Water quality judgment techniques and methods
Yancheng Rongtai Labware Co.,Ltd , https://www.rongtailab.com
Fish cannot survive without water, and "fishing requires good water," a common saying that highlights the critical role of water quality in aquaculture. The success of fish farming depends heavily on the condition of the water body. Factors such as the levels of organic and inorganic matter, the presence and abundance of natural food sources like plankton, and various physical and chemical properties of the water all play a significant role in fish growth and development.
Water, like land, can be "fat" or "thin." The term "fat water" refers to the richness of the water, primarily determined by the amount of plankton, which serves as a key food source for fish. Since plankton has color, its concentration affects how much sunlight can penetrate the water. In practice, the "fatness" of water is often assessed by measuring its transparency.
### Transparency Measurement Method
Transparency is a measure of how far light can penetrate into the water. It is influenced by the presence of plankton, organic debris, sediments, and other suspended particles. During summer and autumn, when plankton blooms are common, transparency tends to be low. In contrast, during winter and spring, when plankton growth is limited, transparency increases. Wind and rain can stir up sediment, reducing transparency, while calm, sunny days allow for higher clarity.
To measure transparency, a standard method involves using a Secchi disk. Alternatively, a simple technique is to hold your hand palm-up in front of your face at a right angle and slowly submerge it into the water until the palm is no longer visible. The depth at which this occurs gives an estimate of the water's transparency. Ideal transparency for fish ponds is typically between 20–40 cm, with 25–30 cm being optimal.
### Judging Water Quality by Color
The color of the water reflects the presence of dissolved substances, suspended particles, plankton, and the surrounding environment. Based on color, water bodies can be classified into several types:
1. **Thin Water**: Light green or blue, with high transparency (60–70 cm or more). Plankton is sparse, but filamentous algae and aquatic plants may dominate.
2. **Bad Water**: Contains many phytoplankton species, but they form a gelatinous or fibrous layer on the surface, making them difficult for fish to digest.
3. **Hazy Dark Gray/Blue-Green**: Low transparency, high turbidity, and a yellow-green film on the surface. Dominated by cyanobacteria, which are hard to digest. This type of water should be refreshed or fertilized.
4. **Cloudy Green**: Thick water with moderate transparency (20–30 cm), often seen in downwind areas with yellow-green suspensions. While suitable for fry, it can easily turn into "green water" if not managed.
5. **Red Clusters**: A red appearance due to excessive zooplankton like cladocerans. This indicates poor water quality and requires adjustment, such as increasing carp stocking or using specific treatments.
6. **Grass Green with Red Film**: Thick water with a "blushing green" or "reddish green" appearance. Initially harmless, but long-term can reduce fish appetite. Quicklime or copper sulfate can help control algae.
7. **Fertilized Water**: Yellow-brown or oil green, with moderate transparency (20–40 cm). Rich in diatoms, cryptophytes, and rotifers—easily digestible by fish. These are ideal for raising whitefish.
8. **Brown Water**: Includes yellow-brown or reddish-brown tones. Often dominated by diatoms and cryptophytes. If dark brown, it may indicate aging water.
9. **Oil-Gray Water**: Soft and cool, with grayish water caused by large populations of phytoplankton and zooplankton like rotifers. Suitable for fry cultivation.
10. **Bad Water**: Reddish-brown in color, containing toxic substances. Not suitable for fish breeding.
11. **Polluted Water**: Unusual colors like red, brown, or milky white, with harmful chemicals such as sulfides and heavy metals. Extremely dangerous for fish.
### The Meaning of “Fat, Live, Tender, and Cool†Water
- **Fat**: High plankton content, with many digestible species; transparency around 30 cm.
- **Live**: Dynamic changes in color and transparency, indicating thriving phytoplankton.
- **Tender**: Fresh and easy to digest, avoiding overgrowth of hard-to-digest species like cyanobacteria.
- **Cool**: Clear, with high transparency (>25 cm), minimal turbidity, and high dissolved oxygen.
Maintaining "fat, live, tender, and cool" water requires regular feeding, fertilizing, and water exchange to sustain good water conditions.
### Four Methods to Assess Water Quality
1. **Look at the Water Color**: Different nutrients lead to different plankton populations, resulting in varied water colors. Brown or green waters are typically rich in digestible plankton.
2. **Observe Changes in Color**: Digestible algae exhibit phototaxis, moving toward the surface during the day and spreading out at night. Regular color shifts indicate healthy, dynamic water.
3. **Check the Surface Film**: Oil films on the downwind side can reveal water quality. Thick, sticky films suggest nutrient-rich water, while blackened or foul-smelling films signal poor conditions.
4. **Monitor Water Blooms**: Algal blooms reflect water health. Certain species, like blue-green algae, can be harmful if unchecked.
By observing these indicators, farmers can effectively manage water quality and ensure a productive and sustainable aquaculture system.