Prevention and control of pathogenic bacteria in fish farms (Javier Gallego, Ohiane Rodriguez i Carlos Velasco)

PREVENTION AND CONTROL OF PATHOGENIC BACTERIA IN FISH FARMS

INTRODUCTION

In the last decades there has been an increase in the number of recognized illnesses with a bacterial origin that affect fish farms which were previously unknown. These new known  illnesses affect mainly the economy (because of the number of death fish), and as a result, the production. This is because of the sanitary control of the product that has increased in comparison to the years when these bacterial illnesses were not known yet.

Until now, the techniques used to solve this problem has been the use of antimicrobial disinfectants and drugs. Because of this, nowadays, there is a new problem due to the selective pressure of bacteria resistant to these antimicrobial compounds. [15]

According to the BOE, there is a strict rule regarding compliance with some standard indicators on the quality of water for human consumption, (RD 140/2003), but there is no clear regulation for the conditions the quality of the wáter used in the system of fish crops. Therefore, until now, the most used indicators for water quality control are pH, turbidity, temperature and dissolved oxygen concentration. (For all these parameters its optimum value varies depending on the species of fish that are produced). [6], [23]

“Studies investigating the microbial community composition in recirculating aquaculture systems (RAS; Schreier et al., 2010) and the microbiome of cultured fish have recently been started (e.g. Llewellyn et al., 2014), yet the detailed characterization of the aquaculture environment in respect to its residing microbiota and its functions are in its infancy.” [4]

WHAT IS IT FISH FARM?

Fish farm is a specialization of aquaculture, which is a method that has as main objective the rational cultivation of fish, that is to say, to control its growth, its feeding and its reproduction. These methods are usually done in natural or artificial lakes. In addition, it can produce two types of fish farming, both intensive and extensive. The intensive one is to achieve production with the most complete control possible and the lakes are technically constructed with an entrance and a water outlet. On the other hand, the control that is exerted on the crop extensively is reduced and it is made in reservoirs, whether natural or artificial.

CAUSED DISEASES BY BACTERIA

When it comes to a production system such as fish farming, that is done with large amounts in small spaces, it influences that there is a higher risk of infection due to diseases of bacterial origin, either by cannibalism or physical contact between individuals. This is because the bacterial ubiquitous behaviour allows them to grow both in the body of the fish and on their skin surface. For this reason, depending on the type of infection that occurs, it requires different methods to prevent it or to remedy it, generating a risk to the environment or to human health. [1] [3]

It should be noted that the production of diseases by bacteria are the group of pathogenic microorganisms with greater importance. In this case the associated diseases are the following:

Table 1: Different characteristics of the diseases analyzed. [3] [5] [10] [11] [12] [19] [21] 

DISEASE	PSEUDOMONIASIS	AEROMONOSIS	FURUNCULOSIS	BACTERIAL KIDNEY DISEASE (BKD)	COLUMNARIOSIS
RESPONSIBLE SPECIES	Pseudomonas sp. , Pseudomonas fluorescens	Aeromonas hydrophila	Aeromonas salmonicida	Renibacterium salmoninarum	Flavobacterium columnare, Flexibacter columnaris
MEMBRANE	Gram negative	Gram negative	Gram negative	Gram positive	Gram negative
AFFECTED FISH SPECIES	All of the fresh and brackish water	Large number of species	Salmonids	Salmonids of freshwater or of sea, and trout	Freshwater or saltwater fish
EFFECTS	Septicemic acute or chronic state; hemorrhages in the skin and internal tissues	Septicemics, internal (ascites) or external infections	Hemorrhages (acute state) and ulcers	Systemic disease with acute and elevated mortality, ascites, septicemic	Rapid mortality (24-72 hours), ulcers
SYMPTOMS	Dark skin, loss of flakes, abdominal ascites, exoftalms	Swollen belly, red spots on the skin, parade of fins	Depigmentation, scaling, scalp bleeding, inactivity of fish, decreased appetite	When the disease is advanced: lethargy (long and deep sleepiness), dark skin, pale gills, hemorrhages in the lateral line	White spots on the head, fins, glands, body and mainly in the mouth. Swollen and mucous glands (hinders breathing). Stranded filaments

Table 2: Different characteristics of the diseases analyzed. [3] [5] [8] [13] [14] [21] 

DISEASE	ESTREPTOCOCOSIS	VIBRIOSIS	PSEUDOTUBERCULOSIS OR PASTEURELOSIS	TENACIBACULOSIS	YERSINIOSIS
RESPONSIBLE SPECIES	Streptococcus sp	Vibrio anguillarum, Vibrio alginolyticus	Photobacterium damselae subsp piscicida	Tenacibaculum maritimum	Yersinia ruckeri
MEMBRANE	Gram positive	Gram negative	Gram negative	Gram negative	Gram negative
AFFECTED FISH SPECIES	Mainly in trout and eel	Salmon, golden, eel, wet, catfish, sea bass, sole, crumb, trout, grouper	Seriola, golden, sea bass, sole, cobia	Marine fish; Turbot, golden, Atlantic salmon, Pacific sardine, trout, Japanese barb, sea bass	Salmonids
EFFECTS	Septicemic and numerous cocs in the examined tissues	Septicemic, internal and external ulcer. Acute or chronic	Septicemia. Growth of bacterial colonies in the liver, kidney and spleen	Necrosis of tissues, ulcers	Lethal, chronic or acute
SYMPTOMS	The fish swim slowly, pool at the edges of the ponds, without appetite, abdominal swelling and prolapse of the anus. Acute in water with high Tª and chronic with low Tª	Rotten skin, appetite loss, visual injuries, abdominal distension, whitening of the corneas, bulging eyes, haemorrhages at the base of the fins	Loss of weight, darkening of the skin and necrosis of the gills	Rotten fins, skin lesions and paleness of the internal organs	No symptoms when the infection is coming. If the infection is mild: lethargy and darkening of the skin. Bleeding in the mouth, congestion of vessels in the mouth area when the effect is chronic

Although the limitation of microorganisms in farms is not exceeded, their control is very difficult because, as they are naturally found in the environment, fish can be affected in any way by pathogens under extreme stress conditions, which is when they are more vulnerable. In any case, the fish farmer does daily controls to observe the behaviour of fish and if they suffer changes in their physical appearance, because, as discussed in the table 1 and 2, they are the symptoms they present when they suffer from any disease. Then the detection in time of the disease allows eradication as soon as possible to avoid the spread to other individuals, and thus reduce the damage. [3]

When anomaly is detected, it is quickly sent between four and six affected fish (which are still alive) and a sample of water to detect the origin of the disease. Water samples are used to rule out that the infection is caused by non-infectious agents (Tª, pH, suspended solids, endogenous and exogenous toxins, mechanical injuries, nutritional disorders). [3]

METHODOLOGY FOR THE TREATMENT OF DISEASES

Before carrying out any treatment, the most convenient or effective would be to prevent this type of disease. Once these illnesses are diagnosed, we show the treatment that must be carried out in the following table:

Table 3: Treatment for each of the diseases analyzed. [3] [10] [12] [18]

DISEASE	PSEUDOMONIASIS	AEROMONOSIS	FURUNCULOSIS	BACTERIAL KIDNEY DISEASE (BKD)	COLUMNARIOSIS
TREATMENT	· Use of antibiotics such as terramycin or oxytetracycline. · Decreased fish density.	·Use of antibiotics such as Streptomycin. ·Elimination of the set of fish to avoid propagation.	·Use of antibiotic such as oxolynic acid and sulfamerazine. ·Drain the pond and disinfect.	·Use of antibiotic such as clindamycin and erythromycin. -Chronic natural.	·Treat or change the water since it is very contagious. ·Use of antibiotic such as potassium permanganate, malachite green or formol 40%.

Table 4: Treatment for each of the diseases analyzed. [3] [8] [14] [13] [17]

DISEASE	ESTREPTOCOCOSIS	VIBRIOSIS	PSEUDOTUBERCULOSIS	TENACIBACULOSIS	YERSINIOSIS
TREATMENT	·Decrease in food and the density of the crop. ·Use of antibiotic such as amoxicillin.	·Use of antibiotics such as sulphamerazine and oxytetracycline. · Do not stress the fish. · Maintenance of fish.	·Use of antibiotics such as oxytetracycline. ·Vaccines currently under development.	·Oral medication by means of antibiotics, such as streptomycin sulphate and penicillin	·Use of antibiotics like oxytetracycline. although only a few can be used frequently.

Although antibiotics are the most used to eradicate the disease, there are diseases such as furunculosis and yersiniosis that treatment can be done through vaccination. [12] [17]

Another method to combat tenacibaculosis is by means of specific methods based on molecular DNA. [2]

By aeromonosis, when aeromonas are mobile, it can not be treated with antibiotics since the disease is self-limiting in chronic cases, although it has an advanced infection if it's use is recommended. [3]

The use of formol as antibiotics to cure the disease causes very negative impacts. Formol baths cause a very serious environmental impact by releasing to the aquatic environment, since it is a very toxic substance. [1]

At the time, when used antibiotics often, it causes the appearance of pathogens resistant to them. In addition, antibiotics can be bioaccumulated to the internal organs of the fish, causing harmful effects on human consumption from it's intake and being a focus of environmental pollution. This is so because some substances are excreted without being metabolized as active metabolites and persist in the environmental for a long time, causing the formation of resistant strains. Therefore, alternative methods should be incorporated to these to minimize both environmental and human impacts. [1]

ALTERNATIVE METHODS

After the appearance of antibiotic resistant bacteria, it has been promoted a research to replace this treatment, hoping the knowing techniques will produce much lower environmental impact. [15]

Some of these alternative methods are:

• Immunostimulants: They are stimulants of the immune system, such as vitamins, extracts of algae and fungi, and some endotoxins that offer animals greater resistance to bacterial, viral or fungal infections, etc ... Levamisol is a immunostimulant product used in carp fish that helps the Vibrio anguillarum resistance. [20], [9]

• Bacteriophages: They are  viruses that attack a specific type of bacteria. These bacteriophages will not affect beneficial bacteria. [18]

• Probiotics: product that has living microorganisms that live in the gastrointestinal tract of the organism. They have beneficial effect for the host. Some examples of probiotic bacteria for the use of aquaculture belong to the genus Lactobacillus, Vibrio, Bacillus, Saccharomyces and Pseudomonas. [7], [16]

• Vaccines: The effectiveness of this method varies depending on the host species, the development phase and the temperature.[24]

• Therapies to inhibit the growth, expression and replication of genes [15]

• Natural Substances: Some plants help to improve the immune system of fishes, as well as show anti-stress, anti-parasitic and antimicrobial effects. This is a consequence of having components such as alkaloids, flavonoids, pigments, phenols, terpens, steroids and essential oils. [15]

CONCLUSIONS

• Since now, the use of antibiotics has been used excessively for the control, eradication and spread of diseases, creating an environmental problem, besides the origin of new strains resistant to treatment.

• There are alternative techniques to the use of antibiotics, with a minor impact that help strengthen the immune system of the ictic fauna, helping to reduce the risk of having diseases.

• The fact that daily fish checks are made, is an insufficient technique, since it does not prevent the appearance of diseases, so it should be with preventive measures such as a microbiological control on water quality, in addition of the physical and chemical controls that are already carried out.

BIBLIOGRAPHY

1. Arijo Andrade, Salvador (2005). La Acuicultura. El Ecologista, (43), 39-41. Extracted from:  https://www.ecologistasenaccion.org/?p=14724

2. Avedaño-Herrera, Ruben. And E. Toranzo, Alicia. And Magariños, Beatriz (2006). Diseases of aquatic organisms: Tenacibaculosis infection in marine fish caused by Tenacibaculum maritimum: a review. Department of microbiology and Parasitology, Faculty of Biology in Institute of Aquaculture, University of Santiago, Santiago de Compostela. Extracted from: https://www.int-res.com/articles/dao2006/71/d071p255.pdf

3. Balbuena Rivarola, Edgar Daniel (2011). Manual básico de sanidad piscícola. Ministerio de Agricultura i Ganaderia - Viceministerio de ganaderia. FAO. Extracted from: http://www.fao.org/3/a-as830s.pdf

4. Bentzon-Tilia, M., Sonnenschein, E. C., & Gram, L. (2016). Monitoring and managing microbes in aquaculture - Towards a sustainable industry. Microbial biotechnology, 9(5), 576-84. Extrated from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4993175/

5. Blanco, M.M. And Liébana, P. And Gibello, A. And Alcalá, C. And Fernández-Garayzábal, J.F. And Domínguez, L (2004). Principales patologías bacterianas en la piscicultura española. Unpublished manuscript, Animal Health Department, Complutense University, Madrid. Extracted from: http://www.adiveter.com/ftp_public/articulo900.pdf

‎6. BOE-A-2003-3596. Extracted from: https://www.boe.es/buscar/act.php?id=BOE-A-2003-3596

7. Chang C, Liu W in Journal of Fish Diseases (2002). An Evaluation of two probiotic bacterial strains, Enterococcus faecium SF68 and Bacillus toyoi, for reducing edwardsiellosis in cultured European eel, Angilla anguilla L. Extracted from: https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1365-2761.2002.00365.x

8. EcuRed (s.d). Estreptococosis. Extracted from: https://www.ecured.cu/Estreptococosis#Tratamiento

9. Edna M, Roets Y, GardinerN, et. al. in Sustainable Aquaculture Techniques (2014). The Use and Benefits of Bacillus Based Biological Agents in Aquaculture. https://www.intechopen.com/books/sustainable-aquaculture-techniques/use-of-probio

10. Fish Diseases: Bacterial Kidney Disease (Bkd). Extracted from: http://www.aun.edu.eg/developmentvet/fish%20diseases/2_3.htm

11. Fish Diseases: Columnaris disease (Saddle back disease). Extracted from: http://www.aun.edu.eg/developmentvet/fish%20diseases/2_10.htm

12. Fish Diseases: Furunculosis disease. Extracted from: http://www.aun.edu.eg/developmentvet/fish%20diseases/2_2.htm

13. Fish Diseases: Photobacteriosis (Pasteurellosis / Pseudotuberculosis). Extracted from: http://www.aun.edu.eg/developmentvet/fish%20diseases/2_8.htm

14. Fish Diseases: Vibriosis disease. Extracted from: http://www.aun.edu.eg/developmentvet/fish%20diseases/2_7.htm

15. García, Jorge (2018). Selección de extractos vegetales como inhibidores de bacterias patógenas de peces y utilitzación en acuicultura. Unpublished manuscript, Master's thesis (research profile) - Master's degree in aquaculture and fishing, Puerto Real. Extracted from: https://rodin.uca.es/xmlui/bitstream/handle/10498/20197/TFM%20Extractos%20vegetales%20inhibidores%20de%20bacterias%20patogenas%20acuicultura%20Jorge%20Garcia.pdf?sequence=1

16. Geovanny D G, Balcázar J, Ma S in Journal of Ocean University of China (2007). Probiotics as control agents in aquaculture. Extracted from: https://link.springer.com/article/10.1007/s11802-007-0076-8

17. Kumar, Gokhlesh. And Menanteau-Ledouble, Simon. And Saleh, Mona. And El-Matbouli, Mansour (2015). Yersinia ruckeri, the causative agent of enteric redmouth disease in fish. US National Library of Medicine, National Institutes of Health - PMC4581093. Extracted from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4581093/

18. Microbe Wiki (2016). Tenacibaculum maritimum. Extracted from: https://microbewiki.kenyon.edu/index.php/Tenacibaculum_maritimum

19. Mulca, Pol (2013). PezAdicto: Columnariosis, columnaris. Extracted from: http://www.pezadicto.com/columnariosis-columnaris/

20. Pérez R, Romeu B, Lastre M, et. Alabama. en VacciMonitor (2014). Inmunopotenciadores para la acuicultura. Extracted from: http://scielo.sld.cu/pdf/vac/v23n1/vac05114.pdf

21. Romano, Luis. And Raibengerg, Fernando (2008). Manual para los Inspectores Sanitarios Acuícolas. Enfermedades virales de importancia en salmonidos. Unpublished manuscript, Aquaculture management SAGPyA. Extracted from: https://www.agroindustria.gob.ar/sitio/areas/acuicultura/sanidad/_archivos//010010_Peces%20Salm%C3%B3nidos/000020_Sanidad%20en%20peces.pdf

22. Ronda C, Vázquez M, López R (2003). Los bacteriófagos como herramienta para combatir infecciones en Acuicultura. Extracted from: http://www.revistaaquatic.com/ojs/index.php/aquatic/article/view/208

23. Sedano, F.; Anguis, V. Calidad del agua en sistemas de recirculación para la acuicultura (SRA) marina – El Puerto de Santa María. Consejería de Agricultura, Pesca y Desarrollo Rural, Instituto de Investigación y Formación Agraria y Pesquera, 2016. 1-17 p. Extracted from: https://www.juntadeandalucia.es/agriculturaypesca/ifapa/-/action/90004fc0-93fe-11df-8d8b-f26108bf46ad/e5747030-1bb8-11df-b7e2-35c8dbbe5a83/es/02f9e190-faff-11e0-929f-f77205134944/alfrescoDocument?i3pn=contenidoAlf&i3pt=S&i3l=es&i3d=e5747030-1bb8-11df-b7e2-35c8dbbe5a83&i3sc&contentId=2681ead5-bc5d-4cff-99bd-96c6dac2cfcc

24. Sommerset I, Krossoy B, Biering E, et. al. in Expert Review of Vaccines (2005). Vaccines for fish in aquaculture. Extrated from: https://www.ncbi.nlm.nih.gov/pubmed/15757476

ANNEX

PSEUDOMONIASIS	Extracted from: https://www.google.es/search?q=PSEUDOMONIASIS&rlz=1C1CHZL_caES759ES759&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjA8_iM3bneAhWsB8AKHe5YDr8Q_AUIDigB&biw=1366&bih=657#imgrc=wjswkWQQrMw7dM:
AEROMONOSIS	Extracted from:  https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=QV7eW_j6K-jPgAalp56IBg&q=AEROMONOSIS&oq=AEROMONOSIS&gs_l=img.3...80711.80711.0.80919.1.1.0.0.0.0.153.153.0j1.1.0....0...1c.1.64.img..0.0.0....0.wnGv5PTvW8Q#imgdii=yTh3SvrGW7AeBM:&imgrc=rzgxJYt5F8wDqM:
FURUNCULOSIS	Extracted from:  https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=KmHeW9fnA-uLgAayyZSAAg&q=PASTEURELOSIS+peces+&oq=PASTEURELOSIS+peces+&gs_l=img.3...2408.3543.0.3565.7.7.0.0.0.0.169.470.0j3.3.0....0...1c.1.64.img..4.1.147...0i30k1j0i24k1.0.L79HP18VTf8#imgrc=LRj31xvSLADsHM:
MALALTIA BACTERIANA DEL RONYÓ (BDK)	Extracted from: https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=KV_eW--VJeWcgAbr7ZIQ&q=MALALTIA+BACTERIANA+DEL+RONY%C3%93+%28BDK%29&oq=MALALTIA+BACTERIANA+DEL+RONY%C3%93+%28BDK%29&gs_l=img.3...149738.149738.0.149936.1.1.0.0.0.0.153.153.0j1.1.0....0...1c.1.64.img..0.0.0....0.op5H5p7HbDs#imgrc=-fPCiSbIenxmzM:
COLUMNARIOSIS	Extracted from:  https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=wF_eW77zMtP5gQb7qLfYDQ&q=COLUMNARIOSIS&oq=COLUMNARIOSIS&gs_l=img.3...78501.78501.0.78702.1.1.0.0.0.0.132.132.0j1.1.0....0...1c.1.64.img..0.0.0....0.NMAydoueeuk#imgrc=0JNj35fGRalgIM:
VIBRIOSIS	Extracted from: https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=KmHeW9fnA-uLgAayyZSAAg&q=PASTEURELOSIS+peces+&oq=PASTEURELOSIS+peces+&gs_l=img.3...2408.3543.0.3565.7.7.0.0.0.0.169.470.0j3.3.0....0...1c.1.64.img..4.1.147...0i30k1j0i24k1.0.L79HP18VTf8#imgrc=NiuRW_zijgHUkM:
TENACIBACULOSIS	Extracted from: https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=kmPeW4OVB4LJgAbAtJLIAg&q=TENACIBACULOSIS+peces&oq=TENACIBACULOSIS+peces&gs_l=img.3...33166.34647.0.34704.9.8.1.0.0.0.149.675.0j5.5.0....0...1c.1.64.img..3.0.0....0.lCiSkROvuDc#imgrc=jpWGl_WUj2pz_M:
YERSINIOSIS	Extracted from: https://www.google.es/search?rlz=1C1CHZL_caES759ES759&biw=1366&bih=657&tbm=isch&sa=1&ei=KmHeW9fnA-uLgAayyZSAAg&q=PASTEURELOSIS+peces+&oq=PASTEURELOSIS+peces+&gs_l=img.3...2408.3543.0.3565.7.7.0.0.0.0.169.470.0j3.3.0....0...1c.1.64.img..4.1.147...0i30k1j0i24k1.0.L79HP18VTf8#imgrc=uHOXU1zNZFoWtM: