A simplified method to estimate Diphyllobothrium spp. infection in salmonids

Area of Science:

• Parasitology
• Aquatic Ecology
• Fisheries Management

Background:

• Fish parasites like Diphyllobothrium spp. pose significant management challenges, causing host mortality and potential zoonotic risks.
• Accurate parasite assessments are crucial for monitoring fish health and managing aquatic ecosystems.
• Conventional parasite detection methods can be time-consuming and resource-intensive.

Purpose of the Study:

• To evaluate the efficacy of a simplified cyst-counting method (CYST) as a proxy for Diphyllobothrium spp. infection in salmonids.
• To compare the accuracy of the CYST method against conventional larval recovery techniques (LARV).
• To determine the potential of the CYST method for extensive parasite assessments in fish monitoring and fisheries management.

Main Methods:

• Collected 365 brown trout and 424 Arctic charr from nine subarctic Norwegian lakes.
• Assessed Diphyllobothrium spp. cysts (CYST) and counted plerocercoid larvae (LARV) using conventional digestive techniques.
• Statistically analyzed the correlation between CYST and LARV counts in both fish species.

Main Results:

• A strong positive correlation and significant linear relationship were observed between log10 CYST and log10 LARV in both brown trout and Arctic charr.
• The CYST method showed a tendency to perform slightly better in Arctic charr than in brown trout, though not significantly.
• The accuracy of the CYST method decreased for parasite intensities exceeding 100, indicating reduced functionality in heavily infected populations.

Conclusions:

• The simplified cyst-counting method (CYST) provides a reliable and time-efficient proxy for assessing Diphyllobothrium spp. intensity, abundance, and prevalence in salmonids.
• This method has significant potential for use in routine fish monitoring and fisheries management surveys, especially when resources for detailed analysis are limited.
• The CYST method offers a practical alternative for estimating Diphyllobothrium spp. burden, contributing to better management strategies for infected fish populations.