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ABSTRACTS OF PRESENTATIONS IN ORDER PRESENTED
<br />RESUMEN
<br />El charalito, Plagopterus argentissimus, es una especie de ciprinido en peligro de desaparici6n en el sistema Virgin
<br />River, Utah. Esta especie fue mantenida por primera vez en cautiverio en el aho de 1979 en la piscifactoria Dexter
<br />National Fish Hatchery, para sostener una poblaci6n viable para prop6sitos de reintroducci6n. Diversos problemas
<br />concernientes con su cultivo ban ocurrido, los cuales van desde la p6rdida en los estanques debido a exceso de macr6fitas
<br />acuaticas, infestaci6n por el cop6podo ancla Lernaea y mas notablemente por el pat6geno Ichthyophthirius multifilis o
<br />"Ich". A principios de 1992 la FDA (Federal Drug Administration) prohibi6 el use de algunos quimioterapeuticos
<br />tradicionalmente utilizados para el tratamiento de Ich. La poblaci6n en cautiverio de charalito es especialmente sensible
<br />a la fuerte proliferaci6n de Ich en la primavera; por tal motivo, m6todos alternativos de control fueron aqui investigados.
<br />Todos los m6todos son basicamente tratamientos de agua, los cuales actdan en las etapas de nado libre de parasitos. El
<br />tratamiento no quimico incluye la ozonizaci6n del agua, la radiaci6n con luz ultravioleta, filtraci6n sub-micron,
<br />incremento del fujo, y temperaturas extremas. Este trabajo, describe los m6todos y resultados de un experimento
<br />utilizando control de temperatura, y discute el estatus reproductivo y patol6gico actual de los peces charalito cultivados
<br />en la piscifactoria.
<br />CONTRIBUTED PAPER
<br />Woundfin background
<br />The endangered woundfin Plagopterus argentissimus is a small cyprinid, first described by Cope in 1874. Its
<br />dorsal fin rays are modified into a spine, which is presumably the source of the common name. It is the most highly
<br />modified of 3 species in the tribe Plagopterini, and the only species in its genus (Miller and Hubbs, 1960). In the
<br />1800's it was found sporadically throughout the lower Colorado River basin, but is currently limited to a short reach
<br />of the Virgin River system, in Utah, Arizona, and Nevada (see Deacon, 1988 for distribution map). At times this
<br />unique species has comprised over 90 % of the fish fauna in the Virgin River system (Minckley, 1973), and at other
<br />times is exceedingly rare. Upstream from Mesquite the populations have not changed much since the 1930's, but
<br />below Mesquite populations have decreased significantly (Cross, 1978). In a 1988 paper, Deacon found that since
<br />1983 the population was approximately unchanged only in the 10 km section between Washington Fields Diversion
<br />and Quail Creek, and had declined dramatically in more than 60% of its remaining range. The species' decline
<br />during this century has been attributed to decreased water flow, introduction of exotic species (especially the red
<br />shiner, Cyprinella lutrensis), and other forms of habitat destruction (Cross, 1978). The woundfin was placed on the
<br />Endangered Species list in 1970 (USFWS, 1984), and the recovery plan for this species includes captive
<br />propagation. For this purpose, it was first brought to Dexter National Fish Hatchery in southeastern New Mexico
<br />in 1979 (DNFH files).
<br />Dexter and Ich
<br />Since that initial collection, there have been many more wild fish taken from the Virgin River (see Table 1).
<br />The profusion of fish brought to Dexter during 1988 was collected prior to the fateful red shiner eradication project,
<br />and consisted mainly of juveniles. The total population size at the hatchery has fluctuated greatly. As well as natural
<br />attrition, individuals have been lost in pond vegetation, overwhelmed with Lernaea infestations, killed during
<br />episodes of intense nitrogen supersatu ration, and the population has been repeatedly decimated by Ichthyophthirius
<br />multifilis, or Ich. The woundfin population is also infected with Asian tapeworms Bothriocephalus acheilognathi (R.
<br />Major, pers. comm.). This parasite was introduced into the country with grass carp Ctenopharyngodon idella, and
<br />most likely introduced into the Virgin River drainage with red shiner Cyprinella lutrensis (Heckman, et al., 1986).
<br />Another species of tapeworm may also be present in the captive population; its identification is pending. Although
<br />fish may not die as a direct result of tapeworm infection, the added stress can affect feeding, reproduction, and
<br />immune responses. At Dexter, however, Ich is the main factor limiting woundfin production (see Figure 1). During
<br />the past 5 years, Ich outbreaks have occurred at least nine times (1988-2 occurrences, 1989-3, 1990-2, 1991-2).
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