Goncharov S. L

Дата канвертавання26.04.2016
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Goncharov S. L., Applicant, Head of the Department of Diagnosis and Fish Disease Control

(scientific adviser Doctor of Veterinary Sciences, Professor N. M. Soroka)

Mykolaiv Regional State Laboratory of Veterinary Medicine


Reviewer Doctor of Veterinary Sciences, Professor V. F. Galat

The distribution of metacercariae of trematodes Paracoenogonimus ovatus (Katsurada, 1914) in the muscle tissue of the population of freshwater fish, such as: roach (Rutilus rutilus), silver bream (Blicca bjoerkna), bream (Abramis brama), crucian (Carassius gibelio), rudd (Scardinius erythrophthalmus), pike (Esox lucius), pikeperch (Sander lucioperca). It is shown that the maximum number of metacercariae P. ovatus was localized in the dorsal muscles, namely near the dorsal fin and amounted to 41,3 % of the total number of identified parasites. The minimum number of indicators fluke metacercariae is observed in the anal fin – 2,1 %.

Keywords: Paracoenogonimus ovatus, metatserkriaе, lowparasitaemia, location.

Statement of the problem. A fishery is one of the most important sectors of livestock, which provides people with valuable dietary food. One of the factors hampering the development of the industry is invasive fish diseases. The impact of helminths on the fish population is due to many factors: the loss, violation of reproduction, delay in growth and development, reduced nutritional status, deterioration of commodity and palatability and others [4].

       Analysis of recent research and publications in which a solution of the problem was offered. Paracoenogonimosis – highly prevalent invasive disease of freshwater fish species of natural pond of Mykolaiv region, caused by the larvae (metacercaria) Paracoenogonimus ovatus (Katsurada, 1914), infesting muscle, gills, brain, liver, kidneys, gonads, the intestinal wall of carp, perch, pike, herring, sturgeon, gobies and some other species of fish [5–9].

Metacercaria P. ovatus are highly pathogenic for yearlings and can reach up to several thousand copies and present danger to mammals consuming infested fish [5, 8, 9].

The aim of the study was to investigate the distribution of metacercaria P. ovatus in muscle tissue of freshwater fish caught in a natural pond of Mykolaiv region.

Objectives: to describe the anatomical areas of predominant metacercaria localization in the body of freshwater fishes, the intermediate host of trematodes P. ovatus.

Materials and methods of the study. During 2012–2015, 35 freshwater fishes caught in rivers Southern Bug and Ingul were investigated. In carrying out their muscle tissue samples were chosen during the autopsy and studied by compressor method using compressor MIS-7. A fish autopsy was performed by conventional methods, particularly I. E. Byhovska-Pavlovska method (1985) and
V. E. Sudarikov method and others (2002) [1, 8]. The species belonging of metacercaria was determined by «Determiner of parasites of freshwater fishes in USSR fauna» (1987) Microscopy was performed using optical equipment: Trinocular microscope Micromed XS – 4130 and binocular stereoscopic microscope – Micromed XS – 6320. Larvae P. ovatus, which were at the stage metacercaria were found in muscle tissue of fish. To determine the quantitative indicators of fish infestation, the method of calculating the total metacercaria in certain areas of the muscle tissue of freshwater fish was used. Definition of areas was performed based on the principle of a division of 6 separate loci according to recommendations of V.Y. Linnik (Pic. 1) [6].

Picture 1. Areas of the body where the fish muscle tissue were taken for research

       Results and discussion. We determined the localization of metacercaria of Paracoenogonimus in roach (Rutilus rutilus), silver bream (Blicca bjoerkna), bream (Abramis brama), crucian (Carassius gibelio), rudd (Scardinius erythrophthalmus), pike (Esox lucius), pikeperch (Sander lucioperca). The majority of metacercaria were found in the superficial layers of muscle tissue at a depth of 2–5 mm. In the deeper layers, the number was much smaller. The maximum intensity of infestation was found in roach – 247 metacercaria, a minimum intensity of infestation was found in pikeperch – 17.

       The largest number of metacercaria, 41,3%, was observed in the area – 2, anatomically framed by cranial and caudal edges of dorsal fins dorsally and median line ventrally. Fewer metacercaria were present in area 1 – framed by occipital part of the cranium cranially, dorsal fin caudally and median line ventrally. Infestation index was 19,8 %. Area 3 was limited by caudal part of dorsal fin cranially, edges of tail fin caudally, median line ventrally. Infestation index was 17,1 %. The area, which was outlined by gill arch cranially, median line dorsally and an imaginary line that starts from the cranial edge of the dorsal fin caudally, was indicated as area 4. Infestation index there was not significant – 6,7 %. The area 5 was outlined by imaginary lines of cranial and caudal edges of the dorsal fin cranially and caudally, respectively, and by median line dorsally. Among areas from the lower part of a fish body, this area had the greatest infestation index – 13,4 %. The last area, number 6, was framed by an imaginary line that originates from the caudal edge of the dorsal fin cranially, the tail fin caudally, and the median line dorsally. This area had the lowest infestation index –1,7 % (see table).

Localization of metacercaria of trematodes P. ovatus by areas in the muscle tissue of freshwater fish (N = 35)

Area of muscle tissue







Average percent of mtc, %







          According to the findings of some researchers, cercariae of P. ovatus are inactive during host search and react only in contact with the fish, which they attach themselves by the abdominal cavity. Cercariae also penetrated through the cut fin of fish. Cercariae that penetrated the fish migrate throughout the muscle tissue of fish body [10].

 прямая со стрелкой 4прямая со стрелкой 15        Most common localization site of metacercaria P. ovatus is muscle tissue. Cercariae penetrating the body of the fish, have a significant mechanical impact on its body.

прямая со стрелкой 13прямая со стрелкой 16прямая со стрелкой 17

Picture 2. Hemorrhages in the muscle tissue of pike after penetration of cercariae P. ovatus
прямая со стрелкой 5прямая со стрелкой 6прямая со стрелкой 7прямая со стрелкой 11прямая со стрелкой 12прямая со стрелкой 18

               Picture 2. Hemorrhages in the muscle tissue of fish after penetration of cercariae P. ovatus

Previously, cercariae penetrate the body of fish through the skin, using the protrusion near an oral sucker. Rejects tail and quickly migrates into the muscle layer, injuring blood vessels towards migration and converted to metacercariae, leading to the emergence of petechial hemorrhages in the muscle tissue (Pic. 2, 3).

         For several days, cercariae are being covered with a thin hyaline membrane formed by secret released by cystogenic cells of larvae’s glands. Over time, hyaline capsule becomes more prominent and much thicker compared to other trematodes – 0,006 mm (Pic. 4).

       Encystation of metacercariae in the body of the fish ends in about the fifth day since the penetration of cercariae. At this time, metacercariae are about 0,4 mm long. Their body is filled transparent cells. In 10–14 days, a cyst is covered connective tissue sheath from the outside. Fully mature secondary excretory system is formed in three weeks. After four weeks, metamorphosis is finished and metacercariae becomes invasive. At this point, the abdominal sucker does not always have time to develop [2, 11].

          Thus, it was found, that the main commercial fish of rivers Southern Bug and Ingul were infested with trematodes – Paracoenogonimosis. Given that P. ovatus is a parasite of domestic and wild carnivores and may pose a potential risk to human when consumed uncooked fish, it is important to carry out a veterinary and sanitary examination and follow preventive measures.

Picture 2. Metacercariae P. ovatus from pike (10x8)

  Conclusion. An intensity of infestation ranged from 247 of metacercariae in roach to 17 in pikeperch. Muscle tissue of fish back was found to be a predominant localization site of metacercariae

P. ovatus. The largest number of larvae was found in the area of the dorsal fin – 41,3 %. The least affected area was located near the tail fin, 1,7 % of the total number of metacercariae counted in studied freshwater fishes.


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