In vivo calibration of juvenile crayfish body length and weight with a photographic-computer method

The aim of this work was to develop a photographic-computer method to determine in vivo the body length and weight of juvenile crayfish based on standards that describe the dependence curves of these characters. The measurement procedure that was developed requires one digital group photograph of a sample generally comprised of thirty or so individuals and an image scale, which is visible within the frame. A special program is used to analyze the image according to the scale on the image. Further, only the cephalothorax length (CL) of specimens from the studied sample that appear in the photograph is measured. Total length (TL) and weight (W) are then calculated with correlation formulae that were developed for the characters analyzed. The following dependencies were calculated from the formulae developed for two-month-old narrow-clawed crayfish, Astacus leptodactylus (Esch.) (n = 101, W = 225.9 ± 67.2 mg, TL = 18.7±2.1 mm): TL = 1.739 CL + 1.1903, W = 0.1306 TL^2.533, W = 0.7635 CL^2.4476. All of the dependencies were highly significant statistically (P < 0.001).