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The Effects of Local Environmental Conditions and the Emergence of Young of the Year on the Regional Distribution, Prevalence, and Intensity of Ergasilus labracis (Copepoda) Parasitic on Three-Spined Stickleback (Gasterosteus aculeatus) from the Bay d'Espoir/Hermitage Bay Region of Newfoundland, Canada

Murray, Harry M., Ang, Keng P.
Comparative parasitology 2018 v.85 no.1 pp. 1-12
Ergasilus, Gasterosteus aculeatus, adults, aquaculture, body length, environmental factors, fish, oxygen, parasites, salinity, temperature, Canada
The effects of local environmental conditions on the regional distribution, prevalence, and infection intensity of Ergasilus labracis (Copepoda) parasitic on 3-spined stickleback (Gasterosteus aculeatus) was investigated in the Bay d'Espoir region of Newfoundland during May to September of 2015. Environmental conditions (e.g., temperature, salinity, and oxygen) were measured monthly at 7 beach sites distributed through the region. Analysis of environmental characteristics indicated that the area could be divided into 3 zones based on salinity (low-salinity zone: 13.56 ± 0.32 practical salinity units [psu]; medium-salinity zone: 21.11 ± 0.04 psu; high-salinity zone: 29.91 ± 0.32 psu). Ergasilus labracis was found to be the most prevalent parasitic copepod sampled from fish in upper Bay d'Espoir (low-salinity and medium-salinity zones: greater than 75%), but rarely on fish from Hermitage Bay/Connaigre Bay (high-salinity zone: less than 15%). Parasite intensities were highest in the low-salinity zone within Bay d'Espoir at 18–22°C, but decreased significantly in Hermitage Bay/Connaigre Bay (salinity > 20 psu; temperature < 18°C. Decreases in parasite prevalence and increases in mean intensity in July and August for low- and medium-salinity zones are likely due to the appearance of smaller young-of-the-year fish hosting fewer parasites, suggesting that during this period larger adults act as the main reservoirs for infection of young-of-the-year fish >3 cm total body length (September). Our data suggest that G. aculeatus could act as a key amplification source for these parasites and thus may impact adjacent aquaculture sites in the bay.