Mid-crop mortality syndrome in Australian prawn farming: a case study

Cullen, B.R., and Owens, L. (2004) Mid-crop mortality syndrome in Australian prawn farming: a case study. In: Papers from Styli 2003: thirty years of shrimp farming in New Caledonia (38) pp. 223-228. From: Styli 2003: thirty years of shrimp farming in New Caledonia, 2-6 June 2003, New Caledonia.

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Prior to 1994, Australia was regarded by industry to be largely free of costly prawn pathogens. In the second half of 1994, several prawn farms in north Queensland reported unusual mortalities of juvenile pond reared Penaeus monodon. Clinically, sick prawns would usually appear after 3-3.5 months of pond culture or when they were around 12-15 g in size. Feed consumption would fall suddenly and lethargic prawns with a slightly dark red colour would appear at the pond edges. Mortalities were up to 80% in some grow-out ponds, with deaths continuing at high levels until the pond was harvested. Increased water exchange and other husbandry changes failed to alter the course of an outbreak. Some affected farms reported cycles of mortalities with peaks and troughs. Farms with the disease were all well established with a long experience in prawn farming. These losses represented a significant impact on the small, but rapidly growing industry and disease was recognised as a major threat to future sustainability. The immediate consequence was a slowing in the rate of industry growth. The inability to control outbreaks of disease with management to optimise pond conditions had serious implications on the future viability of prawn farming in Australia. A number of aspects were investigated including pathology, microbiology, pond water quality, intake water quality, bloom composition, blue-green algal bloom, feed quality and pond management. The pathological findings were inconclusive, and investigations failed to identify any consistent factor or detectable water quality problem associated with the disease outbreaks. The disease was referred to as Mid Crop Mortality Syndrome (MCMS). It was unique to Australia; the literature does not describe similar conditions in any other countries which culture P. monodon (e.g. Indonesia, Thailand, Philippines). Investigations which began in April 1995 demonstrated that a virus or viruses were associated with the disease. Initial MCMS investigations found at least 4 virus-like particles by electron microscopy. Spawner-isolated mortality virus (SMV, a parvo-like virus) and gill -associated virus (GAV, a yellowhead-like virus) have been the subject of ongoing investigations. The MCMS viruses were highly infectious. They were able to be spread during an outbreak by healthy prawns eating infected prawn tissue and via contaminated water. This indicated that farms needed to consider the movement of sick prawns and water transfer when trying to control an MCMS outbreak. The viruses can be transmitted vertically through hatcheries to postlarvae. Chlorine disinfection was highly effective for destroying MCMS viruses, whereas dessication by drying was not. MCMS has declined since 1998, probably due to the implementation of wholefarm destocking and pond disinfection on many affected prawn farms. There has been a re-emergence of MCMS-like mortalities, sometimes linked to lapses in control strategies. Research is required to understand the role of different viruses and environmental factors that trigger MCMS-like diseases, and to ultimately try to develop and implement cost-effective processes using sensitive detection tests and other procedures to reduce on-farm mortalities.

Item ID: 7840
Item Type: Conference Item (Research - E1)
ISBN: 978-2-84433-134-2
Keywords: mariculture; penaeids; Australia; ecology; pathology; physiology
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Original title: Styli 2003 trente ans de crevetticulture en Nouvelle-Caledonie

Date Deposited: 21 Jun 2010 01:42
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0707 Veterinary Sciences > 070712 Veterinary Virology @ 100%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830199 Fisheries - Aquaculture not elsewhere classified @ 100%
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