Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Fisheries Research art. 105425 [8 p.] automatic fish measurement catch size structure image analysis reef fish MADAGASCAR TULEAR BAIE 2020 fdi:010077864 ENG Fisheries Research 0165-7836 ISI:000509622800003 10.1016/j.fishres.2019.105425 https://www.documentation.ird.fr/hor/fdi:010077864 https://www.documentation.ird.fr/intranet/publi/2020/02/010077864.pdf 223 Horizon (IRD) Measuring fish length is useful for exploring size structure of catches and fishing effects on marine resources. However manually measuring large numbers of individuals requires time-consuming manipulations, which are hardly operational in the context of tropical small-scale fisheries. To overcome this limitation, we developed a method to automatically measure total fish length using digital images and an analytical procedure using the ImageJ software. For testing this procedure, a total of 180 fishes (3 to 50 cm TL) from 19 families, presenting two color patterns and two caudal fin types, were obtained from small-scale fishers in southwestern Madagascar in 2018. We took standardized images of the fishes using a locally made, cost-effective camera-equipped device. The accuracy of fish size estimates and the time taken for measurements were compared across the ImageJ automatic procedure, manual measurements made on-screen using ImageJ, and measurements using an ichthyometer, the latter providing the reference fish length. The ImageJ automatic measurement procedure reached 98.4% accuracy while the measurement time was reduced by 57% and 40% compared to the measures using an ichthyometer and ImageJ on-screen tools, respectively. We conclude that the automatic measurement procedure provides very effective results for fish < 50 cm TL. This method is relevant for governmental, non-governmental, and research organizations that investigate size-related fishing and management impacts on fish community structure and dynamics. 040 ; 122 UR250 Madagascar