The importance of molting for growth in farmed shrimp is reviewed in relation to the physiological cycle, induction triggers, behavioral and compositional changes, elements for successful molting and potential strategies for moulting management.
Molting helps shrimp to increases their size and weight and it is repeated throughout their life cycle. Therefore, farmers always want to stimulate shrimp molting to improve the productivity and quality of shrimp when harvested. Besides, shrimp molting evenly helps increase resistance to bacteria, viruses that cause disease. However, the molting process of shrimp needs to be provided with a full range of factors such as minerals, dissolved oxygen, nutrition, ... so if the farming conditions are not favorable or lack of nutrients, shrimp will molt difficult leading to stunt and grow slowly. This article will provide many causes leading to molt slowly in shrimp and recommend some good products to support for molting process in shrimp as well.

1. Lack of nutrition

Shrimp molting slowly is mainly due to lack of nutrition, insufficient quality to fill in the shell or the shell is not forming a good cell membrane that's why it does not crack to molt. Shrimp need to supply enough feed with a total protein content of 32-45% to molting well. 

2. Water quality

Poor cultural environment inhibits activities, greatly affects the molting process of shrimp. Therefore, it is necessary to measure environmental parameters such as pH, alkalinity, dissolved oxygen, the temperature… regularly.

a) The dissolved oxygen (DO)

This is a particular factor that should be mentioned. Because, the oxygen demand during the molting process of shrimp is twice as high, so when the shrimp show signs of molting preparation, it is necessary to increase the fan, aeration to supplement dissolved oxygen content. Maintain dissolved oxygen in the range 4 - 6 mg / l during the molting process of shrimp.

b) Salinity

The higher the salinity in shrimp ponds, the higher the dissolved mineral content available in the pond and vice versa. Therefore, for shrimp ponds with low salinity, it is necessary to increase mineral supplementation for shrimp. However, if the salinity is higher than 25 ‰, the shells are usually thick and hard, prolonging the molting time of the shrimp. 

c) pH

Shrimp molts when pH reaches 7 - 8.5 and best 7.5 - 8. To stabilize the pH, it is necessary to maintain the transparency of the pond water from 30 - 40 cm.

- If pH <7.5, need to apply lime (CaCO3, Dolomite) at a dose of 10-20 kg / 1,000 m3 of water; - If pH> 8.5, use 1 kg of Vime-Bitech with molasses 6 kg / 2,000 m3

d) Alkalinity

During the growth process, shrimp need a lot of minerals, so it is necessary to maintain alkalinity of 120 mg CaCO₃ / l or more by using an increase of alkalinity of 10 kg / 1,000m3 of water, using at 9-10 PM

3) Feed management

Supply enough feed to shrimp, in the first month of culture feed 8-10% of the total weight of the farmed shrimp and the next months feed with 5-7% the total weight of shrimp. Adjust the quantity of feed during the day to monitor the number of leftovers on the trays. Appropriate feed conversion according to growth stage, mouth size, and nutritional needs according to the manufacturer's instructions. In the case of converting foods, mix the old and new foods for at least 3 days.

Mineral supplement: Provide adequate minerals necessary to help shrimp molt better.

Actively add the essential substances such as:

- Vimekat: 5ml / kg of feed, because in Vimekat contains Butaphosphan, which improves digestion and food use efficiency, helps create new shells, helps shrimp quickly harden shell, inhibits and destroy pathogenic bacteria in the intestinal tract of shrimp. Butaphosphan enhances and restores metabolic disorders, and reduces stress when shrimp are exposed to adverse environmental conditions.

- Lactozyme: 5-10g / kg of food, with Phytase in the composition to help convert phosphor in food into easily absorbed phosphor - prevent soft shell, stimulate to growth.

- Organic: 5-10 g / kg feed (inhibits Vibrio bacteria causing intestinal disease for shrimp)

- Canxiphot: 5ml / kg feed, provide trace minerals and macronutrients for shrimp.

Shrimp often molt at night, so minerals should be supplemented in the evening meal.

4/ Infection of some diseases

During the farming process, shrimps are infected with some diseases such as fungus, sea-weed alga, and stunted shrimp... these are some reason cause shrimp molting slowly or unable to molt. Prevent diseases by managing the pond water quality well, ensuring the oxygen demand for shrimp by stabilizing the algae in the pond to minimize the algae bloom appear in shrimp ponds; apply well all of pond management practices to protect shrimp’s health.