The Introduction of Nonnative Fishes into Freshwater Systems of Peru

Abstract

Since the 1930s, alien fishes (fishes not native to Peru) have been introduced into the freshwater systems of Peru for different purposes such as fish farming, the ornamental fish trade, public health applications, and sport fishing. The fish were introduced either deliberately or casually into the three hydrographic systems of the country (Amazon, Pacific coastal rivers, and Lake Titicaca). To date, 20 alien species have been found in the continental water systems of Peru: Aristichythys nobilis, Carassius auratus, Cichlasoma nigrofasciatum, Ctenopharyngodon idella, Cyprinus carpio, Gambusia cf. affinis, Hypophthalmichthys molitrix, Odonthestes bonariensis, Oncorhynchus mykiss, Oreochromis aureus, Oreochromis hornorum, Oreochromis mossambicus, Oreochromis niloticus, Oreochromis urolepis, Poecilia reticulata, Poecilia velifera, Tilapia rendalli, Trichogaster leerii, Xiphophorus helleri, and Xiphophorus maculatus. Nativespecies transfers have also occurred; seven Peruvian species have been transferred from lowland forest waters to water systems of both the highland forest and the coast (reservoirs): Arapaima gigas, Astronotus ocellatus, Brycon cephalus, Cichla monoculus, Colossoma macropomum, Piaractus brachypomus, and Prochilodus nigricans. Herein, we present an overview of the current situation of these species introductions and transfers in Peru based on both fieldwork and a review of the pertinent literature. We then focus on the three alien species most frequently found in natural environments but not previously evaluated for their impacts. Our surveys in the aquatic basins of the Parque Nacional R�o Abiseo (PNRA; high-altitude, Amazon River system) show that the alien Oncorhynchus mykiss (rainbow trout) is the dominant species and that the three native species usually common in Peruvian highland Andean river basins (Astroblepus spp.) are present only in low numbers. The other two alien species—Oreochromis niloticus (tilapia) and Poecilia reticulata (guppy)-are well established and widely distributed in both the Huallaga (highland forest, Amazon River system) and Rio Grande (Pacific Ocean coastal system) river basins. We also discuss other introductions and transfers. For example, the introduction of Odonthestes bonariensis (pejerrey argentino) and Oncorhynchus mykiss into Lake Titicaca caused a negative impact on native Orestias species and the transfer of the giant Amazonian fish Arapaima gigas (paiche) initiated a chain of introductions and impacts in Sauce Lagoon. The introduction of species into nonnative waters is a complex problem without a unique solution. We give some suggestions for the control of both O. mykiss in the PNRA and O. niloticus in the Huallaga River basin and for the practice of environmentally sustainable aquaculture. Minimally, it is necessary to establish biological monitoring programs in the affected river basins and, for comparison to the affected basins, to obtain adequate data on the distributions and relative abundances of native species in analogous unaffected basins. We also recommend that environmental education programs be developed and promulgated to inform the public of the general problem.