Nephrocalcinosis in juvenile farmed Atlantic Salmon (Salmo salar) may be linked to osmoregulatory stress.

Nephrocalcinosis is a widespread challenge in intensive production of salmon smolt. There is however no consensus on its aetiology, which makes it problematic to implement proper measures to limit its development. We performed a survey of nephrocalcinosis prevalence and environmental factors in 11 different hatcheries in Mid-Norway as well as a 6-month monitoring in one of the hatcheries. A multivariate analysis indicated that the most influencing factor for the prevalence of nephrocalcinosis was the supplementation of sea water during smolt production. In the 6-month monitoring, the hatchery introduced salinity in the production water prior to the change in day length. Mismatch in those environmental signals may increase the risk for developing nephrocalcinosis. Salinity fluctuations prior to smoltification can cause osmotic stress and result in unbalanced levels of ions in fish blood. This was clearly illustrated in our study, as the fish experienced chronic hypercalcaemia and hypermagnesaemia. Both magnesium and calcium are excreted over the kidneys and it is possible that their prolonged, elevated levels in plasma resulted in an oversaturation of the urine when finally excreted. This again could have led to the aggregation of calcium deposits within the kidney. This study indicates a relationship between osmotic stress induced by salinity changes in juvenile Atlantic salmon and the development of nephrocalcinosis. Other factors that may affect the severity of nephrocalcinosis are currently subjects for discussion.

Isolation, identification, and pathogenic characteristics of Nocardia seriolae in largemouth bass Micropterus salmoides.

The largemouth bass Micropterus salmoides is an important freshwater aquaculture fish in China. Recently, largemouth bass at a fish farm in Guangdong province experienced an outbreak of a serious ulcer disease. As part of the investigations conducted to identify the aetiology and identify potentially effective control measures, we isolated a pathogenic bacterium (NK-1 strain) from the diseased fish. It was identified as Nocardia seriolae through morphological observation, physiological and biochemical analysis, and molecular identification, and its pathogenicity was verified by experimental infection. Pathological changes in the diseased fish included granulomatous lesions in the liver and spleen, destruction of renal tubules, necrosis of intestinal epithelial cells, infiltration of inflammatory cells in the brain, vacuolation of cells, and swelling and cracking of the mitochondria and endoplasmic reticulum. Bacterial detection using qPCR showed that the spleen and intestine were the main organs targeted by N. seriolae. The mortality of largemouth bass experimentally infected with N. seriolae at 21°C was significantly lower than that in fish infected at higher temperatures between 24 and 33°C; there were no significant differences in the levels of mortality at these higher temperatures. The level of mortality of largemouth bass infected with N. seriolae was lowest at a neutral water pH of 7 but increased significantly at higher and lower pH. Of the tested Chinese herbal medicines, Chinese sumac Galla chinensis and Chinese skullcap Scutellaria baicalensis exhibited the best antibacterial effects. This study lays a foundation for the clinical diagnosis and scientific control of ulcer disease in largemouth bass.

Epizootics of Pseudomonas anguilliseptica among cultured seabream (Sparus aurata) populations: Control and treatment strategies.

The present study was investigating the clinical pictures, prevalence, as well as the ecological conditions associated with Pseudomonas anguilliseptica outbreaks in four cultured seabream, Sparus aurata farms at different localities in Egypt during winter of 2016. The phenotypic and genotypic patterns of Pseudomonas isolates were investigated. The existence of intraspecific heterogeneity among different isolates was analyzed using Restriction Fragment Length Polymorphism (RFLP) technique. Attempts on disease control using antibiogram or dietary supplement were also considered. To achieve these goals, various commercial antibiotic discs were analyzed against Ps. anguilliseptica isolates using the disc diffusion method. Additionally, the impact of one-month dietary incorporation with 3% garlic extract or 0.5% potassium diformate on S. aurata viability and response for prolonged bathing treatment with florfenicol was evaluated following challenge with the virulent strain of Ps. anguilliseptica. Most of the naturally infected fish displayed spiral-swimming behavior with no obvious external lesions. The prevalence of infections in the four investigated farms (F1, F2, F3, and F4) were 44.9, 69.04, 67.72, and 83.4%, respectively. Water analysis revealed a significant variation in total hardness, pH, dissolved oxygen (D.O), ammonia and salinity among different localities. All isolates were rather uniform in most of the biochemical characteristics and were identical on the basis of RFLP analysis. The analyses of PAF-PAR gene pointed out specific amplification bands of 439 bp length. The antibiogram revealed a potential activity of florfenicol, ciprofloxacin, nitrofurantoin, and oxytetracycline against all isolates. Experimentally challenged fish fed on garlic extract or potassium diformate presented lower mortality and better therapeutic response to florfenicol than those fed on a normal basal diet. In conclusion, Ps. anguilliseptica is a prevalent pathogen among cultured seabream where dietary inclusion of 3% garlic extract or 0.5% potassium diformate seemed to improve seabream health status and subsequently, increase the efficacy of the treatment with the selective antibiotic.

Cavisoma magnum (Cavisomidae), a unique Pacific acanthocephalan redescribed from an unusual host, Mugil cephalus (Mugilidae), in the Arabian Gulf, with notes on histopathology and metal analysis.

Cavisoma magnum (Southwell, 1927) Van Cleave, 1931 was originally described from a sea bass, Serranus sp. and spotted surgeonfish, Ctenochaetus strigosus (Perciformes) off Sri Lanka before its more recent redescription from milkfish in the Philippines in 1995. These reports were based on only light infections of their host fishes. Of the few flathead grey mullets, Mugil cephalus (Mugilidae), that we examined in the Arabian Gulf, one fish was infected with 1,450 worms. One milkfish, Chanos chanos (Chanidae), from the same location in the Arabian Gulf, was also heavily infected with specimens of C. magnum. The descriptions of this unique large worm are revised and for the first time, we provide SEM images, new systematic observations, metal analysis of hooks showing extremely high levels of sulfur, and histopathology in the mullet intestinal tissue. Adjustments and corrections of previous descriptive accounts are made. The histopathology studies show extensive damage to the host intestinal tissue including epithelial necrosis, hemorrhaging and worm encapsulation. There is an extensive amount of host connective tissue surrounding the worm. Results of x-ray analysis displayed high levels of sulfur in proboscis hooks, especially at the tips and edges of these attachment structures.

Concurrent jellyfish blooms and tenacibaculosis outbreaks in Northern Norwegian Atlantic salmon (Salmo salar) farms.

Tenacibaculosis is an increasing problem in the Norwegian Atlantic salmon aquaculture industry causing significant economic losses. In September 2015, two separate outbreaks of suspected tenacibaculosis occurred at two Atlantic salmon farms in Finnmark County in Northern Norway. The events resulted in major losses of smolts newly transferred into seawater. Prior to, and during the outbreaks, large numbers of small jellyfish, identified as Dipleurosoma typicum (Boeck) were observed in the vicinity of the farms and inside the net-pens. This study investigates the possible link between the jellyfish, Tenacibaculum spp. and the tenacibaculosis outbreaks. Bacteriology, histology, scanning and transmission electron microscopy, and real-time RT-PCR screening were performed on both fish and jellyfish samples. Based on the findings, Tenacibaculum finnmarkense was found to be the dominant bacteria associated with the tenacibaculosis outbreaks at both sites and that D. typicum is unlikely to be a vector for this fish pathogenic bacterium. However, results do show that the jellyfish caused direct damage to the fish's skin and may have exacerbated the bacterial infection by allowing an entry point for bacteria.

Pansteatitis in polluted Olifants River impoundments: nutritional perspectives on fish in a eutrophic lake, Lake Loskop, South Africa.

This study compares the aetiology of pansteatitis in Lake Loskop, relative to two other impoundments along the Olifants River. Macroscopic and microscopic pathology, age determination and analysis of stomach content, fatty acids and stable isotopes explain the high prevalence of pansteatitis in Oreochromis mossambicus (Peters) and several other species in Lake Loskop. All the dietary indicator comparisons between pansteatitis-affected and healthy fish fail to support a systemic cause. Pansteatitis in Lake Loskop was linked to size and weight of O. mossambicus, but not to ontogenic age. Fish in Lake Loskop showed abnormally high omega-3 to omega-6 fatty acid ratios normally only found in marine fish with no significant difference in degree of assimilation of these fatty acids between pansteatitis-affected and healthy fish. This explains the vulnerability to, but not the occurrence of, pansteatitis. As a cause for the pansteatitis, these results point towards sporadic vitamin E-depleting trigger events, known sporadic fish die-off occurrences that provide surviving fish with a rich source of rancid fats on which to scavenge. The mechanism ties pansteatitis to eutrophication and trophic cascade effects, the intrinsic drivers of the disease and suggests an adaptive management strategy that might be applied by relevant conservation authorities.

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt.

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post-smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg-1 ) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na+ , K+ -ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.

Total mercury and selenium concentrations in Sarpa salpa and Balistes capriscus and in their respective Digenean endoparasites Robphildollfusium fractum and Neoapocreadium chabaudi from Tunisia.

The present study reports the levels of mercury and selenium in Sarpa salpa and Balistes capriscus collected along the coast of Mahdia and Sfax (Tunisia). The systems constituted by S. salpa and Robphildollfusium fractum and by B. capriscus and Neoapocreadium chabaudi were tested as potential bioindicators to monitor environmental Hg pollution in marine ecosystems. Mercury and selenium concentrations were assessed in kidney, liver and muscle of 51 S. salpa and of 45 B. capriscus as well as in their respective endoparasites R. fractum and N. chabaudi. The Se:Hg molar ratios were evaluated for both species across the study areas. Surprisingly, the Se:Hg molar ratio in B. capriscus muscle from Mahdia is significantly lower than in Sfax. Our results indicate that some parasites may also be implicated in the amount of Se and Hg available in tissues and therefore contribute to oscillations of the Se:Hg molar ratios. In the model involving the carnivorous species (B. capriscus), the 5.1-times higher levels of mercury in N. chabaudi than in B. capriscus muscle in Sfax enable this fluke to be a sensitive biomonitoring tool for Hg pollution. The present results confirm that the habitual consumption of S. salpa should not suppose any potential health risk for Tunisian people. On the other hand, the consumption of B. capriscus may be of concern and further monitoring is advisable, since the Hg average concentration in Mahdia was above the maximum allowed Hg concentration in the edible portion of fish fixed by the European Union.

The pathology of selenium deficiency in Cyprinus carpio L.

Selenium is essential for the normal life processes, and all animals, including fish, need this inorganic element. In order to research the pathology of selenium deficiency in common carp, Cyprinus carpio L., 360 juvenile carp were allocated to three treatments. Each treatment containing 120 fish was randomly divided into four groups, fed with purified diets containing selenium at 0, 0.15, 0.30 and 0.45 mg kg(-1). The results indicated that the morbidity and mortality rates of the test groups were negatively correlated with the level of selenium in the diets. The morbidity and mortality rates were, respectively, 46.7%, 33.3%, 13.3%, 0 and 26.7% 16.7%, 6.7%, 0. The affected fish exhibited pathological changes, such as 'thin back disease' and lordosis. Histologically, there was no abnormality observed in muscles, liver and pancreas. Ultrastructurally, there was swelling of the mitochondria of the cardiac muscle cells, the liver cells and renal tubular epithelial cells, with disintegration and lysis of the cristae of the mitochondria which vesiculated. Serum glutamic oxaloacetic transaminase and glutamic pyruvic transaminase levels were increased and the activity of the serum glutathione peroxidase and the serum superoxide dismutase was decreased; in contrast, the serum malonaldehyde concentration was increased.

Effectiveness of emamectin benzoate for treatment of Lepeophtheirus salmonis on farmed Atlantic salmon Salmo salar in the Bay of Fundy, Canada.

Emamectin benzoate (an avermectin chemotherapeutant administered to fish as an in-feed treatment) has been used to treat infestations of sea lice Lepeophtheirus salmonis on farmed Atlantic salmon Salmo salar in the Bay of Fundy, New Brunswick, Canada, since 1999. This retrospective study examined the effectiveness of 114 emamectin benzoate treatment episodes from 2004 to 2008 across 54 farms. Study objectives were to establish whether changes in the effectiveness of emamectin benzoate were present for this period, examine factors associated with treatment outcome, and determine variables that influenced differences in L. salmonis abundance after treatment. The analysis was carried out in 2 parts: first, trends in treatment effectiveness and L. salmonis abundance were explored, and second, statistical modelling (linear and logistic regression) was used to examine the effects of multiple variables on post-treatment abundance and treatment outcome. Post-treatment sea lice abundance increased in the later years examined. Mean abundance differed between locations in the Bay of Fundy, and higher numbers were found at farms closer to the mainland and lower levels were found in the areas around Grand Manan Island. Treatment effectiveness varied by geographical region and decreased over time. There was an increased risk for unsuccessful treatments in 2008, and treatments applied during autumn months were more likely to be ineffective than those applied during summer months.

Jellyfish as vectors of bacterial disease for farmed salmon (Salmo salar).

Swarms or blooms of jellyfish are increasingly problematic and can result in high mortality rates of farmed fish. Small species of jellyfish, such as Phialella quadrata (13 mm in diameter), are capable of passing through the mesh of sea cages and being sucked into the mouth of fish during respiration. Results of the current study show that the initial damage to gills of farmed Atlantic salmon, likely produced by nematocyst-derived toxins from the jellyfish, was compounded by secondary bacterial infection with Tenacibaculum maritimum. Results also demonstrate that these filamentous bacteria were present on the mouth of the jellyfish and that their DNA sequences were almost identical to those of bacteria present on the salmon gills. This suggests that the bacterial lesions were not the result of an opportunistic infection of damaged tissue, as previously thought. Instead, P. quadrata is probably acting as a vector for this particular bacterial pathogen, and it is the first time that evidence to support such a link has been presented. No prior literature describing the presence of bacteria associated with jellyfish, except studies about their decay, could be found. It is not known if all jellyfish of this and other species carry similar bacteria or the relationship to each other. Their source, the role they play under other circumstances, and indeed whether the jellyfish were themselves diseased are also not known. The high proteolytic capabilities of T. maritimum mean that partially digested gill tissues were readily available to the jellyfish, which rely heavily on intracellular digestion for their nutrition.

Observations and treatment of Nitzschia sturionis on Atlantic sturgeon from Chesapeake Bay.

From 2004 to 2008, 10% of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus examined during a bycatch study of Maryland's Chesapeake Bay were infested with the trematode Nitzschia sturionis on the skin and gills. The parasite intensity increased on 75% of infested fish 4-24 months after being placed in captivity. Mean parasite intensity increased to a greater extent on the skin (up to 100-fold) than on the gills (up to 16-fold). Atlantic sturgeon that were infested with N. sturionis gained weight at a reduced rate or lost weight compared with uninfested fish. Skin lesions associated with N. sturionis progressed from a few reddened foci to hemorrhagic ulcers and depigmentation, while gill lesions showed a less-dramatic progression. Host tissues identified in the intestinal ceca of N. sturionis consisted primarily of malpighian cells, but small amounts of blood were also found in worms attached to lesions in the skin and gills. An Atlantic sturgeon infested with approximately 500 worms was successfully treated with a 3-h bath of praziquantel at 10 mg/L. This first report of N. sturionis from Chesapeake Bay extends the parasite's reported southern range in North America.

Does the capacity for energy utilization affect the survival of post-smolt Atlantic salmon, Salmo salar L., during natural outbreaks of infectious pancreatic necrosis?

If osmotic stress and reduced seawater tolerance are predisposing factors for infectious pancreatic necrosis (IPN) outbreaks in farmed Atlantic salmon, increased survival by enhancing access to energy would be expected. The aim of the present study was, therefore, to increase energy access in 1-year old Atlantic salmon after sea transfer by increasing the level of dietary fat, by exchanging some of the dietary oil with more easily oxidized medium chain triacylglycerols, or by dietary supplementation of potentially energy enhancing additives such as clofibrate and tetradecylthioacetic acid (TTA). A natural outbreak of IPN occurred 8 weeks after sea transfer, and a significant dietary effect explaining 76% of the variation in mortality was observed. Relative percentage survival for the fish fed TTA in sea water was 70% when compared with the unsupplemented control, reducing mortality from 7.8 to 2.3%. Muscle fat content and plasma chloride were related to IPN mortality, suggesting that reduced hypoosmoregulatory capacity might be a predisposing factor to the onset of an IPN outbreak. Based on the observation of a threefold increase in white muscle mitochondrial fatty acid oxidizing activity by TTA, it is suggested that TTA has resulted in a re-allocation of dietary fatty acids from storage to energy producing oxidation.

Shark cartilage, cancer and the growing threat of pseudoscience.

The promotion of crude shark cartilage extracts as a cure for cancer has contributed to at least two significant negative outcomes: a dramatic decline in shark populations and a diversion of patients from effective cancer treatments. An alleged lack of cancer in sharks constitutes a key justification for its use. Herein, both malignant and benign neoplasms of sharks and their relatives are described, including previously unreported cases from the Registry of Tumors in Lower Animals, and two sharks with two cancers each. Additional justifications for using shark cartilage are illogical extensions of the finding of antiangiogenic and anti-invasive substances in cartilage. Scientific evidence to date supports neither the efficacy of crude cartilage extracts nor the ability of effective components to reach and eradicate cancer cells. The fact that people think shark cartilage consumption can cure cancer illustrates the serious potential impacts of pseudoscience. Although components of shark cartilage may work as a cancer retardant, crude extracts are ineffective. Efficiencies of technology (e.g., fish harvesting), the power of mass media to reach the lay public, and the susceptibility of the public to pseudoscience amplifies the negative impacts of shark cartilage use. To facilitate the use of reason as the basis of public and private decision-making, the evidence-based mechanisms of evaluation used daily by the scientific community should be added to the training of media and governmental professionals. Increased use of logical, collaborative discussion will be necessary to ensure a sustainable future for man and the biosphere.

The suprapopulation dynamics of Bothriocephalus acheilognathi in a North Carolina reservoir: abundance, dispersion, and prevalence.

A 2 1/2-year study (September 1980-March 1983) of abundance, dispersion, and prevalence of the pseudophyllidean cestode, Bothriocephalus acheilognathi, in 3 species of fish (Gambusia affinis, Notropis lutrensis, and Pimephales promelas) was conducted in 3 ecologically distinct areas of a North Carolina cooling pond. Mean infrapopulation density and prevalence differed by site, season, and species and size of hosts. Degree of aggregation and abundance and prevalence of gravid worms differed by species of host. Abundance of gravid worms was significantly lower in metapopulations from localities that received power plant effluents. The differences in infrapopulation density, prevalence, and aggregation appeared to be related to predator-prey interactions, which varied with season and local community structure. Differences in abundance of gravid worms, on the other hand, were probably caused by differential suitability of hosts and by local variation in selenium concentration in the water column. Thus, it appears that both biotic and abiotic components of the host community determined the suprapopulation dynamics of B. acheilognathi in Belews Lake.

[An outbreak of lipoid liver degeneration (LLD) in Atlantic salmon (Salmo salar) in a fish farm and attempts to cure the disease (author's transl)]. / Et terapiforsøk ved et utbrudd av lipoid leverdegenerasjon (LLD) hos laks i oppdrett

A description of a field experiment on the therapeutic effect of 4 different drugs against lipoid liver degeneration is given in a natural outbreak of the disease in a fish farm. The diagnosis was based on pathological and histopathological changes in the liver and characterized on the basis of the degree of ceroid deposited in the liver cells. The size and weight of the fish had no influence on the deposition, but it was shown that LLD caused a higher mortality in Atlantic salmon than in rainbow trout, showing a weekly mortality of 2.5 and 0.3%, respectively. In the field experiments therapeutic effect was obtained with 1) Vitamin E, mixed into the feed in amounts of 90 mg alpha-tocopherol + 450 mg ethoxyquin pr. kg wet feed. 2) A combination of alpha-tocopherol and selene mixed into the diet in amounts of 20 mg tocopheryli acetas and 0.4 mg natrii seleniis pr. kg wet feed. The cause of the disease is not verified, but it seemes that rancid material in the diet was the main etiological factor. Predisposing factors influencing the peroxydation of the feed under practical conditions in Norwegian fish farms have been discussed.