The entrance of the Yellow River into the sea serves as the primary source of eel fry, and through improved survival rates of natural seedlings in Haipu, eels have become a key species for breeding in the Yellow River Delta. From 1998 to 2000, we utilized old shrimp ponds in Dongying City's shrimp farms, relying on the cultivation of basic biological feeds to temporarily raise sea-caught fry. This method proved successful for three consecutive years, providing valuable hands-on experience and significant economic returns. The project was recognized by experts from the Shandong Provincial Science and Technology Commission and has reached a leading domestic standard. Below is an overview of the technology used:
**I. Holding Technology**
1. **Pond Conditions**: We used pond No. 5 of Team 1 at the shrimp farm in Dongying City, covering 50 mu. The pond is rectangular with a central ditch, equipped with inlet and drainage gates. The depth ranges from 1 to 2 meters, with a muddy-sandy bottom that had not been dredged.
2. **Stocking Preparation**: Before stocking, the pond was drained and disinfected using quicklime at a rate of 75 kg per mu. After 48 hours, water was introduced from the intersection of the Guangli and Yihong Rivers. The water is brackish, with salinity between 5‰ and 15‰, mixing fresh and seawater. Natural food sources such as silkworms, clams, prawns, and snails were cultivated. Water was introduced on March 10th each year, using high tide water. A mesh cone-type net was installed at the inlet to trap small organisms, while a 20-mesh net was placed at the outlet. Two days after the first water intake, the pond was flushed twice before gradually filling it to 80 cm to allow natural reproduction of food.
3. **Seed Stocking**: By late March, naturally grown sea fry were collected. The seedlings measured 1.5 to 3.0 cm in length, and the salinity at the river mouth was around 20‰. These seedlings needed desalination. Weak or injured ones were removed, and the salinity was adjusted to match the pond’s level. Seedlings were stocked within 7 days to avoid size differences and competition for food.
4. **Key Management During Holding Period**
(1) **Water Quality Control**: Maintaining stable water conditions was crucial due to fluctuating salinity and water quality. For the first 15 days, only high-tide water was added, increasing the pool level to 1.8 meters. Every 10–20 cm of water added, the inlet net was replaced with an 8-mesh nylon net to prevent fish from escaping. Fresh water was regularly exchanged to promote growth.
(2) **Feed Management**: The seedlings primarily fed on naturally occurring prawns and snails. Small nets were used periodically to check food availability. If insufficient, live prawns were introduced.
**II. Key Considerations**
Through three years of testing, we found that improving eel fry survival required attention to three areas:
1. Ensuring healthy, uniform seedlings with no injuries and timely stocking.
2. Stabilizing the pond environment by carefully managing water intake and drainage.
3. Guaranteeing an adequate supply of natural food sources.
**III. Advantages of the Holding Technology**
1. Eel fry raised in low-salt environments are more marketable. They can survive in brackish waters, which is ideal for wintering. In the Yellow River Delta, brackish water is easily accessible, making this approach promising for future development.
2. Utilizing existing shrimp ponds increases efficiency and reduces risk. After raising eels until late May, the ponds can be repurposed for low-salt shrimp like Chinese shrimp or Penaeus vannamei. Any weak eels can help control shrimp diseases, further enhancing productivity.
Clostridium Butyricum
C. butyricum, a butyrate-producing, spore-forming anaerobic bacterium, is found in a wide variety of environments, including soil, cultured milk products, and vegetables. It is also present in the human gut: it is detected in 10–20% of the adult human population and is often one of the earliest colonizers in infants. In the human gut, where it is considered a ‘symbiont (living together with the host), C. butyricum has a fermentative lifestyle and can consume undigested dietary fibers and generate short-chain fatty acids (SCFAs), specifically butyrate and acetate. Butyrate is one of the dominant fermentation end-products and is produced by C. butyricum via the butyrate kinase (buk) pathway. SCFAs produced by microbial organisms in the colon are known to have myriad and important effects on host health, including modulating intestinal immune homeostasis, improving gastrointestinal barrier function, and alleviating inflammation. As such, butyrate-producing organisms like C. butyricum have become attractive candidates to test for beneficial effects in a host. Genomic analyses are increasingly identifying novel bacterial strains with health-promoting potential that are distinct from classic probiotics (Lactobacilli and Bifidobacteria).
C. butyricum is a species that encompasses various known strains, some of which have genes equipping them to produce toxins. However, genomic analyses confirm that other strains do not have these genes nor other markers of pathogenesis potential, and that these nonpathogenic strains have excellent potential to benefit host health through several mechanisms. Certain strains of C. butyricum have been used as a probiotic for decades. Strain MIYAIRI 588 (or MIYARI 588; CBM 588), first isolated from the feces of a healthy human by Dr. Chikaji Miyairi in 1933, and later from soil in 1963, is a commercially-available, over-the-counter probiotic widely used in Japan, Korea, and China for the treatment of (antimicrobial-associated) diarrhea. Strain CBM 588 is also authorized under the regulation of the European Parliament and of the Council as a novel food ingredient. Its widespread use is enabled by its safe, nonpathogenic and nontoxic profile: studies have shown that it is sensitive to antibiotics, devoid of pathogenic markers, and lacks clostridial toxin genes.
butyrate, immunity, intestinal barrier, inflammation
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