Dear Dr. Kada,
Penaeus vannamei molt every four days until they are about 2 g, molting less frequently as they get older...
... depending on the (1) prevailing environmental culture water parameters including climatic condition and the (2) health status of the shrimps, with Penaeus monodon molting less frequently than Penaeus vannamei in general.
In ground-elevated indoor shrimp RAS, ROUND TANKS are cheaper to construct using only lightweight materials compared to above-ground raceways-type encasements.
By forming a slightly slanted bottom towards a sump pit at the center along with the positioning of the RAS return-lines along the wall of the round-shaped tank whether clockwise or counter-clockwise, one can create a centrifugal current that can eventually concentrate the molt casings, fecal debris, and detritus to the central sump where these can be sucked out either by gravitational force or via a pump suction-line.
Or with a large ground-excavated shrimp RAS, whether a ROUND POND, HEXAGONAL POND, or SQUARE POND, a larger central sump can be installed for the same purpose with greater efficiency than with ground excavated rectangular pond.