Abstract
exploring the antiparasitic potential of black soldier fly (BSFL)-based preparations for the treatment of Gyrodactylus turnbulli, a monogenean parasite
Introduction
Parasitic infections caused by monogenea are a major concern in aquaculture, threatening fish health, growth, and overall farm productivity. The limited availability of approved and effective treatments, combined with their limited effectivity and associated health and environmental risks, necessitates the development of safer and more sustainable alternatives. Prior studies demonstrated that fatty acid ethyl esters (FAEEs), especially ethyl laurate, originated from lauric acid (C12:0) and possessed significant antiparasitic properties.
Black soldier fly larvae (BSFL) efficiently convert organic waste into nutrient-rich biomass, offering a sustainable source of protein and lipid. BSFL is also rich in lauric acid, with proven anti-parasitic properties.
Methodology
The anti-parasitic effect of a range of BSFL-based waste material and preparations are considered. These include BSFL extracts with different solvents, including ethyl acetate, ethyl ether and ethanol, as well as frass, which is the BSFL excretion. In addition, FAEE prepared through transethylation of dried BSFL biomass was tested.
The different preparations are initially tested ex-vivo, using tail fin clips from Gyrodactylus turnbulli-infected guppies. For this, infected fish are anaesthetised, euthanised, and tail fins containing at least five parasites are placed in 24-well plates with sterile tap water. The preparations tested are added at different concentrations, with appropriate controls. Parasite mortality and detachment are monitored. Effective preparations are further evaluated in vivo with infected guppies.
Results
Fatty acid composition of BSFL contained 56.1% lauric acid (C:12) and the FAEE preparation was respectively rich in ethyl laurate (the FAEE of lauric acid). Transethylation of dry BSFL powder provided 478 mg FAEEs per gram of BSFL. The FAEE preparation was diluted in ethanol at 38 mg/ml. This preparation was used for analysis.
BSFL-derived FAEEs induced 100% mortality of the parasite within 4 h at a concentration of 1.25 µl/ml FAEE-BSFL preparation in ethanol. This contains 75 µM ethyl laurate and is derived from 31 µg/ml BSFL powder. In vivo, complete elimination of the parasites was achieved from a concentration of 0.65 µl/ml FAEE-BSFL in ethanol. Toxicity tests confirmed no toxicity to the fish at the tested concentrations. The analysis of BSFL extracts with different solvents and frass is underway.
Conclusions
This study supports the integration of BSFL-based preparations into parasite management for aquaculture. FAEE-based preparation was shown to be effective for the treatment of G. turnbulli in guppies. The effect on other monogenean parasites in different fish species can be considered. Therapeutics based on natural sources like BSFL are potentially sustainable and cost-effective avenues for parasite treatment in aquaculture.