A shortening effect of KK-42 on the moult cycle of juvenile Macrobrachium nipponense (De Haan, 1849) (Decapoda, Palaemonidae)

Abstract

The imidazole derivative KK-42 is frequently used as an insect growth regulator. However, the effect of KK-42 on prawn growth remains largely unknown. To explore the effect of KK-42 on the moult cycle of juvenileMacrobrachium nipponense(De Haan, 1849), 1.2-2.0 cm long prawns were collected from aquaculture grounds, and acclimated at 26 ± 1°C in running-water tanks for one week before the experiments. The prawns were soaked with KK-42 solution at a concentration of 1.95 × 10−4 mol/l (treatment group) or without KK-42 solution (control group) for 1 min. Thereafter, a part of the prawns was used to measure body growth rate and moult cycle, and the rest, being at intermoult stage (C) and premoult stage (D), were used to quantitatively analyse the mRNA level of the cuticular chitinase1 gene (Mnchi-1) and chitinase activity. The results showed that the average body weight of the treatment group was significantly higher than that of the controls. Meanwhile, the body growth rate increased more than 16% in the first two weeks after KK-42 treatment. The duration of the moulting period of the juvenile prawns was shortened by KK-42 treatment in the first two cycles among four consecutively-determined moult cycles, from 8.70 ± 1.07 and 9.81 ± 0.43 days to 6.93 ± 0.97 and 8.11 ± 1.20 days, respectively. The cuticularMnchi-1mRNA level as well as the chitinase activity at stage C showed an over 10- and 2-fold increase, respectively, after KK-42 treatment. However, at stage D, only amodestrise was observed at 12 h (). The results suggest that KK-42 can significantly up-regulate the cuticularMnchi-1gene expression and chitinase activity of the prawns at stage C, which may be one of the potential mechanisms of producing the KK-42-shortened moult cycle for juvenileM. nipponense.