Traditional methods of cultivating single-cell algae involve building seed chambers and following a structured process of seed preservation, inoculation, expansion, and production. This method ensures the purity of the seed culture and minimizes contamination from pests like protozoa. However, for crustacean larvae such as crabs, using open ponds to cultivate unicellular algae is more cost-effective and practical. These larvae are less vulnerable to protozoa and do not require pure cultures of specific species. Instead, a mixed community of various algae and small amounts of micro-zooplankton often provides better nutritional value and quality. Since pond algae, water, and airborne spores are naturally abundant, there's no need for external introduction—only proper selection of the breeding pond and minimal human intervention can lead to success.
First, general proliferation:
1. Selecting the right pool: For algal cultivation, it's best to choose older pools with thick sediments, which contain a rich variety of "algae species" in the form of spores and provide ample nutrients for their growth. However, these pools may also harbor dormant eggs of filter-feeding zooplankton, which can become a threat. Ideally, select water bodies that are fertile but have fewer predators. Large shrimp ponds or catfish rearing ponds are good options. Avoid long-term use of ponds for bottom-dwelling fish like snails or clams. The size and depth of the pond should match the target species, but avoid those with serious leaks.
2. Cleaning the pond: Use lime (freshwater) or bleach (saltwater) to clean the pond. Drained ponds are preferable as they reduce chemical usage and promote rapid algal growth. According to research by Lei Yan et al. (1983), drained ponds show faster algal development than non-drained ones.
3. Water injection: Use deep well or groundwater, which has fewer predators and debris, as the preferred water source. If natural seawater or freshwater is used, it must be sterilized or filtered through a 150-mesh sieve. The depth of the water depends on the target species, but it should be shallow enough to support algal reproduction and water quality control.
4. Fertilization: In clear ponds, without fertilizer, ammonia nitrogen can reach 3.88 mg/L, and active phosphorus can reach 0.18–0.22 mg/L. Within a week, the pond can meet algal needs. However, as algae consume nutrients, fertilization should begin after 7–8 days. Apply small amounts frequently, mixing inorganic and organic fertilizers based on the species being cultured.
5. Controlling predators: Protozoa, rotifers, and crustaceans can prey on algae. While these organisms typically appear later and in smaller numbers, their spores or eggs can still contaminate the pond. If they become problematic, different treatments apply: trichlorfon can kill crustaceans, chlorine can control rotifers, and physical filtration helps manage protozoa.
Second, special group proliferation:
In open-pool monoculture, achieving a pure strain of algae is difficult due to environmental complexity. However, certain ecological communities may thrive under favorable conditions. For example, flagellate algae, known for their mobility and digestibility, can be cultivated successfully in open systems. Special attention should be given to water depth, organic fertilizer application, and selective grazing by zooplankton to maintain balance.
Dinoflagellates and small non-flagellates are also important for aquatic food chains. They require shallow, open areas and inorganic fertilizers to flourish. Integrating fish and algae in polyculture can further enhance productivity. Cyanobacteria, while sometimes toxic, have valuable roles in aquaculture, especially in oxygenation and nutrient cycling. Proper water depth, phosphorus-rich environments, and controlled pH levels are crucial for their successful cultivation.
Third, identifying phytoplankton in aquaculture:
Understanding the types and characteristics of phytoplankton is essential for effective aquaculture. Based on biomass, water quality is classified into several levels, each with distinct visual and biological indicators. Additionally, water bloom types—such as dinoflagellate, green algae, or cyanobacteria blooms—offer insights into the nutritional value and health of the aquatic environment. Farmers often rely on visual cues like water color, clarity, and changes in transparency to assess water quality, which aligns with scientific measurements of plankton density and diversity.
In summary, while traditional methods of algal cultivation emphasize purity and control, modern practices favor open systems that leverage natural biodiversity. By understanding the dynamics of different algal groups and their interactions, aquaculturists can optimize production, improve water quality, and ensure sustainable growth.
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