Cause Of Mass Mortality Research Articles

Evaluation of treatment efficacy of doxycycline and albendazole against scuticociliatosis in olive flounder (Paralichthys olivaceus)

Scuticociliatosis is a leading cause of mass mortality in cultured olive flounder (Paralichthys olivaceus) in Korea. However, still no effective treatment measures have been developed. In the present study, we selected two drugs, doxycycline and albendazole, that were demonstrated to have high in vitro scuticocidal activity and possess ability to cross blood–brain barrier (BBB), and evaluated their treatment efficacy against scuticociliatosis caused by Miamiensis avidus in olive flounder. In both oral and bath treatment experiments, groups of fish fed a diet containing doxycycline or bathed with freshwater containing doxycycline showed clearly higher survival rates than control groups. Although the groups of fish fed a diet containing albendazole or bathed with freshwater containing albendazole showed higher survival rates than the control group, the rates were greatly lower than those of the groups treated with doxycycline. Poor intestinal absorption, low solubility in water, and low lipophilicity of albendazole were considered as the possible cause of the low efficacy. In conclusion, the present results suggest that doxycycline can be used to treat systemic scuticociliatosis in olive flounder through oral administration and bath.

Abalone farm discharges the withering syndrome pathogen into the wild

An intracellular bacterium Candidatus Xenohaliotis californiensis, also called Withering-Syndrome Rickettsia-Like Organism (WS-RLO), is the cause of mass mortalities that are the chief reason for endangerment of black abalone (Haliotis cracherodii). Using a real-time PCR assay, we found that a shore-based abalone farm (AF) in Santa Barbara, CA, USA discharged WS-RLO DNA into the ocean. Several other shore-based AFs discharge effluent into critical habitat for black abalone in California and this might affect the recovery of wild black abalone. Existing regulatory frameworks exist that could help protect wild species from pathogens released from shore-based aquaculture.

Effects of Temperature upon Water Turnover in Fish Ponds in Northern Thailand

Fish culture in earthen ponds is an important source of income for farmers in northern Thailand. Water quality in ponds has strong impacts on fish production farmers’ return and is sensitive to weather and climate. Low levels of dissolved oxygen in fish ponds are major cause of mass mortality. Stratification with depth in ponds followed by rapid turnover or exchange of surface and bottom water can expose fish to dangerously low dissolved oxygen levels. The main purpose of this study was to observe the effects of weather on stratification and subsequent water turnover in fish ponds in northern Thailand, especially in the winter and rainy season, when stratification was expected to be most severe. Temperature and water quality measurements were made in fish ponds at 18 farms with depths ranged from 0.8-2.0 m and size of 0.16-0.64 ha. Measurements were made during January and May 2013. Fish farm pond sites were divided into two groups based on elevation above sea level: low ( 400 masl) and categorized into 3 types of farming: commercial, integrated and subsistence. In lower elevation sites, water turnover occurred at night between 22.00 and 02.00 in winter and between 18.00 and 02.00 in rainy season. At higher elevation, turnover occurred in ponds between 20.00 and 22.00 in winter and between 14.00 and 18.00 in rainy season. Turnover was slower in the lower elevation than in higher elevation zones and generally occurred earlier during the rainy season than in the winter. Mean DO in winter was significantly higher (p<0.05) than in rainy season, whilst water temperature and amount of ammonia-nitrogen during the rainy season was significantly higher (p<0.05) than in winter. Turnover improves distribution of dissolved oxygen through the water column and minimizes organic matter accumulation. Cloud cover during the rainy season may have contributed to limit oxygen production and thus may have significantly affect water quality in ponds. Fish farmers should consider more explicitly the role of temperature and cloud conditions when managing dissolved oxygen levels in their fish ponds. Therefore, efficient pond aeration or pond mixing strategies for reducing stratification still plays an important component for providing sound pond management in tilapia production ponds.

有明産タイラギの生物モデルによる大量へい死原因仮説

有明産タイラギの生物モデルによる大量へい死原因仮説

Bottom culture of the sea cucumberApostichopus japonicusSelenka (Echinodermata: Holothuroidea) in a fish farm, southern China

The bottom culture of southward-transplanted sea cucumber Apostichopus japonicus in a subtropical fish farm was investigated in a field study at Dapeng Cove, Daya Bay, from January 5-August 5 2011, with the aim of finding the ideal period for culturing A. japonicus in fish farms, and developing an integrated multi-trophic aquaculture (IMTA) in southern China. Results showed that the bottom-cultured sea cucumbers survived well (100%) before summer, survival rates decreased to 65.00 +/- 21.21% in July, and all animals had died at the end of the study. Specific growth rates of the sea cucumbers were high during winter (1.05 +/- 0.03% d(-1)), decreased in early spring (0.44 +/- 0.11% d(-1)) and became negative in the following months. Growth rate was mainly influenced by water temperature, dissolved oxygen and sulphide content; the anoxia caused by water column stratification at the sea-floor in the summer were the main causes of mass mortality. Our results indicate that bottom culture in the temperate season (winter and spring, optimally from late November to early April) is a viable way to rear the deposit feeder A. japonicus underneath a subtropical fish farm.

패류(Scapharca broughtonii) 유래의 용혈활성 미생물 다양성 분석

The southern coast of Korea is important for the ark shell (Scapharca broughtonii) aquaculture, but the productivity was rapidly reduced during the previous decade by mass mortality. To overcome this economic loss, investigations only focused on environmental factors, and microbiological researches were performed insufficiently. In this study, two sites (Gangjin and Jinhae bay) were selected for their high and low rate of mortality, respectively, and the existence of microflora from underwater sediments in the bodies of S. broughtonii was analyzed. We screened the whole body of each sample and chose unique colonies, which exhibit alpha- and beta-hemolytic activity, for identification. The microflora in S. broughtonii was less variable than sediments, and restricted species were isolated. We identified 17 genera of 88 species and 16 genera of 64 species from the two bays, respectively. A major proportion was comprised of Bacillus species, with the Bacillus cereus group being the most common species among the Bacillus strains, while Paenibacillus, Lynsilbacillus, and Vibrio species were the second most abundant species. At the genus level, there were no significant microbial differences between the two coastal regions. 64 species were isolated from rare site (Jinhae bay), but more species (88) with greater variety were isolated from the frequent site (Gangjin bay). Therefore, it was assumed that the cause of mass mortality lay in the difference in specie-level diversity, and conducting investigations on the diagnosis of pathogenic species by challenging tests using isolated unique species.

Comparative analysis of expressed sequence tags (ESTs) between normal group and softness syndrome group in Halocynthia roretzi

To identify the cause of mass mortality in ascidians, we constructed cDNA libraries of both the normal and softness syndrome group in Halocynthia roretzi. To perform comparative analysis of transcripts between the two groups, we sequenced about 1,000 random clones. All the sequences obtained from the clones were processed to remove the vector region and low quality sequences through base calling and vector trimming. We collected 906 sequences with average length of 463 bp in the normal group and 1014 sequences in the softness syndrome group with an average length of 696 bp. Clustering and assembling of EST sequences using TGICL package resulted in 906 distinct sequences composed of 517 singletons and 77 contigs in 75 clusters in normal group and 1014 distinct sequences composed of 707 singletons and 120 contigs in 120 clusters in the softness syndrome group. All sequences derived from the two groups were compared against the NCBI Non-redundant database using BLASTX algorithms. As a result, 493 sequences in the normal group and 861 sequences in the softness syndrome group had significant hits within the database. In addition, we listed genes that showed differential expression in the softness syndrome group. Transcript levels of calponin increased by 11-fold and both E3 ubiquitin-protein ligase MARCH3 and selenium dependent salivary glutathione peroxidase by 5-fold in the softness syndrome group. Also, the expression of four genes including muscle actin increased by 4-fold. In contrast, we observed down-regulation of genes encoding trypsinogen 1, cathepsin D protein, serine protease, and halocidin precursor, decreasing by more than 6-fold. Herein, we identified differential expression of genes involved in the contraction and regulation of muscle cells and immune reaction in H. roretzi with softness syndrome. This study is the first report on gene expression changes occurring in H. roretzi with softness syndrome and would be useful in further studies.

Identification of Aeromonas salmonicida in European perch from North Lithuanian rivers during mass mortalities in 2008

Abstract The investigation was carried out to ascertain the cause of mass mortalities in European perch (Perca fluviatilis L.) in North Lithuanian rivers in 2008 that reached a maximum in mid-autumn at a water temperature of 6°C. Marked changes were detected in morphophysiological parameters (spleen-, gill-, liver- and heart-somatic indices), which corresponded to changes in haematological parameters (leukocyte count was significantly elevated or reduced) of the infected fish. The viable bacterial counts in the gill, liver and kidney of infected live fish samples ranged from 2.3±0.3 × 103 to 6.3×00B1;0.4 × 103 c.f.u./g. The BOX-PCR fingerprinting technique was used for characterization and identification of the isolated bacterial strains from liver and kidney of infected perch. The bacterial isolates were identified by sequence analysis of the 16S rRNA gene. Pathogenic Aeromonas salmonicida subsp. salmonicida has been identified as a possible causative agent of the observed mortality in European perch.

Epizootics in harbour seals (&lt;i&gt;Phoca vitulina&lt;/i&gt;): clinical aspects

Epizootic diseases causing considerable mortality in harbour seal populations have mainly been reported from the waters of the United States and Europe. Such die-offs were largely attributable to viral infections. Several hundred individuals died from respiratory infections caused by Influenza A viruses at the coast of New England, USA, in 1979, 1980 and 1982. More than 53,000 harbour seals were killed in European waters by Phocine Distemper Virus (PDV), a morbillivirus,in two outbreaks in 1988 and 2002. For several other epizootics of smaller scale in the waters of the Atlantic and Pacific coast of the USA and, most recently, in Danish and Swedish waters in 2007 the causes remain unclear, although characteristic respiratory symptoms and interstitial pneumonia suspicious of viral etiology were detected as well as occasionally bacterial infections caused by Erysipelothrix rhusiopathiae and Pseudomonas aeruginosa. Mass mortalities caused by biotoxins, direct human interactions or changes in oceanographic conditions have so far not been described for harbour seals. However, high organochlorine loads detected in European harbour seal populations and suspected to impede immune functions, were considered an aggravating factor in the 1988 morbillivirus epizootic. Establishing supranational stranding networks is a key prerequisite for the detection of future unusual die-offs in marine mammals. Detailed post-mortem investigations of all organ systems are essential for targeted etiological studies towards the causes of mass mortalities in seals.

Survival of the Ark Shell, Scapharca subcrenata and Physiological and Histological Changes at Decreasing Salinity

We examined physiological and histological responses related to the survival, oxygen consumption, excretion, and O/N ratio of the ark shell, Scapharca subcrenata, as a result of salinity changes. The 20-day (median lethal salinity) at was 13.87 practical salinity units (psu; confidence limits 10.30-18.74 psu), whereas the 14-day at was 12.59 psu (confidence limits 8.03-18.16 psu). In conditions of decreasing salinity, the osmolarity of individuals acclimated within 5 h above 26.4 psu but required more than 60 h below 13.2 psu. Oxygen consumption and ammonia excretion rates varied irregularly as salinity decreased. The O/N ratio was 19 and 27 at water temperatures of and , respectively, but decreased to 1-10 as salinity declined. The effects of decreasing salinity were observed in the histological changes to each organ of S. subcrenata. As salinity decreased, cilia fell off, the epithelial layer underwent necrosis and vacuolation, the connective tissue layers of the mantle and visceral mass were destroyed, and hemocytes increased in the gills. The results of this study could prove important in investigating causes of mass mortality and managing shellfish aquaculture farms.

Detection of Marteilia refringens using nested PCR and in situ hybridisation in Chamelea gallina from the Balearic Islands (Spain)

In the course of a histopathological survey performed to discover the cause of mass mortality of the striped clam Chamelea gallina in the Balearic Islands (Spain, Mediterranean Sea), we detected a Marteilia-like parasite in 3 clams. Molecular methods were applied to identify the parasite. DNA extracted from a paraffin block was used to carry out a PCR assay for Marteilia refringens detection based on a rDNA sequence of the parasite (the intergenic spacer of ribosomal genes, IGS). The nucleotide sequence of the IGS amplified fragment and the positive signal obtained by in situ hybridisation analysis with a M. refringens-specific probe allowed us to confirm the presence of this parasite in the digestive gland tissue of C. gallina.

Functional characterization of the RNase III gene of rock bream iridovirus

All of the fully sequenced iridoviruses have an ORF resembling a putative RNase III gene. However, to the best of our knowledge, functional characterization of the iridovirus-encoded RNase III has not been done. In the present study, we have characterized the putative RNase III of rock bream iridovirus (RBIV), the major cause of mass mortality of cultured rock bream Oplegnathus fasciatus in Korea. RBIV RNase III has a single N-terminal endonuclease domain followed by a C-terminal double-stranded RNA (dsRNA) binding domain. The true presence of the predicted ORF encoding RNase III in RBIV was confirmed by temporal transcription analysis of the ORF in RBIV-infected grunt fin (GF) cells. Comparing the catalytic activity to that of previously reported RNase III proteins, including Escherichia coli RNase III, the present RBIV RNase III had different features in that: (1) the dsRNA substrate was cleaved by the RBIV RNase III at high concentrations of Mg(2+) (5-20 mM) at low salt concentration (50 mM), but the enzyme activity was completely inhibited at 200 mM NaCl (within physiological ranges) irrespective of Mg(2+) concentrations (0.5-20 mM); (2) the substrate dsRNA was cleaved at low concentrations of Mn(2+) (0.5-1 mM) at low salt concentration (50 mM) and was cleaved by increasing Mn(2+) (5-20 mM) at 200 mM salt. These features of RBIV RNase III are similar to E. coli RNase III devoid of the C-terminal dsRBD region. The exact role of the RNase III in RBIV replication is not known, and further studies are needed to elucidate whether the RNase III is involved in the suppression of host RNA interference, which attacks viral mRNAs, or in the processing of viral RNAs for effective replication.

DNA damage as a biomarker for assessing the effects of suspended solids on the orange-spotted grouper, Epinephelus coioides

In Hong Kong, suspended solids (SS) introduced by dredging and mud disposal activities are a major cause of mass mortality in cage-cultured marine fish. We have used DNA damage in liver cells, as determined by the comet assay, to assess the impact of SS on the orange-spotted grouper Epinephelus coioides. Seabed sediments were collected from a heavily polluted site in Victoria Harbor and two less polluted sites in Port Shelter and Mirs Bay. Sediments from Victoria Harbor contained higher levels of copper (Cu) and polycyclic aromatic hydrocarbons (PAHs) than those from the other sites. In a 10-day experiment, SS from all three sites induced significant increase in comet tail length, but not in percentage (%) tail DNA. In a 20-day experiment, fish exposed to polluted SS from Victoria Harbor exhibited a significant increase in comet tail length after 5 days and % tail DNA after 10 days. After a 10-day recovery period, however, DNA damage was reduced as tail length and % tail DNA returned to control levels. These results suggest that DNA damage measured by the comet assay is a highly sensitive biomarker for assessing the genotoxic effects of SS to marine fish.

Physiological Responses of the Ark Shell Scapharca broughtonii (Bivalvia: Arcidae) to Decreases in Salinity

The ark shell (or 'blood clam') Scapharca broughtonii is a filter-feeding bivalve that has red blood and inhabits waters approximately 10m in depth off the southern coast of South Korea. This study was part of a larger research project investigating the causes of death and restoration of shellfish resources, which are important aquaculture products in South Korea. We examined physiological responses related to survival, respiration, excretion, and amino acid changes as a result of changes in salinity. The 9-day median lethal salinity (<TEX>$LS_{50}$</TEX>) was 16.5 psu with confidence limits of 14.9-18.1 psu. At <TEX>$25^{\circ}C$</TEX>, the oxygen consumption and ammonia-nitrogen excretion rates were increased with decreases in salinity. Although the osmolality of individuals was acclimated within 2 h at 26.4 psu and 12 h at 19.8 psu, it took more than 5 days at a salinity of 13.2 psu, whereas no individuals acclimated and all died at a salinity of 6.6 psu. Of the amino acids present in the blood, taurine and alanine increased in response to decreased salinity. Tissues of the gill and the mid-gut gland were affected by decreasing salinity. These data will provide important fundamental information for examining the causes of mass mortality of shellfish in the summer.

Change of pathogenicity in Olive flounder Paralichthys olivaceus by co-infection of Vibrio harveyi, Edwardsiella tarda and marine birnavirus

Recently, mass mortality of adult flounder showing ascites occurred at many aquaculture farms in Korea. While we investigated the cause of the mortality, marine birnavirus (MABV-F) and bacteria (Vibrio harveyi and Edwardsiella tarda) were isolated from diseased fish. By the intraperitoneal (IP) injection with MABV-F, the virus strain did not show pathogenicity to the flounder. When the fish co-infected with MABV-F (IP) and V. harveyi or E. tarda (immersion), the cumulative mortality did not show any significant difference with control group. In contrast, the case of co-infection with MABV-F and bacteria by IP, cumulative mortality reached more than 90%. Most of the moribund and dead fish except for the mock-infected fish displayed ascites, and the virus and bacteria were re-isolated from all the dead and moribund fish except for the control fish. The results indicate that the cause of mass mortality of the adult fish may be due to bacterial infection. Higher mortalities may occur due to co-infection of MABV-F and bacteria, although MABV-F alone did not cause direct mortality.

THE CRAYFISH PLAGUE IN THE CZECH REPUBLIC - REVIEW OF RECENT SUSPECT CASES AND A PILOT DETECTION STUDY

There are only very limited reports about the occurrence of the crayfish plague in Czechia. In recent years, mass mortalities of Astacus spp. with symptoms of possible crayfish plague were noticed in three streams in the country – two in Central Bohemia (1998-9) and one in Silesia (2004). Three dead individuals from the last outbreak were examined for the presence of the crayfish plague pathogen, Aphanomyces astaci, by observation of the presence of hyphae in their cuticle and by a PCR-based diagnostic method. In all three cases the detection was positive. Although causes of mass mortalities from two other localities lack such a direct confirmation, the indirect evidence supports the same conclusion. The main potential vector of A. astaci in Czechia is the American spiny-cheeck crayfish Orconectes limosus, widespread in large rivers of the western part of the country and in various isolated standing waters. Using the same molecular method, we investigated the presence of A. astaci in living O. limosus individuals from six localities (three running and three standing waters). The analysis indicated the presence of the pathogen in animals from five out of six investigated Orconectes populations. One of them is present in the stream where two European Astacus species had gone extinct in 1998-9. Our results suggest that the crayfish plague is still present in Czechia, and that populations of O. limosus represent a reservoir for the crayfish plague pathogen, which directly endangers populations of the native crayfish.

Cyanobacteria blooms—A possible cause of mass mortality of Lesser Flamingos in Lake Manyara and Lake Big Momela, Tanzania

Limnological studies were conducted in three alkaline lakes (Lake Big Momela, Manyara and Embagai) with the aim of investigating the cause of mass mortality of the Lesser Flamingos in Lake Manyara and Lake Big Momela during July–August 2004. High concentrations, up to 150 million filaments per liter of the potentially toxic planktonic cyanobacterium Arthrospira fusiformis were found in surface scum of Lake Big Momela where Lesser Flamingos were dying at a rate of between 15 and 50 individuals per day during the study period. Gut content analyses indicated that A. fusiformis was the main food item in moribund flamingos. Mouse bioassay suggested that the crude microalgal extract dominated by A. fusiformis was toxic with all mice close to death becoming lethargic, with loss of balance, uncoordinated movements, intermittent tremors, dyspnoea with gasping followed by respiratory arrest. This observation gives circumstantial evidence that A. fusiformis at such high concentrations was toxic to the Lesser Flamingo in Lake Big Momela.

Hailstorms as a Cause of Mass Mortality of Swainson's Hawks in Their Wintering Grounds

We describe a mass mortality event of wintering Swainson's hawks (SH, Buteo swainsoni) in central Argentina during November 2003. One hundred thirteen SH were found dead as a consequence of a single hailstorm. In addition, 14 hawks with severe injuries were recovered alive, but only 10 of these survived 1 wk later. Another 45 dead birds of 11 species were collected in the area. Interviews with local land-owners conducted in other areas of the SH wintering grounds provided further evidence of past hailstorm-related mortality involving SH, suggesting that such events commonly occur in the Argentine Pampas. This potential cause of mass mortality of SH wintering in agricultural areas of Argentina may be significant when added to the increased mortality associated with poisoning events during the last decade.

Effect of lowered salinity on the survival, condition and reburial of Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae)

Abstract Mass mortalities of fauna are known to occur in estuarine environments during flood events. Specific factors associated with these mortalities have rarely been examined. Therefore, the effect of exposing, to lowered salinities, an infaunal bivalve that is susceptible to mass mortalities during winter flooding in a southern Australian estuary was tested in the present study. In a laboratory experiment, low salinities (≤6 parts per thousand [ppt]), which mimicked those expected during flood events in the Hopkins River estuary, were shown to affect Soletellina alba, both lethally and sublethally. All bivalves died at 1 ppt, while those at 6 ppt took longer to burrow and exhibited a poorer condition than those at 14 and 27 ppt. The limited salinity tolerance of S. alba suggests that lowered salinities are a likely cause of mass mortality for this species during winter flooding.

Vacuolating encephalopathy and retinopathy associated with a nodavirus-like agent:a probable cause of mass mortality of cultured larval and juvenile Atlantic halibut Hippoglossus hippoglossus

Vacuolating encephalopathy and retinopathy associated with a nodavirus-like agent:a probable cause of mass mortality of cultured larval and juvenile Atlantic halibut Hippoglossus hippoglossus