The Fish Vet's Blog

The spawning principles slide show at this website gives a good overview..

http://www.syndel.com/Spawning-Information-Documents

I thought I’ll share with you the Asian Fisheries Society newsletter.

What’s in it?

• Ninth Symposium on Diseases in Asian Aquaculture (DAA9) that will be held in Ho Chi Minh, Vietnam on 24-28 Nov 2014. For updates see link: http://www.daa9.org
• Comments on the 22-24 Aug 2013 Fish Pathology Workshop, Murdoch University, Perth, Western Australia.
• Call for Expression of Interest in post-DAA9 Fish Pathology Workshop in Ho Chi Minh, Vietnam in Nov 2014
• Survey on demand for short courses in Aquatic Animal Health
• Book review – Fish Vetting Essentials By Dr Richmond Loh & Dr Matt Landos
• Upcoming Events.
• Articles on Biosecurity and Fish Health Management (link)
• Diseases of Asian seabass (or barramundi) Lates calcarifer Bloch (link)

 

Download the full newsletter by clicking on the link below:

AFS NEWSLETTER 13 JAN 2014_FINALv4

Abstract

Other than the study by Griffiths (2009) on gill diseases, there has been no comprehensive study and report on the major diseases of Asian seabass (or barramundi) Lates calcarifer Bloch. It is a food fish species of growing importance in Asia and Australia. This study investigates some of the major diseases encountered in the various stages of the culture of L. calcarifer, at the histopathological, ultrastructural and molecular levels. Culture practices can have significant impacts on fish health. Disease outbreaks are influenced by factors involving the host, environment and pathogen. Current knowledge on diseases of L. calcarifer, and these factors which may influence disease outbreaks are discussed in Chapter 1.

This is the first report of an intestinal Eimeria infection in L. calcarifer. The Eimeria infection was associated with severe pathology and significant mortality in the absence of other pathogens. It was detected in diseased L. calcarifer in all five nurseries in Ca Mau, Vietnam. Although these were small scale nurseries which stocked an average of 3000 to 5000 fish at any one time, a mortality rate of up to 30% was reported and is the cause of significant economic losses for these nurseries. Moderate to heavy Eimeria infestation were observed in greater than 80% of diseased fish examined. This high rate of Eimeria infestation is suspected to be linked to the low daily water exchange rates practised in these nurseries. However, the examination of only diseased fish does not allow the determination of prevalence. A systemic iridovirus infection was concurrently observed in some of the fishes but was not consistently present when compared to the Eimeria infection. Molecular analysis showed that the Eimeria of L. calcarifer from Vietnam formed clades with the Eimeria detected in L. calcarifer cultured in Australia, but clustered separately from other known Eimeria species. Although Cryptosporidium was detected in these L. calcarifer tissues, it could not be demonstrated histologically or ultrastructurally, suggesting a low grade infestation or perhaps an environmental contaminant in fish tissues tested. In situ hybridization using labeled PCR products showed that labeled DNA probes generated from 18S PCR products could not be used to distinguish between closely related genera such as Cryptosporidium and Eimeria. Future investigation to determine the origin, transmission and risk factors associated with this Eimeria infestation in L. calcarifer are needed.

‘Scale drop syndrome’ is a novel disease first reported in L. calcarifer in Penang, Malaysia in 1992. Cases with similar gross and clinical presentations were observed in Singapore in 2002, 2006 and 2009. Affected fish have loose scales, which dropped off easily when handled. The disease was initially observed in 100-300g fish, and later in larger fish up to 5kg bodyweight. Cumulative mortalities of 40 to 50% were reported by farms, posing significant economic losses of larger more valuable fish. This investigation forms the first pathological description of ‘scale drop syndrome’ (SDS) in L. calcarifer. To aid recognition of new cases for study, a case definition was developed for ‘scale drop syndrome’ in L. calcarifer as a systemic vasculitis associated with tissue necrosis in all major organs including the skin, with apparent targeting of cells of epithelial origin. Attempts to isolate or detect the causative agent(s) by cell culture, PCR and immunohistochemistry have proven unsuccessful. Further studies to elucidate the definitive aetiology, isolate the causal agent(s) and reproduce the disease will help better understanding and control of SDS.

Although systemic iridoviral disease has been previously reported in many freshwater and marine fish species, this study forms the first report of this disease in L. calcarifer. Systemic iridoviral disease was observed in 5 to 20g L. calcarifer usually 2 to 3 weeks post-transfer into sea cages at two farms. Inclusion bodies suggestive of a systemic iridovirus infection were observed in clinically healthy L. calcarifer from the land-based nursery of one of these two farm; the presence of an iridovirus infection was supported by positive PCR results using Red Sea bream iridovirus (RSIV) primer 1. The presence of inclusions was not accompanied by any tissue necrosis in these clinically healthy fish. This finding suggested that the systemic iridovirus infection occurred before stocking at sea, and did not originate from wild fish or older fish in adjacent sea cages as initially suspected by this farm. Immunohistochemistry on tissues of clinical cases of systemic iridovirus gave positive results using the Red Sea bream iridovirus monoclonal antibody (RSIV M10), although intensity varied between tissues, possibly related to varying exposure of different tissues to fixation chemicals. Inclusion bodies in clinically healthy fish from the same farm did not show positive reaction with RSIV M10. This may be due to a lack of antigenic expression by the viral infected cells at this early stage of infection.

Viral nervous necrosis (VNN) is a serious disease of hatchery reared L. calcarifer fry in this study. Mortalities of 50 to 100% were reported in 3wo fry. VNN can be difficult to diagnose in older fry, where it can be associated with few vacuolations or an absence of viral inclusions

‘Pot belly disease’ (PBD) was previously reported in L. calcarifer fry less than 1g, in association with an intracellular coccobacillus infection and mortalities of 80 to 100%. In this study, PBD was observed in 120g L. calcarifer at two sea cage farms, in association with significant granulomatous enteritis. The extent of the granulomatous enteritis is likely to have an effect on affected fish. It was observed concurrently with systemic iridoviral disease at one farm and nocardiosis at another farm. Diagnosis by histopathology and the lack of other confirmatory tests for PBD may result in underdiagnosis of this disease. The epidemiology of PBD needs further study to establish origin and modes of transmission, to facilitate better disease control.

Diseases associated with infections by ubiquitous bacteria such as Vibrio, Tenacibaculum were commonly observed in L. calcarifer post-handling. Tenacibaculosis and vibriosis often occurred concurrently with other diseases such as streptococcosis, systemic iridviral disease or PBD. Streptococcosis can affect fish up to 3kg bodyweight, resulting in significant mortalities greater than 40 to 50%. Like SDS, because streptococcosis can affect up to market size fish, they can cause considerable economic losses. Although vaccines against Streptococcosis are available, conflicting views are held on the efficacy of Streptococcus vaccines by various research groups. Overall, the South-east Asian L. calcarifer farms which practiced vaccination against Streptococcus iniae reported a reduction of mortality, especially in fish greater than 1 to 1.5kg bodyweight.

Nocardiosis has been reported as an emerging disease in marine food fish species caused by acid fast filamentous branching bacterium. Although nocardiosis was observed histopathologically in L. calcarifer at two sea cage farms, the numbers of samples examined were small and no other tests were attempted due to lack of suitable samples. More intensive and extensive study is needed to determine the significance of nocardiosis in L. calcarifer. Chronic granulomatous enteritis was not uncommon in the cases submitted to the Fish Health Laboratory in Perth. Although the peritonitis was associated with heavy bacteria infection, it is unclear if these are secondary invaders. Schipps, Bosmans & Humphreys (2009) reported that Vibrio harveyi and Photobacterium damsela damsela vaccinations appeared to be not efficacious, suggesting that these bacteria were not the primary cause of the disease.

It is well recognized that disease outbreaks in farmed fish are influenced by the interaction between host, the environment and pathogens. While serious diseases are often reported in association with specific aquatic pathogens, not much is known about the risk factors which trigger fish disease outbreaks. Disease outbreaks often occur after stressful events such as net transfers, recent handling or poor water quality. In fact, diseases are often caused by ubiquitous pathogens that are commonly present in the culture environment. Although further research is necessary to gather more information to improve diagnosis and management of specific diseases, general health management strategies can be applied at the various stages in the culture of L. calcarifer to minimize disease outbreaks. This is discussed for L. calcarifer in Chapter 6.

Observations of types of disease agents may be influenced by site conditions or the types of tests or materials examined. For example, some parasites may be more prevalent in certain sites where intermediate hosts abound, or loosely attached ectoparasites may be lost unless wet mount microscopic examinations of fresh tissues were carried out. The study of emerging diseases such as scale drop syndrome (SDS) or pot belly disease (PBD) in L. calcarifer has been hampered by lack of confirmatory diagnostic tools and inadequate knowledge on critical epidemiological factors such as mode of transmission or potential reservoirs. While ideally identification and isolation of the causal agent will help fulfil Koch’s postulates, it may be possible to improve the understanding of disease via cohabitation or infectivity trials using tissue homogenates from diseased fish when pure isolates are not available. There is a need to conduct research to not only establish a definitive aetiology, but also to identify risk factors to facilitate successful disease control. The successful management of disease in aquaculture does not lie in any one strategy but an integrated management of all risks encountered during the culture cycle against disease occurrence or incursions.

Publication Type:	Thesis (PhD)
Murdoch Affiliation:	School of Veterinary and Biomedical Sciences
Supervisor:	Nicholls, Philip and Jones, Brian
URI:	http://researchrepository.murdoch.edu.au/id/eprint/14817

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Yours sincerely,

Dr Richmond Loh DipProjMgt, BSc, BVMS, MPhil (Pathology) Murdoch, MANZCVS (Aquatics & Pathobiology), CertAqV.
Aquatic Veterinarian | Adjunct Lecturer Murdoch University | President WAVMA |
Secretary Aquatic Animal Health Chapter – ANZCVS.
The Fish Vet, Perth, Western Australia, AUSTRALIA. Mobile Veterinary Medical & Diagnostic Services for fish and other aquatic creatures.
http://www.thefishvet.com.au
Ph: +61 (0)421 822 383
Skype: thefishvet

Looking for more books? Check out this site.

Q: What do you call someone who’s obsessed with fish?

A: A FINatic!

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Yours sincerely,

Dr Richmond Loh
DipProjMgt, BSc, BVMS, MPhil (Pathology) Murdoch, MANZCVS (Aquatics& Pathobiology), CertAqV WAVMA.
The Fish Vet, Perth, Western Australia.
Veterinary Medicine for fish.
W: http://www.thefishvet.com.au
E: thefishvet
P: +61 (0)421 822 383

One of my colleagues has asked me to circulate this short survey with the hope of developing training courses that are better suited to aquatic animal health personnel.

Thank you in advance for taking the time to complete this survey comprising 12 short questions.

You may contact Dr Susan Gibson-Kueh for further information on: S.Kueh@murdoch.edu.au

Please use this link to the survey: https://www.surveymonkey.com/s/ShortCrsAquaticHealth_MurdochU5

read more here

In his Presidential address, he says,”The discipline of aquatic veterinary medicine can be described as both a niche, and the fastest growth area in veterinary science. The WAVMA is dedicated to reinvent veterinary science by bringing aquatic veterinary medicine to the forefront, creating new opportunities, positioning ourselves for the future, by building a competitive advantage and harnessing the skills of its members.”

“The vision for this year is to promote and fine tune our existing programs, and to create more opportunities for aquatic veterinarians. We need to enhance market access of aquatic veterinarians and improve, not only the awareness of aquatic veterinarians, but also client perception of our area of expertise. By doing these things, we can really grow the World Aquatic Veterinary Medical Association.”

“So what have we for the year ahead? My challenge for this year is to promote and fine tune our existing programs, and to create more opportunities for aquatic veterinarians. We need to enhance market access of aquatic veterinarians and improve, not only the awareness of aquatic veterinarians, but also client perception of our area of expertise. By doing these things, we can really grow the World Aquatic Veterinary Medical Association.”

“Three areas we will concentrate on in the year ahead are:
1. Relevance: to satisfy the needs and wants of its members, through support, CEPD, recognition of prior experience and defending the aquatic area for the veterinary profession.
2. Pre-eminence: about growing the WAVMA brand within our profession (to our colleagues) and outside our profession (to our clients) by promoting the value and utilisation of suitably qualified aquatic veterinarians to our clients.
3. Reach: through the internet (social media) and engaging in open dialogue with other organisations.”

“To increase our presence and visibility, we need to be present in our clients’ forums, such as at aquaculture conferences, ornamental fish shows and on line. After attending some of the presentations by our members, I realise that we are sitting on a gold mine of practical experiences that are not taught at university or at any other educational institution. I would like to show case our members’ skills and knowledge by ramping up the WebCEPD, and open it up to the world. This will not only help increase visibility of the presenters, but will increase the public’s appreciation for aquatic veterinarians. So, I look forward to receiving requests for topics, and offers to present webinars.”

“We are also looking at fostering more inter-organisational collaborations. Because, the more people we have working together to achieve a common goal, the faster we can arrive. Join our cause to unleash your potential and to seek new possibilities. Enquire now about taking up some leadership roles, to help develop programs & set future directions.”