ABSTRACT
Whitefish are susceptible to infestation by a number of parasites including protozoa, trematodes, nematodes, and cestodes. Larvae of two species of the nematode family Anisakidae, the “seal or cod worm” (Phocanema decipiens) and the “herring worm” (Anisakis simplex), are commonly found in Pacific cod fillets. Parasite infestation renders fish unmarketable for reasons of human health and aesthetics. Infestation in humans can be extremely pathogenic if ingested in raw, uncooked, or marinated form. The only commercial method of detecting parasites is candling, which involves inspecting each fillet over an illuminated translucent surface. Candling cannot detect parasites embedded deeper than 6 mm in fish muscle. Research has shown that candling removes only 60–70% of nematodes present. Recent efforts to improve detection efficiency of candling were not successful. The candling process is labor intensive (accounting for approximately 50% of costs) and is the rate limiting step during whitefish fillet production, directly impacting product quality. Various alternatives for detecting parasites in fillets have been investigated. These include laser candling, ultraviolet light, conventional X-ray, ultrasonic waves, scanning laser acoustic microscope (SLAM) technique and the pulse-echo technique. The major problem in application of these techniques is the inability to distinguish parasites from the surrounding flesh. The physical properties used to differentiate the nematode and surrounding tish tissue are very similar. None of these methods proved successful due to low sensitivity, poor resolution, and slow throughput. We have taken a different approach to parasite detection. Instead of complex pattern recognition, the presence of a parasite is ascertained by current (signal) detection. This new technique is based on the electrical properties of fish muscle and associated parasites. The presence of parasite is determined by variations in electromagnetic field strength produced by distortion in current flow patent around the parasite.
