“Biocontrol strategy to reduce skin fluke infections by targeting the parasite’s pre-infection stages (6929)”

Biocontrol strategy to reduce skin fluke infections by targeting the parasite’s pre-infection stages

Infections by skin flukes (Monogenea: Capsalidae) pose serious challenges in mariculture, causing growth retardation, secondary infections, and increased mortality in farmed fish. These parasites inflict substantial economic losses globally, particularly in the farming of groupers, seabreams, amberjacks, and many other species. Owing to their direct lifecycle and rapid proliferation, managing skin fluke infections requires frequent deworming treatments, such as chemical bathing. However, these treatments are costly, labor-intensive, and time-consuming, placing significant operational and financial burdens on fish farmers. In addition, the stress and fasting period associated with bath treatments further impair fish growth. Therefore, developing effective methods to reduce infection, as well as treatment frequency is urgently needed. To date, no preventive strategy has been successfully established for skin fluke infections in cage culture systems.

This study explored a novel biocontrol approach targeting the parasite’s pre-infection stages, namely eggs and hatched larvae (oncomiracidia), to reduce infection risk. We screened multiple fish species for their ability to consume skin fluke eggs and identified five candidates that actively fed on the eggs of Neobenedenia girellae and/or Benedenia seriolae. Among them, Girella leonina (Girellidae), and Siganus fuscescens (Siganidae) were selected as “egg-remover” and co-cultured with juvenile Seriola species in experimental cages. Cages stocked with egg-remover fish showed marked reduction in biofoulings, highlighting their dual role as effective “cage-cleaners”. Juvenile Seriola co-cultured with egg-removers exhibited significantly lower levels of skin fluke infection, reduced mortality, and improved growth performance. These beneficial effects were consistent across repeated trials involving both N. girellae and B. seriolae infections. Furthermore, the egg-remover species were shown to be highly resistant to skin flukes and possess market value, contributing additional income opportunities for fish farmers.

We also assessed the role of filter-feeding bivalves in removing oncomiracidia from the water column. Tank experiments demonstrated that oysters, mussels, and clams effectively reduced larval density over time. Exposure trials with Seriola juveniles in tanks containing live oysters showed promising reductions in infection compared to tanks with only oyster shells, although results varied between trials.

Our findings suggest that co-culturing fish species that consume parasite eggs, alongside incorporating filter-feeding bivalves to lower larval abundance, offers an innovative and eco-friendly strategy for the sustainable management of skin fluke infections in cage aquaculture.

1. SHIRAKASHI, SHO, KINDAI UNIVERSITY, Presenter
2. TOMITA, YUKI, KINDAI UNIVERSITY, Author
3. NOBUHISA, HATTORI, KINDAI UNIVERSITY, Author
4. KAZUO, OGAWA, Meguro Parasitological Museum, Author