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1.
Hydrogen peroxide has been the only medicine used to treat salmon infected with sea lice [Lepeophtheirus salmonis (Krøyer)] on many farms in Scotland since 1992 and reports have suggested reduced treatment efficacy. The present study tests the sensitivity of sea lice to exposure to hydrogen peroxide under farm conditions and also in vivo by comparing lice from a farm with suspected resistance and lice from a farm that had not been pre‐exposed to hydrogen peroxide. In bin treatments on fish from a farm treated with hydrogen peroxide on 41 occasions, numbers of ovigerous lice declined by only 15% and 16% in two replicates and other mobile stages by 25%. Where hydrogen peroxide had not been used, ovigerous females declined by 90% and 87% and other mobile lice stages by 97% and 99%. These trials and observed poor efficacy of cage treatments, for example only 7.5% reduction in lice numbers when fish were treated with 2000 p.p.m. for 20 mins, indicated resistance of lice to hydrogen peroxide. The mechanisms involved in the development of resistance, possible genetic selection for lice with reduced carapace permeability or detoxifying enzymes such as catalase, or tolerance through induction by subtherapeutic exposure are reviewed. Implications for lice control strategies relying on hydrogen peroxide are discussed.  相似文献   

2.
Nocardiosis in sea bass, Lateolabrax japonicus, in Taiwan   总被引：8，自引：0，他引：8  
An epizootic in pond cultured sea bass, Lateolabrax japonicus , was caused by Nocardia sp. in Taiwan, in September and October 1997. The cumulative mortality within 1 month was 17.5% (3500 out of 20 000 fish) and diseased fish were 7 months old with total lengths from 25 to 30 cm. Multiple, yellowish white nodules, 0.1–0.2 cm in diameter, were scattered in the gill, heart, liver, spleen and kidney. Histopathologically, typical granulomatous lesions appeared in those organs. The morphology of isolated bacteria from brain heart infusion (BHI) medium or Lowenstein–Jensen medium (LJM) were bead-like filaments, as shown by Ziehl-Neelsen's (ZN) staining method. The gross lesion and histopathological changes found in experimentally infected fish were similar to those in naturally infected fish. Based on the growth characteristics, morphological and biochemical properties of the bacterium, and histopathological changes, the isolated bacteria were identified as Nocardia seriolae . This is the first report of N. seriolae -infected sea bass in aquaculture.  相似文献   

3.
The abundance of salmon lice and the physiological effects of infection were examined in two stocks of sympatric sea trout and anadromous Arctic char in northern Norway. One stock feed in a coastal area with extensive salmon farming (exposed locality), while the other feed in a region with little farming activity (unexposed locality). The results showed that the lice infection was significantly higher at the exposed locality, at which the mean intensity of infection peaked in June and July at over 100 and 200 lice larvae per fish respectively. At the exposed locality we also observed a premature return to freshwater of the most heavily infected fish. Such behaviour has previously been interpreted as a response by the fish to reduce the stress caused by the infection and/or to enhance survival. Blood samples taken from sea trout at sea at the exposed locality showed a positive correlation between intensity of parasite infection and an increase in the plasma cortisol, chloride and blood glucose concentrations, while the correlations from sea trout in freshwater were more casual. Several indices pointed towards an excessive mortality of the heaviest infected fish, and 47% of the fish caught in freshwater and 32% of those captured at sea carried lice at intensities above the level that has been shown to induce mortality in laboratory experiments. Furthermore, almost half of all fish from the exposed locality had lice intensities that would probably cause osmoregulatory imbalance. High salmon lice infections may therefore have profound negative effects upon wild populations of sea trout. At the unexposed location, the infection intensities were low, and few fish carried more than 10 lice. These are probably within the normal range of natural infection and such intensities are not expected to affect the stock negatively.  相似文献   

4.
The transmission of viral encephalopathy and retinopathy (VER) was investigated in juvenile sea bream, Sparus aurata L. Two different infection routes [intraperitoneal (i.p.) and intramuscular injection (i.m.)] were tested at two different temperatures (20 and 26 °C) using sea bream of mean weight 0.7, 2 and 4 g, as well as an immersion challenge performed at 26 °C with sea bream of 0.7 g. Successful transmission of the disease was only achieved by i.m. injection. Mortalities of 100% occurred in sea bream of 0.7 g at day 15 post-infection and 47% in sea bream of both 2 and 4 g at day 30 post-infection in all the experimental infections at 26 °C. No mortalities were ever observed with infections at 20 °C. When mortalities were observed, the virus was detected by immunoperoxidase staining in the SSN-1 cell line inoculated with tissues from infected fish. Histological examination of both normal and infected fish showed a vacuolization in the bipolar and granular layers of the retina of the infected sea bream. This is the first experimentally induced transmission of VER in sea bream. Differences were observed at the time of disease onset depending on water temperature, the route of infection and the age of the juvenile fish.  相似文献   

5.
Challenge methods for inducing nocardiosis, caused by Nocardia seriolae in yellowtail, Seriola quinqueradiata, were evaluated. The first method involved intraperitoneal injection of 1.1 x 10(2), x 10(3) and x 10(4) cfu of N. seriolae; the second was by bath immersion with three different concentrations of bacterial suspension for 10 min; the third was by intradermal injection using a multipuncture device; the fourth was by oral administration using a tube; the fifth was based on the co-habitation of uninfected fish with others that had been artificially infected, i.e. intraperitoneally or by immersion for 10 min. The LD(50) values for the infection trials were 1.9 x 10(2) (intraperitoneal injection), 1.5 x 10(4) mL(-1) (immersion), 4.3 x 10(6) (intradermal injection) and 1.7 x 10(7) (oral administration). In the co-habitation challenge, mortalities were 70% and 50% in groups of non-infected fish mixed with fish infected by the i.p. injection and immersion methods, respectively. Fish challenged by intraperitoneal injection developed adhesions. Fish challenged by other methods did not show any gross clinical signs and moribund fish were similar to natural infection.  相似文献   

6.
The use of wrasse as cleaner fish in farming of Atlantic salmon, Salmo salar L., is now widespread in Scotland, Ireland and Norway, but little is known about the susceptibility of these fish to the common pathogens of cage-cultured salmon. The susceptibility of goldsinny wrasse, Ctenolabrus rupestris L., to infectious pancreatic necrosis virus (IPNV) was investigated. Captive-bred C. rupestris were infected with IPNV-Sp (Shetland strain) using a bath challenge method. Two infection doses were used, low (4.1 × 105 pfu mL−−1) and high (2.4 × 106 pfu mL−−1), with two replicates for each experiment. Bathing times were 1 h for the low dose and 5 h for the high dose. A maximum prevalence of infection (30%) was seen 2 weeks post-infection in replicate 1 of the low dose experiment and was accompanied by low tissue titres. The tissue titres dropped to an undetectable level by 4 weeks post-infection. In the high dose experiment, a high prevalence of infection was seen along with moderate titres in tissues as well as a marked pathological response. Both prevalence and intensity declined rapidly and the fish recovered. In the high dose experiment, faecal titres followed the same pattern as those in the tissues. The implications for the use of wrasse in the farming of Atlantic salmon are discussed.  相似文献   

7.
The skin fluke Neobenedenia girellae has become a serious problem in Japan since the 1990s. Present control methods focus on the removal of the attached parasite and these post-infection treatments are often labor intensive, time consuming, and/or stressful to fish. Chub mackerel Scomber japonicus are highly susceptible to N. girellae. However, because of their sensitive nature, bath treatments may cause mortality. In this study, we investigated the efficacy of cage shading to reduce skin fluke infection and the frequency of conventional post-infection treatments. Juvenile mackerel were reared in cages with or without shade for 3 months and their skin fluke infections were monitored. We performed either freshwater baths or oral administration of praziquantel if fluke intensity exceeded the given criteria. In unshaded cages, 3 total bath treatments or 6 total drug treatments were conducted. In contrast, no treatment was required for the shaded cage. The overall fluke intensity in the shaded cage was less than half that of the unshaded cages, despite the lack of treatments. This study demonstrated for the first time the practical use of shading in fish farms to reduce skin fluke infection.  相似文献   

8.
An epizootic in pond cultured three striped tigerfish, Terapon jarbua , in Taiwan was caused by Nocardia seriolae . Diseased fish first showed clinical signs and mortalities in February and March 2003. The cumulative mortality within 2 months was 2.4% (1200 of 50 000) and affected fish were 7 months old with total lengths from 18 to 25 cm. Most affected fish were pale and lethargic with haemorrhages and ulcers on the skin. The most significant gross pathological changes were varying degrees of ascites and enlargement of the spleen, kidney and liver. Obvious white nodules, varying in size, were found in these organs. Bacteria were either coccal or filamentous in appearance, with bead-like forms. Isolates from diseased fish were characterized using the API ZYM (Analytical profile index; Bio Mérieux, France) systems and conventional tests and identified as Nocardia sp. The isolate was designated NS127 and was confirmed as N. seriolae by a polymerase chain reaction assay that gave the expected specific 432 bp amplicon. In addition, its 16S rDNA sequence gave 100% sequence identity with N. seriolae . A partial sequence of the 16S rRNA gene, heat shock protein gene and RNA polymerase gene (rpo B) of NS127 and the type strain of N. seriolae BCRC 13745 formed a monophyletic clade with a high sequence similarity and bootstrap value of 99.9%. White nodules induced in experimental fish were similar to naturally infected cases and N. seriolae was re-isolated on brain heart infusion agar. This is the first report of N. seriolae -infection in three striped tigerfish in aquaculture.  相似文献   

9.
Abstract. An increase in mortalities, due to the failure of some smolts to feed after transfer to sea cages, has been observed in many fish farms during the last 2 years. In the present study mortalities were as high as 9–5% and the majority of these appeared 7–9 weeks post-transfer. Comparisons of length-weight relationships between the initial group of smolts released in the cage and at 3-, 6- and 8-wcek intervals after transfer showed that a proportion of the fish had lost weight. The condition factor of individually measured fish also confirmed that with increasing time after transfer some fish were in a much poorer condition.
The feeding of smolts after transfer was not related to their size. The fork length distribution of feeding and non-feeding fish showed that feeding fish were recruited from all size classes of the initial population.
The lack of appetite in smolts after transfer was demonstrated by the reduced number of fish feeding and by the amount of food consumed. In the first week after transfer only 10% of the fish were feeding in the sea cage, increasing to 65% after 5 weeks. In the tanks (where there were no failed smolts) 95% of the smolts were feeding within 5 weeks after transfer, whereas in the sea cage it took 8 weeks before this figure was reached.  相似文献   

10.
ABSTRACT:   The objective of this study was to evaluate the effects of ozone, hydrogen peroxide and removal of infected eggs (five times per day) on prevention of fungal infection on Iranian sturgeon Acipenser persicus . The effects of 0.05, 0.1 and 0.15 p.p.m. of ozone, and 500 and 1000 p.p.m. of hydrogen peroxide in two different egg disinfection procedures (with and without removal of infected eggs) were examined on hatching ratio. Egg disinfection by 1000 p.p.m. hydrogen peroxide (with removal of infected eggs) resulted in the greatest hatching ratio (78%) among all treatments. Among ozone treatments, 0.15 p.p.m. (with removal of infected eggs) showed the highest hatching ratio (76.4%). The hatching ratio of the control group (without disinfectant and removal of infected eggs) was 34.4%. Removal of infected eggs increased the hatching ratio by 16.1% compared to treatments without infected egg removal, and there was a significant difference ( P  < 0.01). Ozone is preferred to hydrogen peroxide because a lower concentration of ozone is required to disinfect the culture medium; consequently, environmental pollution will be decreased. A low correlation ( r  = −0.35) was observed between hatchery water temperature and fungal infection percentage in the control.  相似文献   

11.
Amoebic gill disease (AGD) is a pathogenic disease in salmonids caused by Neoparamoeba perurans. Treatment of AGD infection has been through freshwater bathing of the fish. However, as the availability of fresh water is often limited, hydrogen peroxide has been introduced as an alternative treatment. This study investigated the effect of hydrogen peroxide as treatment for AGD‐infected salmon (Salmo salar L.,) at different seawater temperatures and hydrogen peroxide dosages. In total, 600 fish were challenged with N. perurans and the severity of the AGD infection was measured using a gill score scale. After challenge and disease development, the fish were distributed into 12 tanks. The treatment was performed at different seawater temperatures (8°C, 12°C, 17°C) using different hydrogen peroxide doses. Each temperature included an untreated control group. Linear models were used to analyse gill score. A significant effect of treatment was found (?0.68 ± 0.05) regardless of dose and temperature, suggesting that hydrogen peroxide was effective in treating AGD. When the model included dose, a negative linear relationship between dose and gill score was found. The study proved that treatment of AGD with hydrogen peroxide was successful, as gills partially recovered following treatment and further disease development was delayed.  相似文献   

12.
Nocardiosis in large yellow croaker, Larimichthys crocea (Richardson)   总被引：3，自引：0，他引：3  
An epizootic in seawater-cage reared large yellow croaker, Larimichthys crocea, in China was caused by a Nocardia sp. from August to October 2003. The cumulative mortality rate was 15% and the diseased fish were 16 months old with individual length varying from 25 to 30 cm. Multiple, white nodules, 0.1-0.2 cm in diameter, were scattered on the heart, spleen and kidney. The morphology of isolated bacteria from Lowenstein-Jensen medium and tryptic soy agar was bead-like or long, slender, filamentous rods. Experimental infection indicated that the isolated bacterium was the pathogen responsible for the mortalities. A partial sequence of the 16S rRNA gene of the organism and the type strain of Nocardia seriolae JCM 3360T (Z36925) formed a monophyletic clade with a high sequence similarity of 99.9%. Based on the morphological, physiological, biological properties and the phylogenetic analysis, the pathogenic organism was identified as N. seriolae. This is the first report on N. seriolae-infected large yellow croaker in aquaculture.  相似文献   

13.
Antifungal agents are essential for the maintenance of healthy stocks of fish and their eggs in intensive aquaculture operations. In the USA, formalin is the only fungicide approved for use in fish culture. However, hydrogen peroxide and sodium chloride have been granted low regulatory priority drug status by the United States Food and Drug Administration (FDA) and their use is allowed. We evaluated the efficacy of these fungicides for controlling fungal infections on rainbow trout eggs. A pilot study was conducted to determine the minimum water flow rate required to administer test chemicals accurately in Heath incubators. A minimum water flow rate of 7.6 1 min−1 was necessary to maintain treatment concentrations during flow-through chemical exposures. The antifungal activity of formalin, hydrogen peroxide, and sodium chloride was evaluated by treating uninfected and 10% fungal-infected (Saprolegnia parasitica) rainbow trout eggs (Oncorhynchus mykiss) for 15 min every other day until hatch. There were no significant differences among treatments in percent hatch or final infection for uninfected eggs receiving prophylactic chemical treatments. Eggs of the negative control group (uninfected and untreated) had a mean hatch exceeding 86%. All chemical treatments conducted on the infected egg groups controlled the spread of fungus and improved hatching success compared with the positive control groups (infected and untreated). Formalin treatments of 1000 and 1500 μl l−1 and hydrogen peroxide treatments of 500 and 1000 μl l−1 were the most effective. Sodium chloride treatments of 30 000 mg l−1 improved fry hatch, but the compound was less effective at inhibiting fungal growths compared with hydrogen peroxide and formalin treatments.  相似文献   

14.
Grouper Epinephelus malabaricus (weighing 46.37?±?5.10?g) previously maintained in 24‰ seawater were transferred to 14, 19, 24 (control), 29, and 34‰ seawater. Serum cortisol, glucose, lactate, and osmolality levels were measured at 7 time points during 240?min. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater significantly increased to the highest after 10 and 20?min, respectively. No significant differences in serum cortisol and glucose levels were observed for the fish after 30?min among all treatments. Serum lactate level of fish transferred to 14, 19, 29, and 34‰ seawater was significantly lower than that of the control fish after 10-30?min. However, no significant differences in serum lactate were observed 60?min among five treatments. The serum osmolality of the fish following 240-min transfer increased directly with salinity, whereas the osmoregulatory capacity value (medium osmolality-plasma osmolality) of the fish following 240-min transfer was inversely related to salinity. It is concluded that grouper showed strong osmoregulation in 14-34‰ seawater. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater increased rapidly in 10-30?min, indicating an early stress response.  相似文献   

15.
一起卵形鲳鳞幼鱼死亡原因的调查   总被引：2，自引：0，他引：2  
对发生于阳江市某网箱养殖场的卵形鲳鲹幼鱼大规模死亡进行了初步调查,发现病鱼症状为体色发黑、螺旋状或旋转游动、反应迟钝、厌食、无寄生虫及细菌感染,通过电镜负染发现有大小为30nm的病毒粒子,初步断定为神经坏死病毒感染。  相似文献   

16.
Atlantic Salmon, Salmo salar L., experimentally infected with marine Eubothrium sp. were kept together with uninfected salmon in the laboratory for 11 months in two tanks, 80 infected and 80 uninfected in each tank. The infected fish had a reduced growth rate compared with the uninfected fish. Significant differences in growth between infected and uninfected fish were not observed until several months post-infection. There was no correlation between the number of Eubothrium sp. and fish weight, indicating that even low intensity alters the growth rate of the salmon. The cestode had the same effect on both sexes of salmon. Haematocrit level was found to be significantly lower in infected compared with uninfected salmon in one of the samples during the experiment.  相似文献   

17.
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18.
Abstract. The spatial distribution of Atlantic salmon, Salmo salar L., in sea cages was observed by echo integration, which measured fish density at seven in depth intervals. At start of feeding the fish swam towards the surface and into the centre of the cage with a subsequent movement downwards and towards the periphery as hunger was reduced. These changes were more rapid at high than at low feeding intensities. The downward migration during feeding was primarily observed as a reduction in fish density in the 0–1 m depth layer and an increase in the 2–3 m depth layer. For a given feeding intensity, the change in fish density in these depth layers was largely explained by time from the start of feeding and initial hunger level, measured as food intake to satiation. The feeding regime also influenced vertical distribution outside feeding periods. Fish that were fed at low intensity swam generally closer to the surface, and this tendency was even stronger when a restricted food ration kept hunger level constantly high. While fish density peaked at a single depth interval at full ration, a bimodal vertical distribution was observed at restricted ration, suggesting that different subgroups of fish had different feeding motivations. The results suggest that the vertical distribution of salmon in sea cages is based on a trade-off between attraction to food and avoidance of the surface. This tendency has been exploited in a new method of demand feeding in commercial farming of Atlantic salmon.  相似文献   

19.
To determine the dynamics of the transmission of Aeromonas salmonicida ssp. salmonicida infection, chinook salmon, Oncorhynchus tshawytscha, were exposed to bacteria by cohabitation. The latent period (time between exposure and infectivity) was determined by exposing a group of chinook salmonid fingerlings to A. salmonicida by bath, then, at daily intervals, by holding five exposed (donor) fish with approximately 50 naive fish for 24 h. The latent period was 3 days post-infection and the time period between the initial exposure to bacteria and the beginning of bacterial shedding was 4.5 days for the same animals. The prevalence and intensity of infection in the donor fish, to which recipient fish were exposed, i.e. the level of exposure, was highly correlated with the development of disease in recipient (susceptible) chinook salmon (r2 = 0.57). An experiment was conducted to determine the daily progress of infection and development of a furunculosis epidemic among recipient fish by cohabiting a single exposed fish with 43 unexposed salmon. At daily intervals, all fish (in seven treatment tanks and one control tank daily) were sacrificed and tested for the presence of A. salmonicida in the kidney (n = 3520). Over 10 days, mean prevalence among recipient fish reached 75% and disease related mortality exceeded 50%. Bacterial concentrations in the water continued to increase over the duration of the experiment in concert with the number of infected animals present in the population.  相似文献   

20.
A bacterial strain, characterized as Vibrio pelagius (Hq 222), was isolated from a turbot, Scophthalmus maximus (L.), larvae mass mortality in a commercial fish farm in Spain. Turbot larvae, post-larvae (0.2 g) and juveniles (5 and 15 g) were experimentally infected. The bacterium appeared to be very virulent for larvae and post-larvae, LD50 being < 5 bacteria mL(-1) for larvae 1 week post-infection and 3.9 x 10(5) bacteria mL(-1) in post-larvae at day 12 post-infection. The bacterial strain was recovered in pure culture from the internal organs of infected fish. Histological lesions in post-larvae exhibited swelling and necrosis of gill secondary lamellae, sloughing of intestinal mucosa and necrosis of haematopoietic tissue in the kidney. Vibrio pelagius (Hq 222) was able to grow in sterile sea water when incubated at room temperature or at 15 degrees C. Vibrio pelagius (Hq 222) was more adherent to the turbot cell lines TV-1 and TF than Escherichia coli. In both cell lines, the number of adhered bacteria increased with incubation time.  相似文献   

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