Reservoir fish farming is a cost-effective and efficient method of aquaculture, as it typically does not require feeding or fertilizing the fish. Instead, fish rely on consuming naturally occurring aquatic organisms. To ensure successful fish farming in reservoirs, it's essential to consider the types and quantities of natural bait available, so that the species and numbers of stocked fish can be appropriately managed.
1. **Stocking Fish Species**
Reservoirs often have high levels of plankton, making them ideal for filter-feeding fish like silver carp and bighead carp. These species grow quickly, reach large sizes, and are widely available, making them the primary candidates for stocking. In addition to these, omnivorous and herbivorous fish such as grass carp, common carp, and tilapia can also be introduced to utilize other food sources. However, these should not be overstocked, as they are not the main focus of the operation.
2. **Stocking Size and Quality**
The size and quality of fingerlings play a crucial role in achieving high yields. For example, common carp and crucian carp should be around 11.55–13.22 cm, while silver carp should be about 13.2–14.85 cm. The size may vary depending on local conditions, reservoir size, and the presence of predatory fish. In well-managed reservoirs with minimal predation, smaller fish can be used. Conversely, larger fish are preferred in more challenging environments. High-quality fingerlings increase survival rates and overall productivity.
3. **Stocking Proportions**
To make the most of the natural food resources in the reservoir, it's important to maintain a balanced mix of fish species. Typically, bighead carp and silver carp should make up 70–90% of the total stock (with bighead carp at 60–70% and silver carp at 30–40%). Other species, such as grass carp and herbivorous fish, can account for 10–30% of the total population. The exact proportions depend on the availability of natural bait and the existing fish populations in the reservoir.
4. **Stocking Density**
The density of fish stocked in a reservoir must be carefully managed to maintain a balance between the fish population and the available natural food supply. Stocking densities can vary based on the trophic level of the reservoir. For highly productive reservoirs, a density of 110–160 fish per 667 square meters is typical. For medium-nutrient reservoirs, the range is 80–110 fish per 667 square meters, and for low-nutrient ones, it’s 50–80 fish per 667 square meters. Adjustments should also be made according to the growth rates and expected production levels of the fish.
5. **Stocking Time and Location**
The best time to stock fish is in early spring when water temperatures are between 6°C and 10°C. At this time, predatory fish are less active, reducing stress on the newly stocked fish. After acclimating to the colder winter conditions, the fish will be ready to grow during the warmer months. Stocking locations should be selected in sheltered, sunny areas of the upper reservoir where food is abundant. If the reservoir is large or a large number of fish are being stocked, multiple sites can be used.
6. **Stocking Precautions**
Stocking should be done on a sunny day to reduce stress on the fish. When introducing them to the water, they should be released slowly so they can swim freely. Before stocking, it’s advisable to disinfect the fish by soaking them in a salt solution of 25–40 g/L for 5–10 minutes. This helps prevent diseases and ensures healthier fish populations in the reservoir.
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