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Morphological changes in silver carp internal organs as their death diagnostic criteria

Parasitological research revealed the fish gills infestatation with Sinergasilus lieni parasitic crustaceans and the eyeballs infestation with Diplostomum spathaceum trematodes larvae.

Extensiveness of silver carp invasion by synergasilosis dyplostomosis pathogens was 100 %, with synergasilus invasion intensivity ranged from 4 to 10 units with an average one of 6.8±0.59 units. Dyplostomum larvae infestation ranged from 3 to 11 units with an average invasion intensity of 7.4±0.57 units per fish.

Autopsy studies of the live and dead fish bodies found out the liver enlargement with its faded texture. The liver could torn easily, its both external and internal color was uneven and ranged from light brown to gray-brown to gray in some places. The color of the liver was yellowish in some samples and the abdominal wall in these samples were of slightly yellow color, the abdominal wall tissue got light yellow. Gallbladder in all the fish was enlarged and contained dark green bile liquid.

Histological examination of internal organs revealed significant structural changes. Much of the renal tubules underwent their substitution with young connective tissue cells (diffuse interstitial nephritis).

The majority of epithelial tubules were in a state of muddy swelling and granular dystrophy. The tubular lumen contained a small amount of oxyphilic protein mass.

Mild congestive hyperemia was revealed in the liver parenchyma. Nearly all hepatocytes were in a state of granular dystrophy of varying intensity.

Physical and chemical analysis of water from the pond was made on the basis of the revealed morphological changes in the studied internal organs of fish.

Most water indicators were within the acceptable standards, although their chromaticity, alkalinity and chlorides content exceeded the standards. The rise of indicators listed in the first study could be caused by the possible arrival of flood water  from the fields into the pond.

While determining the total microbial contamination of water we found out that the quantity of the latter amounted to 1636.6 CFU/cm3. The content of the Escherichia coli bacteria made the average of 92.6 CFU/cm3. The amount of therrmostable intestinal bacteria were within 3 CFU/cm3.

It was found out that the studied silver carp fish were 100 % infected with parasitic S. lieni crustaceans and D. spathaceum trematode larvae on the average invasion intensity of 6.8±0.59 and 7.4±0.57 parasites per fish.

Histological examination indicates durable fish intoxication by toxic substances in small concentrations that were flowing into the pond with sewage water from the field for a long time, which resulted in the fish immunodeficient condition, cirrhotic changes in the kidneys and liver granular dystrophy.

Increased alkalinity of water and increased chloride content is evidence of toxic substances entrance to the pond with floodwater, or due to natural state of water. We believe that the pond water quality must be subjected to a monitoring assessment all year long.

Key words: fish, silver carp, synergasilosis, dyplostomosis, invasion intensity, extensiveness of invasion, mortem, histology, water, chemical composition, liver, spleen, kidneys.

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