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 and results in high mortality rates when spring arrives in the second year. Based on years of practical experience in crab farming, the author outlines the causes of early maturation and the necessary precautions below.
First, the reasons for early maturation:
1. Feeding with excessively fine bait, especially an overabundance of animal feed, combined with a rich supply of natural food sources in the pond, accelerates the growth of some crabs and promotes premature sexual development.
2. The effective accumulated temperature increases, which speeds up gonad development. In particular, when crabs are raised in ponds or paddy fields, the shallow water warms up faster than in lakes or rivers. Since crab farming typically occurs during the hot summer and autumn months, the consistently high water temperature further accelerates both growth and gonadal maturation.
3. Natural crab seedlings usually begin to appear in early June, but farmed seedlings often emerge as early as March, extending the growth period by two to three months. Additionally, the use of plastic greenhouses enhances cultivation conditions, leading to larger, more precocious crabs.
4. Overly low stocking density can also contribute to early maturation, as it reduces competition and allows crabs to grow more rapidly.
Second, signs of sexual maturity:
1. Female crabs show a mature abdomen with a fully developed umbilicus, while male crabs develop a rigid, bony structure on their abdomen, with longer and darker hair indicating maturity.
2. Sexually mature crabs often have uneven shells, with visible irregularities on the back.
3. When examining the head area, if two purple stripes are visible in the liver region, or if there are eggs or two white masses (testes), this indicates that the gonads are mature.
Third, preventive measures:
1. Control feeding practices, especially the amount of animal-based feed. Maintain proper water quality and avoid overfeeding.
2. Increase the water depth in the pond and change the water regularly during hot seasons. Using river or lake water helps lower the temperature, slowing down the maturation process.
3. Remove aquatic plants covering more than 50% of the pond surface to reduce direct sunlight exposure, thereby lowering the effective accumulated temperature and delaying growth.
4. Preferably use human-bred seedlings in May, allowing them to grow into marketable crabs within 3–4 months.
5. Increase the stocking density appropriately, ideally more than one-third higher than the normal breeding density, to slow down growth and prevent early maturation.
By implementing these strategies, farmers can better manage the growth and maturation of crabs, improving survival rates and overall productivity.
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