Fish community composition was assessed among six macrophyte habitats, including hydrilla, Hydrilla verticillata (L.F.) Royle, common native species (bulrush, Scirpus spp., muskgrass, Chara spp., eelgrass, Vallisneria americana Michx. and Illinois pondweed, Potamogeton illinoensis Morong) and no-plants, to assess potential impacts of recent hydrilla colonisation on the littoral fish community at Lake Izabal, Guatemala. Fish biomass was significantly different among habitats, with hydrilla supporting the highest fish biomass. Fish density did not differ significantly among habitats. Total fish species richness was similar (12-15 species) among habitats, but community composition changed with macrophyte presence. Biomass of mojarra, Cichlasoma maculicauda Regan, which supported the most important subsistence fishery at the lake, was significantly different among habitats and had the greatest biomass in the hydrilla habitat. Although hydrilla may adversely affect native plants, lake access and other uses, it provided useful fish habitat and likely was not detrimental to the Lake Izabal fish community composition.K E Y W O R D S : aquatic plants, cichlids, fish assemblage, Hydrilla verticillata.

Revista Mexicana de Biodiversidad 89 (Suplem. 2018): S118 -S130 Suplemento Peces nativos y pesca artesanal en la cuenca Usumacinta, GuatemalaNative fish fauna and artisanal fisheries in the Usumacinta basin, ResumenLa ictiofauna nativa de la cuenca del río Usumacinta se documentó en el noroeste de Guatemala para conocer la composición de los peces nativos en 20 sitios y su importancia en la pesca artesanal. El estudio incluyó recolecta de las especies con diversas artes de pesca, evaluación de abundancia de las especies mediante muestreos en transectos e identificación de las mismas en los mercados de venta, y en entrevistas con pescadores. Se identificó un total de 54 especies, 38 géneros, 18 familias y 8 órdenes. Las familias más abundantes fueron Characidae (3 especies), Poeciliidae (12 especies) y Cichlidae (22 especies), y en términos de riqueza el 68% de las especies corresponden a las familias Cichlidae y Poeciliidae. Al menos 38 especies nativas y 7 exóticas fueron identificadas en la pesca artesanal, de las cuales Centropomus undecimalis., Megalops atlanticus y Atractosteus tropicus son de alto valor comercial. Entre las 7 especies exóticas identificadas solo las especies del género Pterygoplichthys no son parte de la pesca artesanal. Los peces del área se dividen en 2 grandes grupos, uno en las zonas bajas de Petén y otro en las zonas altas de Las Verapaces y la pesca artesanal varía de acuerdo con este patrón. Según el estudio, a pesar de las especies exóticas, la pesca en la cuenca del Usumacinta está basada principalmente en especies nativas. Se requieren medidas de control del pez diablo exótico Pterygoplichthys spp. para evitar la propagación de sus poblaciones y mitigar los efectos negativos en la comunidad íctica nativa. AbstractThe native fish fauna was characterized in 20 sites along three drainage areas of the Usumacinta river basin in northwestern Guatemala to understand the native fish fauna contribution and its importance to artisanal fisheries.

Age, growth, and mortality were assessed in Giant Cichlids Petenia splendida from lakes in northern Guatemala by using cross-sectioned sagittal otoliths. Marginal increment and edge analyses of Giant Cichlid otoliths indicated that one annulus formed per 12-month period in Lakes Yaxhá and Petén Itza. Opaque zone formation was associated with the peak of the rainy season from May to September. Ages ranged from 0 to 8 years for Giant Cichlids in Lake Yaxhá and from 0 to 5 years in Lake Petén Itza. Within both lakes, males were larger than females, although the difference was slight in Lake Petén Itza. Lake Yaxhá Giant Cichlids had faster growth rates than those from Lake Petén Itza, and fish over 2 years old from Lake Yaxhá were larger at age than fish from Lake Petén Itza. This is counter-intuitive because Lake Petén Itza is heavily exploited, whereas Lake Yaxhá is unfished. However, long-term exploitation in Lake Petén Itza may have resulted in selection for fish with reduced growth rates. Alternatively, the mesotrophic state of Lake Yaxhá may explain the differences in growth, although areas of Lake Petén Itza are changing from oligotrophic to meso-eutrophic due to rapid cultural eutrophication. Total mortality (Z) estimates for Giant Cichlids were 0.81 for Lake Yaxhá, with most of the age structured on 2-4-year-old fish, and 1.05 for Lake Petén Itzá, where the age structure was dominated by 0-2-year-old fish; these results were consistent with expectations based on the low fishing pressure in Lake Yaxhá.

The number and diversity of source populations may influence the genetic diversity of newly introduced populations and affect the likelihood of their establishment and spread. We used the cytochrome b mitochondrial gene and nuclear microsatellite loci to identify the sources of a successful invader in southern Florida, USA, Cichlasoma urophthalmus (Mayan cichlid). Our cytochrome b data supported an introduction from Guatemala, while our microsatellite data suggested movement of Mayan Cichlids from the upper Yucatán Peninsula to Guatemala and introductions from Guatemala and Belize to Florida. The mismatch between mitochondrial and nuclear genomes suggests admixture of a female lineage from Guatemala, where all individuals were fixed for the mitochondrial haplotype found in the introduced population, and a more diverse but also relatively small number of individuals from Belize. The Florida cytochrome b haplotype appears to be absent from Belize (0 out of 136 fish screened from Belize had this haplotype). Genetic structure within the Florida population was minimal, indicating a panmictic population, while Mexican and Central American samples displayed more genetic subdivision. Individuals from the Upper Yucatán Peninsula and the Petén region of Guatemala were more genetically similar to each other than to fish from nearby sites and movement of Mayan Cichlids between these regions occurred thousands of generations ago, suggestive of pre-Columbian human transportation of Mayan Cichlids through this region. Mayan Cichlids present a rare example of cytonuclear disequilibrium and reduced genetic diversity in the introduced population that persists more than 30 years (at least 7–8 generations) after introduction. We suggest that hybridization occurred in ornamental fish farms in Florida and may contribute their establishment in the novel habitat. Hybridization prior to release may contribute to other successful invasions.

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