In several fishing ponds located in Qufu, Shandong Province, traditional fish species such as squid, tilapia, and grass carp were once commonly used. However, within a short period, the ponds experienced an overpopulation of young fish, leading to excessive oxygen production and subsequent fish diseases. This decline in water quality significantly reduced the hooking rate, discouraged anglers, and negatively impacted the overall efficiency of the fishing operations. To address these challenges, biological measures were introduced, including the introduction of filter-feeding fish, predatory species, and the cultivation of aquatic plants. These strategies effectively resolved the issues, improving both water quality and angler satisfaction. Here's a detailed breakdown of the methods implemented:
First, the selection of fish species in the ponds was diversified by introducing filter-feeding and predatory fish, along with other varieties that enhanced the fishing experience for guests.
1. **Filter-feeding Fish Cultivation**: Species like silver carp and bighead carp were added to the ponds. These fish help control algae and plankton levels by feeding on them, thus maintaining water clarity and balance. The recommended stocking density is 150–250 fish per acre, with each fish weighing over 100 grams. The density of silver carp is typically around 20–30 per mu, and this practice not only improves water quality but also increases income by more than 600 yuan per acre.
2. **Predatory Fish Introduction**: Black bass, catfish, and other aggressive species were introduced to manage the population of wild fish. These predators help reduce competition for food and space, ensuring better conditions for target species. Stocking rates can reach up to 30–50 fish per acre or 200–300 stingrays, depending on pond size and management goals.
3. **Egg-Eating Fish**: Although not aggressive, species like the mud minnow are effective at consuming fish eggs, reducing the number of juvenile fish that could otherwise overcrowd the pond. A typical stocking density is about 100 fish per mu, with a weight of 50 kg or more per acre being ideal.
Second, the cultivation of aquatic plants—both submerged and floating—was introduced to further improve the ecosystem.
1. **Submerged Plants**: These grow entirely underwater and help absorb excess nutrients, regulate pH, and increase dissolved oxygen through photosynthesis. Species like water chestnut, barnyard grass, and black algae are suitable. However, they should not be planted in ponds primarily stocked with grass carp or catfish, as these species may feed on them.
2. **Floating Plants**: These grow on the water surface and have root systems that extend below. They absorb nitrogen and phosphorus, helping to control water eutrophication. They also provide shade, lower water temperature, and create natural hiding spots for fish. Water hyacinth, water lettuce, and water peanuts are commonly cultivated. Water peanuts are particularly adaptable and can even be grown on land. It’s important to use frames made of bamboo and anchors to prevent drifting.
Third, several key considerations must be taken into account:
1. **Feeding Practices**: After planting aquatic vegetation, regular feeding should continue. Fish should be fed daily at 1% of their total weight, with feed placed in designated areas and given at consistent times. The feed is usually a mixture of sinking pellets and binding agents, designed to match the taste and composition of bait provided to anglers.
2. **Stock Management**: All raised fish are intended for catch-and-release or harvest. For example, head lice and predatory fish are often caught during regular fishing activities. Therefore, it's essential to monitor and adjust stocking levels accordingly. Mud minnows have high survival rates and rarely need additional stocking. In contrast, black bass populations may need to be controlled. Anglers should be informed about the specific techniques required for catching these fish, and appropriate tackle and bait should be prepared accordingly.
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