Effects of formaldehyde treatment on blood parameters and gill histology in rainbow trout (Oncorhynchus mykiss) infested with Trichodina sp.

Year 2025, Volume: 14 Issue: 3, 131 - 138, 30.09.2025

Akif Er

https://doi.org/10.33714/masteb.1751242

Abstract

This study evaluates the effects of formaldehyde (formalin) treatment on hematological parameters and gill histology in rainbow trout (Oncorhynchus mykiss) infested with Trichodina sp. In the experiment, rainbow trout (Oncorhynchus mykiss) naturally caught from a local facility and heavily infested with Trichodina sp. were divided into two groups: one treated with a formalin bath (150 ppm for 45 minutes) and one untreated. While no Trichodina sp. parasites were detected in the treated group, a 10% mortality rate was observed in the untreated group. Hematological analyses showed significant time-dependent increases in leukogram (WBC (White Blood Cell count,) LYM (Lymphocytes), GRAN (Granulocytes)) and erythrogram parameters (RBC (Red Blood Cell count,) HGB (Hemoglobin concentration,) and HCT (Hematocrit)) levels in the formalin-treated group. These findings indicate that the immune and hematopoietic systems recovered post-infestation. Histological evaluations revealed severe lamellar fusion, hyperplasia, telangiectasia, and epithelial lifting in untreated fish, while these findings were mild in the formalin-treated group and showed a tendency to return to normal over time. In conclusion, formaldehyde application not only reduced the parasite load but also improved the physiological health of the fish. It is suggested that formalin application at an appropriate dose and under controlled conditions could be a safe and effective antiparasitic method in aquaculture.

Keywords

Aquaculture health management , Ectoparasitic infestation , Fish parasite control , Hematology , Histopathology , Formalin bath

Ethical Statement

Current study was checked and approved by the Ethical Local Committee of the Recep Tayyip Erdogan University (Decision No: 2023/08).

Thanks

I would like to thank Dr. Mert Minaz and Prof. Dr. Şevki Kayış for their assistance in analyzing and visualizing the data.

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