# CYPOR Variability as a Biomarker of Environmental Conditions in Bream (Abramis brama), Roach (Rutilus rutilus), Perch (Perca flavescens), and Pike-Perch (Sander lucioperca) from Lake Ladoga

## TL;DR

This study shows that the CYPOR enzyme in fish livers can detect pollution in Lake Ladoga, helping monitor environmental health.

## Contribution

The study introduces CYPOR as a novel biomarker for assessing environmental stress in fish.

## Key findings

- CYPOR levels in fish livers were significantly higher in polluted areas compared to healthy fish.
- Fish from polluted areas showed liver damage and antibiotic-resistant bacteria.
- The study proposes an integrated method for assessing aquatic ecosystem health.

## Abstract

Fish are valuable indicators of aquatic ecosystem health because their physiological condition reflects the quality of their habitat. The liver is particularly important, as it is responsible for detoxifying harmful substances and therefore responds sensitively to pollution. This study investigated how the ecological condition of the littoral zones of Lake Ladoga influences fish health. Forty fish belonging to the carp and perch families were collected from twelve coastal sites. Water quality was assessed, and hematological, bacteriological, and histological examinations of the fish were conducted to evaluate their health status. The results revealed that the coastal areas of Lake Ladoga are exposed to significant pollution. Although the bacterial species isolated from the fish were typical for healthy individuals, many showed resistance to several antibiotics, which is a matter of concern. The blood tests indicated structural abnormalities in red blood cells, and liver tissue showed changes consistent with toxic damage. In fish from polluted areas, the level of a key liver enzyme (CYPOR) involved in detoxification was markedly higher than in healthy fish. These findings suggest that CYPOR can serve as a sensitive biomarker for environmental stress, supporting more effective monitoring of aquatic ecosystems.

The fish liver, as the main detoxification organ, is highly susceptible to xenobiotic exposure, often resulting in various hepatopathies. The cytochrome P450 system plays a central role in xenobiotic metabolism, with cytochrome P450 reductase (CYPOR) supplying the electrons required for CYP enzyme activity. This study aimed to evaluate the relationship between the ecological state of a reservoir and fish health, including CYPOR levels, through hematological, bacteriological, and histological analyses. Samples of water and fish were collected from 12 littoral sites of Lake Ladoga. A total of 1360 specimens of fish from carp (Cyprinidae) and perch (Percidae) families were examined. For histological examination and CYPOR level determination, we selected 40 specimens using a blind randomization method. This sample size was sufficient for statistical analyses. Hematological smears were stained with azure eosin; bacteriological cultures were grown on multiple media; liver samples were stained with hematoxylin and eosin and Sudan III. CYPOR levels in liver homogenates were measured by ELISA-test. Physical and hydrochemical analyses indicated a high pollution level in the littoral zones. Isolated bacterial species were non-pathogenic but exhibited broad antibiotic resistance. Hematological evaluation revealed erythrocyte vacuolization and anisocytosis. Histological analysis showed marked fatty degeneration in hepatocytes, indicating toxic damage. CYPOR concentrations ranged from 0.3–0.4 ng/mL in healthy fish to 5–6 ng/mL in exposed specimens, showing strong correlation between environmental influence and enzyme activity. These findings demonstrate the potential of CYPOR as a sensitive biomarker for biomonitoring programs. The integrated methodological approach provides a model for assessing aquatic ecosystem health and identifying zones requiring priority remediation.