Distribution of two species of Kudoa (Myxozoa: Multivalvulida) in the offshore population of the Pacific hake, Merluccius productus (Ayres, 1855)

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Abstract
Samples of pacific hake (Merluccius productus), a total of 581 fish, were collected along its distribution range from California [USA] to Vancouver Island [Canada]. The fish were examined for prevalence and intensity of infection with Kudoa thyrsitis and K. paniformis (Myxozoa). Fish age 4+ (and older) were more heavily infected than those age 3+, the most heavily infected part of the fish being the dorsal musculature directly behind the head. Although the prevalence of infection with K. thyrsitis increased in a northerly direction, its intensity was markedly lower than the intensity of infection with K. paniformis. Fish of comparable age and size were twice as heavily infected with K. paniformis off California as those taken off Vancouver Island. Fish infected with K. thytrsitis appeared to show a much stronger reaction to the presence of the parasite by producing relatively more black pseudocysts than those infected with K. paniformis. Reasons for this fact and for the observed pattern of parasite distribution are discussed.