Assessment of Bolbophorus damnificus prevalence and cercariae shedding in Planorbella trivolvis populations from catfish aquaculture ponds in Mississippi, USA

Abstract

Bolbophorus damnificus (Digenea: Bolbophoridae) causes significant losses in US catfish aquaculture. Little is known regarding the prevalence of infected snail hosts during outbreaks. To assess prevalence of snails observed shedding Bolbophorus spp. cercariae, as well as snails that were infected but not observed shedding cercariae, Planorbella trivolvis (n = 8,159) were collected from 14 catfish production ponds with B. damnificus activity in Mississippi, USA. Individual snails were placed in 10 ml of filtered (20 μm) reservoir pond water and observed for 48 hr for cercariae release. Identification of B. damnificus or Bolbophorus sp. type II cercariae was confirmed by duplex PCR. Genomic DNA was isolated from ~100 non‐shedding snails from each pond and the PCR assay used to identify the presence of B. damnificus or Bolbophorus sp. type II infected snails. The prevalence of snails shedding B. damnificus ranged from 0.23 to 13.6%. Observation of cercariae shedding underestimated true B. damnificus and Bolbophorus sp. type II prevalence in 42.9 and 64.3% of sampled ponds, respectively. Prevalence of B. damnificus infected snails was typically <3%, indicating numbers of infected snails during outbreaks are low and mitigation efforts may be successful simply by reducing snail numbers and not require complete eradication.

Comparative Mortality of Juvenile Channel and Hybrid Catfish Exposed to Bolbophorus damnificus Cercariae

“…The most effective strategy for managing B . damnificus is by reducing snail populations in ponds (Venable et al 2000; Mitchell and Hobbs 2003; Terhune et al 2003; Wise et al 2006, 2008; Mitchell et al 2007; Gunn et al 2020). Although the metacercarial cyst can persist in catfish for over 12 months (Mitchell et al 2011; Gunn 2020), once the source of infection is removed, the growth, feed consumption, disease resistance, and survival of affected cohorts are comparable to those of parasite‐free cohorts (Wise et al 2013).…”