Protective Effects of Combined Utilization of Quercetin and Florfenicol on Acute Hepatopancreatic Necrosis Syndrome Infected Litopenaeus vannamei

Abstract

This study aimed to determine the immunity, survival rate, and disease resistance of Litopenaeus vannamei treated using quercetin and florfenicol alone or in combination, after infection with acute hepatopancreatic necrosis syndrome caused by Vibrio parahaemolyticus (VPAHPND). After infection with VPAHPND, different types of feed were given to the shrimp for 5 days, including a control diet (drug-free), florfenicol only diet (15 mg/kg), quercetin only diet (400 mg/kg), a low-dose florfenicol/quercetin combined diet (200 mg/kg quercetin + 7.0 mg/kg florfenicol), a moderate-dose florfenicol/quercetin combined diet (400 mg/kg quercetin + 15 mg/kg florfenicol), and a high-dose florfenicol/quercetin combined diet (800 mg/kg quercetin + 30 mg/kg florfenicol). The cumulative mortality of shrimp was significantly reduced in the drug combination groups compared with either drug used alone (p < 0.05). The density of Vibrio was significantly lower and the immune parameters were significantly increased in the drug combination groups compared with either drug used alone (p < 0.05). Moreover, in the drug combination groups, the hepatopancreas tubules showed better integrity and structure compared with those when either drug was used alone. Therefore, compared with single drug treatment, the florfenicol and quercetin combination enhanced disease resistance, survival, and immune activity of VPAHPND-infected shrimp. When the combination treatment is used, the dosage of florfenicol can be reduced and a better therapeutic effect is obtained.

Keywords: Litopenaeus vannamei; VPAHPND; florfenicol; immunomodulation; quercetin.

Figure 1

The (A) protection rates and (B) cumulative mortality of VP_AHPND-infected L. vannamei in each experimental group at different times after drug treatment. One-way ANOVA and Duncan’s multiple range test were used to analyze the significant differences among different groups, and different letters represent significant differences between groups (p < 0.05).

Figure 2

The VP_AHPND density in the hepatopancreas of L. vannamei at different times after drug treatment. One-way ANOVA and Duncan’s multiple range test were used to analyze the significant differences among different groups, and different letters represent significant differences between groups (p < 0.05).

Figure 3

The THC levels (A), HEM levels (B), and antibacterial activity (C) in L. vannamei at different times following drug treatment. One-way ANOVA and Duncan’s multiple range test were used to analyze the significant differences among different groups, and different letters represent significant differences between groups (p < 0.05).

Figure 4

Immunity-related enzyme activities in drug-treated L. vannamei. (A) PO, (B) SOD, (C) GSH-Px, (D) LZM, (E) ACP, and (F) AKP in L. vannamei acellular hemolymph after different times of drug treatment. One-way ANOVA and Duncan’s multiple range test were used to analyze the significant differences among different groups, and different letters represent significant differences between groups (p < 0.05).

Figure 5

Immunity-related factors’ gene expression in drug-treated L. vannamei. (A) Alf, (B) CatB, (C) Cru, (D) Lec, (E) Lzm, and (F) Tlr in L. vannamei hemocytes at different times after drug treatment. One-way ANOVA and Duncan’s multiple range test were used to analyze the significant differences among different groups, and different letters represent significant differences between groups (p < 0.05).

Figure 6

Changes in the histology of drug-treated L. vannamei hepatopancreases at 5 days. (A) Control, (B) infection only, (C) florfenicol, (D) quercetin, (E) LDC, (F) MDC, and (G) HDC group. Scale bar = 50 μm.