A simple photogrammetric, non-destructive method for measuring individual biomass in tubular soft-bodied organisms has been developed using Eisenia andrei. Photographic procedures can be easily performed with low cost digital cameras and the number of pictures to be processed can be reduced to two per animal (Variation Coefficient ≤ 3.5%) even at sizes ~10 mg live weight. Image analysis was undertaken using CobCal 2.0© software. No bias was induced by body position. Accuracy in terms of the regression coefficient of the equation (y=a*xb) relating portrayed area (mm2) to live weight (mg) was 98%. Two different procedures were designed for laboratory and field uses. No differences between methods appeared at sizes over eight mg live weight, resulting in a common function relating image area to live weight results (PS = 3.27*LW0.681). Below 8 mg, the weight exponent remained unchanged but the value for the elevation rose to 4.21 indicating an increase of surface exposure to the camera lens in newly-hatched worms: the visible part of the geometric area (cylinder shape) enlarged from 34% to 43.52%. As a conclusion this non-invasive procedure proved suitable for worms ranging from sizes of 0.2 to 3 000 mg live weight to determine biometric parameters such as length, volume, surface or body weight, which are key factors for interpreting physiological responses to underlying growth patterns.
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