Resumen. Se determinó el estatus actual de conservación de 6 peces dulceacuícolas nativos de la península de Baja California (Entosphenus tridentatus, Oncorhynchus mykiss nelsoni, Fundulus lima, Cyprinodon macularius, Gasterosteus aculeatus y Gobiesox juniperoserrai), incluidos en la Norma Oficial Mexicana 059-2010, a partir de la información obtenida durante el periodo 2000-2014. Con excepción de E. tridentatus en la cuenca del río Santo Domingo y de G. juniperoserrai en la cuenca de Las Pocitas-San Hilario, la mayoría de las especies fueron registradas en las cuencas hidrológicas muestreadas. Oncorhynchus mykiss nelsoni registró una marcada fluctuación poblacional en el río San Rafael, en estrecha relación con la dinámica del flujo hidrológico y los eventos de incendio forestal. Fundulus lima presentó su probable extirpación en 4 cuencas: San Javier, Bebelamas, San Luis y Las Pocitas-San Hilario, lo cual contrasta con el hallazgo de una nueva población en el arroyo Santa Cruz. Cyprinodon macularius en su población remanente más importante en Baja California -lagunas de la planta geotérmica cerro Prieto-denotó fluctuaciones interanuales relacionadas directamente con el nivel de inundación de las lagunas y la disponibilidad de hábitat. Gasterosteus aculeatus exhibió un descenso poblacional progresivo en la localidad más austral de su distribución (río El Rosario), además de la extirpación de la población de la bocana del río Santo Domingo y el redescubrimiento de una nueva población en la bocana del río Cantamar. Gobiesox juniperoserrai, especie conocida sólo de la localidad tipo, es determinada como extirpada.Palabras clave: peces nativos, distribución, consideraciones taxonómicas y bioecológicas.

We documented the distributional status of 27 exotic fish species in the inland waters of the Baja California Peninsula, Mexico, based on voucher specimens collected from 122 sites between 1977 and 2010, and on published records. The species reported here are representatives of genera from the Atlantic drainages of North America (Ictalurus, Ameiurus, Pylodictis, Morone, Lepomis, Pomoxis, Dorosoma, Cyprinella, and Micropterus), Middle America (Poecilia, Gambusia, and Xiphophorus), Eurasia (Cyprinus and Carassius), and Africa (Tilapia and Oreochromis). The family containing the highest number of species is Centrarchidae (7 species) followed by Ictaluridae and Poeciliidae (6 species each). Four species were determined to be invasive due to their wide distribution and fast dispersal through the Peninsula (Gambusia affinis, Poecilia reticulata, Lepomis cyanellus, and Tilapia sp. cf. zillii). We analyze the impacts of exotic species on the native populations of 3 species with problems of conservation: Cyprinodon macularius (endangered), Fundulus lima (endangered), and Gasterosteus aculeatus (vulnerable). Alien fishes have been introduced for a variety of reasons in Mexico: ornament, sport, aquaculture, biological control, and by accident. In some cases fish introductions were carried out for more than one reason.

We present the relationships between fork length and total weight for 14 fish species from the Segura River basin (southeastern Spain): Barbus sclateri, Chondrostoma polylepis, Gobio lozanoi, Aphanius iberus, Micropterus salmoides, Lepomis gibbosus, Carassius auratus auratus, Cyprinus carpio carpio, Sander lucioperca, Gambusia holbrooki, Liza ramado, Mugil cephalus, Atherina boyeri and Pomatoschistus marmoratus. Significant length-weight relationships were found for all species. The values of the exponent b of the length-weight relationships ranged from 3.82 for Sander lucioperca to 2.59 for Micropterus salmoides.

The age and growth of sand smelt, Atherina boyeri (Risso 1810), in the Mar Menor (SE Iberian Peninsula) were studied in samples taken from catches of local fishermen obtained between November 1997 and September 1998. The maximum lengths were 94 mm (FL, fork length) in females and 87 mm (FL) in males. Age determination based on scale readings and validated by length frequency analysis shows that the population has a 3-year life cycle. Females were significantly longer than males in each of the age classes. Both sexes of the sand smelt grow allometrically (b ¼ 3.113 males; b ¼ 3.043 females) and attain approximately 56.2% of their maximum fork length in their immature first year, after which the annual growth rate drops quickly. The highest growth rate was observed from winter to spring (G L ¼ 16.01 males 1+; G L ¼ 11.25 males 2+; G L ¼ 17.18 females 1+; G L ¼ 9.62 females 2+). The condition cycles were similar for both sexes, with a minimum in June-July and two maximums in April and November.

Summary The native continental ichthyofauna of Chile has a low richness in species and marked endemism in comparison to the rest of South America. Since the end of the 19th century 26 fish species have been introduced into the Chilean systems. The study covers the trophic ecology of three native and two exotic fish species from the Chillán River. Stomach contents were analyzed and prey items identified at the family level, then compared with the environmental availability by sampling the benthos and using Ivlev’s Electivity Index to determine the degree of election. The relative importance of each prey item was determined and the Morisita Index applied to determine the level of overlap. The results indicate a greater trophic spectrum for introduced rather than for native species. The Relative Importance Index identified Chironomidae as the most important prey item for all species studied. An elevated overlap was observed between the diets of the five species, being greater within the native and introduced species (> 0.9) than between the two groups (< 0.8). These results do not reveal competition, but allow the authors to infer the negative effects of the introduced species to the conservation of native fish.