Aquaculture and microbiological problems

 

Aquaculture and microbiological problems in aqua culturing

What is Aquaculture?

Aquaculture is the breeding, rearing, and harvesting of fish, shellfish, algae, and other organisms in all types of water environments.

Introduction

Aquaculture is the rearing of aquatic species under controlled conditions, and includes the production of fish, shellfish, plants (seaweeds), alligators, amphibians, crocodiles and turtles. The process includes self-contained processes starting with the acquisition of eggs and sperm from dedicated brood stock through to market-sized individuals, such as Atlantic salmon.

Origin of Aquaculture

Aquaculture may be traced back to common carp (Cyprinus carpio) culture in China, which is considered to have been developed during 2000–1000 BC. Fan Lai (a politician turned fish culturist, in ancient China during the 5th century BC) wrote a landmark publication on fish culture in ~500 BC; this was the earliest known monograph on carp culture. Since then, aquaculture has expanded to most countries, particularly in the years after the Second World War.

Reasons for Aquaculture

•     Animals for re-stocking waterways for subsequent capture by anglers
•     Ornamental fish, e.g. goldfish and Koi carp, for the pet industry
•     Specimens for biotechnology to prevent the harvesting of possibly rare species from the wild
•     Rare species for release into the aquatic environment, to protect biodiversity

Aquaculture Sites

Aquaculture may occur in freshwater, estuarine or marine habitats, and involve pond (Fig. 1), tank (Fig. 2) and cage culture systems (Fig. 3) for fish, ponds and tanks for shrimp, and ropes suspended in the water column for bivalves. Sites range in size from those capable of producing a few tonnes up to those producing thousands of tonnes.

Microbiological Problems

Spoilage

It is speculative how much production may be lost to spoilage after harvesting, with culprits including Shewanella putrefaciens, which produces trimethyl-amine from trimethylamine oxide in fish tissues. Trimethylamine is odorous, and is a characteristic indicator of spoilage.

Diseases

A wide range of organisms, including bacteria, viruses and eukaryotic parasites, are associated with disease, which may decimate production and render the survivors unsalable because of the presence of unsightly lesions. Epidemics do occur, and may have profound consequences for local economies. For example, infectious salmon anaemia, a Listed Disease by the World Organization for Animal Health, was the latest in a long line of diseases that devastated Chilean salmon production during 2007–2011 when production plummeted by several hundred thousand tonnes, leading to the loss of jobs and social unrest in the rural areas of the south.

First reported in 2009, early mortality syndrome (EMS) has spread across Asian shrimp production, notably white-leg and black tiger shrimp, causing heavy (up to 100% within 30 days) losses in China, Malaysia, Thailand and Vietnam. The condition is infectious, and has been linked with Vibrio parahaemolyticus. EMS has followed on from white spot syndrome (caused by Whitespot Syndrome Baculovirus complex), which led to the virtual collapse of the shrimp farming industry in China during 1993, spreading across southern and eastern Asia by 2011, and resulting in substantive losses.

Aeromonas salmonicida, which is the cause agent of a haemorrhagic septicaemia termed furunculosis, has been a major problem of salmon and trout culture in the UK, although currently it is less problematic. Instead, the organism may be found in carp culture, particularly in Eastern Europe where it causes unsightly ulcers, including a condition known as carp erythrodermatitis.

The threat of disease has prompted detailed research into the development of suitable control measures. From the previous dominance of antibiotics and other antimicrobial compounds, attention has moved towards water treatments/disinfection, vaccines, immune stimulants and better management regimes. In Asia, much work has focused on the benefit of probiotics and plant products that confer health benefits, including protection against specific diseases.

Zoonosis

Fortunately, there is only limited evidence for the occurrence of human diseases resulting from exposure to aquaculture. There is some evidence for Aeromonas, Edwardsiella, Erysipelothrix, Mycobacterium, Streptococcus and Vibrio infections resulting from exposure to fish or shellfish. In 1996, the Toronto Star reported seven Streptococcus iniae infections in humans after buying and handling tilapia. The presumption was that the organism moved from the tilapia to the humans. A second example is Vibrio vulnificus, which may infect humans leading to fatalities through the consumption of contaminated molluscs. To re-iterate, the incidences of these infections is mercifully rare.

 

Gram-negative bacteria	Gram-positive bacteria
Vibriosis (V. anguillarum, V. harveyi clade, V. parahaemolyticus, Aliivibrio salmonicida (V. salmonicida), V. vulnificus , Photobacterium damselae)	Mycobacteriosis (Mycobacterium fortuitum, M. marinum, Nocardia asteroides, N. crassostreae (ostreae), N. seriolae)
Aeromonasis (Motile Aeromonas spp.:Aeromonas caviae, A. hydropila, A. sobria, A. veronii, A. jandaei; A. salmonicida)	Streptococcosis (Streptococcus agalactiae, S. iniae, Lactococcus garvieae, Aerococcus viridans)
Edwardsiellosis (Edwardsiella anguillarum, E. ictaluri, E. piscicida, E. tarda, Yersinia ruckeri)	Renibacteriosis (Renibacterium salmoninarum)
Pseudomonasis (Pseudomonas anguilliseptica, P. fluorescens)	Infection with Anaerobic Bacteria (Clostridium botulinum, Enterobacterium catenabacterium)
Flavobacteriosis (Flavobacterium branchiophilum, F. columnare, F. psychrophilum, Tenacibaculum maritinum)
Infection with Intracellular Bacteria (Piscirickettsia salmonis, Hepatobacter penaei, Francisella noatunensis, Chlamydia spp.)

Figure 2 Bacterial Diseases affecting the Aquaculture