Comparative Therapeutic Effects of Natural Compounds Against Saprolegnia spp. (Oomycota) and Amyloodinium ocellatum (Dinophyceae)

Abstract

The fish parasites Saprolegnia spp. (Oomycota) and Amyloodinium ocellatum (Dinophyceae) cause important losses in freshwater and marine aquaculture industry, respectively. The possible adverse effects of compounds used to control these parasites in aquaculture resulted in increased interest on the search for natural products with antiparasitic activity. In this work, eighteen plant-derived compounds (2 ′ ,4 ′-Dihydroxychalcone; 7-Hydroxyflavone; Artemisinin; Camphor (1R); Diallyl sulfide; Esculetin; Eucalyptol; Garlicin 80%; Harmalol hydrochloride dihydrate; Palmatine chloride; Piperine; Plumbagin; Resveratrol; Rosmarinic acid; Sclareolide; Tomatine, Umbelliferone, and Usnic Acid) have been tested in vitro. Sixteen of these were used to determine their effects on the gill cell line G1B (ATCC ® CRL-2536 TM) and on the motility of viable dinospores of Amyloodinium ocellatum, and thirteen were screened for inhibitory activity against Saprolegnia spp. The cytotoxicity results on G1B cells determined that only two compounds (2 ′ ,4 ′-Dihydroxychalcone and Tomatine) exhibited dose-dependent toxic effects. The highest surveyed concentrations (0.1 and 0.01 mM) reduced cell viability by 80%. Upon lowering the compound concentration the percentage of dead cells was lower than 20%. The same two compounds revealed to be potential antiparasitics by reducing in a dose-dependent manner the motility of A. ocellatum dinospores up to 100%. With respect to Saprolegnia, a Minimum Inhibitory Concentration was found for Tomatine (0.1 mM), Piperine and Plumbagin (0.25 mM), while 2 ′ ,4 ′-Dihydroxychalcone considerably slowed down mycelial growth for 24 h at a concentration of 0.1 mM. Therefore, this research allowed to identify two compounds, Tomatine and 2 ′ ,4 ′-Dihydroxychalcone, effective against both parasites. These compounds could represent promising candidates for the treatment of amyloodiniosis and saprolegniosis in aquaculture. Nevertheless, further in vitro and in vivo tests are required in order to determine concentrations that are effective against the considered pathogens but at the same time safe for hosts, environment and consumers.

Essential Oils of Sage, Rosemary, and Bay Laurel Inhibit the Life Stages of Oomycete Pathogens Important in Aquaculture

“…In addition, β-pinene and 1,8-cineole (present in significant amounts in both sage and bay laurel essential oils) were positively correlated with the inhibition of S. parasitica zoospore germination, explaining the similar EC 50 values of these two essential oils for S. parasitica zoospore germination (EC 50 0.012 and 0.013 µL/mL, respectively). Some of these compounds were previously reported to exhibit good anti-oomycete [ 44 , 55 ] and antifungal [ 56 , 57 , 58 , 59 ] activity. For example, camphor (up to 38.06 µg/mL) progressively slowed down the mycelial growth of S. parasitica and S. delica , while thujone and β-pinene (500 and 1000 µg/mL, respectively) inhibited the mycelial growth of S. parasitica [ 44 , 55 ].…”

“…Some of these compounds were previously reported to exhibit good anti-oomycete [ 44 , 55 ] and antifungal [ 56 , 57 , 58 , 59 ] activity. For example, camphor (up to 38.06 µg/mL) progressively slowed down the mycelial growth of S. parasitica and S. delica , while thujone and β-pinene (500 and 1000 µg/mL, respectively) inhibited the mycelial growth of S. parasitica [ 44 , 55 ]. Moreover, α-thujone and camphor have potent antifungal activity against Fusarium graminearum , F. culmorum , and Schizosaccharomyces pombe , which is mainly explained by the induction of oxidative stress and subsequent apoptotic cell death, but also by a decrease in genomic stability and epigenetic changes [ 56 , 57 , 58 , 59 ].…”

First insights into oxidative stress and theoretical environmental risk of Bronopol and Detarox® AP, two biocides claimed to be ecofriendly for a sustainable aquaculture

“…in particular, was demonstrated in rainbow trout (Oncorhynchus mykiss) and salmonid eggs (Branson, 2002;Sudova et al, 2007). However, it was found toxic for phyto-and zooplankton (Tedesco et al, 2018) in the water due to rapid degradation into toxic persistent by-products (e.g., 2-bromo-2-nitroethanol, bromonitromethane, tri (hydroxymethyl) nitromethane, nitromethane, 2-bromoethanol, formaldehyde) (Cui et al, 2011). Though no data on the oxidative stress driven by Bronopol on aquatic organisms are available.…”

“…Within this scenario, Detarox® AP has one of the best-balanced formulations (20% hydrogen peroxide, 5% peracetic acid, and 10% acetic acid) (Perdomini-ioc.com, 2017) and so may offer a theoretical compromise between efficacy and safety. Although Detarox® AP inhibited a growth of the fungi S. parasitica and S. delica (Tedesco et al, 2018) and proved to be efficacious in the treatment of European eels (Anguilla anguilla) infested with the protozoan Trichodina jadranica (Madsen et al, 2000), its toxicity for aquatic invertebrates has not yet been investigated.…”

Isolation, molecular identification, and pathological lesions of Saprolegnia spp. isolated from common carp, Cyprinus carpio in floating cages in Mosul, Iraq

“…Saprolegnia parasitica is responsible for substantial fish mortality [ 10 ]; Saprolegnia spp. infections are closely associated with catastrophic losses in fish production in both freshwater and marine aquaculture industries [ 11 ]. Pathogenic oomycetes also infect fish eggs and cause considerable losses in fish hatcheries [ 12 ].…”