Antifungal Activity of Rhein and Aloe‐Emodin from Rheum palmatum on Fish Pathogenic Saprolegnia sp.

Abstract

Saprolegnia infections cause severe economic losses among freshwater fish farming. In this study, two known compounds, rhein and aloe‐emodin, were isolated from Rheum palmatum, and the in vitro inhibitory activity of both compounds against mycelial growth and spore germination of Saprolegnia was tested. Both rhein and aloe‐emodin were able to decrease Saprolegnia mycelial growth and spore activity in all tested concentrations after exposure for 48 h. Complete inhibition of mycelial growth was observed at 20 mg/L for rhein and at 50 mg/L for aloe‐emodin, while spore germination was 100% prevented at 16 and 40 mg/L for rhein and aloe‐emodin, respectively. Because rhein showed stronger in vitro anti‐Saprolegnia activity, it was further tested in vivo to measure the prevention and treatment efficacy on Saprolegnia infection of grass carp. Its acute activity to grass carp was also evaluated. The results revealed that exposure to rhein at 20 mg/L for 7 d could prevent 93.3% of infections by Saprolegnia in abraded grass carp, while 67.7% of infected fish could be recovered by treatment with rhein. The 48‐h median lethal concentration (48 h‐LC50) to grass carp was 148.5 mg/L, which is about 7.4 times the effective dose indicating the safety for the use of rhein. This study suggests that rhein has promising anti‐Saprolegnia activity and may be an option in preventing and controlling Saprolegnia infection.

In vitro screening for the antifungal activity of some Egyptian plant extracts against the fish pathogen Saprolegnia parasitica

“…Only few candidates of the tested plant extracts demonstrated in vitro anti-fungal effects against S. parasitica. This finding is in agreement with other related plant extracts and active principals tested by other researchers (Hu et al, 2019;Khosravi et al, 2012;Soltani et al, 2020;Tampieri et al, 2003;Yao et al, 2017;Zeng et al, 2019). It was found that monoterpenic aromatic compounds were very active against cutaneous saprolegniasis in fish (Pirbalouti et al, 2009;Tampieri et al, 2003).…”

“…Accordingly, worldwide investigators have mined the folk traditional medicines for a candidate. Many studies demonstrated promising anti-fungal activity of plant extracts against fish pathogenic fungi, in vivo fish experiments proved the efficacy by various plant extracts (ALsafah & AL-Faragi, 2017;Cao, Ou, Li, Yang, Zheng, & Lu, 2014;Chukanhom, Borisuthpeth, & Hatai, 2005;Hussein, El-Feki, Hatai, & Yamamoto, 2002;Hussein, Wada, Hatai, & Yamamoto, 2000;Ilondu, Arimoro, & Sodje, 2010;Yao et al, 2017;Zhen, Wang, Fan, & Lui, 2014). Furthermore, inhibition of fish egg mycosis was observed by other extracts (Khosravi, Shokri, Sharifrohani, Mousavi, & Moosavi, 2012;Li & Liu, 2015;Zeng et al, 2019).…”

“…Furthermore, inhibition of fish egg mycosis was observed by other extracts (Khosravi, Shokri, Sharifrohani, Mousavi, & Moosavi, 2012;Li & Liu, 2015;Zeng et al, 2019). Other in vitro screening studies showed significant anti-Saprolegnia activity of many extracts (Gormez & Diler, 2014;Hu et al, 2013;Huang et al, 2015;Macchioni, 1999;Mori, Hirose, Hanjavanit, & Hatai, 2002;Rai, Kaushal, & Acharya, 2002;Rai, Soni, & Acharya, 2000;Udomkusonsri, 2007;Yao et al, 2017).…”

The efficacy of Virkon-S for the control of saprolegniasis in common carp, Cyprinus carpio L

“…The inhibitory effects of Virkon-S on spore germination were tested using two methods. First, the minimum fungicidal concentration (MFC), defined as the lowest concentration of a chemical that prevents germination or the visible growth of spores, was determined as described previously ( Yao et al, 2017 ; Hu et al, 2013 ). Spore suspension containing oospores and zoospores was prepared as described as Yao et al (2017) .…”

Peer Review #2 of "The efficacy of Virkon-S for the control of saprolegniasis in common carp, Cyprinus carpio L (v0.1)"

“…119 First, the minimum fungicidal concentration (MFC), defined as the lowest concentration of a 120 chemical that prevents germination or the visible growth of spores, was determined as described 121 previously (Yao et al, 2017;Hu et al, 2013). Spore suspension containing oospores and 122 zoospores was prepared as described as Yao et al (2017). S. parasitica was cultured on PDA at 123 25°C for 12 days to induce spores.…”