DEVELOPMENT OF A DIAGNOSTIC MOLECULAR MARKER FOR PHILONEMA SPP (NEMATODA, DRACUNCULOIDEA) INFECTING SALMONIDS IN BRITISH-COLUMBIA

We developed a species specific DNA probe based on differential PCR am plification that distinguishes two congeneric nematode parasites of sa lmonids in British Columbia: Philonema agubernaculum Simon and Simon, 1936, usually parasitic in lake resident rainbow trout, Oncorhynchus m ykiss; and P. oncorhynchi Kuitunen-Ekbaum, 1933, parasitic in anadromo us sockeye salmon, O. nerka. The region differentially amplified was t he D3 expansion domain of the 28S rDNA. Sequences of the two species d iffer in two parts of the domain, one a single base substitution and t he other a three base duplication in P. oncorhynchi. A primer specific to P. oncorhynchi (amplifying P. oncorhynchi, not P. agubernaculum) w as defined in the duplication region. Using differential amplification , we showed that sockeye smelts are infected with P. agubernaculum, al though returning adults harbour only P, oncorhynchi. This technique co uld conceivably be used to quantify the frequency of heterologous infe ctions in the wild, before infecting worms are identifiable at the spe cies level based on morphological criteria.