At present, many farmers still rely on traditional farming methods that primarily use green feed. While the application of this approach is expanding and becoming more diverse, it has several disadvantages that can negatively impact the economic returns of aquaculture. According to our field investigations, the overall breeding efficiency is low, and some farmers have even suffered significant losses. Therefore, we strongly advise farmers not to rely heavily on green feed—feeding more than 1% of the fish's body weight in green feed or using it as the sole source of nutrition for fish farming. Below is a detailed analysis of the negative factors associated with green feed-based aquaculture.
First, green feed-based fish farming leads to a high incidence of diseases and low survival rates. Many farmers have observed that ponds where green feed is the main food source, especially for herbivorous fish like grass carp, experience a significantly higher rate of illness. This is largely due to overfeeding green feed, which results in nutritional deficiencies, particularly in protein. Over time, this causes physiological issues such as osmotic imbalance and edema. These conditions often manifest as skin redness, followed by damage to intestinal cells, liver dysfunction, and enteritis. In confined environments like cages or enclosures, grass carp may only consume green feed, leading to malnutrition, poor growth, and increased mortality.
Second, overfeeding green feed leads to water pollution and a deteriorating environment. The excessive organic matter from both the feed and fish waste increases the risk of disease outbreaks. Poor water quality not only raises the incidence of diseases but also leads to mass fish deaths, commonly referred to as "pan-pool" events. When dissolved oxygen levels drop too low, fish suffocate, and the accumulation of organic acids further reduces their ability to utilize oxygen, causing physiological hypoxia. This results in slow, chronic death and reduced productivity.
Third, fish grow slowly and aquaculture yields are low when relying heavily on green feed. Our surveys show that fish ponds using green feed typically produce around 250 kg per mu, far below the yield achieved with compound feeds. This is due to insufficient nutrients, high disease rates, and poor water quality. Additionally, the breeding cycle is shorter, and fish often struggle to adapt after being moved to larger bodies of water, further reducing growth potential.
Fourth, the cost of raising fish with green feed is high, and the economic returns are low. Although some farmers believe green feed is cheaper, the reality is different. Green feed has a lower nutrient density, requires more labor, and leads to higher costs for drugs and maintenance. For example, feeding 1 kg of grass carp with sudangrass costs 4.8 yuan, compared to 4.0 yuan for rice cake and 4.37 yuan for pellets. Furthermore, the feed conversion ratio is worse, and the need for frequent medication increases expenses.
In conclusion, while green feed has its place in aquaculture, it should be used cautiously. During peak growth periods, feed amounts must be strictly controlled. For high-yield ponds producing over 500 kg per mu, green feed should not exceed 10%. In ponds producing 500 kg, it can be up to 15%, and in lower-yield areas, it should not go beyond 25%. Careful management is essential to ensure both fish health and profitability.
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