This study had the objective of evaluating the duration of the moulting cycle stages of Macrobrachium rosenbergii, using the method of setogenesis. The experiment was conduced in the Prawn Farming Laboratory of the Federal University in Paraiba, in the town of Bananeiras, Paraiba, Brazil. Fifteen prawns (5.7 ± 0.3 g) were distributed in 3 aquariums (60 x 30 x 40 cm), maintained in natural photoperiod (12 x 12 hours), at a controlled temperature (28 °C), and feed was offered 3 times a day (8 a.m., 12 and 16 p.m.), throughout the experimental period. For identification, the animals were marked with colored silicone rings on the ocular peduncle and with colored plastic discs fixed on the carapace. From the setogenesis method, the prawns were classified into stage A, B, C, D0, D1, D2 or D3 of the moulting cycle. Setogenesis was observed stereomicroscopically every day, at the same time, 7 a.m., from the first ecdysis to the next ecdysis. The duration of the moulting cycle was 27.7 ± 3.2 days, and the intermoult stage (C) was the longest (8.0 ± 2.38 days). Stage A was the shortest (1 day), and the pre-moult stage (stages D) lasted 12.98+1.65 days. We concluded that juvenile of M. rosenbergii have a diecdysis type moulting cycle with shorter intermoult than pre-moult periods.

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