Freshwater Bathing Research Articles

Dynamics of Gill Responses to a Natural Infection with Neoparamoeba perurans in Farmed Tasmanian Atlantic Salmon.

Gill health has become a significant global challenge for Atlantic salmon (Salmo salar) aquaculture, particularly during the marine phase of farming. The increasing prevalence of gill pathologies has been linked to rising seawater temperatures, underscoring the need to evaluate existing tools for monitoring gill health and to develop novel approaches for early detection. In this study, we investigated the gill responses of commercially farmed Atlantic salmon to natural infection with Neoparamoeba perurans during an outbreak of amoebic gill disease (AGD) in Tasmania. Our focus spanned the low AGD prevalence, high AGD prevalence, and post-freshwater treatment stages of the outbreak. Evaluations of gill tissue included assessments of the gross AGD score, histopathological score, abundance of N. perurans (measured by 18S rRNA gene expression), and expression levels of inflammation-related transcripts. We demonstrated a strong correlation between different measures of AGD-related gill pathology and significant differences between distinct stages of the N. perurans outbreak. Post-treatment, fish exhibited considerable variability in their responses to the freshwater bath, highlighting the necessity for personalized management strategies that consider genetic, environmental, and health status factors. The expression patterns of angiogenin-1 (ANG1) and complement C1q tumour necrosis factor-related protein 3-like (C1QTNF3) emphasize their potential as biomarkers for early detection of gill damage in salmon aquaculture worldwide.

Hematological parameters of Mugil liza mullet submitted to different concentrations of formalin and freshwater

Lebranche mullet, Mugil liza is a species of high economic value for fishing. Despite the importance of the species, little is known about the effects of therapeutic baths on the hematological parameters of mullet. Such parameters are important tools for facilitating the early detection of diseases and illnesses that may impair the performance of the animals. This study evaluated the hematological parameters of mullet submitted to therapeutic baths with formalin and freshwater. For the experiment a total of 108 mullets were used, divided in groups of six individuals per tank. In this experiment, immersion baths were tested for 1 hour in freshwater (zero salinity), formalin at concentrations: 150, 200, 250, 300 and 350 mg L-1 in seawater and a control (without formalin and parasitized), in triplicate. After the immersion bath, fish blood was collected from the caudal vein for evaluation of hematological parameters. The blood was destined to erythrogram, leukogram, thrombogram and glucose determinations. The hematological analyses found significant difference in the number of erythrocytes, lymphocytes, hematocrit, hemoglobin, MCV, MCH, MCHC and glucose. However, there was no significant difference in thrombocyte, total leukocyte, monocyte and neutrophil values. It is concluded that 150 mg L-1 formalin concentration and freshwater bath for one hour can be used for mullet as it causes mild hematological changes.

Biofluorescent response in lumpfish Cyclopterus lumpus to a therapeutic stressor as assessed by hyperspectral imaging

The demand for lumpfish (Cyclopterus lumpus) as a biological control for salmon lice is increasing. However, lumpfish welfare is considered a limiting factor within aquaculture operations. Identifying a noninvasive parameter that measures subclinical stress in lumpfish is a key goal for improving their welfare. The lumpfish is documented to emit green and red biofluorescence within the blue shifted light of their environment. Here we show that lumpfish fluorescence responds to a therapeutic stressor within a controlled experiment. Lumpfish (n = 60) underwent a 3-h freshwater bath therapeutant to evaluate whether fluorescence spectra produced by the species respond to external stimuli. Lumpfish were quickly scanned under a hyperspectral camera (400–1000 nm spectral range) prior to and after treatment. The lumpfish were randomly divided into 3 groups with identical treatment. All groups increased fluorescence emissions, though the level of change depended on whether the averaged, red, or green spectra were analyzed; the control group (n = 20) remained constant. All lumpfish emitted green fluorescence (~ 590–670 nm) while a portion (49%) produced red fluorescence (~ 690–800 nm). As lumpfish fluorescence shifts in response to the applied stressor, this study provides insight into how fluorescence may be incorporated into the welfare management of lumpfish.

Comparison of non-medicinal delousing strategies for parasite (Lepeophtheirus salmonis) removal efficacy and welfare impact on Atlantic salmon (Salmo salar) hosts

AbstractSince salmon lice have developed resistance to pesticides, non-medicinal delousing treatments have become increasingly used to remove the parasite from fish on salmon farms in Norwegian waters. These novel techniques are an important means of controlling epidemics of lice at farms for maintaining the health of farmed fish and for preventing the spread of lice to wild salmonid populations. However, some treatments are associated with higher mortality rates and negative welfare impacts on the host fish. Furthermore, it is unclear how effective each treatment is in removing lice compared to alternatives. Here, in a controlled laboratory environment, we tested the efficacy of mechanical, warm water (28 °C and 34 °C), and freshwater treatments alone and in combination, and examined their welfare impact on host fish. Regardless of treatment group or control, the handling of fish through the experiment led to a reduction in lice load and decline in fish welfare. Among the treatments examined, the freshwater bath alone and in combination with other treatments had the greatest delousing efficacy. The 34 °C warm water baths also significantly reduced lice loads but led to worse welfare outcomes with fish having a higher prevalence of injuries and reduced growth and condition factor. Delousing treatments were however not associated with long-term effects on neuroendocrine parameters or stress coping ability, suggesting that immediate welfare impacts from these procedures are generally reversible. It was also found that sedating fish prior to treatment was shown to mitigate the welfare impact. These findings are useful for the needed optimization of delousing strategies for greater delousing efficacy and reduced welfare impact on fish.

Reciprocal hybrids of Atlantic salmon (Salmo salar) x brown trout (S. trutta) confirm a heterotic response to experimentally induced amoebic gill disease (AGD)

Amoebic gill disease (AGD) affects global marine aquaculture production of Atlantic salmon, requiring costly reiterative treatment and negatively impacting fish performance and welfare. Although there has been gradual and ongoing progress in genetic selection to improve host resistance to the causative agent (Neoparamoeba perurans) there has been little focus on the response of interspecific hybrids to AGD challenge. Previous research has demonstrated that Atlantic salmon x brown trout hybrids had reduced requirement for freshwater bathing (based on gross gill signs) during chronic natural AGD exposure, yet there has been no histological or molecular evidence confirming differential host response or parasite abundance. In this study we exposed Atlantic salmon (SS), brown trout (TT) and their reciprocal interspecific hybrids (TS and ST) to a single laboratory challenge (∼700 amoebae.l−1 for 18 days) and compared the resultant infection and disease signs characteristic of AGD. Gill score was significantly higher in SS than in TT and hybrids. Copy number quantification of amoebae on gills was higher in salmon than in hybrids or trout but did not differ between hybrids and trout. Gill histopathology confirmed both an increased amoebae abundance and higher expression of host tissue reaction in SS with significantly higher percentages of lesions harboring hyperplastic lesions. Mid-parent and best-parent heterosis of resistance to N. perurans and host response (gill lesions) was confirmed but did not differ between hybrid crosses. Although limited to a single laboratory infection event, our results support previously reported observations (from natural infection/reinfection) of reduced AGD signs in trout and interspecies hybrids. We conclude that interspecies hybrids have potential to improve our understanding of salmonid resistance to amoebic branchitis and support future gene-based research toward fish disease management.

Epidemiological and Clinical Characteristics of Imported Schistosomiasis in a Tertiary Teaching Spanish Hospital, 2015- 2022

Background: Schistosomiasis is a parasitic disease greatly present in tropical and subtropical areas, and frequently diagnosed in travelers and migrants. Methods: This report summarizes epidemiological and clinical data from retrospective cases of imported schistosomiasis diagnosed from January 2015 to May 2022 in a national referral center for tropical diseases in Madrid, Spain. Results: From a total of 9,929 patients attended in our clinic in the study period there were 477 schistosomiasis diagnosis (4,4%). Time elapsed from travel to diagnosis was 120 days (IQR 26-680). Most cases (28.1%) were diagnosed in immigrants from endemic areas, followed by 24.5% of travelers. In up to 34.5% of cases the diagnosis was a result of screening in asymptomatic subjects, 17% presented fever and 15% diarrhea. Almost all cases were diagnosed by serology and eggs in urine or feces were identified in only 11 patients (2.2%). Conclusions: Imported schistosomiasis is a chronic and asymptomatic disease that can be diagnosed in most patients by serology. It is important to advice travelers to avoid freshwater baths in endemic areas and get screened if they have been exposed to the parasite.

How delousing affects the short-term growth of Atlantic salmon (Salmo salar)

Infestations with salmon lice and subsequent salmon lice management is one of the most challenging and costly aspects of marine salmonid aquaculture. Both the handling and treatment, specifically non-medicinal treatment, against salmon lice cause stress and physical injuries to the host, the Atlantic salmon (Salmo salar). This in turn leads to reduced appetite and increased mortality. In this study, we have estimated the short-term growth loss of Atlantic salmon related to treatments (thermal, mechanical, hydrogen peroxide bath, freshwater bath and combination medicinal baths) for removal of salmon lice. To achieve this, we have obtained daily production data at cage-level from 2014 to 2019 from three large Norwegian aquaculture companies. We have used the registered feed-amount, number of fish and seawater temperature at cage level to calculate the thermal growth coefficient (TGC) of 635 fish-groups the week before a pre-treatment starvation period and the week after 2530 different treatments to estimate the reduction in TGC. We modelled this outcome using a mixed effect linear regression model, with treatment method as the main fixed effect of interest and fish weight, seawater temperature, smolt-age and year-class included as fixed effects. Results showed a period of suboptimal feeding and growth after all treatment methods, where non-medicinal treatment methods had a significantly larger negative effect on growth compared to medicinal treatments. The results also showed that timing of treatment played a role in the outcome of a treatment. The short-term biomass-loss in one cage following one non-medicinal treatment was estimated to 31,200 kg (average cage containing 150,000 fish weighing 3 kg, and seawater temperature of 10 °C). Thus, there could exist a potential for increased production in the Atlantic salmon aquaculture industry by reducing the number of delousing operations.

Investigating the impacts of H2O2 treatment on gills of healthy Atlantic salmon reveals potential changes to mucus production with implications on immune activity

Current treatment strategies for relevant infectious diseases in Atlantic salmon (Salmo salar L.) include the use of low salinity or freshwater bathing. However, often availability is restricted, and hydrogen peroxide (H2O2) is used as an alternative. The potential impacts of H2O2 on fish mucosal tissues, especially the gills therefore need to be considered. In this study the mucosal and immunological effects of H2O2 treatment on the gills of healthy Atlantic salmon were examined by gene expression (qPCR) and immunohistochemistry (IHC) investigating T-cell, B-cell, and mucin activity. Healthy fish were treated with H2O2 and sampled at different times: 4 h, 24 h and 14 days post-H2O2 treatment (dpt) (total n = 18) to investigate the effect of holding time and H2O2 treatment. Treatment with H2O2 resulted in up-regulation of markers for T-cell activity and anti-inflammatory response and down-regulation of mucin expression in the gills at 14 dpt compared to fish sampled prior to treatment (0h; n = 5 fish). These findings were supported by IHC analysis, which despite being highly variable between samples, showed an increase in the number of CD3+ T cells at 14 dpt in 50% of treated fish compared to pre-treatment fish. The results from this study suggest that H2O2 treatment does not immune compromise healthy Atlantic salmon after 14 dpt (i.e., post-recovery) but modulates gill immune activity and disrupts the mucus covering of the gills. However, further studies are required to determine whether the effects observed are related to H2O2 treatment in isolation or other variables such as holding time or environmental factors.

Monitoring of Leptospira species diversity in freshwater bathing area and in rats in Paris, France

Leptospirosis is a neglected zoonotic disease with a worldwide distribution caused by bacterial pathogenic Leptospira. Rodents are considered as the main reservoir of Leptospira and transmission usually occurs through exposure to urine-contaminated environment. However, interactions between environment, rodent reservoir and human leptospirosis remain poorly studied.Here, we evaluated the concentration of Leptospira in surface water and captured rats in the city of Paris (France) from 2018 to 2020 using an integrity qPCR (Quantitative Polymerase Chain Reaction). All environmental samples (n = 1031) were positive for saprophytic Leptospira but pathogenic Leptospira P1 group were only found in 40% (n = 363; 2018) to 0% (n = 264; 2020) of samples. In the same time, analysis of 200 brown rat corpses trapped in the city, showed about 15% of positivity for Leptospira but the different method used for rats conservation (based on presence or absence of conservative agent) showed important variations in the Leptospira prevalence. Metagenomic analysis, based on rrs gene sequencing, was also carried out to evaluate the distribution of Leptospira in samples. Results could indicate that some species of Leptospira are found in surface waters as well as rats, but further study is needed to accurately describe the nature of the link between these two reservoirs.Quantification of Leptospira and pathogenic species description circulating inside animal reservoir living in the vicinity of freshwater in urban areas, will be helpful to understand the eco-epidemiology of leptospirosis and to establish prevention and intervention strategies, especially in the context of organization of recreative activity events in these urban areas.

Evaluation of Low Temperature and Salinity as a Treatment of Atlantic Salmon against Amoebic Gill Disease.

Amoebic gill disease (AGD) is a significant health issue for Atlantic salmon farmed in a marine environment. While the disease is currently managed using freshwater or hydrogen peroxide baths, there is a need to develop other treatments. The aims of this study were to examine the effect of salinity (0 ppt and 35 ppt) and temperature (3 °C and 15 °C) on attachment and survival of Neoparamoeba perurans in vitro over short exposure times (15 min and 2 h) and to assess the efficacy of reduced temperature (3 °C) as treatment for Atlantic salmon affected by AGD. In vitro freshwater 3 °C was at least as effective as freshwater 15 °C and the attachment was significantly lower after 2 h in freshwater 3 °C than freshwater 15 °C. In vivo there was no difference between the fish treated with freshwater 15 °C for 2 h or freshwater 3 °C. This study showed that despite exposure to low temperature reducing attachment of N. perurans to their substrate in vitro, 15 min cold-water bath treatment was not more effective at reducing AGD in Atlantic salmon than current commercial 2 h freshwater bath.

Monitoring of Leptospira Species Diversity in Freshwater Bathing Area and in Rats in Paris, France

Monitoring of Leptospira Species Diversity in Freshwater Bathing Area and in Rats in Paris, France

Evaluation of the Infectious Potential of Neoparamoeba perurans Following Freshwater Bathing Treatments.

Freshwater bathing for 2–3 h is the main treatment to control amoebic gill disease of marine-farmed Atlantic salmon. Recent in vitro studies have demonstrated that amoebae (Neoparamoeba perurans) detach when exposed to freshwater and that some eventually reattach to culture plates when returned to seawater. Here, we evaluated the potential for gill-detached N. perurans to survive a commercially relevant treatment and infect AGD-naïve fish and whether holding used bathwater for up to 6 h post treatment would lower infectivity. AGD-affected fish were bathed in freshwater for 2 h. Naïve salmon were exposed to aliquots of the used bathwater after 2, 4, 6 and 8 h. The inoculation was performed at 30 ppt for 2 h, followed by gradual dilution with seawater. Sampling at 20 days post inoculation (dpi) and 40 dpi confirmed rapid AGD development in fish inoculated in 2 h used bathwater, but a slower AGD development following exposure to 4 h bathwater. AGD signs were variable and reduced following longer bathwater holding times. These results suggest that viable amoebae are likely returned to seawater following commercial freshwater treatments, but that the risk of infection can be reduced by retention of bathwater before release.

Mycosands: Fungal diversity and abundance in beach sand and recreational waters — Relevance to human health

The goal of most studies published on sand contaminants is to gather and discuss knowledge to avoid faecal contamination of water by run-offs and tide-retractions. Other life forms in the sand, however, are seldom studied but always pointed out as relevant. The Mycosands initiative was created to generate data on fungi in beach sands and waters, of both coastal and freshwater inland bathing sites. A team of medical mycologists and water quality specialists explored the sand culturable mycobiota of 91 bathing sites, and water of 67 of these, spanning from the Atlantic to the Eastern Mediterranean coasts, including the Italian lakes and the Adriatic, Baltic, and Black Seas. Sydney (Australia) was also included in the study. Thirteen countries took part in the initiative. The present study considered several fungal parameters (all fungi, several species of the genus Aspergillus and Candida and the genera themselves, plus other yeasts, allergenic fungi, dematiaceous fungi and dermatophytes). The study considered four variables that the team expected would influence the results of the analytical parameters, such as coast or inland location, urban and non-urban sites, period of the year, geographical proximity and type of sediment. The genera most frequently found were Aspergillus spp., Candida spp., Fusarium spp. and Cryptococcus spp. both in sand and in water. A site-blind median was found to be 89 Colony-Forming Units (CFU) of fungi per gram of sand in coastal and inland freshwaters, with variability between 0 and 6400 CFU/g. For freshwater sites, that number was 201.7 CFU/g (0, 6400 CFU/g (p = 0.01)) and for coastal sites was 76.7 CFU/g (0, 3497.5 CFU/g). For coastal waters and all waters, the median was 0 CFU/ml (0, 1592 CFU/ml) and for freshwaters 6.7 (0, 310.0) CFU/ml (p < 0.001). The results advocate that beaches should be monitored for fungi for safer use and better management.

Genetic structure and diversity in Neochen jubata (Aves: Anatidae) from the Araguaia River, GO, Brazil

Abstract: The Orinoco Goose (Neochen jubata) is a few-known and endemic Anatidae to South America, inhabiting sandy beaches along medium and large rivers, with a well-developed riparian forest and in swamp savannas and large freshwater baths. Recent data indicate the presence of longitudinal migratory behavior, and despite them, there are no records on the genetic profile of this species. The Araguaia River region, in the municipality of Luiz Alves, Goiás, receives an undetermined number of ducks seasonally, and there is little information about the individuals who visit this place, constituting the ideal scenario for a study able to offer a genetic overview perspective of this species and to understand the relationship between these individuals better. For this, we genetically characterized 61 individuals sampled in three distinct years of collection using microsatellite molecular markers and mitochondrial DNA. Genetic diversity analyses revealed low levels of heterozygosity for all sampled groups. However, they are within the equilibrium proposed by Hardy-Weinberg (HWE), as inbreeding or drift are not acting in these groups. The parentage analysis supports it, showing a high number of unrelated individuals over the years. AMOVA showed a significant difference among groups. These results may reflect the structure of this migratory species in that region, with the paired differentiation test of individuals from 2013 and 2014 being more similar to each other than those from other years, indicating a possible genetic structure diagnosed by the years of capture. However, there is a high allelic sharing among the three sampled groups, suggesting that these individuals are a population that connects over time and that they have a philopatric relationship with the location. The results found in this study constitute an initial milestone for the genetic knowledge of the mallard duck that should be raised in many other genetic studies.

A High Throughput Viability Screening Method for the Marine Ectoparasite Neoparamoeba perurans

The marine protozoan parasite Neoparamoeba perurans has been established as the causative agent for amoebic gill disease (AGD) in Atlantic salmon (Salmo salar). Freshwater bathing is the only routinely used treatment for AGD in Australia while hydrogen peroxide (H2O2) is used in countries with cooler water temperatures. The identification of new treatments that do not rely on either freshwater or H2O2 bathing is highly sought. However, in vitro based methods for high throughput screening of antiparasitic compounds have not been established for this parasite. To this end the present study evaluated two in vitro bioassays based on metabolic energy production and cellular membrane integrity to distinguish between amoebistatic (crenated or pseudocyst forms with recovery possible) and amoebicidal (death) activity. Amoebae were subject to either freshwater, H2O2 or chloramine-T for 4h treatment and assessed 24h after recovery. Visualization by microscopy and bioassay assessment 24h post-treatment confirmed that H2O2 and freshwater are 95% amoebicidal albeit due to different mechanisms of action. These data are consistent with other studies where amoebae have been observed to recover following exposure to these compounds and provide evidence for the inclusion of a recovery component to differentiate between the mechanism of action of amoebicidal and amoebistatic treatments. Together these bioassays are a critical tool for high throughput screening of novel and more effective treatments against AGD.

Evaluation of sodium percarbonate as a bath treatment for amoebic gill disease in Atlantic salmon

Amoebic gill disease (AGD), caused by Neoparamoeba perurans, is a major health challenge for Atlantic salmon aquaculture globally. While freshwater bathing for 2 hr is effective in reducing infection severity, there is need for more rapid and lower cost alternatives. To this end, a combination of sodium percarbonate (SPC) in freshwater was examined for its treatment efficacy. Initial in vitro studies showed a reduction in amoeba viability when exposed for 30 min to freshwater containing >500 mg/L SPC. Subsequently, AGD-affected salmon were bathed for 30 min in 16°C freshwater containing 100, 500 or 1,000 mg/L SPC, or for 2 hr in 16°C freshwater to mimic industry practice. Treatment at the highest SPC concentration caused extensive gill damage and substantial mortality. Neither occurred to a significant extent at lower SPC concentrations. Gill pathology of surviving fish 10 days post-treatment (dpt) was comparable to or more severe than pre-treatment, and significantly (p < .001) more severe than in 2 hr freshwater bathed fish. N. perurans DNA was confirmed by qPCR in all treatment groups at 10 dpt. The data indicate that a 30-min exposure to SPC in freshwater is not a suitable alternative to existing freshwater treatment of AGD.

Radonotherapy in restoring statokinetic functions in the patients with occupational joint damage

The results of the use of natural radon water in the form of general baths in patients working in the coal mining and metallurgical industry, with occupational diseases of the joints and spine, at the stage of rehabilitation are presented. Studies have shown that the course application of radon therapy has a pronounced analgesic and anti-inflammatory effect, a general sedative effect helps to restore the volume of movements in the affected joints, normalizes the statokinetic functions of the musculoskeletal system, slows down the progression of the joint process and the development of dystrophic changes in the musculoskeletal system.Indicators of statodynamic functions of the musculoskeletal system in patients with occupational diseases of the joints and spine in the rehabilitation system against the background of course use of natural radon waters in the form of shared baths were studied. The aim of the study is to explore the effect of radon waters of natural origin on the dynamics of statodynamic parameters according to the data of a stabilometric study in patients working in the coal mining and metallurgical industry, with occupational diseases of the joints and spine.Patients with occupational diseases of the joints and spine in rehabilitation were prescribed general radon baths (the main group). The control group of patients received freshwater baths. Before and after treatment were carried out studies of the static-dynamic functions stabiiloplatform (soft ware-hardware complex for clinical motion analysis “Biomechanics” published by the scientific-medical firm MBN), with the help of which the indicator of the common center of mass, the flexor setting up of the thigh, the coefficient of weight load on the foot, the inter-limb asymmetry, the vertical stance was determined in the initial position and in the Romberg position.The use of common radon baths in the main group allowed to normalize the statokinetic functions of the musculoskeletal system in the form of reducing the period of alignment of the pelvic flexor installations and asymmetry of the distribution of weight load on the affected limb; increasing the level of adaptation of patients to functional loads against the background of reducing pain and inflammatory syndrome. There were no significant changes in these indicators in the control group. The use of general radon baths on the rehabilitation stage in patients working in the coal mining and metallurgical industry, with occupational diseases of the joints and spine, helps to restore the statodynamic functions of the musculoskeletal system, the disappearance of pain syndrome, and reduces inflammation.The authors declare no conflict of interests.

Effect of radon therapy on epithelial cells of the respiratory tract mucosa in patients with occupational chronic obstructive pulmonary disease

The influence of natural radon waters on the state of the respiratory tract mucosal cells in patients working in the coal and metallurgical industries with occupational chronic obstructive pulmonary disease was studied. The positive effect of common radon baths on the restoration of cytological changes in the respiratory mucosa was revealed.Indicators of local immunity of the respiratory tract mucosa in patients with occupational chronic obstructive pulmonary disease on the background of the use of general radon baths.The aim of the study is to explore the effect of natural radon water in the form of shared baths on epithelial cells of the respiratory mucosa in patients with occupational chronic obstructive pulmonary disease based on the analysis of cytological changes in the respiratory mucosa. Patients of the main group with professional chronic obstructive pulmonary disease were given general radon baths from a natural source in sanatorium conditions. Patients in the control group had shared freshwater baths. All patients before and after treatment studies were conducted cytologic changes in the smears from the mucous membrane of the nose and phlegm. The use of common radon baths in the main group revealed a pronounced corrective effect on the function of cellular protection of the respiratory mucosa, which was expressed in a significant decrease in destructive processes in cells of all types with an increase in their functional activity, normalization of mucociliary clearance. There were no significant changes in indicators in the control group.The use of common radon baths at the stage of rehabilitation in workers of the coal and metallurgical industry with professional chronic obstructive pulmonary disease leads to the restoration of the integrity of the cellular composition of the epithelial cover of the respiratory tract mucosa, preserves the functional activity of cells of local protection factors.The authors declare no conflict of interests.

The Effects of Short Freshwater Bath Treatments on the Susceptibility to Different Stages of Neobenedenia girellae Infecting Barramundi (Lates calcarifer)

Neobenedenia girellae is one of the most pathogenic parasites affecting marine fish in captivity conditions. The use of chemicals for parasite prevention and treatment have several benefits; however, they can cause various negative side-effects. In an effort to discover cost-effective and sustainable practices, our current study was aimed at investigating the efficiency of freshwater treatments on N. girellae. A challenge test was conducted to produce infected fish which became materials for the freshwater immersion experiments. The duration and reaction of the parasites at different development stages from eggs to adult parasites were examined. Our findings revealed that 100% of the adults and oncomiracidia of N. girellae were killed quickly in freshwater. The eggs of N. girellae, however, were highly resistant to freshwater with a hatching success rate of more than 95% in all the freshwater immersion treatments (2, 5, 10 and 30min). The eggs hatched mainly on day 7 and finished hatching on day 8. Thus, the freshwater immersion method can be applied to treat N. girellae at most stages excepted for the egg stage. The best practical treatment for this parasite is to perform a replicated immersion recommended 8 days following the first treatment.

The Effects of Short Freshwater Bath Treatments on the Susceptibility to Different Stages of Neobenedenia girellae Infecting Barramundi (Lates calcarifer)

Neobenedenia girellae is one of the most pathogenic parasites affecting marine fish in captivity conditions. The use of chemicals for parasite prevention and treatment have several benefits; however, they can cause various negative side-effects. In an effort to discover cost-effective and sustainable practices, our current study was aimed at investigating the efficiency of freshwater treatments on N. girellae. A challenge test was conducted to produce infected fish which became materials for the freshwater immersion experiments. The duration and reaction of the parasites at different development stages from eggs to adult parasites were examined. Our findings revealed that 100% of the adults and oncomiracidia of N. girellae were killed quickly in freshwater. The eggs of N. girellae, however, were highly resistant to freshwater with a hatching success rate of more than 95% in all the freshwater immersion treatments (2, 5, 10 and 30min). The eggs hatched mainly on day 7 and finished hatching on day 8. Thus, the freshwater immersion method can be applied to treat N. girellae at most stages excepted for the egg stage. The best practical treatment for this parasite is to perform a replicated immersion recommended 8 days following the first treatment.