STRATEGIES FOR THE PREVENTION AND CONTROL OF AEROMONIASIS IN TROUT

СТРАТЕГИИ ПРОФИЛАКТИКИ И БОРЬБЫ С АЭРОМОНИОЗОМ У ФОРЕЛИ

Сулейманова Афет Валентин кызы

д-р философии по биологии, доцент, Ветеринарный научно-исследовательский институт при Министерстве сельского хозяйства Азербайджана, Азербайджан, г. Баку

Abstract. During 2012-2022, we conducted studies on the prevalence of parasitic diseases among trout species in the Republic of Azerbaijan. A total of 668 specimens were examined using the complete parasitological dissection method. The bacterial furunculosis caused by the pathogens from the species Aeromonas salmonicida, Aeromonas hydrophila, Pseudomonas fluorescens, and Vibrio anguillarum recorded in brown (Salmo fario) and rainbow trout (Salmo gairdneri). The species Aeromonas salmonicida demonstrated the highest pathogenicity. The prevalence rate of furunculosis was 56.8%. Several veterinary drugs were tested, and the highest effectiveness was observed in the drug “Antibak-100.” This preparation was tested and implemented in trout farms in Azerbaijan.

Аннотация. В период с 2012-2022 гг. нами были проведены исследования по распространению паразитарных заболеваний среди форелевых рыб в условия Азербайджанской республики. Всего было исследовано 668 экземпляров методом полного паразитологического вскрытия. У исследованных видов пятнистой (Salmo fario) и радужной (Salmo gairdneri) форели был выявлен бактериальный фурункулез, вызванный возбудителями, принадлежащим видам Aeromonas salmonicidae, Aeromonas hydrophila, Pseudomonas fluorescens и Vibrio anguillarum. При этом, наибольшей патогенностью отличался вид Aeromonas salmonicidae. Процент зараженности фурункулезом составил 56.8%. В целях оздоровительных мероприятий по борьбе с фурункулезом был применен ряд ветеринарных препаратов, наибольшей эффективностью отличался препарат “Antibak-100”. Этот препарат был испытан и внедрен в форелевых хозяйствах Азербайджана.

Keywords: trout, Causative Agent, Furunculosis, Prevalence Rate, Antibacterial Drug

Ключевые слова: форелевые рыбы, Возбудитель, Фурункулез, Зараженность, Антибактериальный препарат

Introduction

Fish are susceptible to various diseases like other living beings. Although the negative impact of diseases that may be recorded among fish inhabiting natural water basins is not strongly felt. This effect is much more pronounced in pond-based commercial fishery farms. Fish that contract diseases experience stunted growth, disruption of reproductive organ functions, deterioration of meat quality to an unfit state, and, in some cases, mass mortality [9, 5, 3, 8]. Therefore, one of the most critical issues in the effective organization and development of commercial pond-based fishery farms is to recognize the symptoms of common fish diseases, understand their causes and the biological characteristics of the pathogens, and implement timely and effective control measures against these diseases. Developing the country's fishing industry is essential to meet the demand for fish meat and its various products. At the same time, the timely detection of infectious and invasive diseases that seriously hinder the development of fisheries, as well as the development and implementation of a system of comprehensive control measures against them, is of particular significance [9, 4].

Bacterial Diseases of Fish

Bacterial diseases of fish are hazardous because controlling them in an aquatic environment is very difficult. The technological conditions of fish reproduction, the degree of intensification processes, and the overall level of fish farming culture during each biotechnological cycle of cultivation and maintenance significantly impact the manifestation and course of bacterial diseases [5].

Among fish raised in natural fishing reservoirs, the most dangerous bacterial pathogens affecting species such as trout and sturgeon include Aeromonas, Pseudomonas, Vibrio, Chondrococcus, Mycobacterium, and others. However, aeromonosis in fish holds the most significant practical significance, see Fig. 1. (A, B, C).

Figure 1. Diseases and causative agents in trout infected with different species of aeromonosis. A. Aeromonosis, Aeromonas hydrophila; B. Pseudomonosis, Pseudomonas fluorescens; C. Vibriosis, Vibrio anguillarum

Furunculosis in Salmonids

Clinical Symptoms and Pathogenesis

This disease induces hematological disorders in the bloodstream of the fish. Infected fish commonly exhibit open wounds at the base of the dorsal and abdominal fins. Furunculosis occurs in two stages, although sometimes a mixed stage can be observed. In the muscle stage, trophic ulcers form, and large, hard or soft furuncles appear on the body surface. The interior of the swelling is filled with blood, pus, and large quantities of bacteria. When the swelling matures, it ruptures and deep ulcers form in its place [6].

Etiology

The causative agent of the disease is a bacterium called Aeromonas salmonicida, measuring 0.8–0.5 micrometres. Furunculosis in salmonids is an infectious disease characterised by the formation of abscesses in the muscle tissue, their rupture leading to red ulcers, significant changes in internal organs, the rapid development of pathological processes, and mass mortality among fish. This bacterium is found in water and silt. Limited water pollution and the decay of plant matter contribute to its persistence and even proliferation [6].

Epizootic Data.

All studies were conducted at the Chaykend salmon hatchery, Zagatala rainbow trout hatchery, Sheki Kirkhbulak trout hatchery, and the Goranboy "Agdja" trout hatchery. The contamination of water with organic matter is one of the main factors contributing to the emergence of the disease in natural water reservoirs [9].

Clinical Symptoms and Pathological Changes in Anatomy in Bacterial Diseases of Trout

Pathological anatomical changes include spotting in the liver and reddened abdominal area. During the progression of the disease, a hemorrhagic inflammatory process develops between the epidermis and dermis, and central trophic ulcers are observed as a result of tissue degradation (Fig. 2, A, B) [6].

Figure 2. Trout infected with the disease caused by Aeromonas salmonicida

Control and Prevention Measures

As a result of scientific research, a preparation called “Antibak-100” was proposed by us for prevention and treatment against bacteria causing aeromonosis in trout (Aeromonas salmonicida, A. hydrophila, Pseudomonas fluorescens, Vibrio anguillarum). The antibacterial efficacy of this preparation was tested under farm conditions [7]. The drug was used according to a specific scheme: 0.5–1 g per 1 kg of live fish weight was mixed into the feed and administered to the fish, achieving 100% treatment effectiveness against the disease. The results obtained under laboratory conditions indicated the need for further application under broader farming conditions. For this purpose, research and trial experiments were conducted at the “Agca Trout” farm in the Goranboy district.

In other experiments conducted to determine the effectiveness of Antibak-100, a total of 73 trout were separately caught from each of two different channels of the same farm and underwent bacteriological examination. Therefore, 29 of the 73 trout (39.7%) seen from the first channel and 33 trout (45.2%) from the second channel were infected by furunculosis. The fish in the first channel were treated with Antibak-100 at a dosage of 0.5–1 g per kg of live weight (once daily for 5 days), and the fish were kept in test ponds with a water temperature of 26°C. The fish from the second channel were kept as a control group.

On the 10th day of the experiment, 52 fish from the first channel and 43 from the control channel were examined. The fish treated with Antibak-100 achieved a 100% therapeutic effect [9]. In the control group, the infection rate remained unchanged [2, 1].

Conclusion

After reviewing and analyzing the above findings and conducting production trials of the Antibak-100 preparation, we reached the following conclusions:

— Under farm conditions, Antibak-100, administered at 0.5–1 g per kg of live trout, demonstrated 100% therapeutic effectiveness against Aeromonas salmonicida.

— This antibacterial drug must be used on a larger scale in trout farms to combat Aeromonas salmonicida infections.