The common pathogenic prodiplostomulum metacercaria in the flesh, mostly near the skin, of pond-produced channel catfish Ictalurus punctatus has been demonstrated to be Bolbophorus damnificus Overstreet & Curran n. sp. The catfish acquires the infection from the snail Planorbella trivolvis, the only known first intermediate host, and the species is perpetuated through the American white pelican Pelecanus erythrorhynchos, as confirmed by experimental infections with nestling and dewormed adult pelican specimens in conjunction with molecular data. It differs from the cryptic species Bolbophorus sp., also found concurrently in the American white pelican, by having eggs 123-129 microm rather than 100-112 microm long and consistent low values for nucleotide percentage sequence similarity comparing COI, ITS 1/2, 18S rRNA and 28S rRNA fragments. Bolbophorus sp. is comparable but most likely distinct from B. confusus (Kraus, 1914), which occurs in Europe and has eggs 90-102 microm long. Its intermediate hosts were not demonstrated. The adults of neither of the confirmed North American species of Bolbophorus were encountered in any bird other than a pelican, although several shore birds feed on infected catfish, and B. damnificus can survive but not mature when protected in the mouse abdominal cavity. B. ictaluri (Haderlie, 1953) Overstreet & Curran n. comb., a species different from B. damnificus, is considered a species inquirenda.

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Trematodes belonging to the genus Bolbophorus have recently been reported as the cause of substantial morbidity and mortality in cultured channel catfish Ictalurus punctatus in Mississippi and Louisiana. Previous investigators identified only a single species, B. confusus. In this investigation, genetic techniques were used to identify all stages of the parasite in all of its hosts. The 18s rRNA genes from specimens collected in Mississippi were sequenced and compared; this analysis revealed that there are two distinct species, B. damnificus (previously identified as B. confusus) and another, undescribed species. (Phylogenetic analysis indicated that a third species, B. levantinus, is also closely related to the Mississippi species.) Species-specific polymerase chain reaction assays capable of identifying and differentiating between these two parasites were developed. Both species were found to infect the first intermediate host (the ram's horn snail Planorbella trivolvis) in commercial channel catfish ponds, but only B. damnificus was recovered from the fish themselves. The new, unidentified Bolbophorus species was determined to be highly pathogenic to a number of fish species. The contribution of B. damnificus to disease in cultured channel catfish remains undetermined. Future investigations of these parasites must now take into account the presence of two distinct species.

Proliferative gill disease (PGD) in channel catfish Ictalurus punctatus is caused by the myxozoan parasite Henneguya ictaluri. Prolonged exposure of channel catfish to the actinospore stage of the parasite results in extensive gill damage, leading to reduced production and significant mortality in commercial operations. A H. ictaluri-specific real-time (Q)PCR assay was used to determine parasite levels in commercial channel catfish ponds and evaluate the risk of losing fish newly stocked into the system. Previous research has shown the H. ictaluri actinospore to be infective for approximately 24 h; therefore, determining the parasite load (ratio of parasite DNA to host DNA) in sentinel fish exposed for 2 separate 24 h periods with a minimum of 1 wk between sampling indirectly represents the rate at which infective actinospores are being released by the oligochaete host and if that rate is changing over time. Alternatively, QPCR analysis of pond water samples eliminates the need for sentinel fish. Water samples collected on 2 separate days, with a minimum of 1 wk between sampling, not only determines the approximate concentrations of actinospores in the pond but if these concentrations are remaining stable. Increases in parasite load (r = 0.69, p = 0.054) correlated with percent mortality in sentinel fish, as did increases in mean actinospore concentrations (r = 0.63, p = 0.003). Both applications are more rapid than current protocols for evaluating the PGD status of a catfish pond and identified actinospore levels that correlate to both high and low risk of fish loss.