John N. Rinne

Factors resulting in decline of the endangered Sonoran topminnow Poeciliopsis occidentalis (Atheriniformes: Poeciliidae) in the United States

The endangered Sonoran topminnow Poeciliopsis occidentalis has steadily declined in distribution and abundance in the past several decades, and currently survives in the United States only in several isolated localities in southern Arizona. This reduction is correlated with, and primarily attributed to, habitat destruction, and introduction and establishment of mosquitofish Gambusia affinis and other exotic fishes. Topminnows have characteristically been reduced in number or replaced within a year or two of introduction of non-native fishes. Other native fishes have experienced similar declines after introduction of exotics, and much of the endemic western ichthyofauna may be vulnerable to extirpation in this manner. Predation by introduced fishes on natives appears to be a likely mechanism of replacement.

Biochemical Genetic Studies of Native Arizona and New Mexico Trout

ABSTRACr-Populations of Gila trout, Salmo gilae, and Apache trout, S. apache, from New Mexico and Arizona, respectively, as well as a trout, Salmo sp., population from the Rio Mayo, Mexico, were analyzed for protein polymorphisms at 36 presumptive genetic loci using starch gel electrophoresis. These data were used: 1) to identify the genetic differentiation between these populations and rainbow trout, S. gairdneri, and cutthroat trout, S. clarki, and; 2) to evaluate purported hybridization between the native populations and introduced rainbow trout. Salmo gilae and S. apache were more similar to each other than either was to S. gairdneri, S. clarki, or Rio Mayo Salmo. Salmo gairdneri showed a greater genetic identity to S. gilae, S. apache, and Rio Mayo Salmo than did S. clarki. In eight of the nine localities inhabited by putative hybrids, no evidence of hybridization was detected. Four streams were inhabited by unhybridized S. apache and four streams inhabited by S. gairdneri. In the latter four streams, S. gairdneri has presumably replaced the native species. In one location the entire sample consisted of hybrids.

Distribution and abundance of the Rio Grande sucker in the Carson and Santa Fe National Forests, New Mexico

Rio Grande sucker (Catostomus plebeius) was once common in the Rio Grande basin; however, its current status in New Mexico is unknown. We surveyed 20 streams for Rio Grande sucker in the Carson and Santa Fe National Forests in northern New Mexico. Rio Grande sucker were found in 3 streams on the Carson National Forest. In 2 of these streams Rio Grande sucker co-occurred with white sucker (Catostomus commersoni). On the Santa Fe National Forest, Rio Grande sucker occupied 11 streams in the Jemez River drainage and 2 streams in the Chama River drainage. Rio Grande sucker co-occurred with white sucker in 1 of the 2 streams draining into the Chama River drainage. The abundance of Rio Grande sucker was inversely proportional to stream gradient.

PARASITES OF SOME FISHES NATIVE TO ARIZONA AND NEW MEXICO

A total of 22 parasitic species (representing 18 genera), were encountered during the examination of 1,695 fishes representing 12 native species from 13 localities in Arizona and New Mexico. The parasites include six Protozoa: Ichthyophthirius multifiliis Fouquet, 1876, Myxobo- lus catostomi Fantham et al., 1939, M. discrepans Kudo, 1920, M. macrocapsularis Reuss, 1906, M. nodularis Southwell and Prashad, 1918, M. oblongus; six Trematoda: Tetraonchus sp., Clinostomum marginatum Rud., 1819, Ornithodiplostomum ptychocheilus Dubois, 1936, Plagioporus sp., Crepidostomum cooperi Hopkins, 1931, and C. farionis (of Miiller, 1784) Nicoll, 1909; four Cestoda: Ligula intestinalis Linnaeus, 1758, Isoglaridacris bulbocirrus Mackiewicz, 1965, Ophiotaenia critica Mpoame and Landers, 1981, Proteocephalus sp.; one Acantocephala: Neoechinorhynchus sp.; four Nematoda: Dacnitoides sp., Camallanus sp., Rhabdochona decatu- rensis Gustafson, 1949, Metabronema salvelini (Fujita, 1922); and one Crustacea: Lernaea cyprinacea Linnaeus, 1761. Seven of these parasites are belived to represent undescribed species and almost all the present parasite reports constitute new host and locality records. Patterns of distribution in space (host and locality specificities) are discussed. Infection levels of all parasites encountered were independent of host sex, suggesting that males and females of the fishes studied are very similar in feeding behavior and habitat selection. Although a number of parasitic species reported may cause damage to individual infected hosts, I. multifiliis seems to be the only of special pathogenic importance for Arizona native fishes.