Some Potential Fish Health Concerns for Threatened and Endangered Species and Other Fishes in the Upper Colorado

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CDOW -BRUSH TEL No.303- 842 -2849 Apr 10,92 14:09 No.003 P.05 . PANE 4 - UPPER COLORADO T&E FISH HEALTH CONCERNS protect the Basin from the Asian tapeworm by requiring inspections of facilities shipping fish into Colorado. However, for a number of reasons, not the least of which was the discovery of the worm's establishment in the Basin, the regulation was dropped several years ago. The Division, however, has to date successfully kept this parasite out of its own warmwater fish culture facilities through careful avoidance. The Asian tapeworm has a somewhat abbreviated life cycle when compared with many other adult tapeworms of fish. Tapeworm eggs released in the feces of infected fish are eaten by planktonic copepods. Within the copepod, a larval Asian tapeworm develops into a procercoid larvae. Then, if the copepod is eaten by a suitable species of fish, the procercoid simply develops into an adult worm in the lumen of the gut. The plerocercoid stage in this instance is deleted from the life cycle. No approved anthelminthic drugs exist for use in fishes. However, the veterinary anthelminthic Droncet (Praziquantel) has been shown experimentally to purge infected fish of Asian tapeworms. An Investigational New Animal Drug (INAD) permit from the FDA would be necessary' before this drug could be used. In addition, if the purpose of its use is to block transmission of the parasite from one place to another, consideration will have to be given for procedures and possibly a holding facility as well. A so- called "anchor worm" - the copepod crustacean parasite Lernaea cyprinacea is known to exist in the Colorado River Basin. Adult females of this species imbed themselves in exposed soft tissues causing large, red welts that often become infected with secondary invading bacteria and fungi. While the abdomens and ovaries of the parasite are exposed and easily visible to the naked eye, a complex anchor and feeding structure lies deep within the flesh to take in nourishment and oxygen from the host fish's blood supply. The nearly microscopic copepodid larvae of this parasite are ecto- parasites of the same or other fishes, clinging to and feeding on the skin. Lernaea has a broad host range that spans several fish families including minnows, suckers, centrarchids, ictalurids and salmonids. Generally it is the fine - scaled and scaleless species that are the most severely affected, often by the sheer magnitude of infection. The parasite appears to be a limiting factor for trout and perhaps some catfish fisheries by greatly limiting the longevity of the host. In addition, the welts and the olive -green "worms" themselves are aesthetically unappealing and can cause anglers to go elsewhere. Lernaea- caused aesthetic damage to ornamental goldfish can amount to many thousands of dollars on a single farm. Lernaea is difficult to control in small pond situations, virtually impossible to control in large bodies of water and extremely difficult to eradicate from any location. The pesticide Masoten (Dylox) is used on non -food fish to kill the copepodid larvae stages of the parasite. Through systematic treatments of a fish culture facility or small pond over the life span of the parasite, a Lernaea infection can be reduced to negligible effect.