Investigating the effect of acute toxicity exposure to combined FeSO4 and FeCl3 in Litopenaeus vannamei through analysis of survival, metal accumulation, oxidative stress, and intestinal flora

Marine shrimp have been studied as bioindicators in environmental monitoring of heavy metal pollution. High levels of heavy metal iron (Fe) are potentially toxic and readily accumulate in organisms, causing damage. Up to now, there are few studies about the toxicity of Fe in the water on shrimp. In this study, the acute toxic effects of different concentrations of combined FeSO₄ and FeCl₃ on Pacific white shrimp (Litopenaeus vannamei) were examined from the aspects of survival, metal bioaccumulation, oxidative stress, and changes in intestinal microbes. The median lethal concentration (LC₅₀) of Fe at 96 h was 5.484 mg/L assessed after 0 h, 24 h, 48 h, 72 h, and 96 h at nominal concentrations of 0.2, 1.0, 5.0, 25.0, 125.0 and 625.0 mg/L for Fe respectively. No deaths were reported in the control group, but a significant rise in mortality was observed as the concentration of Fe increased every 24 h. A higher concentration of Fe exposure (1 % 96h- LC₅₀, 0.05484 mg/L; 10 % 96h-LC₅₀, 0.5484 mg/L) resulted in a significant rise of Fe concentration in the muscle tissue by 16.94 and 16.89 folds. Fe exposure significantly reduced superoxide dismutase (SOD) and catalase (CAT) activities and elevated malondialdehyde (MDA) levels. The acute exposure to Fe altered the intestinal flora of L. vannamei, including several beneficial bacteria such as Acidimicrobiia and Clostridia, and they were presently lower in the Fe2 group compared to the control group. The findings suggested that exposure to Fe causes noticeable Fe bioaccumulation, oxidative stress, and disruption of intestinal microbiota in L. vannamei.