The cause of high mortality in Bethany

The cause of high mortality in Bethany

The nation

The cause of high mortality in Bethany 1 May 8, 2023

For the first time, the Colombian Agricultural Institute (ICA) confirmed that another bacterium, different from aeromone, typical of the reservoir, caused the fourth death at the Betania Hydroelectric Power Plant. Other factors precipitated the emergency. scoop.


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The high mortality of fish registered in the Betania reservoir last March was caused by a native bacterium aggravated by the adverse environmental and sanitary conditions that encouraged the new “attack” even on land ponds.

The Colombian Agricultural Institute (ICA), in charge of preserving the sanitary status of the country, confirmed that the “unusual mortality” was caused by other risk factors that allowed the unusual spread of the bacteria.

“The report from one of our private laboratories registered with the ICA confirms that we had additional cases of unusual mortality and the first diagnosis attributed streptococcus agalactias of serotypes 1A and 1B as a possible cause,” revealed the veterinarian, María Fernanda Serrano, national manager of the aquaculture health program.

“The mortality in addition to the outbreak was facilitated by overdensity, inadequate practices, high concentrations of ammonia; low oxygen concentrations, increased PH, even in some cases due to the operation of projects without complying with biosafety standards”, he declared.

The preliminary report was revealed last Thursday at the first academic day of the International Aquaculture Fair that takes place at the Convention Center.

Although the multinational Enel (formerly Emgesa), owner of the Betania and El Quimbo dams, ruled out the low levels of the reservoir due to reduced flow rates, the initial report contemplates low oxygen levels due to inadequate management in some projects.


The epidemic outbreak that caused the high mortality was reported for the first time in LA NACIÓN on March 27 when it was in its final phase. However, the emergency began in January and worsened in mid-April, before Easter, when tons of inert material surfaced in various fish farming projects.

The first case was filed on January 30, 2023. However, it was never reported. Due to a ‘secret pact’ between the producers, the cases were not notified to the health authorities and they preferred to handle the emergency in complete secrecy.
Two months later, due to the journalistic note, the alarms were triggered. As of that date, the ICA began the investigation late, when mortality was declining and the dead material had already been removed from the reservoir.

From that moment on, it declared an early warning and began passive surveillance in two properties located in the reservoir. At that time, two other cases were reported, one in the Betania reservoir in Yaguará and another in Campoalegre.

The cause of high mortality in Bethany 7 May 8, 2023
The preliminary results revealed by the ICA.

Confirmed cases

The administrators of the fish farms reported that mortality worsened as of March 16. When the investigations began on March 27, mortality, as recorded by LA NACIÓN, had already been removed from the reservoir. In total, six notifications were made in fish projects in the Betania reservoir with similar clinical signs.

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“On the same days that we began the inspection, we received a report from one of our private laboratories registered with the ICA indicating that we had additional cases of unusual mortality and that they already had a diagnosis whose possible cause was streptococcus agalactia of serotypes 1A and 1B” , said the official, attached to the Technical Directorate of Health.


“In these six cases we have a total population of ten million animals with a morbidity of 1.52% of the animals and a morbidity of 2%,” revealed the official responsible for the ICA aquaculture health program:

According to the preliminary results in these six farms, of the ten million fish in the cages, 5.6 million were infected and only 152,512 died, as shown in the graph.

The health authority determined a morbidity and mortality rate of 1% in these properties, which means that the sick animals died.

“In these first notifications we found that there was indeed an ‘unusual mortality’ not so much because of the volume of dead animals but because of the stage where the mortality was taking place,” the official noted.

Although the inert load had been removed, the researchers found in these reported farms the clinical characteristics of the infection (lack of appetite, lethargy, erratic swimming, and death).

But, in addition, serious injuries throughout the body such as hemorrhagic liver, large gallbladder, foot injuries.

Following the protocols, the ICA technicians took samples for histopathology, bacteriology and molecular biology analysis by

Mortality rates

Once the emergency was confirmed, the technical team made 25 visits to the area, confirming 29 sources of infection.

“In the active surveillance work we found 29 properties or 29 sources of unusual mortality. Of these outbreaks, 23 correspond to farms with production in cages and six farms with production in ponds”, the official specified.

“We found a morbidity rate, that is, sick animals of 15% of the population, and a mortality rate of 12.2%.”

“Of this 15% of the sick population, 81% died. In other words, of the total number of fish that were sick, 81 percent died. This means that we had a high lethality of the animals that got sick.”


However, the volume was not determined. According to the analysis, 15 of the 29 farms visited had dissolved oxygen measurements less than 3.6, which is ideal. In addition, 19 of the 29 farms studied registered temperatures between 26 and 29 degrees Celsius, which is the ideal temperature for the reproduction of this streptococcus bacterium.

“These different measurements of water quality predispose the severity of the outbreaks to be greater. Obviously, we found another risk factor. Of these 29 farms, nine are not certified as biosecure by the ICA. They did not have measures that would reduce the admission or the spread of diseases”, the veterinarian said.

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The outbreaks were initially reported on properties located in the Betania dam. Subsequently, we received notifications in properties located in ponds (outside the reservoir). This means that the outbreak has left the reservoir and is present in inland ponds, representing further spread.

still dormant

The impact of this outbreak was not only due to the serotype, this outbreak depends on other additional conditions such as management conditions and environmental conditions. In these cases we found that there were increased population densities; dissolved oxygen decreased. In water quality we found some problems with ammonia, but also an altered PH and ideal water temperature for the bacteria.

“The bacteria has not disappeared and these conditions are general for both serotype A and serotype B. We have to work on actions that help us mitigate the main risk factors.”

“The good news is that this outbreak is not a zoonosis problem (which can be transmitted to humans by direct contagion) but it is a risk factor for producers,” explained Serrano.

“Streptococcosis is the main cause of high mortality in the fish industry. However, the variety “agalactiae” and the variety “s.iniae” are the ones that have been reported most frequently causing septicemia and meningoencephalitis in tilapias,” reported the veterinarian, Carlos Mario Rocha.

Aeromonas, currents in the reservoir, the main culprit in past emergencies, were also found.

The cause of high mortality in Bethany 8 May 8, 2023
The slaughter in Bethany.

scientific analysis

Due to the difficulties for the precise identification of streptococci spp by traditional diagnostic methods and because the clinical-pathological picture presented by fish affected by this type of bacteria is very similar, a private laboratory associated with Agrosavia.

The disease, according to preliminary results, affected a high population of older fish in various parts of the reservoir that typically presented exophthalmia and unilateral and bilateral corneal opacity, body darkening, apathy and incoordination, which led to the declaration of ‘unusual mortality’.

The preliminary diagnosis known by LA NACIÓN was based mainly on clinical signs, histopathological lesions and microbiological isolation; however, it was subjected to molecular techniques with a highly specialized laboratory that confirmed the presence of the bacteria in presumably affected animals.

other factors

The appearance of the disease, according to the preliminary study, is related to the intensification of culture methods that favor the dissemination and manifestation of potential pathogens such as bacteria.

This high-impact disease would be associated with bacteria of the streptococcus genus, a group of microorganisms widely distributed in nature, according to laboratory results.

This bacterial disease, according to the first laboratory diagnosis, evidenced the classic granulomatous lesions that affected the spleen, brain, liver, and kidney of the animals.

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Affected fish may show disoriented and erratic swimming movement due to meningoencephalitis, unilateral or bilateral exophthalmia with or without corneal opacity, and periocular hemorrhage.

The preliminary study revealed a variety of infectious agents of viral origin such as anemones and other bacteria that can impact productivity in the reservoir and in land ponds.

“The sick fish showed characteristic signs of septicemia (serious infection) associated with bacteria of the streptococcus genus, one of the pathogens that most affect tilapia, causing high mortality,” explained Serrano de La Cruz.

“The appearance of the disease is normally related to stress due to inadequate handling, high densities, temperature changes, inadequate nutrition and poor water quality.

Streptococcosis is characterized as a chronic disease with manifestations of disoriented and erratic swimming, lethargy, unilateral or bilateral exophthalmia with or without opacity of the cornea, periocular hemorrhage and even loss of the eyeball, hemorrhages in the skin, especially at the base of the fins. .


The complex differentiation of its species made it necessary to hire a highly specialized laboratory to adequately identify the characteristics of each species through three different classification systems, which allowed knowing the serological, hemolytic and biochemical properties of the strains, explained Pilar Donato. , the principal investigator of the Global Health Research Unit laboratory, specializing in genomic surveillance.

“Thanks to the application of genetic-molecular procedures such as hybridization and sequencing of the 16S RNA gene, it was possible to identify with greater precision the different etiological agents that cause streptococcosis in aquatic species,” explained the professional, linked to the Genetics Unit. and Molecular Medicine.

shoots overall They usually occur when fish have been exposed to stressful conditions, such as an increase in water temperature, suboptimal water oxygen levels for the species, or overcrowding for prolonged periods.

On alert

However, fish farmers considered that it highlights a latent problem in an industry that is growing.

“Streptococcosis is responsible for 40 percent of the cause of 40 or 50% of fish mortality historically. It is a bacterium, it is not zoonotic, that is, it does not affect human health, it is a bacterium that is in the environment, it is normally in the environment, anywhere and in any body of water,” explained Manuel Macías, one of the most experienced fish farmers in Huila.

“What happens is that if this microorganism finds other conditions to proliferate, it is fatal for the animal, but if it has a strengthened immune system, functioning well, with low levels of stress, if it is well fed, with a good level of oxygen, the animal will not nothing is wrong with him,” he insisted.

Now, I believe, we are learning to handle these emergencies, environmentally and healthily, he concluded.



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