The impact of fixation, preservation, and freezing on fish morphology in three cichlid species, with a discussion of this study in relation to museum fish specimens

The impact of different preservation procedures, including formalin fixation, ethanol preservation, and freezing, on the morphometric traits of fish preserved in museum specimens is tested in three different cichlid species: Oreochromis aureus (Steindachner, 1864), Coptodon zillii (Gervais, 1848), and Oreochromis niloticus (Linnaeus, 1758). The primary goal was to determine morphometric differences resulting from these procedures and identify correction values to reconstruct the original dimensions of the body. Our results support that shrinkage of morphological variables, such as total length (TL), standard length (SL),and head length (HL), is present in the three methods tested, depending on species, measurement, and treatment. This shrinkage is also supported by a least-squares regression analysis showing that length loss increases proportionally with larger fish sizes for the species under study. These findings are important as they confirm the differences observed among preservatives in all species, supporting the argument against significant morphometric biases related to freezing, while suggesting that standardized protocols be used with fixatives. These findings not only offer directions for those working with fish collections but also highlight the need for thorough documentation of preservation methods, in order to help future taxonomical and ecological research in ichthyology.