THE EFFECTS OF EYESTALK, LEG, AND UROPOD REMOVAL ON THE MOLTING AND GROWTH OF YOUNG CRAYFISH, PROCAMBARUS CLARKII

ISAMU NAKATANI ¹ and TAKASHI TSU ¹

¹ Department of Biology, Faculty of Science, Yamagata University, Yamagata, 990 Japan

1. Removal of a pair of eyestalks induces precocious molt and accelerates the growth of the crayfish, Procambarus clarkii.

2. Removal of three pairs of walking legs or a pair of uropods induces precocious molt without any effects on the growth of the body.

3. The average time required for 50% of the individuals to reach the fifth molt after the intial molt is 39 days for eyestalkless crayfish, 99 days for legless, and 136 days for uropodless crayfish. The untreated crayfish (controls) required 164 days to attain the fifth molt.

4. The average percentage of increase in carapace length at the time of the fifth molt is 9.6% for the untreated crayfish, 17.6% for eyestalkless, 8.9% for legless, and 9.4% for the uropodless group.

5. The mortality during the approximately eight-month experimental period was 5:23 for the untreated group, 12:23 for the eyestalkless group, 2:23 for the legless group and 2:23 for the uropodless group. The eyestalkless crayfish were healthy until the third molt, but experienced great mortality at the time of the fourth and fifth molt. The failure of molt in eyestalkless crayfish may be due to too rapid increase in the body size, imparing preparations for molt.