1. Abstract

In modern facility-based aquaculture and recirculating aquaculture systems (RAS), the rearing tank serves as the core production unit. The tank's geometric configuration directly determines the facility’s space utilization, the hydrodynamic characteristics of water flow, the system’s self-cleaning efficiency, and feed conversion rates and final yield. Currently, the mainstream RAS pond configurations include circular ponds, octagonal ponds, D-end ponds, square-cornered round-bottom ponds, and raceway ponds, all of which exhibit significant differences in aquaculture performance compared to traditional earthen ponds. Today, we officially release the *Comparative Assessment Report on Hydrodynamics and Production Efficiency of Modern Aquaculture Tank Designs*. Based on actual aquaculture trial data, this study systematically examines five key performance metrics — weight gain rate, feed conversion ratio (FCR), survival rate, annual yield, and economic benefits — to comprehensively compare the performance of these six tank designs, providing industry professionals with a scientific basis for selecting the most suitable design.

2. Overview of Six Types of Aquaculture Ponds

Figure 1: Overview of Schematic Diagrams of Different Types of Aquaculture Ponds

Table 1: Detailed Description of Different Types of Aquaculture Ponds

3. Comparison of Farming Performance

We compared five aspects of farming performance: weight gain rate, feed conversion ratio (FCR), survival rate, comprehensive performance evaluation, and annual yield and economic benefits. Since the farming cycle for shrimp is shorter than that for fish, and 90 days coincides with a complete shrimp farming cycle, we used a 90-day shrimp farming cycle as an example for the weight gain rate.

3.1 Weight Gain Rate

The weight gain rate is a key indicator for measuring aquaculture performance. In a 90-day shrimp farming trial, significant differences in weight gain were observed among different pond types.

Figure 2: Comparison of Weight Gain Rates in Shrimp Across Different Pond Types (90-Day Trial)

Table 2: Growth Trends and Rankings by Pool Type

The circular pond ranked first with an average daily weight gain of 28.5 g and an SGR of 4.2% per day, which is 70% higher than that of traditional earthen ponds. This is primarily due to the superior aquatic environment created by the uniform, rotating water flow in the circular pond and its highly efficient removal of uneaten feed and feces.

3.2 Feed Conversion Ratio (FCR)

Feed costs account for 50%-60% of total aquaculture costs, and the feed conversion ratio (FCR) directly determines the economic profitability of aquaculture. There are significant differences in FCR among different pond types.

Figure 3: Comparison of Feed Conversion Ratios for Shrimp and Fish in Different Pond Types

Table 3: Comparison of Feed Conversion Ratios and Feed Waste Rates for Shrimp and Fish in Different Pond Types

The FCR for prawns in circular ponds is just 1.15, a 36 per cent reduction compared to the 1.80 recorded in traditional earthen ponds. Based on a feed cost of US$1.20 per kilogramme of prawn feed, circular ponds save US$770 in feed costs for every 1,000 kg of prawns produced.

3.3 Survival Rate

Figure 4: Comparison of survival rates of prawns and fish in different pond types

Table 4: Comparison of survival rates and causes of mortality in prawns and fish across different pond types

The survival rate of shrimp in circular ponds is 92 per cent, which is 24 percentage points higher than the 68 per cent recorded in traditional earthen ponds. This high survival rate is primarily attributable to: strong self-cleaning capabilities, with no dead zones where debris accumulates; uniform and stable water quality, which reduces stress; and a closed environment, which lowers the risk of disease.

3.4 Six-dimensional comprehensive performance evaluation.

Figure 5: Comparison of the overall performance of six types of pool-type radars

A comprehensive assessment was carried out across six dimensions: self-cleaning, uniformity of water flow, space utilisation, stocking density, ease of harvest and construction costs.

Table 5: Comprehensive Comparison of Six Pond Types

The octagonal tank scored slightly higher than the circular tank, with an overall score of 8.3 compared to 8.2, with its main advantage being greater space utilisation. However, the circular tank remains the optimal choice in terms of self-cleaning and uniform water flow. For high-density RAS aquaculture, the circular tank remains the preferred option; for projects with limited space within the facility, the octagonal tank is the best alternative.

3.5 Annual Output and Economic Benefits

Figure 6: Comparison of annual output and net profit across different pond types (shrimp RAS)

Table 6: Annual Output, Production Batches, Net Profit and Payback Period for Different Pool Types

Circular ponds can generate an annual net profit of US$15-18 per square metre, which is 6-10 times that of traditional earthen ponds. Although the initial investment in circular ponds is higher, the investment can be recouped within 2–3 years, after which they continue to generate substantial profits.

4. Recommendations for selecting aquaculture ponds

Finally, with regard to selecting pond types for different scenarios, we offer the following recommendations:

Table 7: Selection of pool types for different scenarios

5. Frequently Asked Questions (FAQ)

Q1: Which should I choose: a circular pond or an octagonal pond?

A: If there is sufficient space available, a circular pond is the preferred choice—it offers the best self-cleaning and water flow performance. If a compact layout is required within a factory building, an octagonal pond is the best alternative — its straight sides facilitate installation against walls and joining of panels, and its overall performance is only 5–10 per cent lower than that of a circular pond.

Q2: Why are raceway tanks unsuitable for high-density shrimp farming?

A: The unidirectional flow design of raceway tanks results in a water quality gradient (differences in dissolved oxygen and ammonia-nitrogen concentrations) between the inlet and outlet ends. Furthermore, there are numerous dead zones in the water flow, and debris tends to accumulate on the tank floor. Shrimp are highly sensitive to substrate quality; the accumulation of debris can lead to substrate degradation and disease outbreaks. Raceway ponds are better suited to fish farming, particularly in medium-density semi-recirculating aquaculture systems.

Q3: Can traditional earthen ponds be converted into RAS circular ponds?

A: Earthen ponds cannot be directly converted into RAS circular ponds, but the following options are available: (1) Construct a greenhouse over the earthen pond and build a new RAS circular pond cluster inside it; (2) Use the earthen pond as a storage pond or ecological treatment pond in conjunction with the newly built RAS system.

Q4: Should PP panels or fibreglass be used for the rearing tanks?

A: PP panels are lower in cost, flexible to process, and easy to weld, making them suitable for most RAS projects, with a service life of 15-20 years. Fibreglass offers higher strength and better resistance to ageing, making it suitable for long-term, high-intensity use or outdoor applications. Choose fibreglass if the budget allows; opt for PP panels if value for money is a priority.

6. Conclusion

There are significant differences in farming outcomes between different pond types. Circular ponds lead across the board in key indicators such as weight gain rate, feed conversion ratio, survival rate, and economic returns, making them the preferred choice for high-density RAS farming. Octagonal ponds are the best choice for indoor facilities because they use space more efficiently. Runway ponds still offer cost advantages in medium-density scenarios. Selecting the appropriate pond type is the first step towards the success of an RAS project and a key factor in determining return on investment.

If you are planning an aquaculture facility or require professional advice on selecting a tank configuration, please do not hesitate to contact us for a bespoke solution tailored to your specific requirements.