Seasonal Water Quality Dynamics in Semi-Intensive Carp Ponds

Last Updated: December 7, 2025
Estimated reading time: 7 minutes

Managing seasonal water quality is the most dynamic challenge in aquaculture, as the physico-chemical environment of a pond shifts dramatically from summer highs to winter lows. Search intent: explain / apply the principles of limnology to manage carp growth across a full calendar year. This post dissects the twelve-month dataset of a composite culture system, revealing how seasonal drivers dictate biological productivity.

Key Takeaways:

• Thermal Control: Water temperature ranged from 12.96°C to 34.37°C, acting as the master switch for fish metabolism and bacterial decomposition.
• Oxygen Paradox: Dissolved Oxygen (DO) was highest in winter (February) due to solubility laws, despite biological production being lower.
• pH Fluctuations: The pH peaked at 9.15 in January, indicating significant shifts in the carbonate-bicarbonate buffer system during colder months.
• Nutrient Accumulation: Nitrates accumulated during colder months (November-January) when biological uptake by plankton and fish was minimal.

The Thermal Master Switch

Fish are poikilothermic (cold-blooded) animals; their entire metabolic engine is revved or throttled by the surrounding water temperature. The thesis provided a comprehensive year-long profile of the pond temperatures, which served as the primary independent variable affecting all other biological processes.

“Significantly lowest water temperature (12.96±0.84) was observed during the month of January… Seasonal fluctuations in the temperature of water significantly influenced the fish growth.” (Zeb, 2016, p. 86)

The data shows a distinct “growth season” and “dormant season.” In months like October (34.37°C) and June (33.34°C), the high temperatures accelerated the decomposition of the poultry manure fertilizer, releasing nutrients rapidly.

This supported high plankton density and rapid fish growth. However, in January, the temperature dropped to ~13°C. At this temperature, the enzymatic activity in Indian Major Carps (Rohu, Catla, Mrigal) slows drastically. Feed consumption drops, and growth halts, regardless of how much food is available.

Student Note: The Optimum Temperature Range for warm-water carps is typically 25–30°C. In this study, deviations below this range (Nov-Feb) caused immediate cessation of significant biomass accumulation.

Professor’s Insight: Farmers must realize that applying fertilizer in January is essentially “banking” pollution; the bacteria cannot process it, and the fish cannot utilize the resulting plankton, leading to sludge buildup.

Month	Temp (°C)	Dissolved Oxygen (mg/L)	Growth Status
October	34.37	8.42	Peak Metabolism
January	12.96	9.56	Metabolic Stasis
February	15.40	9.74	Slow Recovery
May	29.02	8.51	Optimal Growth
Fig: Inverse relationship between Temperature and Dissolved Oxygen across seasons (Zeb, 2016, Appendix Tables).

Dissolved Oxygen and Solubility Laws

One of the most critical variables for aquatic life is Dissolved Oxygen (DO). The study highlights a classic limnological principle: the solubility of gases decreases as water temperature increases. Consequently, the “best” oxygen levels were recorded during the months with the “worst” growth.

“Significantly highest mean value of dissolved oxygen was observed during the month of February (9.74±0.11mgL-1) that was non-significantly different from that of in January.” (Zeb, 2016, p. 86)

During the hot months (June-August), DO levels hovered around 8.0–8.3 mg/L. While this is sufficient for carp, it is dangerously close to stress levels if a bloom crash occurs, considering the high biological oxygen demand (BOD) from the decomposing manure.

In winter, despite the lack of intense photosynthesis, the cold water naturally held more oxygen (up to 9.74 mg/L). This provides a safety buffer during the winter, but it is metabolically useless because the fish are dormant.

Student Note: Solubility is a physical property. Even if photosynthesis is zero, cold water can hold more oxygen via diffusion from the atmosphere than warm water can hold during a plankton bloom.

Professor’s Insight: The danger zone is late summer nights; high water temperatures reduce oxygen capacity, while peak bacterial respiration (processing the manure) consumes what little oxygen is available.

pH and Alkalinity Cycles

The pH of the pond water is a reflection of the carbon cycle. In this study, the pH remained alkaline throughout the year (range 8.27–9.15), which is ideal for carp culture. However, the peak in alkalinity and pH during winter months offers insight into the chemical buffering capacity of the system.

“The average pH value was found to be significantly highest during the month of January (9.15±0.11) whereas it was the lowest in August (8.27±0.12).” (Zeb, 2016, p. 86)

In summer, high respiration rates from bacteria and fish produce CO2. When CO2 dissolves in water, it forms carbonic acid, which naturally lowers the pH. This explains the lower pH values in August. In winter, respiration rates plummet.

With less CO2 being pumped into the system by biological activity, the equilibrium shifts, and the pH rises. The study also noted that Total Alkalinity was significantly affected by season, acting as a buffer that prevented lethal pH swings despite the heavy organic loading.

Student Note: A pH range of 7.5 to 8.5 is considered optimal. A value of 9.15 (January) is high but tolerable for carps; however, it increases the toxicity of ammonia, which is a risk factor even in cold water.

Professor’s Insight: If pH consistently exceeds 9.0 in the afternoon, it indicates excessive phytoplankton photosynthesis removing all free CO2; this can lead to ammonia toxicity spikes.

Nutrient Dynamics: Nitrates and Phosphates

The availability of nutrients determines the carrying capacity of the semi-intensive pond. The study tracked Nitrates and Total Phosphates, identifying them as limiting factors for plankton growth.

“The mean nitrate concentration was significantly higher during the month of November (2.69±0.15mgL-1) whereas the same was significantly lowest (1.37±0.19mgL-1) during March.” (Zeb, 2016, p. 102)

This trend illustrates the concept of “Nutrient Uptake.” In March, as temperatures rise and the spring plankton bloom begins, the plankton rapidly consume the available nitrates, driving the concentration in the water down. In November, as the bloom dies off and growth stops, nitrates accumulate in the water column because they are not being utilized. This seasonality confirms that the biological engine of the pond turns on and off with the sun.

Student Note: Phosphates are often the primary limiting nutrient in freshwater; the study found non-significant differences in phosphate levels between treatments, suggesting it was used up as fast as it was added (rapid turnover).

Reviewed and edited by the Professor of Zoology editorial team. Except for direct thesis quotes, all content is original work prepared for educational purposes.

Real-Life Applications

1. Winter Maintenance: Since fish metabolism and bacterial decomposition halt in January (12.96°C), farmers should stop organic fertilization. Adding manure in winter creates a “time bomb” of sludge that releases toxic gases when the water warms in spring.
2. Summer Aeration: In months like October (34.37°C), the capacity of water to hold oxygen is low, but fish oxygen demand is at its peak. Mechanical aeration is most critical during these hot months to prevent suffocation.
3. Stocking Calendars: Understanding that growth is minimal from November to February allows farmers to plan stocking. Fingerlings stocked in March will hit the ground running, maximizing the growth season.
4. pH Management: If pH climbs too high (>9.0) in winter, farmers should be wary of adding any nitrogen source that could convert to toxic un-ionized ammonia.
5. Productivity Prediction: By measuring temperature, a farmer can predict the NCR (Nitrogen Conversion Ratio). If the temp is <20°C, feed efficiency will be poor; if 28-30°C, efficiency will be maximal.

Why this matters: Aligning farm management activities (feeding, fertilizing, harvesting) with the natural seasonal rhythm of the water body prevents waste and maximizes biological performance.

Key Takeaways

• Temperature Dominance: Every aspect of the pond—from chemistry to fish growth—is enslaved by the seasonal temperature curve.
• The Winter Trap: High dissolved oxygen in winter gives a false sense of security; the ecosystem is actually stagnant, and pollutants (nitrates) are accumulating.
• The Summer Risk: High temperatures drive growth but jeopardize safety due to low oxygen solubility; this is the high-risk/high-reward season.
• Biological Uptake: Nutrient levels (Nitrates/Phosphates) are lowest when productivity is highest, proving that the ecosystem is efficiently converting chemicals into biology.
• Alkaline Buffering: The system maintained a healthy alkaline pH (above 8.0) year-round, proving that poultry manure, when applied correctly, supports a stable chemical environment.
• Predictable Cycles: These seasonal patterns are repetitive; farmers can create rigid annual schedules for inputs based on these predictable limnological shifts.

MCQs

1. During which month was the water temperature recorded as the lowest?
A) December
B) January
C) February
D) November
Correct: B
Explanation: The study recorded the lowest mean temperature of 12.96°C in January, coinciding with the period of halted fish growth.

2. Why was the pH of the pond water highest in January (9.15)?
A) High rates of bacterial decomposition.
B) Maximum fish respiration.
C) Reduced biological production of CO2.
D) Application of lime.
Correct: C
Explanation: In winter, respiration by fish and bacteria (which produces CO2 and acidifies water) is minimal. This lack of CO2 production shifts the carbonate equilibrium, raising the pH.

3. What happens to nitrate levels in the pond during the spring bloom (March)?
A) They increase significantly.
B) They remain constant.
C) They decrease significantly.
D) They become toxic.
Correct: C
Explanation: As the plankton bloom initiates in the warming spring water, they rapidly uptake available nutrients, causing the nitrate concentration in the water column to drop.

FAQs

Q: Can I feed my carp in the winter?
A: You can, but it is economically inefficient. The study showed that in January (12.96°C), the Nitrogen Conversion Ratio was very poor (1:0.68), meaning inputs were not converting to flesh. Maintenance feeding is the most you should do.

Q: Why is high dissolved oxygen in winter not beneficial for growth?
A: Oxygen is necessary for metabolism, but temperature determines the rate of metabolism. Even with abundant oxygen, the enzymes driving digestion and muscle building cannot function efficiently at low temperatures.

Q: Does poultry manure lower the pH of the pond?
A: Initially, decomposition releases CO2 which can lower pH. However, the study shows the ponds remained alkaline (pH > 8.0). This suggests the buffering capacity (Alkalinity) of the water was sufficient to counteract the acidity from decomposition.

Q: What is the significance of Electrical Conductivity (EC) in this study?
A: EC measures dissolved salts. It fluctuated seasonally but generally tracked with nutrient loading. It is a good proxy for the total nutrient load available in the water column for plankton.

Lab / Practical Note

Sampling Time: The thesis specifies that water samples were collected on a fortnightly basis. For consistent Seasonal Water Quality data, samples must be taken at the same time of day (e.g., 8:00 AM – 10:00 AM) to account for the diurnal flux of oxygen and pH driven by sunlight and photosynthesis. Comparing an 8 AM sample from June with a 4 PM sample from January would yield invalid results.

External Resources

• Water quality management in aquaculture (FAO)
• Temperature effects on fish metabolism (ScienceDirect)

Sources & Citations

Thesis Citation:
Zeb, J. (2016). Optimization of protein level in supplementary feeds for fish rearing under semi-intensive composite pond culture systems (Doctoral dissertation). Department of Zoology, Wildlife and Fisheries, University of Agriculture, Faisalabad. Pages 1-162.

Note on Content: Monthly physico-chemical data (Temp, pH, DO, Nitrates, etc.) were sourced directly from Appendix Tables 35-50 and the Results section (pp. 85-106).

Invitation: If you are the author of this thesis and wish to provide updates or corrections, please contact us at contact@professorofzoology.com.

Author Box
Jhan Zeb holds a PhD in Zoology from the University of Agriculture, Faisalabad. His research provides a detailed chronological analysis of pond ecology, linking environmental variables to commercial fish production.

Reviewer: Abubakar Siddiq

Note: This summary was assisted by AI and verified by a human editor.