Effects of Seasonal Variation on Fish Health and Water Quality

Abstract

Seasonal fluctuations in freshwater ecosystems strongly influence water quality and the physiological condition of fish populations. The present study was conducted to evaluate the effects of seasonal variation on fish health and selected water quality parameters in a freshwater reservoir over three distinct seasons: pre-monsoon, monsoon, and post-monsoon. Water samples were analyzed for temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), turbidity, and total dissolved solids (TDS), while fish specimens were examined for external lesions, parasitic infestations, fungal infections, and overall health status. The results demonstrated significant seasonal variations in water quality. Water temperature ranged from 24.8°C (post-monsoon) to 31.2°C (pre-monsoon), while pH remained within 7.2–8.3. Dissolved oxygen decreased to 4.7 mg/L during the monsoon and increased to 7.3 mg/L in the post-monsoon season. BOD varied between 2.4 and 4.6 mg/L, whereas COD ranged from 12.8 to 24.5 mg/L, with the highest values recorded during the monsoon owing to increased runoff and organic matter input. Turbidity increased markedly from 18.6 NTU in the pre-monsoon to 62.4 NTU during the monsoon. Examination of 180 fish specimens (60 per season) revealed disease prevalence of 15.0% in the pre-monsoon, 36.7% during the monsoon, and 18.3% in the post-monsoon. Parasitic infestations accounted for 48.5% of all recorded cases, followed by bacterial infections (31.8%) and fungal diseases (19.7%). Pearson correlation analysis indicated a significant negative relationship between dissolved oxygen and disease prevalence (r = ?0.79, p < 0.01) and a positive correlation between turbidity and disease incidence (r = 0.74, p < 0.01). The findings demonstrate that seasonal deterioration of water quality, particularly during the monsoon, adversely affects fish health and increases disease occurrence. Regular monitoring of water quality and timely management interventions are therefore essential for maintaining healthy freshwater fish populations and ensuring sustainable aquatic ecosystem management.

Introduction

Freshwater ecosystems are among the most productive yet vulnerable environments, supporting rich biodiversity and providing essential services such as fisheries, irrigation, drinking water, and ecosystem conservation. Fish are key indicators of aquatic ecosystem health, but their survival and productivity are strongly influenced by seasonal changes in water quality. Variations in rainfall, temperature, runoff, and hydrological conditions alter important physicochemical parameters such as water temperature, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), turbidity, and total dissolved solids (TDS). These changes directly affect fish metabolism, immunity, reproduction, and susceptibility to diseases.

The present study evaluates the impact of seasonal variation on water quality and fish health in a freshwater reservoir in Kaushambi District, Uttar Pradesh, between March 2024 and February 2025. The objectives were to assess seasonal changes in key water quality parameters, determine the prevalence of common fish diseases, and examine the relationship between environmental conditions and fish health to support sustainable fisheries management and freshwater conservation.

The literature review highlights that seasonal fluctuations significantly influence freshwater ecosystems by altering physicochemical characteristics, microbial diversity, and fish physiology. Previous studies have demonstrated that poor water quality, heavy metal contamination, elevated temperature, reduced dissolved oxygen, and increased organic pollution increase disease susceptibility in fish. Although many investigations have independently examined water quality, microbial contamination, or fish diseases, relatively few have integrated these factors into a comprehensive seasonal assessment under natural reservoir conditions.

The study employed a field-based observational design involving three sampling stations representing the inlet, central, and outlet regions of the reservoir. Monthly water samples were analyzed for temperature, pH, DO, BOD, COD, turbidity, and TDS using standard APHA procedures. A total of 180 freshwater fish belonging to Catla catla, Labeo rohita, and Cirrhinus mrigala were examined for external disease symptoms, including skin lesions, fin erosion, hemorrhages, gill discoloration, excessive mucus secretion, ulcers, and parasitic infestations. Statistical analyses included descriptive statistics, one-way ANOVA, Tukey's post hoc test, and Pearson's correlation analysis.

The results showed significant seasonal variation in water quality. During the monsoon season, turbidity, BOD, COD, and TDS reached their highest levels due to increased runoff and organic pollution, while dissolved oxygen declined to its lowest level (4.7 ± 0.4 mg/L). In contrast, the post-monsoon season exhibited the best water quality, with the highest dissolved oxygen (7.3 ± 0.3 mg/L) and the lowest BOD and COD values.

Fish health also varied seasonally. Of the 180 fish examined, 42 (23.3%) were diseased, with the highest disease prevalence occurring during the monsoon (36.7%), compared to 15.0% in the pre-monsoon and 18.3% in the post-monsoon season. Common clinical signs included skin ulcers, hemorrhagic lesions, fin erosion, pale gills, excessive mucus secretion, abnormal swimming behavior, and parasitic infestations. Among the recorded diseases, parasitic infections (47.6%) were most common, followed by bacterial infections (31.0%) and fungal infections (21.4%).

Correlation analysis revealed significant relationships between water quality and fish disease prevalence. Disease occurrence showed a strong negative correlation with dissolved oxygen (r = –0.79), indicating that lower oxygen levels were associated with higher disease incidence. Significant positive correlations were observed with turbidity (r = 0.74), BOD (r = 0.69), COD (r = 0.66), TDS (r = 0.58), and temperature (r = 0.53), while pH had only a weak association.

Conclusion

The present study clearly demonstrates that seasonal variation exerts a significant influence on both water quality and fish health in the freshwater bodies of Kaushambi District, Uttar Pradesh. Marked fluctuations in physicochemical parameters, particularly dissolved oxygen, turbidity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total dissolved solids (TDS), were observed across the three seasons. Among them, the monsoon season showed the greatest deterioration in water quality due to increased surface runoff, sediment deposition, and organic matter input. These environmental changes created unfavourable conditions for fish survival and were associated with the highest incidence of bacterial, fungal, and parasitic diseases. The study revealed a strong negative relationship between dissolved oxygen and disease prevalence, while turbidity, BOD, and COD exhibited positive correlations with fish disease occurrence. These findings indicate that deterioration in water quality weakens fish immunity and increases their susceptibility to infections. Conversely, the post-monsoon season showed relatively improved water quality, accompanied by a reduction in disease prevalence, highlighting the importance of favourable environmental conditions for maintaining healthy fish populations. The results emphasize that seasonal monitoring of physicochemical parameters and fish health should be an integral component of freshwater ecosystem management. Regular assessment can provide early warning of environmental degradation and facilitate timely interventions to minimize disease outbreaks and sustain fish production. Measures such as controlling agricultural runoff, reducing domestic waste discharge, maintaining riparian vegetation, and implementing scientific water quality management practices are essential for protecting freshwater resources. Overall, the study provides valuable baseline information for fisheries managers, environmental agencies, and policymakers, contributing to the sustainable conservation and management of freshwater ecosystems in Kaushambi District and other similar regions of India under changing climatic and anthropogenic conditions.

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Copyright

Copyright © 2026 Ishant Kumar Soni, Mahendra Kumar Upadhyay. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.