Low-Dose Formalin Treatment for Gyrodactylus sp. Infection in Rainbow Trout (Oncorhynchus Mykiss) Cultured in a Low-Head Recirculating Aquaculture System in Vietnam

Date Received: Jul 17, 2025

Date Accepted: Jan 08, 2026

Date Published: Mar 31, 2026

DOI: https://doi.org/10.31817/vjas.2026.9.1.03

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Issue: Vol. 9 No. 1 (2026): Vietnam Journal of Agricultural Sciences

Section:

ANIMAL SCIENCE – VETERINARY MEDICINE – AQUACULTURE

How to Cite:

Chi, T., Tram, P., Binh, P., Lam, N., Hai, N., Giang, L., & Giang, P. (2026). Low-Dose Formalin Treatment for Gyrodactylus sp. Infection in Rainbow Trout (Oncorhynchus Mykiss) Cultured in a Low-Head Recirculating Aquaculture System in Vietnam. Vietnam Journal of Agricultural Sciences, 9(1), 2814–2822. https://doi.org/10.31817/vjas.2026.9.1.03

Low-Dose Formalin Treatment for Gyrodactylus sp. Infection in Rainbow Trout (Oncorhynchus Mykiss) Cultured in a Low-Head Recirculating Aquaculture System in Vietnam

Tran Thi Kim Chi 1 , Phan Thi Tram 1 , Phan Trong Binh 1 , Nguyen Khac Lam 2 , Nguyen Thanh Hai 1 , Luu Thi Ha Giang 1   , Pham Thai Giang (*) 1

  • Corresponding author: [email protected]
  • 1 Research Center for Coldwater Aquaculture, Research Institute for Aquaculture No. 1 (RIA1), Bacninh 16000, Vietnam
  • 2 Center for Agricultural Extension, Ministry of Agriculture and Environment, Hanoi 12000, Vietnam

    • Keywords

    Low dose formalin, Gyrodactylus sp, rainbow trout, low-head RAS

    Abstract


    Recirculating aquaculture systems (RAS) for rainbow trout (Oncorhynchus mykiss) have been widely implemented worldwide. However, their adoption in Vietnam has occurred only over the past decade and remains limited due to several operational challenges. Among these, disease management is particularly difficult because chemical treatments can disrupt the microbial community within the biofilter. This study assessed the effectiveness of a low-dose formalin treatment for controlling Gyrodactylus sp. infection in rainbow trout reared in a recirculating aquaculture system (RAS). During a mortality episode associated with Gyrodactylus sp. infestation, formalin was applied at concentrations of 15-20ppm for 10h per day over three consecutive days. Water-quality parameters, parasite infection intensity, and fish mortality were systematically monitored throughout each treatment period. The results indicated that after three days of treatment, fish mortality significantly decreased, while parasite infection dropped 95.3-96.7%. The results also revealed fluctuations in water quality parameters, including temporary increases in COD, N-NH₄⁺, and N-NO₂⁻ concentrations, associated with a decline in nitrifying microbial activity. Nevertheless, these changes remained within acceptable limits and did not cause severe system disruption. The findings demonstrate that low-dose formalin treatments effectively reduce mortality in infected rainbow trout without severely impairing the beneficial microbial community in RAS.

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