Shrimp are arthropods, and therefore have an exoskeleton. That is to say, they are encased in an external skeleton rather than an internal one, providing protection and support for the body.
Moulting of the exoskeleton is a process needed in order for the shrimp to grow. It is necessary because unlike skin the chitinous cuticle of the shrimp is rigid and can not grow with the rest of the body.
There are two main stages to moulting…
Apolysis is the separating of the cuticle from the body-cells underneath (the epidermis). The epidermal cells secrete fluid in order to loosen the exoskeleton. These cells also secrete enzymatic fluid, which digests the old cuticle once the upper layers of the new cuticle have been formed by the epidermis. During the digestion of the old cuticle the new cuticle continues to develop underneath.
Ecdysis is the expulsion of the old cuticle. Whilst still encased in the old cuticle, the shrimp is described as being ‘pharate’. The shrimp bends its body into an ‘n’ shrimp to put stress on the weakened old cuticle, thus splitting it. It then springs out of the old exoskeleton. The expelled cuticle is called an ‘exuvia’.
Following moulting the shrimp is very vulnerable. This is because it is ‘teneral’; its new cuticle has not yet hardened. It is during this period that the shrimp grows, as the new exoskeleton is not yet rigid enough to prevent growth and can be stretched to accommodate.
Shrimp can have difficulties when moulting for the following reasons:
- Disease (particularly bacterial infections)
- Incorrect water parameters
These difficulties can vary significantly. One example is splitting between the carapace and abdomen, (right). Another commonly seen example is all extremities of the cephalothorax bending upwards, giving the shrimp a ‘flat’ face. These shrimp are usually beyond help, and this should be seen as a warning of an emergency. Check for diseases in your shrimp, revise their diet and test the water parameters immediately.