Identification of the key pathogens responsible for production losses at grouper nurseries in Aceh Indonesia
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1
University of Sydney, Faculty of Veterinary Science, Australia
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2
Brackish Water Aquaculture Development Center, Indonesia
Introduction
Grouper is a commercially important high value marine fish belonging to the genus Epinephelus. They are ideal for aquaculture due to their rapid growth, hardiness in intensive rearing and strong market price. Grouper is widely cultured across in Indonesia and it is destined for export to live seafood markets in Hong Kong, China, Singapore and other Asian countries. In Indonesia, following metamorphosis to a juvenile, grouper are grown in estuary nursery ponds for several months prior to entry to sea cages for grow out to market sized fish. The nurseries found in Aceh, Indonesia are considered traditional and small-scale farming. The nurseries are located in coastal areas close to the sea as they rely on tidal action for water exchange. There are minimal biosecurity measures used and disease outbreaks are rarely reported to the local district office. Grouper nurseries in Aceh, Indonesia play a significant role in supplying fingerlings to sea cage grow out production in South-East Asia.
This study focused on the nursery stage of grouper production that typically encompasses the growing of fish from 2 cm to 10 cm over a 2-3 month period. Fish farmers have reported the survival rates at grouper nurseries are usually around 75%. However, this can plummet to 15% during the annual rainy season from November to December. Low survival in the rearing ponds is thought to be associated with deleterious changes in water quality, which results in large scale disease outbreaks. Many farms will go as far as to stop production during this time to reduce disease outbreaks. Importantly, although disease is thought to play a significant role in mortality, it is not known which pathogens are actually causing these outbreaks leading to significant production losses. The objective of this study was to identify the pathogens and associated diseases that contribute to production losses during the rainy season in grouper nurseries.
Methods
A cross sectional study was conducted at grouper nurseries in Aceh, Indonesia. The farms were selected based on several criteria including the availability of fish in the farm at the time of the study, willingness to participate and personal safety. At each farm, a population was defined as fish of the same species and age and a maximum of two populations were sampled at each farm. A sample size of 30 fish per population was used to provide 95% confidence of detecting disease at a minimum expected prevalence of 10%. Equal numbers of fish were selected by dip net from randomly selected hapas (small net-pens used to contain fish within a pond) and ponds. Each population was sampled for molecular testing of viruses, bacteriology and examined for ectoparasites. Histopathology was used to confirm the disease pathogenesis associated with viral infections. A total of ten populations were sampled from seven different farms.
Results and Discussion
This study identified the key viral diseases and parasitic infestations were associated with high mortality during the rainy season in Aceh, Indonesia. Testing revealed that the majority of grouper populations were infected with nervous necrosis virus and Megalocytivirus. Ectoparasites were detected in all sampled populations with at least two-thirds of fish showing infestation with at least one species of parasite. The most common parasites observed were protozoa and monogeneans. The prevalence of significant pathogens and associated diseases is paramount to developing control measures (e.g. vaccine development and biosecurity measures) representing significant future investment. The results of this study will be used to provide recommendations for farm-relevant and practical interventions to improve production and provide income stability.
Acknowledgements
Acknowledgements
This study was funded by the Australian Government through the Australian Centre for International Agricultural Research and a John Allwright Fellowship (B. Sah Putra).
Keywords:
Viral nervous necrosis,
Megalocytivirus,
Grouper,
Infectious diseases epidemiology,
Red sea bream iridovirus
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Oral
Topic:
Aquatic Animal Epidemiology
Citation:
Sah Putra
B,
Hick
P,
Rimmer
M,
Khairul
R,
Evarianti
E,
Nurbariah
N,
Royani
R,
Tajussalatin
T,
Muslim
M and
Becker
J
(2016). Identification of the key pathogens responsible for production losses at grouper nurseries in Aceh Indonesia.
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00049
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Received:
28 Jul 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
Dr. Joy Becker, University of Sydney, Faculty of Veterinary Science, Camden, NSW, 2570, Australia, joy.becker@sydney.edu.au