Mechanical means of prevention
• The fish evisceration is recommended before cooking or freezing. Evisceration should be done as soon as possible after fishing. This procedure diminishes the risk of larvae migration. Indeed, larvae that may be present in the fish digestive tract can migrate in the fillets after the death of the fish. But the evisceration does not completely prevent the parasite risk because larvae can also be present into the fillets before catching the fish.
• The trimming of the fish fillets: parts of the fillets surrounding the visceral cavity (= the flanks) are removed. The trimming eliminates the most highly infected parts of the fillets that are close to the visceral cavity. Thus, the parasite risk is reduced but not completely eliminated.
• The meticulous observation of the filet, by trans-illuminating the fillet on a candling table for example, allows the manual elimination of visible larvae. This technique is time-consuming and not always efficient according to the species (dark flesh) or to the thickness of the filet. When preparing raw fish in carpaccio or sushi/sashimi, the cook should finely slice the fillet, be meticulous and remove any larvae eventually present in the flesh. Freezing is required (see below) prior to the consumption of a raw fish fillet.
The temperature as a prevention mean
• To maintain the cold chain: it reduces the mobility of the parasite larvae and thus diminishes the risk of larvae migration towards the consumed parts of the fish.
• The freezing is efficient to eliminate the infectious risk at certain temperature/time pairs. The efficiency depends on the thickness of the piece to be frozen, its weigh, the species and the fat contents. Official standards are available. The fish must be frozen at -20°C in all parts of the product during at least 7 days (domestic freezer).
• Cooking allows the efficient killing of the parasite larvae. A temperature of 60°C must be reached in the center of the product during at least one minute (70°C for microwave cooking). For a 3 cm-thick filet, cooking should be 10 minutes long.
Other prevention methods
The salting, marinating and cold smoking methods are overall inefficient to eliminate the infectious risk. Of note, some efficient salting methods exist for herrings (kippers): immersion in saturated salted solution for at least 16 days at 15°C.
Irradiation or pressure methods are inefficient because efficient doses are too strong and would alter the product.