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Nadine
Age: 42
Joined: 23 Jan 2006
Posts: 26
Location: Germany
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Molting of freshwater shrimps
Many a shrimp keeper is deeply shocked when discovering an exuvia (the shed exoskeleton, the shrimp's "shell") in the shrimp tank for the first time. Very often they assume that it's a dead shrimp.
Shrimps have an chitinous exoskeleton. This exoskeleton forms the integument (the outside body coverage) of these animals and consists of several layers; it coats all their body parts of the body even including the antennae and the other extremities.
- Epicuticula (at the very outside, thin, proteinaceous)
- Exocuticula (sklerotized (hardened, of greek skleros = hard) by phenolic connections cross-linking proteins and chitin)
- Endocuticula (soft, internal layer)
Exo- and endocuticula together are called procuticula. There is no exocuticula at the joints, therefore the skin there is soft and mobile. For additional strenght, mineral salts are stored in the procuticula, crustaceans mainly use e.g. calcium carbonate and calcium phosphate.
The colors of the animals form as follows: by the storage of pigments in the procuticula, by chromatophores (cells with pigments in their cytosol) under the cuticula, or by blood shining through thin skin or organs.
The exoskeleton or integument does not only protect the animals from mechanical influences from the outside and provide a border for muscles and organs. Layers of wax in the epicuticula also provide protection against evaporation. The one large disadvantage of the exoskeleton is the fact that this carapace of thick and highly specialized extracellular matrix can't grow along. Therefore the life of a shrimp is frequently determined by a trueful dramatic event, the molt.
This is a complex procedure steered by many hormones, during which relatively often deadly accidents may happen.
Shrimps need to shed their shells all their lives long. In the first growth phase nearly daily, later, with increasing age, they molt only approx. every 4 weeks.
In nature the shedding is initialized by molting hormones during certain cycles. Under the old exoskeleton a new, larger, folded skin forms; lost extremities can be regenerated.
Some days before the molt food intake is stopped, since internal organs are concerned in the process as well. The shrimp looks for a quiet place, and is very sensitive to disturbances during this time. Among other important minerals, the valuable calcium is absorbed from the old skin. The shrimp begins to inflate its body with water until the old integument opens up at a break section between the carapax and 1. abdominal segment. The shrimp snaps out of its old shell and begins to take in water in order for the new skin to stretch. Thus it grows into its new, larger skin. As the new shell must harden some time, the shrimp is unprotected in this phase and therefore very vulnerable.
Since shrimps are fertile only a short time after the molt, they set off odoriferous substances (pheromones) briefly after shedding their skin in order to signal their readiness to mate.
This complex hormone-steered procedure is naturally very sensitive to stress, change of the water parameters and to bad keeping conditions. Therefore it has to be made certain that the animals are kept in good conditions, have sufficiently peace and possibilities to retreat.
You can provoke premature molts by doing your water change with very cold water, however some factors do speak against this. For example the shrimps' skins may not be fully developed yet, and females will lose their eggs when molting.
Shrimp regard the exuvias as food and take in important minerals and proteins when eating them, so you don't have to remove the empty shrimp shells from the tank - they are taken care of.
Video of molting shrimp
Source : RWTH Aachen
German version written by Blue Shrimp |
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