{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T02:56:24Z","timestamp":1773888984350,"version":"3.50.1"},"reference-count":32,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2025,7,1]],"date-time":"2025-07-01T00:00:00Z","timestamp":1751328000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004837","name":"Ministry of Science, Innovation and Universities, the Spanish Research Agency","doi-asserted-by":"publisher","award":["RYC2022-036557-I"],"award-info":[{"award-number":["RYC2022-036557-I"]}],"id":[{"id":"10.13039\/501100004837","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100004837","name":"Ministry of Science, Innovation and Universities, the Spanish Research Agency","doi-asserted-by":"publisher","award":["101074197"],"award-info":[{"award-number":["101074197"]}],"id":[{"id":"10.13039\/501100004837","id-type":"DOI","asserted-by":"publisher"}]},{"name":"European Social Fund Plus (FSE+)","award":["RYC2022-036557-I"],"award-info":[{"award-number":["RYC2022-036557-I"]}]},{"name":"European Social Fund Plus (FSE+)","award":["101074197"],"award-info":[{"award-number":["101074197"]}]},{"name":"European Commission","award":["RYC2022-036557-I"],"award-info":[{"award-number":["RYC2022-036557-I"]}]},{"name":"European Commission","award":["101074197"],"award-info":[{"award-number":["101074197"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Effective monitoring of fish passage through river barriers is essential for evaluating fishway performance and supporting adaptive river management. Traditional methods are often invasive, labor-intensive, or too costly to enable widespread implementation across most fishways. Infrared (IR) beam-break counters offer a promising alternative, but their adoption has been limited by high costs and a lack of flexibility. We developed and tested a novel, low-cost infrared beam-break counter\u2014FishTracker\u2014based on open-source Raspberry Pi and Arduino platforms. The system detects fish passages by analyzing interruptions in an IR curtain and reconstructing fish silhouettes to estimate movement, direction, speed, and morphometrics under a wide range of turbidity conditions. It also offers remote access capabilities for easy management. Field validation involved controlled tests with dummy fish, experiments with small-bodied live specimens (bleak) under varying turbidity conditions, and verification against synchronized video of free-swimming fish (koi carp). This first version of FishTracker achieved detection rates of 95\u2013100% under controlled conditions and approximately 70% in semi-natural conditions, comparable to commercial counters. Most errors were due to surface distortion caused by partial submersion during the experimental setup, which could be avoided by fully submerging the device. Body length estimation based on passage speed and beam-interruption duration proved consistent, aligning with published allometric models for carps. FishTracker offers a promising and affordable solution for non-invasive fish monitoring in multispecies contexts. Its design, based primarily on open technology, allows for flexible adaptation and broad deployment, particularly in locations where commercial technologies are economically unfeasible.<\/jats:p>","DOI":"10.3390\/s25134112","type":"journal-article","created":{"date-parts":[[2025,7,1]],"date-time":"2025-07-01T06:56:54Z","timestamp":1751353014000},"page":"4112","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Design and Initial Validation of an Infrared Beam-Break Fish Counter (\u2018Fish Tracker\u2019) for Fish Passage Monitoring"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2384-9085","authenticated-orcid":false,"given":"Juan Francisco","family":"Fuentes-P\u00e9rez","sequence":"first","affiliation":[{"name":"Group of Applied Ecohydraulics, Department of Agricultural and Forest Engineering, Sustainable Forest Management Research Institute, University of Valladolid, ETSIIAA, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-4065-4543","authenticated-orcid":false,"given":"Marina","family":"Mart\u00ednez-Miguel","sequence":"additional","affiliation":[{"name":"Group of Applied Ecohydraulics, Department of Agricultural and Forest Engineering, Sustainable Forest Management Research Institute, University of Valladolid, ETSIIAA, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3765-9007","authenticated-orcid":false,"given":"Ana","family":"Garc\u00eda-Vega","sequence":"additional","affiliation":[{"name":"Group of Applied Ecohydraulics, Department of Agricultural and Forest Engineering, Sustainable Forest Management Research Institute, University of Valladolid, ETSIIAA, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3687-9902","authenticated-orcid":false,"given":"Francisco Javier","family":"Bravo-C\u00f3rdoba","sequence":"additional","affiliation":[{"name":"Group of Applied Ecohydraulics, Centro Tecnol\u00f3gico Agrario y Agroalimentario ITAGRA.CT, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4566-9499","authenticated-orcid":false,"given":"Francisco Javier","family":"Sanz-Ronda","sequence":"additional","affiliation":[{"name":"Group of Applied Ecohydraulics, Department of Agricultural and Forest Engineering, Sustainable Forest Management Research Institute, University of Valladolid, ETSIIAA, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Lucas, M., and Baras, E. 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