antimicrobial use in aquaculture: important bacterial

Antimicrobial Use in Aquaculture:

Important Bacterial Diseases of Aquatic Animals

Eduardo M. Leaño

Network of Aquaculture Centres in Asia-Pacific

Bangkok, Thailand

[email protected]

mailto:[email protected]

Why do we use antimicrobials in aquaculture?

For prevention and treatment of aquatic animal diseases, especially

bacterial diseases;

Disease outbreaks are one of the serious causes of economic loss in many aquaculture operations around the world. Mainly a result of transboundary movement (trading) of live aquatic animals.

Aquatic animal diseases

Movement of live aquatic animals and aquatic animal products within and across national boundaries is a necessity for economic, social and development purposes;

Trading/Movement

May lead to introduction of new and emerging pathogens and to disease establishment – may pose risks to importing country’s aquatic animal health status;

WSD

AHPND

HPM-EHP

KHV

DIV 1

TILV

Aquatic animal diseases

❑ Increasing intensification

✓ More disease outbreaks and disease emergencies

❑ Continued diversification of species

✓ Increased risk of introduction and spread of pathogens (Trans-boundary pathogens)

❑ Continued diversification of farming systems

✓ Potential for spread of pathogens to wider geographical areas

❑ Economic and social cost of disease is enormous

Smith, 2017

The availability of antibioticsproduced a total revolution in our thinking about the

control of infectious diseases

We now have a “magic bullet”

A drug that attacks invading bacteria but has no effectin the host…

Commonly used antibiotics in aquaculture

Ibrahim et al., 2020

Tetracyclines (Oxytetracycline, Doxycycline, Tetracycline)Amphenicols (Florfenicol, Thiamphenicol)Sulfonamides (Sulfadiazine, Sulfamonomethoxine,Trimethoprim-sulfonamide)Macrolides (Erythromycin, Tylosin)Quinolones (Flumequine, Oxolinic acid, Enrofloxacin)

Problem

The more we use antibiotics, the more they become

ineffective;

In most aquaculture operations in the region, antibiotics

are used without proper veterinary prescriptions.

Antibiotics/antimicrobials should be used responsibly

(prudent use of antimicrobials);

Antimicrobials: commonly refer to Antibiotics

Prudent use of antibiotics: we need to know our enemy

ANTIBIOTICS: commonly used against bacterial pathogens

What are bacteria?• Microscopic, single-celled

organisms

Prudent use of antibiotics: we need to know our enemy

What are bacteria?

• Oldest life form in this planet• Survived for 4 billion years: remarkable ability to adapt to

changes in their environment;• Protean microbes: mutable, flexible, versatile, adaptable

and capable of adopting many forms

(Smith, 2017)


Bacteria adapt to their environment

• In the presence of chemical agents in their environment that are harmful to them, bacterial population will adapt;

• Strains and species that are not affected by the chemicals will emerge.

(Smith, 2017)


Haenen, 2017

Bacterial Diseases of Cultured Aquatic Animals

• Vibriosis in marine fish;

• Motile Aeromonas Septicaemia (MAS) in freshwater fish;

• Acute Hepatopancreatic Necrosis Disease (AHPND) of marine shrimps.

Vibriosis in marine fishes

• Caused by a group of bacteria called Vibrio, a Gram-negative that are ubiquitous in the marine and estuarine ecosystems;

• Main species involved in disease outbreaks: Vibrio anguillarum, V. salmonicida and V. vulnificus

https://www.cdc.gov/vibrio/index.html

Signs of the disease include:• Lethargy• Tissue and appendage necrosis• Slow growth• Skin discoloration• Red necrotic lesions in the abdominal muscle• Erythema (bloody blotches) at the base of the fins, vents and

mouth



Seabass Snapper

Grouper Milkfish

• Vibrios usually abound in warm (>15oC) in saline and estuarine aquatic environment;

• Present a constant threat to many cultured marine finfishes;

• Mortalities (in severe cases/outbreaks) can be as high as 100%


Control of infection in aquaculture:

• Use of antibiotic-medicated feeds: oral route• May become ineffective in time due to development of resistance to

antimicrobial compounds of the bacterial pathogens;• May also result to accumulation of residual antibiotics in fish tissues if

used unresticted;

• Alternatives to antibiotics include the use of immunostimulants, vaccines, probiotics and quorum sensing.


Motile Aeromonas Septicaemia of Freshwater Fish• Acute, sub-acute or chronic infectious disease of all freshwater fishes,

especially cultured species such as carps, catfish, snakehead and tilapia;

• Caused by motile Aeromonas group including: A. hydrophila, A. caviae, A. sobria

Motile Aeromonas Septicaemia of Freshwater Fish

Disease signs:• Acute (dropsical form): rapid fatal septicaemia with few gross

signs; exophthalmia; reddening of the skin; accumulation of fluid in scale pockets and abdominal cavity.

• Chronic (ulcerative form): dermal ulceration with focal haemorrhages and inflammation; severe tail and fin rot.

Predisposing factors for infection and outbreak:• Stress due to high temperature, overcrowding and low dissolved

oxygen;• Malnutrition;• Heavy infestation of parasites;• Organic pollution (high ammonia and nitrite levels);• Physical injuries;• Spawning activities;• Rough handling and transportation.



Tilapia

Catfish

Carps


Prophylactic treatment (prevention):• NaCl bath (1-3%) or KMnO4 bath (2-4 mg/L)

Treatment and Control:• Medicated feeds (oxytetracyline at 2-4mg/kg; Sulfamerazine at

264 mg/kg);• Prolonged bath treatment with KMnO4 (2-4 mg/L).

Acute Hepatopancreatic Necrosis Disease (AHPND) in Marine Shrimps

Also known as early mortality

syndrome (EMS);

Disease causing unusually heavy

shrimp mortality approx. within the

first 35-45 days of culture;

Source: T Flegel

Photo from D.V. Lightner

(www.enaca.org)

Normal

hepatopancreas

AHPND

hepatopancreas

Medial sloughing of HP cells: The key diagnostic feature needed for

confirmation



Causative agent(s?):

Vibrioparahaemolyticus(containing toxin plasmids PirA/B)

Pir: Photorhabdus insect-related (Pir) toxin-like genes

Vibrio harveyi

Vibrio owensii

Vibrio campbelli

Vibrio punensis


Preventive Measures• AHPND detection has improved the supply of “clean” broodstock and PLs;

• AHPND (prevention) has been improved by management changes, which focus more on environmental (and feeding) management and biosecurity measures;

• Improvement of health status of broodstock and production of healthy (more resistant) PLs for grow-out culture.

Few last words….• Bacterial pathogens of aquatic animals: ubiquitous in the aquatic

environment;

• Their population can be manipulated (aquaculture setting) through:✓ Environmental manipulation (proper water management);✓ Proper feeding management;✓ Prevent build-up of organic matter;✓ Other biological manipulations to prevent dominance of bacterial

pathogen(s) population (probiotics, effective microorganisms, recent innovations on biological measures for disease prevention).

Recent Innovations that can Contribute to Prevention of Diseases (including bacterial) and Overall Farm Biosecurity

Kawahigashi, 2016

Shrimp Toilet: discharge of sludge wastes during grow-out culture operation

Biofloc System: A biofloc floccule is a miniature, loosely held collection of materials (uneaten feed, faeces, detritus and other particles) and attached organisms (bacteria, protozoa, nematodes, phytoplankton and fungi) kept in suspension by strong agitation of water in a pond or tank.

Ray, 2012;Thong, 2014;

Recent Innovations that can Contribute to Prevention of Diseases (including bacterial) and Overall Farm Biosecurity

Romano, 2017

Aquamimicry: is a concept that strives to simulate natural estuarine conditions by creating zooplankton blooms (mainly copepods) as supplemental nutrition to the cultured shrimp and beneficial bacteria to maintain water quality.

Green water system: technique that cultures shrimps in water that is abundant in phytoplankton e.g.Chlorella, turning the water green hence, its name. It is usually produced from growing tilapia (either monocultured or co-cultured with shrimps).

Al-Sofyani, 2017;Tran et al., 2014;Lio-Po et al., 2002.

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antimicrobial use in aquaculture: important bacterial

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