Double-crested cormorants have steadily increased in the Mississippi Delta. This bird serves as a definitive host for digenetic trematodes, many of which infect fish. To identify these digeneans in cormorants and determine the impact these infections have on wild fish in the Mississippi Delta, two surveys were done. Cormorants were collected for two years in the Mississippi Delta. At necropsy trematodes were collected and identified morphologically and molecularly as: Austrodiplostomum ostrowskiae, Hysteromorpha triloba, Drepanocephalus spathans, Ascocotyle longa and Pseudopsilostoma varium. Additionally, 14 fish species were collected from a Mississippi Delta lake. Fish were examined for parasites and Posthodiplostomum minimum metacercariae were found in multiple organs in 6/14 fish species. The 18S gene sequences of these metacercariae were identical to published P. minimum sequences, whereas the cytochrome oxidase I (COI) sequences matched published COI sequences for Posthodiplostomum sp. 3, 5 and 8, suggesting subspecies of Posthodiplostomum in this fish population.

Six species of haplosplanchnids are reported in this study. Haplosplanchnus caudatus (Srivastava, 1939) Skrjabin and Guschanskaja, 1955 was found in large numbers in 8 of 9 Mugil cephalus. H. purii Srivastava, 1939 was found in small numbers in 2 of 9 Liza vaigiensis and 1 of 9 Mugil cephalus. Both of these findings represent a new locality record. Schikhobalotrema southi n. sp. is described from a single specimen from Scarus rivulatus. S. scari n. sp. from the same host is also described from a single specimen. Schikhobalotrema sp. is described but not named because of insufficient data. Hymenocotta mulli Manter, 1961 from Mugil cephalus and Liza vaigiensis is also reported, based on one specimen from each host. New synonyms: Haplosplanchnus stunkardi Gupta and Ahmad, 1979 is a synonym of H. caudatus (Srivastava, 1939) Skrjabin and Guschanskaja, 1955. H. otolithi Gupta and Ahmad, 1979 is a synonym of H. purii Srivastava, 1939. Neohaplosplanchnus ablennis Abdul-Salam and Khalil, 1987 is transferred to the genus Schikhobalotrema becoming S. ablennis n. comb. A key to the genus Schikhobalotrema including the new species is included.