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A simple method to detect body morphological abnormalities in juvenile cyprinid fish—a case study on ide Leuciscus idus

Korwin-Kossakowski, Michał, Myszkowski, Leszek, Kamiński, Rafał
Aquaculture international 2017 v.25 no.2 pp. 915-925
Leuciscus idus, aquaculture, case studies, digital images, fish, juveniles, morphometry, rearing
Juvenile fish intensively reared under controlled conditions with formulated dry diets often differ in body shape from those fed natural food. These differences, initially invisible by eye and harmless to the fish, over the course of rearing may develop into severe, irreversible body deformities, which can adversely influence fish performance, welfare and production effectiveness in aquaculture. Early detection of the development of deformities makes it possible to implement a procedure to stop or mitigate them. The aim of this study was to create a simple, quick, reliable and safe morphometric method for the early detection of subtle abnormalities in juvenile fish, based solely on basic analysis of digital photographs of individual fish. Three of the six analysed shape variables detected small, yet highly significant (P < 10⁻⁶), differences in body shape between ide juveniles fed a formulated dry diet and those fed natural food. The proportion of the caudal length to the fork length (CLFL) was lower, and the first spiny ray of the caudal fin (angle of the first spiny ray of the upper part of the caudal fin (CRA)) was more bent in fish fed the former diet than those fed the latter. These shape variables (CLFL and the angle CRA) were independent of fish size in both groups. The method described in this study proved to be sufficiently sensitive to detect subtle differences in the body shape of juvenile fish intensively fed different diets. The method is simple and inexpensive and can be easily applied in aquaculture practice.