Polychaetes (Perinereis helleri) reared in sand beds filtering nutrients from shrimp (Penaeus monodon) culture ponds can transiently carry IHHNV

Abstract

A polychaete-assisted sand filter (PASF) system has been developed to help remove nutrients from aquaculture pond wastewater whilst also producing polychaetes that are highly prized as bait by recreational anglers and as a dietary supplement to improve the fecundity of shrimp broodstock. Whilst rearing polychaetes in PASF beds offers potential to reduce impacts of sourcing them from the wild, the use of wastewater from ponds rearing shrimp such as Penaeus monodon will present a biosecurity risk of viruses being transferred to, and potentially amplified in, the worms. To assess such risks for transmitting infectious hypodermal and haematopoietic necrosis virus (IHHNV), groups of 3 or 4 PASF beds seeded with sand worm (Perinereis helleri) juveniles were supplied with wastewater from ponds of P. monodon with either high-load or low-load IHHNV infections. TaqMan real-time qPCR identified low loads of IHHNV (≤878 IHHNV DNA copies 200 ng−1 TNA) in most worms from PASF beds supplied wastewater from the high-load pond. IHHNV was either not detected or detected at the qPCR test sensitivity limits in worms from beds supplied wastewater from the low-load pond. Purging harvested worms of their gut contents in clean filtered seawater for 2 days significantly reduced IHHNV loads. Reverting PASF beds to clean seawater for 8 weeks before harvest also significantly reduced worm loads of IHHNV. Daily additions of a commercial probiotic to the sand bed surface for 4 weeks prior to clean seawater application provided no discernible benefit to IHHNV clearance. While clearly demonstrated to be capable of carrying IHHNV, the remediation measures examined suggest potential to ameliorate the infection transmission risks of P. helleri reared in PASF beds supplied with shrimp pond wastewater as a nutrient source.