Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7209
Title: A statistical analysis of the distribution of a larval nematode (Anisakis sp.) in the musculature of chum salmon (Oncorhynchus keta–Walbaum)
Author: Anthony J. Novotny, Joseph R. Uzmann
Publication Year: 1960
Journal: Experimental Parasitology
Volume: 10
Issue: 2
Pages: 245-262

The pepsin–HCl digestion technique is probably the best method of isolating Anisakis larvae from the musculature of chum salmon.  Some losses can be expected due to breakage of the resistant cuticle of Anisakis, and can be estimated to be about 6% when counting the parasites with the unaided eye.

Comparisons of Anisakis infections of the dorsal and ventral musculature indicated that very few larvae are found in the dorsal portions (above the lateral line).  Forty–seven per cent of the fish had no dorsal infections, and 90% of the fish had less than 10% of total infection in the dorsal musculature.  Comparisons of Anisakis infection ratios of the right and left sides below the lateral line showed some variation.  Chi–square tests of the hypothesis that 50% of the infections occur in either side indicated no significant differences.  There were indications that large total infection intensities displayed less variation.  Comparisons of Anisakis infections of the anterior and posterior portions of the lateral musculature indicated that the infections were greater in the anterior portions.  Calculated 95% confidence limits showed 50.0 to 59.0% infection in the anterior portion compared to 41.0 to 50.0% in the posterior portion.  Analyses of the Anisakis distributions within the anterior portions of the lateral musculature were hindered by extreme variation in the counts.  In general, an average of 60% of the anterior portion infections occurred in the upper two quadrants of musculature, and 40% in the lower two quadrants.  Changes in distributional patterns were affected by total parasite density, rather than by age or geographical location.  For purposes of comparing infection rates in chum salmon, distributional patterns indicate that the minimum sample of musculature which should be taken from each fish is one side below the lateral line.  The one factor which probably contributes the greatest effect on distributional patterns of Anisakis within chum salmon musculature is the total intensity of infection (or population density of Anisakis) within each fish.

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