Pond ecological recirculating aquaculture, commonly known as "raceway fish" farming, is a high-density aquaculture model that involves constructing water channels to divide the pond into a fish farming zone and a water purification zone, utilizing mechanical equipment to promote water flow. Pei County, located by the shores of Weishan Lake with abundant water resources, is a natural site for freshwater aquaculture. The county has 40,900 mu of high-standard fish ponds, including 1,200 mu dedicated to pond ecological recirculating aquaculture, with a water channel area of 10,450 m². The main aquaculture species include largemouth bass, grass carp, and crucian carp, with an annual production of approximately 2,100 tons. Due to its high stocking density, ease of management, high-quality aquatic products, and economic benefits, the area dedicated to pond ecological recirculating aquaculture is expanding year by year. By the end of 2024, Pei County had 486 sets of mechanical equipment for ecological recirculating freshwater fish farming, achieving a comprehensive mechanization level of 87.5%.
I. Application and Analysis of Mechanized Technology and Equipment
Pond ecological recirculating aquaculture integrates mechanized technologies and equipment for aeration, feeding, water quality monitoring, fish waste removal, harvesting, and dredging. This analysis is based on the example of Pei County Runwo Aquatic Farming Family Farm, which has a pond area of 103 mu and employs the pond ecological recirculating aquaculture model. The farm currently has 8 water channels with a total area of 880 m², primarily farming largemouth bass.
1. Mechanized Aeration Technology and Equipment
The aquaculture zone in pond ecological recirculating systems accounts for only 2–5% of the total water surface, with a stocking density approximately 21.2 times that of conventional pond farming. For example, a 220 m³ water channel stocks 33,881 largemouth bass, achieving a density of 80.5 kg/m³. Thus, mechanized aeration is critical.
Pei County Runwo Aquatic Farming Family Farm equips each water channel (5 m wide, 22 m long, 2.5 m deep, with 2 m water depth) with one 2.2 kW air-lift aerator. Four water channels share one 3 kW vortex air pump with multiple nano-aeration tubes. The 101.7 mu purification zone is equipped with one 1.5 kW surge aerator, three 3 kW paddlewheel aerators, and three 3 kW jet aerators, forming a closed water circulation system.
Trials confirm that this aeration setup meets the needs of high-density farming. The air-lift aerator not only provides oxygenation but also pushes water, continuously renewing water in the channels and flushing fish waste and residual feed into the waste collection area. Nano-aeration tubes, arranged along the bottom of the channels, ensure fine bubbles for better oxygen dissolution, maintaining oxygen levels in the lower water layers. Jet aerators in the purification zone enhance oxygenation, promote vertical water exchange, improve water quality, and drive water circulation. Aquatic plants and filter-feeding fish further purify the water.
The combined action of these aerators maintains a dissolved oxygen (DO) level above 6 mg/L, ensuring optimal water quality. Operational protocols include:
- Air-lift aerators: Low flow in early stages (0.1–0.3 m/s), operating 24 hours during mid-to-late stages (except during feeding).
- Nano-aeration devices: Frequent operation in mid-to-late stages to maintain DO at 6–8 mg/L.
- : Operate from 5:00 to 17:00, off at night.
Most farms in Pei County use a combination of aerators with automated controls based on water quality monitoring, setting upper and lower DO limits to automatically start/stop aerators. This ensures DO levels above 6 mg/L, reaching over 7 mg/L during feeding, essential for high-density recirculating aquaculture.
2. Mechanized Water Quality Monitoring Technology and Equipment
An automated pond oxygenation control system monitors key parameters like DO, temperature, and pH. The system consists of an automatic oxygenation controller, water sensors, and a mobile client. It enables real-time monitoring, mobile alerts, and automated aerator control based on preset DO limits.
Advantages include reduced labor, high precision, and energy savings. A drawback is sensor fouling, requiring weekly cleaning to maintain accuracy.
- Place sensors in low-oxygen areas (e.g., downwind).
- Fix probes vertically, with the waterline 2–3 cm below the outlet, 5–20 m from aerators.
- Set DO limits according to species; for largemouth bass, lower limit at 5 mg/L, upper limit at 8 mg/L.
3. Mechanized Feeding Technology and Equipment
Each water channel is equipped with one 60 kg intelligent feeder. These feeders allow remote management via mobile phones, offering precise weighing, timed feeding, automatic shutdown when empty, data logging, and fault alerts. They can integrate with smart monitoring to observe feeding and fish behavior.
To accommodate narrow channels, side panels are added to reduce the feeding spread, preventing feed from exceeding channel boundaries.
Daily feed amounts are determined by species, growth stage, season, and weather, divided into 3–4 timed feedings. Mechanized feeding reduces labor, minimizes waste, improves feed utilization, lowers costs, and reduces harmful bacteria and gases, saving 10–15% compared to manual feeding.
4. Mechanized Fish Waste Treatment Technology and Equipment
One waste collection tank is installed for every 5–8 water channels, each equipped with a suction system comprising a traction system, guide rope movement system, underwater vacuum, automatic control system, pipelines, and electric pumps. This system collects and discharges fish waste and residual feed in one operation.
Driven by air-lift aerators, waste is pushed to the collection tank and pumped to rice fields as fertilizer-a task impossible manually.
- Maintain a 25 cm gap between the underwater vacuum and tank bottom.
- Clean 1.5 hours after feeding.
- Regularly clean the vacuum to prevent clogging.
5. Dredging Technology
- Water channels: Emptied and disinfected with chlorine dioxide or quicklime.
- Purification zone: Dredged with large bulldozers when silt depth exceeds 15 cm, every 3–5 years.
Bulldozers efficiently remove silt down to new soil, with productivity 10 times that of suction dredgers and 50 times manual dredging.
6. Equipment Matching Scheme
Pei County has developed a machinery matching scheme for pond ecological recirculating aquaculture to ensure optimal water quality and oxygenation. Table 1 outlines the equipment scheme for a 100 mu water area with 8 channels.
II. Comparative Analysis: Ecological Recirculating Aquaculture vs. Conventional Pond Mechanized Aquaculture
1. Aquaculture Effectiveness
Ecological recirculating aquaculture offers higher stocking density, better water quality control, improved feed utilization, reduced labor, environmental sustainability, lower risks, and higher economic returns. Specific comparisons are detailed in Table 2.
2. Economic Benefits
Integrated mechanization reduces risks, labor, and costs while increasing efficiency, density, and yield. For example, Pei County Runwo Aquatic Farming Family Farm achieves an average yield of 1,573.4 kg/mu (largemouth bass: 1,306.3 kg/mu; silver and bighead carp: 267.1 kg/mu). This represents an increase of 294.3 kg/mu for largemouth bass and 16.4 kg/mu for silver and bighead carp compared to conventional ponds, with an additional profit of 7,553 yuan/mu. Details are shown in Table 3.
III. Issues and Recommendations
1.
: The minimum feeding spread exceeds channel width, causing cross-feeding and waste. Runwo Farm modified 60 kg vibrating feeders with adjustable baffles to control the feeding spread, resolving the issue.
: Insufficient oxygenation and flow. Technicians improved them by:
Replacing the single injector with three injectors.
Adding a vortex air pump to the air intake.
These enhancements increased DO levels, water flow, and velocity, ensuring a fresh water supply to the farming zone.
2.
: Manufacturers should incorporate adjustable baffles to adapt to different channel widths.
Increase air intake motor power for greater airflow.
Develop multi-injector models to enhance water flow capacity, ensuring a continuous supply of oxygen-rich water to the farming zones.