Abstract

Comparative studies on the noble crayfish (Astacus astacus (L.) and signal crayfish (Pacifastacus leniusculus [Dana]) have been carried out in Lake Slickolampi (60° 01' N, 23° 34' E) since 1971. Crayfish for this study have been trapped and juveniles collected by electric fishing and dredge sieving. The mean total length of age 0+ Astacus astacus in autumn varied in different years between 18.6-30.0 mm and age 1+ between 36.6-48.0 mm and for Pacifastacus leniuscu/us between 26.2-33.6 mm and 61.0-62.2 mm respectively. So A. astacus grew by an average 10 mm in their first and 21 mm in their seoond summer and P. leniusculus 20 mm and 30 mm respectively. The mean increase in carapace length per moult was 5.3 mm and 4.7 mm for adult Astacus males and 4.0 mm and 3.0 mm for females. Growth per moult among Pacifastacus was greater; in males over the equivalent period on average 5.5 mm and 4.8 mm and in females on average 4.6 mm and 4.5 mm. The swifter growth rate in Pacifastacus compared to Astacus revealed by this study in the same enviroment is due in the main to the higher moulting frequency in mates, but also to the greater increase in length per moult in females.

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