Estimation of shrimp (Pandalus borealis) carapace length by image analysis

An image analysis technique was examined to assess its ability to estimate automatically the carapace length of shrimp (Pandalus borealis). Carapace length, pixel area, and weight were measured in a sample of 285 shrimp. An accurate slide calliper was used to measure the carapace length (13-30 mm) by an experienced operator with a precision (standard deviation) of similar to 0.2 mm. A high-resolution still image camera was used to produce an 1810 x 1710 pixel colour image containing all 285 shrimp. The individual shrimp were segmented from the background by intensity thresholding. A linear model on a log-log scale of length in relation to pixel area yielded a precision of 0.43 mm. Despite differences in precision, the length frequency distributions based on manual and imaging techniques were similar. The central processing unit time spent by the image analysis program was <0.01 s per shrimp. This indicates the potential for precise, efficient, automatic processing of large numbers of shrimp lengths by, for example, video records of shrimp on a moving transport band.