At present, in the process of crab farming, a common issue is that the crabs grow too large and reach sexual maturity at an early stage. This leads to significant challenges during winter survival, resulting in high mortality rates when the crabs enter their second year. Based on years of practical experience in crab farming, the author has summarized the main causes of early maturation and provides some key precautions.
**First, the reasons for early maturation:**
1. Feeding crabs with overly fine bait, especially excessive amounts of animal-based feed, combined with abundant natural food sources in the pond, can cause rapid growth in some individuals, leading to premature sexual development.
2. The effective accumulated temperature increases, which speeds up gonad development. In ponds and rice fields, where water levels are shallow, the water warms up faster than in larger bodies of water like lakes or rivers. Since crab farming typically occurs during the hot summer and autumn months, the consistently high temperatures further accelerate both growth and sexual maturation.
3. Natural crab seedlings usually start appearing in early June, but farmed seedlings often emerge as early as March, extending the growth period by 2 to 3 months. With the use of plastic greenhouses to enhance cultivation, this results in larger, more precocious crabs.
4. Overly low stocking density can also contribute to early maturation, as it reduces competition for resources and allows crabs to grow faster and mature earlier.
**Second, signs of sexual maturity:**
1. Female crabs develop a fully matured abdomen, while male crabs show hardened, bony structures and longer, denser hairs, along with darker coloration.
2. Crabs that have reached sexual maturity often display uneven shells.
3. By opening the crab's head, you can observe two purple stripes in the liver area, indicating egg development, or two white masses representing mature testes.
**Third, preventive measures:**
1. Control feeding practices, particularly limiting the amount of animal-based feed. Water conditions should be carefully managed to avoid overfeeding.
2. Increase the water depth in the farming area and change the water during hot seasons. Using river or lake water helps lower the temperature and slow down growth.
3. Remove aquatic plants covering more than 50% of the pond surface to reduce direct sunlight and lower the effective accumulated temperature, slowing down crab development.
4. Use human-bred seedlings from May, allowing them to grow into marketable crabs within 3–4 months.
5. Increase the stocking density appropriately, ideally exceeding one-third of the normal breeding density to promote balanced growth and delay sexual maturity.
By implementing these strategies, farmers can better manage the growth cycle of crabs, reduce early maturation, and improve overall survival and yield.
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