Post 8: Gill Flukes

Gill flukes are highly infectious, 1-2 mm long, flatworm parasites commonly found in fresh and salt water aquariums (Klinger & Floyd 1998). This post will focus on the monogenean trematodes-trematodes being a common name for the flukes, and monogenean which describes the host-site specific life cycle of the parasite. Monogenean trematodes affect the gills, skin and fins of the host fish (Klinger & Floyd 1998).

Gill flukes can enter an aquarium water body through water exchanges, transplants of live rocks or be brought in with introduced fish. Gill fluke parasites are equipped with hooks which they use to latch onto their host-with the parasites life span being roughly 7-9 days (Ogawa 2015).

Directly diagnosing flukes through visual observation of the parasite is unlikely until the later stages of infection. Fish that are infected can almost always be seen participating in 'flashing', where the fish brushes the infected area on the sides or bottom of the tank due to physical irritation (Kiskaroly 1977). In the later stages, flukes growing on the fishes gills will interfere with respiration, thus the host will either be seen gasping for air (generally at the surface where oxygen diffusion is greatest), or lethargically sitting at the bottom as it dies.

Preventative steps can be taken to avoid outbreaks of gill flukes, such as fresh water bathing new fish and live rocks before introducing them into a saltwater aquarium; although doing this to fish that have suffered a prolonged fluke infection can cause further damage to the skin and fins (Ogawa 2015). Praziquantel has been shown to be effective in treating gill flukes and other aquatic worm parasites as it generally only requires 1-2 treatments and is non toxic to plants (Ishimaru et al 2013).

Gill fluke vs Skin fluke in fish 

References:

Ishimaru, K. Mine, R. Shirakashi, S. Kaneko, E. Kubono, K. Okada, T. Sawada, Y. Ogawa, K 2013, '

Praziquantel Treatment against Cardicola Blood Flukes: Determination of the Minimal Effective Dose and Pharmacokinetics in Juvenile Pacific Bluefin Tuna', 'Aquaculture', vol. 402-403, pp. 24-27

Kiskaroly, M 1977, 'Study of the Parasite Fauna of Freshwater Fishes from Fish Ponds of Bosnia and Herzegovina. A. Monogenean Trematodes 1. I. Cyprinid fish ponds', 'Veterinaria', vol. 26, pp. 195-208

Klinger, R. Floyd, R 1998, 'Introduction to Freshwater Fish Parasites', 'University of Florida-Fredrick, Aldridge & Jerome' 

Ogawa, K 2015, 'Diseases of Cultured Marine Fishes caused by Platyhelminthes (Monogenea Digenea, Cestoda)', 'Parasitology', vol. 142, pp. 178-195




  

Post 7: Taura Syndrome in American Shrimp Farming

Shrimp farming is occasionally reliant on capturing wild shrimp in a post-larvae stage for grow out or for broodstock prposes (Argue et al 2002). Unfortunately this stocking technique means potentially introducing diseased shrimp into a facility. One such virus that has caused billions of damge to shrimp stocks since the 1990's within the American region alone is a disease now known as Taura Syndrome in the Aparavirus genus (Lightner 2011).

Taura Syndrome emerged in 1992 in Ecuador and since then, certain species have shown great susceptibility-specifically the Whiteleg Shrimp (Litopenaeus vannamei) where outbreaks have occuered throughout the entirity of the species life cycle (Lightner et al 1995). Diagnosis of the disease in a farm setting occurs generally after noticing significant mortalities of shrimp in ponds/the presence of birds feeding on deceased shrimp (Brock 1997). further visual diagnosis of Taura Syndrome are the presence of multifocal, melanized spots on the body and tail of those effected (Lightner at al 1995).

Taura Syndrome induced melanized spots

    
 No current cure for Taura Syndrome currently exists, however resistance to the virus has been discovered in individuals of L. vannamei, which are undergoing selective breeding to pass on this resistance to future stocks (Argue at al 2002).


References:

Argue, B. Arce, S. Lotz, J. Moss, S 2002, 'Selective Breeding of Pacific White Shrimp (Litopenaeus vannamei) for Growth and Resistance to Taura Syndrome Virus', 'Aquaculture', vol. 204, pp. 447-460

Brock, J 1997, 'Taura Syndrome, a Disease Important to Shrimp Farms in the Americas', '
World Journal of Microbiology and Biotechnology', vol. 13, pp. 415-418


Lightner, D 2011, 'Virus Diseases of Farmed Shrimp in the Western Hemisphere (the Americas): A Review', 'Journal of Verterbrate Pathology', vol. 106, pp. 110-130

Lightner, D. Redman, R. Hasson, K. Pantoja, C 1995, 'Taura Syndrome in Penaeus vannamei (Crustacea: Decapoda): Gorss signs, Histopathology and Ultrastructure', 'Diseases of Aquatic Organisms', vol. 21, pp. 53-59

Post 6: Lymphocystis

Lymphocystis is a common viral disease, occuring in more than 100 marine and freshwater fish species (Yan et al 2011).
Lymphocystis is reported widely in home aquariums and is associated with fish facing high levels of stress; which is usually attibuted to poor water quality (Lawler & Donnes 1977) or the stress of moving fish from one environment to another e.g. moving fish from the pet shop to the home aquarium.
Lymphocystis causes hypertrophy (increase in volume) of the tissue cells of infected fish, which leads to visible white, pinprick nodules forming usually on the fins and body (Lawler & Donnes 1977). Unfortunately the formation of these nodules often lead to a mis-diagnosis of Ichthyophthirius multifillis (Fresh Water White Spot Disease).

The diagnosis of Lymphocystis is difficult in the early stages due to its similar resemblance to Fresh Water Whitespot Disease, however the white nodules in Lymphocystis will clump together to form large clusters, usually within two weeks of exhibiting symptoms (Paperna et al 1982). Infected fish also exhibit swimming difficulty and may also be inactive due to a breathing difficulty associated with nodules growing over the gills (Paperna et al 1982).

Viruses can evolve rapidly because they lack many factors that correct impurities in their DNA or RNA that exist in humans. Therfore mutations in viruses are a common occurence (Bamford et al 2002). Because of this, there is no existing cure for Lymphocystis. Therefore treatment should be focused on decreasing the stress on infected fish to allow the immune system to fight the virus and to decrease the risk of secondary infections.  

    

Early stage Lymphocystis

Late stage Lymphocystis

References:

Bamford, D. Bernett, R. Stuart, D 2002, 'Evolution of Viral Sructure', 'Theoretical Population Biology', vol. 61, pp. 461-470

Lawler, A. Donnes, J 1977, 'New Hosts for Lymphocystis, and a List of Recent Hosts', 'Journal of Wildlife Disease' vol. 13, pp. 307-312

Paperna, I. Sabnai, H. Colorni, A 1982, 'An Outbreak of Lymphocystis in Sparas aurata L. in the Gulf of Aqaba, Red Sea', 'Journal of Fish Diseases', vol. 5, pp. 433-437

Yan, X. Wu, Z. Jian, J 2011, 'Analysis of the Genetic Diversity of the Lymphocystis Virus and its Evolutionary Relationship with its Host', 'Virus Genes, vol. 43, pp. 358-366

Post 5: Vibriosis-An Examination of one of the most Recurring Bacterial Diseases in the Marine Environment

In 1997, Japanese researchers captured both juvenile and adult individuals of Estuary Cod, Mangrove Grouper and Napoleon Fish and transported these individuals back to Gondol Research station. In less than a week after transportation, all captured fish had died (Zafran et al 1998).
The cause of which came to be regarded as the most common bacterial disease in marine fishes; Vibriosis-from the genus Vibrio (Zafran et al 1998).

Bacteria in the Vibrio genus have evolved to become highly versatile, as strains of the disease have been documented to infect fish in marine, brackish and freshwater environments (Bullock 1977).
A study on Vibrio cholerea even found significant genotypical and phenotypical trait variations within the individual bacterial species (Cho et al 2010).

Signs of Vibriosis in juvenile fish simply appear simply as having a darker body coloration and a loss of appetite (Munn 2008), with older fish displaying haemorrhaging from hemorrhagic septicaemia and/or ulcerative lesions occurring on the fishes skin. Fish that are infected in the eyes also exhibit eye bulging (Zafran et al 1998).

A control of Vibriosis in an aquaculture or aquarium setting involve maintaining high water quality and a low density of fish within the tank in order to avoid any further stress on the fishes immune system. Administration of antibiotics is also a valid treatment to stop the spread of the disease, usually the use of the broad-spectrum antibiotic; OxyTetra Cycline over an 8-10 day period (Zafran et al 1998).

A snapper with the whole Vibrosis package; darker skin, lesions and haemorrhaging.

Stay tuned for more exciting pathogens and parasites.

References:

Bullock, G 1977, 'Vibriosis in Fish', 'U.S. Fish and Wildlife Service'.

Cho, Y. Yi, H. Lee, J. Kim, D. Chun, J 2010, 'Genomic Evolution of Vibrio cholerae', 'Current Opinion in Microbiology', vol. 13, pp. 646-651

Munn, C 2008, 'Vibriosis in Fish and its Control', 'Aquaculture Research', vol. 8, pp. 11-15

Zafran, A. Rosa, D. Koesharyuni, I. Johnny, F. Yuasa, K 1998, 'Manual for Fish Diseases Diagnosis', 'Japan International Cooperation Agency'.