Evaluation of chemical treatments to mitigate or eradicate Gnathia maxillaris infestations

Abstract

Summary The eradication of the haematophagous isopod ectoparasite Gnathia maxillaris was not achieved after several years of physical elimination of larvae by filtration and chemical treatment with trichlorfon in a captive marine fish population in exhibition aquaria. In this study, different in vitro laboratory assays were performed to find effective alternative anti‐parasitic treatments to trichlorfon (lufenuron, emamectin benzoate, cypermethrin and abamectin). The lethal concentration 50 (LC50) values at 96 hr were calculated for each compound using both larval stages (zuphea and praniza); morphological deformities generated throughout the life cycle, reduction in egg laying and survival of adult forms were also determined. Abamectin, cypermethrin and emamectin benzoate proved effective at limiting further Gnathia maxillaris development, but their efficacy at eradicating an infestation in large tanks was not supported by laboratory assays. However, the use of lufenuron proved to be a good substitute for trichlorfon when treating this type of infestation in large‐volume tanks (LC50 55.8 mg m−3 for praniza). Routine lufenuron treatment once a month via an oral dose at 10 mg kg−1 body weight eradicated G. maxillaris from the exhibition aquaria.

Antiparasitic approaches and strategies in European aquaculture, with emphasis on Mediterranean marine finfish farming: Present scenarios and future visions

“…The high efficacy of LUF against sea lice was recently evidenced and attributed to the rapid impact on moulting processes 204 . Interestingly, LUF administered at 10 mg/kg eradicated the isopod Gnathia maxillaris from aquarium fish 205 . There is no academic information on the toxicity of the compound on non‐target organisms.…”

“…204 Interestingly, LUF administered at 10 mg/kg eradicated the isopod Gnathia maxillaris from aquarium fish. 205 There is no academic information on the toxicity of the compound on non-target organisms. LUF is a new in-feed antiparasitic agent in fish medicine and consequently, any attempt to evaluate its potential as a fish antimicrobial in Mediterranean aquaculture is relatively premature.…”