Glutaraldehyde Efficacy Against Cryptocaryon irritans Tomonts, Inducing ROS Generation and DNA Damage and Controlling Cryptocaryoniasis in Larimichthys crocea Factory‐Style Aquaculture

Cryptocaryon irritans is a pathogenic ciliate that causes cryptocaryoniasis and substantial economic losses in the mariculture industry. This study evaluated antiparasitic effects of glutaraldehyde (GA) against C. irritans tomonts and its therapeutic potential during C. irritans infection in large yellow croaker (Larimichthys crocea). In vitro, screening demonstrated that GA aquatic disinfectant (GA-ad) significantly inhibited tomont development, achieving half lethal concentration (LC50) at 10.23 μL/L for 8 h treatment. Toxicity test showed that three 8 h treatments with GA-ad at 10 times concentration of LC50 (102.3 μL/L) were safe for the fish. Therapeutic application of GA-ad (1 × LC50 = 10.23 μL/L, and 2 × LC50 = 20.46 μL/L) in the treated groups survived L. crocea till 63% and 100% on Day 21 (Relative tomont number, RTN = 0), while in the infected group (untreated) survival rate was 0% by day nine (RTN = 39.48). For the mechanistic study, GA chemical reagent (GA-cr, 10.23 μL/L, Pure GA = 5.12 μL/L) was used which induced oxidative stress and lipid peroxidation in tomonts, as evidenced by increased ROS and MDA level, reduced GSH:GSSG and CAT activity, and increased T-SOD activity. Additionally, the mRNA expression of P21, P53, Nqo1 and Gst were significantly upregulated in GA-cr treated tomonts. Collectively, these findings indicate that GA-cr disrupts redox homeostasis, induces oxidative and DNA damage that ultimately leads to cell cycle arrest in C. irritans. Overall, 20.46 μL/L of GA-ad is highly effective for controlling cryptocaryoniasis in L. crocea aquaculture.