish farms remains difficult to determine at an early stage. Detecting infected fish in time is an essential step in preventing the spread of disease. The aim of this work was to detect fish infected with epizootic ulcerative syndrome and fish lice Argulus spp. METHODS:An improved YOLO (You Only Look Once) version 5 (YOLOV5) model was developed. In the context of transfer learning, our improved model used a pretrained model on binary images. The improved model was deployed and integrated into a Raspberry Pi board. RESULTS:The experimental results showed that it is more effective than a simple YOLOV5 model. CONCLUSIONS:Using the evaluation metrics of precision, recall, mAP50 (mean average precision at an intersection over union threshold of 0.50), and mAP50-95 (average of the mAP values calculated for intersection over union thresholds ranging from 0.50 to 0.95 in steps of 0.05), our new model achieved accuracy rates of 0.944, 0.969, 0.989, and 0.954, respectively.
