Bullacta exarata, commonly known as the spit iron snail, wheat snail, plum snail, or yellow mud snail, is a species of gastropod belonging to the family Adiluaceae. Native to the brackish waters of the Western Pacific, this mollusk is widely distributed along the northern and southern coasts of China, especially in Zhejiang Province, where it thrives in areas like Ningbo and Zhoushan. As one of the most economically valuable shellfish in the region, the snail is prized for its delicious meat and high nutritional value, making it a popular delicacy among locals.
However, due to environmental degradation and habitat loss, natural populations have declined significantly. In response, large-scale aquaculture has emerged as a sustainable alternative, with Bullacta exarata now playing an important role in coastal shellfish farming.
**Biology of Mud Snails**
**(I) Morphological Characteristics**
The body of the mud snail is elongated and smooth, with the front end referred to as the head plate and the rear as the mantle. The head is large and plump, lacking true antennae and featuring degenerated eyes. The lateral parts are well-developed, with most of the shell covering the body. The shell, which is oval-shaped and relatively thin, is typically yellow or white and does not fully enclose the snail. It lacks a spiral tower or umbilical opening, and the shell mouth is wide and smooth. Adults often display fine lines on the outer shell surface, while the inner edge remains smooth.
**(II) Ecological Habits**
These snails inhabit tidal flats, preferring muddy or soft sandy substrates. They are most abundant in sheltered inner bays, where they can be found in the mid- to low-tide zones. During high tide, they burrow into the sediment, emerging after the tide recedes to feed. In rainy or cold weather, they dig into the sand and remain hidden until conditions improve. Their optimal temperature range is 10–25°C, with survival possible between -1.5°C and 33°C. They also tolerate a wide range of salinity (1.005–1.020) and pH levels (3.74–9.0), with the best growth occurring between pH 6.11 and 8.01.
Mud snails are omnivorous, feeding on benthic diatoms, organic debris, small crustaceans, and invertebrate eggs. They use their radula to scrape food from the surface. Growth is slow during the larval stage, but once they mature, their development slows further. Maturity is reached when the shell height reaches about 15 mm, and most individuals die shortly after mating.
**(III) Breeding Behavior**
Bullacta exarata is a hermaphroditic species that reproduces through cross-fertilization. The gonads, called "bisexual glands," are located on the left side of the shell and produce both male and female gametes. Spawning occurs on the mudflat, with mating lasting around 15 minutes. Eggs are laid in gelatinous egg sacs, which are buried in the sand. After four days of development, the eggs hatch into free-swimming larvae, which later settle and metamorphose into juvenile snails.
**Cultivation of Mud Snails**
**(I) Natural Seed Collection**
During the breeding season (March–November), natural seedlings can be collected from tidal flats. Spring seedlings are preferred due to more stable temperatures. Seedlings are scraped from dense areas and sorted by size before being raised in ponds. Depending on the scale, they can be harvested within 1–4 months.
**(II) Earth Pond Cultivation**
This semi-artificial method involves preparing shallow ponds with rich benthic diatom content. After disinfection and preparation, snails are introduced, and organic fertilizers are used to stimulate algae growth. Larvae are raised under controlled conditions, with water changes and feeding carefully managed. After several weeks, they are transferred to outdoor ponds for further growth.
**(III) Indoor Artificial Cultivation**
Indoor nurseries mimic natural conditions, using still water and feeding larvae with microalgae. Water is changed daily, and as the snails grow, the density is adjusted. Once they reach a certain size, they are moved to outdoor environments for final cultivation.
**Management Practices**
**(A) Water Management**
Maintaining proper water levels is crucial. When tides are low, extra water should be stored to prevent dehydration. Controlled exposure helps promote growth.
**(B) Predator Control**
Birds, crabs, and other predators pose a threat. Regular monitoring and pesticide application help manage these risks.
**(C) Preventing Escape**
Snails may escape if conditions are unfavorable. Fences made of mesh or barriers can help keep them in place.
**(D) Fertilization**
Applying organic and inorganic fertilizers enhances the availability of food, promoting better growth and productivity.
**(E) Monitoring**
Regular observation ensures early detection of issues such as migration or disease, allowing timely interventions.
**(F) Harvesting**
Mud snails are typically harvested after 1.5–3 months, depending on growth rates. Hand collection or specialized nets are used, with hand-picking yielding higher quality results.
With careful management and sustainable practices, the cultivation of Bullacta exarata continues to support both ecological balance and economic growth in coastal regions.
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