Energetic Changes in Coho Smolts Induced by the Presence of the Nematode Parasite Philonema agubernaculum
Figure 1. Coho salmon smolt heavily parasitized by the nematode Philonema agubernaculum. It was caught in Auke Creek, Juneau, Alaska in 2003. Photo by Mark Carls.
A recent article by Lawrence Schaufler, Johanna Vollenweider, and Adam Moles from the Habitat & Marine Chemistry Program at Auke Bay Laboratories (ABL) examines the lipid storage effects of a severe parasitic worm infection of coho smolts in Juneau, Alaska. Fifty-five percent of the coho salmon collected from Auke Creek in 2003 for this study were significantly parasitized by one or more Philonema agubernaculum helminths.
The most heavily parasitized smolts examined contained 11 individual nematodes, an average parasite length of 108 mm, a total combined parasite mass of 848 mg, and a resulting body/parasite mass ratio of 13:1. No significant difference was observed in the length or weight of the parasitized versus unparasitized smolts, but parasitized coho had 36% less total lipid than unparasitized fish. The types of lipids (storage, structural, etc.) also varied between the two groups. None of the nematode-infected fish examined contained detectable amounts of the storage lipid triacylglycerol (TAG), in contrast to the uninfected fish. Parasitized fish also had significantly higher levels of free fatty acids (which can be a sign of lipid metabolism) than did the unparasitized fish.
The observed differences suggest that the parasites are either harvesting energy directly from the hosts or are placing additional energetic demands on the smolts in order to cope with the infection.
The article appears in the January 2008 issue of Comparative Biochemistry and Physiology, Part B, published by Elsevier.
