Introduction
Climate change-induced water scarcity is increasingly recognized as a major limiting factor for the sustainability of freshwater pond aquaculture (Boyd and Tucker, 2012). Reduced water availability, elevated summer temperatures, and intensified eutrophication pressure threaten the productivity of traditional carp farming systems across Europe. In pond aquaculture, management interventions that improve oxygen dynamics and ecological buffering capacity are becoming essential to maintain production while minimizing environmental deterioration.
Water depth and aeration are two critical management tools that may mitigate climate-associated production risks. Increased pond depth can stabilize thermal regimes, dilute nutrient concentrations, and improve dissolved oxygen profiles, while supplemental aeration can reduce hypoxia-induced physiological stress (Stone et al., 2014). However, their combined effects on fish growth, water chemistry, stress physiology, and disease dynamics remain insufficiently quantified under commercial semi-intensive carp farming conditions.
This study evaluated the main and interactive effects of pond depth (1 vs. 1.5 m) and aeration regime (nighttime vs. nighttime + daytime aeration) on production performance, water quality, glucose-based stress response, and fish health during the first production season of juvenile common carp.
Materials and Methods
A 2×2 factorial design with two replicates per treatment was conducted over 90 days in eight experimental ponds (470 m2 each) at HAKI, Hungary. Treatments included: Water depth: 1 m vs. 1.5 m; Aeration: nighttime only (22:00–10:00) vs. nighttime + 2 h daytime aeration (14:00–16:00). Each pond was stocked with 1260 common carp juveniles and fed standardized commercial diets. Production metrics included total biomass, survival, feed conversion ratio (FCR), specific growth rate (SGR), and final body weight. Environmental parameters included dissolved oxygen (DO), temperature, turbidity, total nitrogen (TN), total phosphorus (TP), chlorophyll a, cyanobacteria, and nutrient ratios. Fish welfare assessments included parasitological and pathological monitoring, while physiological stress was evaluated through plasma glucose and cortisol measurements. Statistical analyses were performed using MANOVA, with significance accepted at p < 0.05.
Results and Discussion
Water depth had a highly significant effect on multiple production and environmental parameters. Ponds maintained at 1.5 m depth achieved substantially higher final biomass (mean 252.5 kg vs. 149.1 kg), survival (66.3% vs. 45.1%), and SGR (5.75 vs. 5.15) compared to shallow ponds (p = 0.01, p = 0.01, and p = 0.03, respectively). Deeper ponds also maintained significantly higher dissolved oxygen concentrations (p < 0.001), lower turbidity (p = 0.02), reduced total nitrogen (p = 0.04), and total phosphorus (p = 0.05), confirming improved ecological stability.
These findings align with previous observations that greater water volume buffers environmental fluctuations and reduces eutrophication risk in pond systems (Boyd, 2020).
Aeration regime showed less pronounced direct effects on growth performance; however, additional daytime aeration significantly reduced fish plasma glucose concentrations (59.4 mg/dL vs. 67.9 mg/dL; p = 0.013), suggesting lower chronic stress exposure. This reduction in glucose indicates improved physiological welfare under enhanced oxygenation, even where biomass gains were not significantly altered. Aeration also significantly influenced TN/TP ratios (p = 0.04), reflecting shifts in nutrient cycling and primary productivity.
Importantly, no statistically significant depth × aeration interactions were observed for major production indicators such as biomass (p = 0.23), survival (p = 0.12), or SGR (p = 0.38), indicating that pond depth was the dominant production driver. Nevertheless, combined deeper-water and enhanced-aeration systems consistently produced the numerically best outcomes, suggesting additive practical benefits.
Fish health surveillance revealed recurrent parasitic and bacterial challenges, including Dactylogyrus spp., Trichodina spp., Aeromonas salmonicida - associated erythrodermatitis, and severe Bothriocephalus acheilognathi infestations with 100% prevalence during peak infection periods. While disease pressure affected all treatment groups, deeper ponds with improved environmental parameters demonstrated better overall resilience and production recovery. The integration of environmental engineering strategies with proactive veterinary interventions appears increasingly essential for climate-resilient pond aquaculture.
Conclusion
This study demonstrates that successful common carp production remains achievable even under reduced water availability and in shallower ponds; however, maintaining greater water depth consistently yields superior production performance, survival, and environmental stability. In scenarios where water scarcity limits the pond's full capacity, maintaining the highest feasible water level is a crucial adaptive strategy to minimize productivity losses. Greater depth offered clear advantages in ecological buffering, water quality, and fish welfare, while supplemental aeration further contributed to reduced physiological stress. Although carp farming can persist under constrained water conditions, these findings highlight that sustaining deeper pond environments whenever possible substantially strengthens resilience, productivity, and long-term sustainability in climate-challenged aquaculture systems.
Acknowledgments: Supported by the AQUASERV TNA infrastructure access project PID36485.
References
Boyd, C. E., and Tucker, C. S. (2012). Pond aquaculture water quality management. Springer Science & Business Media.
Boyd, C. E. (2000). Water quality: an introduction. Springer Science & Business Media.
Stone, N. M., Shelton, J. L., Haggard, B. E., & Thomforde, H. K. (2013). Interpretation of water analysis reports for fish culture (p. 4606). Stoneville, Mississippi: Southern Regional Aquaculture Center.