Nematodes in Fresh Market Fish of the Washington, D.C. Area

For this study 1,010 fresh whole fish belonging to 14 families, 20 genera, and 23 species were bought in retail markets of the Washington, D.C. area. Most of the fish had been caught in Chesapeake Bay and adjacent waters. Examination for parasitic roundworms, i.e., nematodes, by dissection, candling or digestion of the flesh, and elution of nonedible viscera produced 6,547 nematodes, mostly alive. Among fish species of which 25 or more were examined, spotted hake ( Urophycis regius ) was the most wormy and white perch ( Morone americana ) the least. Only two of the nematodes were recovered from fish flesh; both were Anisakis sp. larvae. Recovered from fish viscera were nine Anisakis sp. larvae. 41 Porrocaecum sp. larvae, 3,221 Thynnascaris spp. larvae and adults, 21 Goezia sp. larvae, and 1,220 Raphidascaris acus larvae. All the aforementioned nematodes are considered to be anisakines; in addition, 225 anisakines were too damaged to be identified more precisely. The other nematodes recovered in the survey were 71 Spinitectus spp. adults and larvae, 114 Bulbodactinis sp. adults and larvae, 108 Metabronema sp. adults and larvae, 111 Spirurinae larvae, 662 Philometra sp. adults and larvae, one Capillaria sp. larva, 447 similar small larvae so undeveloped that they could not be identified, and 294 other nematodes too damaged even for general classification. Only the Anisakis sp. larvae are considered pathogenic to human consumers of raw or semiraw fish. The low incidence of pathogenic anisakines in these fish intermediate hosts is attributed to the absence of definitive hosts (marine mammals) from Chesapeake Bay and adjacent waters. Thirty genera of anisakine nematodes are distinguished morphologically.