Parasitic Copepoda from Louisiana Fresh Water Fish

Abstract

No truly monographic survey of the parasitic Copepoda of American freshwater fish has been made. Wilson, in his numerous papers surveying taxonomic groups, necessarily included freshwater species. In two papers (Wilson, 1914 and 1917) he dealt with freshwater forms exclusively. Numerous papers and bulletins on the parasites of freshwater fish mention copepods, usually rather incidentalIy. Argulus sp. and Ergasilus caeruleus appear to be the most widespread species in such literature. The present report is based upon material from Louisiana freshwater fish collected during 1955 and kindly sent to me by Dr. Harry J. Bennett of Louisiana State University. There were 49 collections in which parasitic copepods had been observed. In a few cases the actual parasites had been separated in vials while in the rest the collections were either pieces of flesh from which lernaeids hung, or gills upon which there were ergasilids. I failed to find parasites in five samples, neither on the gills nor in the slime and detritus in the bottom of the containers. These probably had ergasilids on them which had become lost or were overlooked. They were from fish well represented by other specimens in this survey. It is my understanding that this material came from the fish recognized to be parasitized with copepods. I have no information which would allow any speculation as to the possible incidence of infection. Five years of experience with Gulf of Mexico copepod parasites lead me to think, considering the difficulties of fair sampling, age factors, life history factors, etc., that statements of incidence of infection for copepodcs have little value. Four genera and 12 species are represented in the collection. Of these, Argulus is the textbook parasitic copepod, readily recognized by its flat, scalelike body and the two ventral suckers. It occurs on the body surface of the fish, where it moves about readily. It has a tendency to let go as the fish is lifted from the water, so that many specimens are lost in this way. It is sometimes found swimming freely in the water. The female leaves the host fish to lay her eggs on some submerged object. Because of this habit it lacks the two egg sacs so typicaI of copepods. Lernaea is also found on the surface, usually back of a fin, with its anchor-like anterior end deeply embedded in the hosts flesh. L. cyprinacea ( = L. carassii Tidd) is regularly referred to as the anchor parasite in texts on fisheries, but I think fishermen who have noticed them refer to the whole genus as anchor worms. The members of the genus Ergasilus are minute gill parasites. Occasionally only a few are present, but they may be so numerous as to suggest that the gills have been peppered. A little magnification will show the second antennae, a pair of vicious appearing claws, clasping the gill filament, either at the very end of the filament or hig,her up. The last of the four genera, Achtheres, could be confused with Salmincola by a determined individual, but the absence of an 378