Resumen Se estudió la comunidad de helmintos de Lithobates spectabilis (n =77) de Las Pilas (altitud baja) y Metznoxtla (altitud alta), Reserva de la Biosfera Barranca de Metztitlán, Hidalgo, México. Se comparó la diversidad de especies mediante los números de Hill a nivel de la infracomunidad y del componente de comunidad, y se calculó la diversidad beta. Se encontraron 5 especies de Digenea, 5 de Nematoda y 2 de Acanthocephala en las ranas de las 2 localidades. La riqueza de especies de parásitos en Las Pilas (9 especies) fue mayor que la de Metznoxtla (7 especies). La comunidad de helmintos en Las Pilas estuvo dominada por nemátodos y en Metznoxtla por digéneos. La especie más prevalente en Las Pilas fue Foleyellides cf. flexicauda (65% de las ranas estaban infectadas) y en Metznoxtla fue Megalodiscus americanus (76% estaban infectadas). Glypthelmins quieta fue la especie con mayor abundancia media en ambas localidades (Las Pilas = 4.5; Metznoxtla = 11.0). La diferencia en la composición de especies entre las 2 localidades fue significativa (Anosim; R = 0.54, p > 0.05). Las diferencias en la composición de especies de helmintos entre las 2 localidades sugieren que las condiciones ambientales locales son diferentes, lo que puede reflejar diferencias en la dieta de los hospederos a nivel local.

Abstract The helminth community of Lithobates spectabilis (n =77) was studied from Las Pilas (low altitude) and Metznoxtla (high altitude), Biosphere Reserve Barranca de Metztitlán, Hidalgo, Mexico. Species diversity was compared at the infracommunity and the component community level using Hill numbers, and the beta diversity was calculated. Five species of Digenea, 5 of Nematoda, and 2 of Acanthocephala were found in the frogs from the 2 localities. The species richness of parasites in Las Pilas (9 species) was higher than that of Metznoxtla (7 species). The helminth community in Las Pilas was dominated by nematodes and, in Metznoxtla, it was dominated by digeneans. The most prevalent species in Las Pilas was Foleyellides cf. flexicauda (65% of frogs were infected) and, in Metznoxtla, it was Megalodiscus americanus (76% were infected). Glypthelmins quieta was the species with the highest mean abundance in both localities (Las Pilas = 4.5; Metznoxtla = 11.0). The difference in species composition between the 2 localities was significant (Anosim; R = 0.54, p < 0.05). The differences in the composition of species of helminths between the 2 localities suggest that local environmental conditions are different, which may reflect differences in local host diet.

Abstract During a study of the helminth parasites of carangid fish of the Gulf of Mexico, Protomicrocotyle mirabilis and a new member of that genus were found. The aim of the present study is to provide new morphological and sequences of 28s rDNA and CO1 mtDNA for P. mirabilis and describe the new species. Between 2005–2022, 73 specimens of Caranx spp. were purchased from local fishermen of the littoral waters of the Gulf of Mexico. Protomicrocotyle veracruzensis sp. nov. is most similar to P. mirabilis than to P. ivoriensis, the only members of the genus known from the Greater Atlantic Ocean Basin. Protomicrocotyle veracruzensis sp. nov. can be distinguished from those two species by the arrangement and number of testes. Measurement data on the haptoral armature for the new species is provided and the potential value and need for comparative data from these structures of other members of the genus is discussed. The results of the molecular analysis and the morphometric analysis of 91 characters confirmed that this new species belongs to Protomicrocotyle.

Resumo Encontraram-se durante um estudo dos helmintos parasitas de peixes carangídeos do Golfo do México, Protomicrocotyle mirabilis e um novo membro do gênero. O objetivo do presente estudo é fornecer novos dados morfológicos e sequências de 28s rDNA e CO1 mtDNA para P. mirabilis e descrever a nova espécie. Entre 2005-2022, 73 espécimes de Caranx spp. foram comprados de pescadores locais das águas litorâneas do Golfo do México. Protomicrocotyle veracruzensis sp. nov. é mais semelhante a P. mirabilis do que a P. ivoriensis, os únicos membros do género conhecidos da Grande Bacia do Oceano Atlântico. Protomicrocotyle veracruzensis sp. nov. pode ser distinguido dessas duas espécies pela disposição e número de testículos. Neste estudo são fornecidos dados de medidas da armadura haptoral para a nova espécie, discutido o valor potencial e a necessidade de dados comparativos destas estruturas de outros membros do gênero. Os resultados da análise molecular e da análise morfométrica de 91 caracteres confirmaram que essa nova espécie pertence ao gênero Protomicrocotyle.

ABSTRACT The present study was carried out to determine the effect of tilapia Oreochromis niloticus on the physical and chemical sediment parameters on an earthen pond in monoculture (shrimp Penaeus vannamei) and co-culture (tilapia-shrimp) during the dry and wet seasons in a commercial farm during the period from mid-September to end-December 2017 and February to mid-May 2018. Chemical and physical analyses were realized on sediment samples from brackish water ponds representing shrimp farms in San Blas Nayarit, Mexico. Concentrations of organic carbon, nitrogen, potassium, magnesium and calcium were higher in co-culture ponds, and there was a tendency to a higher concentration of phosphorus and sodium in the sediment of monoculture ponds. The texture of the ponds showed a tendency in the dry season to increase the percentage of clay in co-culture due to the effect of bioturbation caused by tilapia. There was no evidence of poor development of sediment quality in any treatment. It was found that tilapia was a factor that affected sediment quality, differences in growth between shrimp monoculture and tilapia-shrimp co-culture can be explained, at least in part, by differences in their sediment.

Abstract: As a part of an ongoing project to inventory the helminth parasites of rodents in México, 30 individuals of Aspiculuris americana were collected inhabiting the intestine from three specimens of the rock mouse Peromyscus difficilis, collected from Cerro Xihuingo, Municipality of Tepeapulco, Hidalgo State, México. This species of nematode parasite different species of the genus Peromyscus (P. gossypinus, P. leucopus, P. maniculatus, and P. floridanus) distributed from Yukon Territory in Canada to Florida in the United States of America. This is the first report of Aspiculuris americana in a Mexican endemic rodent, widening the known distribution of the species to the southern portion of the country.

Resumen: Como parte de un proyecto para inventariar los parásitos helmintos de roedores en México, se recolectaron 30 individuos de Aspiculuris americana que parasitan el intestino de tres especímenes del ratón de las rocas Peromyscus difficilis, recolectados en Cerro Xihuingo, Municipio de Tepeapulco, Estado de Hidalgo, México. Esta especie de nematodo parasita diferentes especies del género Peromyscus (P. gossypinus, P. leucopus, P. maniculatus y P. floridanus) distribuidas desde el territorio de Yukon en Canadá hasta Florida en los Estados Unidos de América. Este es el primer informe de Aspiculuris americana en un roedor endémico mexicano, ampliando la distribución conocida de la especie a la parte sur del país.

Abstract Staff turnover is a costly phenomenon in terms of productivity and performance. The variable that best predicts this phenomenon is the intention to leave, but in Mexico there are few empirical works on said variable. The objective of this research was to investigate whether emotional exhaustion, organizational cynicism, and violation of the psychological contract precede the intention to leave. To this end, a quantitative, empirical, and transversal research was carried out on a sample of 201 operational staff in the auto-parts maquila export industry located in Ciudad Juárez, Chihuahua, Mexico. Partial least squares structural equation modeling (PLS-SEM) was used as the statistical technique. The results indicate that the emotional exhaustion and cynicism of the employee lead to the intention to leave and that, comparatively, cynicism has greater influence. However, the predictive relationship between the violation of the psychological contract and the intention to leave was rejected.

Resumen La rotación de personal es un fenómeno costoso en términos de productividad y desempeño. La variable que mejor la predice es la intención de rotar, pero en México son escasos los trabajos empíricos sobre ella. Esta investigación tuvo por objetivo indagar si el agotamiento emocional, el cinismo organizacional y la violación del contrato psicológico, influyen sobre la intención de rotación. Para ello, se realizó una investigación cuantitativa, empírica y transversal, en una muestra de 201 empleados operativos en la industria maquiladora autopartista para la exportación, localizada en Ciudad Juárez, Chihuahua. Como técnica estadística se utilizó la modelación estructural PLS. Los resultados indican que el agotamiento emocional y el cinismo del empleado llevan a la intención de rotar, y comparativamente, es mayor la influencia del cinismo. Sin embargo, la relación predictiva entre la violación del contrato psicológico y la intención de rotar, se rechazó.

Abstract Specimens of Xiphophorus birchmanni (Teleostei: Poeciliidae) (55 individuals) (Sheepshead swordtail) were collected from 2 localities in the Pánuco River drainage from Hidalgo and Veracruz [at Atlatipa (n = 26) and Benito Juárez (n = 29), respectively], México. The structure of the parasite communities of fish from the 2 localities was examined and compared. Helminths from 10 taxa were recovered: 6 species of larval digeneans (Posthodiplostomum sp., Uvulifer sp., Centrocestus formosanus, Ascocotyle sp., Haplorchis pumilio, and Echinostomatidae gen. sp.); 2 adult monogeneans (Urocleidoides vaginoclastrum and Gyrodactylus sp.); 1 larval cestode (metacestode stage; Glossocercus auritus); and 1 larval nematode, Eustrongylides sp. Urocleidoides vaginoclastrum and C. formosanus were the most frequent and abundant species. The remaining taxa were rare and found at low mean abundance. Component community and infracommunity differences observed in this study could be attributed to abiotic and biotic environmental factors resulting from the geographic separation of these localities during the orogeny of the Sierra Madre Oriental that restricted fish to isolated localities.

Resumen Se revisaron 55 ejemplares de Xiphophorus birchmanni (Teleostei: Poeciliidae) (espada del tempoal), recolectados de 2 localidades [Atlatipa (n = 26) y Benito Juárez (n = 29)] de la cuenca del río Pánuco pertenecientes a los estados de Hidalgo y Veracruz, México, respectivamente. La estructura de las comunidades de parásitos fue examinada y comparada. Se reportaron 10 especies de helmintos, 6 metacercarias Posthodiplostomum sp., Uvulifer sp., Centrocestus formosanus, Ascocotyle sp., Haplorchis pumilio y Echinostomatidae gen. sp.; 2 monogéneos, Urocleidoides vaginoclastrum y Gyrodactylus sp.; 1 larva de céstodo (estadio metacéstodo), Glossocercus auritus, y una larva del nemátodo Eustrongylides sp. Urocleidoides vaginoclaustrum y C. formosanus fueron las más frecuentes y abundantes, mientras que el resto de las especies fueron raras y poco frecuentes. Las diferencias observadas a nivel de comunidad componente e infracomunidad entre las localidades estudiadas, pueden ser atribuidas a factores bióticos y abióticos resultado de la separación geográfica de las localidades durante la orogenia de la sierra Madre Oriental, que restringe y aísla a los peces.

Resumo O exame helmintológico do trato digestivo de nove espécimes de Aetobatus cf. narinari (arraia pintada) revelou a presença de uma nova espécie de cestódeo do gênero Acanthobothrium. As arraias foram coletadas de quatro locais no México: Laguna Términos, ao sul de Isla del Carmen e nas águas marinhas ao norte de Isla del Carmen e Champotón, no estado de Campeche, e Isla Holbox, estado de Quintana Roo. A nova espécie foi denominada Acanthobothrium marquesi, pertencente a uma espécie da categoria 3 (estrobilo longo, tendo mais de 50 proglotes, numerosos testículos, superiores a 80, e ovários assimetricamente lobados). Apenas outra espécie deste gênero, Acanthobothrium tortum pertence a categoria 3, no Oceano Atlântico Ocidental. Acanthobothrium marquesi n. sp. se distingue de A. tortum por ser mais longo (26,1 cm vs. 10,6 cm), possuir maior número de proglotes (1.549 vs. 656), ter um escolex maior (707 µm de comprimento por 872 µm de largura vs. 699 µm de comprimento por 666 µm de largura), e botridias maiores (626 µm de comprimento por 274 µm de largura vs. 563 µm de comprimento por 238 µm de largura). Este é o primeiro relato de uma espécie de Acanthobothrium do Golfo do México.

Abstract The helminthological examination of nine individuals of Aetobatus cf. narinari (spotted eagle ray; raya pinta; arraia pintada) revealed the presence of an undescribed species of cestode of the genus Acanthobothrium. The stingrays were collected from four locations in México: Laguna Términos, south of Isla del Carmen and the marine waters north of Isla del Carmen and Champotón, in the State of Campeche, and Isla Holbox, State of Quintana Roo. The new species, nominated Acanthobothrium marquesi, is a category 3 species (i.e, the strobila is long, has more than 50 proglottids, the numerous testicles greater than 80, and has asymmetrically-lobed ovaries); at the present, the only category 3 species that has been reported in the Western Atlantic Ocean is Acanthobothrium tortum. Acanthobothrium marquesi n. sp. can be distinguished from A. tortum by length (26.1 cm vs. 10.6 cm), greater number of proglottids (1,549 vs. 656), a larger scolex (707 µm long by 872 µm wide vs. 699 µm long by 665 µm wide), larger bothridia (626 µm long by 274 µm wide vs. 563 µm long by 238 µm wide). This is the first report of a species of Acanthobothrium from the Mexican coast of the Gulf México.

Resumo Neonchocotyle violantei n. sp. (Monogenea: Hexabothriidae) infecta brânquia de Pseudobatos lentiginosus, (Rhinopristiformes, Rhinobatidae) de águas litorâneas ao largo da costa de Celestún, Yucatán, México. É atribuído a Neonchocotyle porque tem, entre outras características, um haptor assimétrico, um receptáculo seminal, um tipo oótipo liso e um ovo com dois filamentos alongados. Difere de Neonchocotyle pastinacae, o único congênere, por ter um corpo pequeno (821 de comprimento por 315 de largura, comprimento a largura = 2,6: 1), dois pares de microganchos entre as ventosas do apêndice haptoral, poros vaginais extracaecais (submarginal) e 5-9 testículos. Este é o primeiro registro de uma espécie de Neonchocotyle no Golfo do México, o primeiro monogenético registrado em P. lentiginosus no México e a segunda espécie de Hexabothriidae relatada no México.

Abstract Neonchocotyle violantei n. sp. (Monogenea: Hexabothriidae) infects the gill of the Atlantic guitarfish, Pseudobatos lentiginosus (Rhinopristiformes, Rhinobatidae) from littoral waters of Celestún, Yucatán, Mexico. It is assigned to Neonchocotyle because it has, among other features, an asymmetrical haptor, a seminal receptacle, a smooth oötype, and an egg with two elongate filaments. It differs from Neonchocotyle pastinacae, the only congener, by having a small body (821 long by 315 wide, length to width = 2.6:1), two pairs of microhooks between the haptoral appendix suckers, extracaecal (submarginal) vaginal pores, and 5-9 testes. This is the first record of a species of Neonchocotyle in the Gulf of Mexico, the first monogenean reported from P. lentiginosus in Mexico and the second species of Hexabothriidae reported from Mexico.

RESUMEN El contrato psicológico es relevante para comprender el comportamiento y el bienestar de los trabajadores. Esta investigación analiza el efecto de la violación del contrato psicológico sobre el cinismo del empleado a través de la mediación del agotamiento emocional. Para ello se realizó una investigación cuantitativa, empírica y transversal a través de una encuesta personal a personal operativo que labora en el sector automotriz de empresas maquiladoras de exportación localizadas en Ciudad Juárez, Chihuahua, México. Mediante un análisis de ecuaciones estructurales se encontró que la violación del contrato psicológico afecta de forma directa e indirecta sobre el cinismo del empleado, a través de la mediación del agotamiento emocional.

ABSTRACT The psychological contract is relevant to understand the behavior and well-being of workers. This investigation analyzes the effect of the violation of the psychological contract upon the employee's cynicism through a mediation of emotional exhaustion. For this purpose, a quantitative, empirical and cross-sectional design research was performed. This was done through a personal poll to workers in the export automotive industry in Ciudad Juarez, Chihuahua, Mexico. Employing a structural equation analysis it was found that the violation of the psychological contract affects employee's cynicism in both direct and indirect ways, through a mediation of emotional exhaustion.

RESUMO O contrato psicológico é relevante para a compreensão do comportamento e bem-estar dos trabalhadores. Esta pesquisa analisa o efeito da violação do contrato psicológico sobre o cinismo dos empregados através da mediação da exaustão emocional. Com este fim, uma pesquisa quantitativa, empírica e transversal foi realizada através de um inquérito pessoal do pessoal operacional que trabalha no setor automotivo de empresas maquiladoras de exportação, localizadas em Ciudad Juarez, Chihuahua, México. Através de uma análise de equações estruturais, verificou-se que a violação do contrato psicológico afeta direta e indiretamente na forma de cinismo do empregado, através da mediação de exaustão emocional.

Objective: To explore the association of three polymorphisms of the serotonin receptor 1Dβ gene (HTR1B) in the etiology of eating disorders and their relationship with clinical characteristics. Methods: We analyzed the G861C, A-161T, and A1180G polymorphisms of the HTR1B gene through a family-based association test (FBAT) in 245 nuclear families. The sample was stratified into anorexia nervosa (AN) spectrum and bulimia nervosa (BN) spectrum. In addition, we performed a quantitative FBAT analysis of anxiety severity, depression severity, and Yale-Brown-Cornell Eating Disorders Scale (YBC-EDS) in the AN and BN-spectrum groups. Results: FBAT analysis of the A-161T polymorphism found preferential transmission of allele A-161 in the overall sample. This association was stronger when the sample was stratified by spectrums, showing transmission disequilibrium between the A-161 allele and BN spectrum (z = 2.871, p = 0.004). Quantitative trait analysis showed an association between severity of anxiety symptoms and the C861 allele in AN-spectrum participants (z = 2.871, p = 0.004). We found no associations on analysis of depression severity or preoccupation and ritual scores in AN or BN-spectrum participants. Conclusions: Our preliminary findings suggest a role of the HTR1B gene in susceptibility to development of BN subtypes. Furthermore, this gene might have an impact on the severity of anxiety in AN-spectrum patients.

Abstract: Parasites are known to be useful as biological tags in distinguishing fish stocks, but the parasite fauna method has received limited use in the fisheries of Mexico. Parasite fauna composition and their infection levels were quantified for Caranx caballus populations at 3 locations on the south central Pacific coast of Mexico. Three hundred eighty-eight fish were collected and examined between December 2009 and February 2012. Twenty-four species of parasites were identified: 2 monogeneans, 6 digeneans, 1 cestode, 5 nematodes, 8 copepods, and 2 isopods. At the component community level, species richness of parasites varied significantly from 9 to 18 (in 2011 and 2012, respectively, for Acapulco Bay), and was similar to previous reports for other species of Carangidae. The component communities and infracommunities of C. caballus exhibited a similar pattern: low species numbers, low diversity, and dominance by a single species. Multivariate discriminant analysis used to distinguish between the C. caballus populations, indicated that each location can be considered as a different fish stock, and that C. caballus, therefore, does not migrate between the studied locations, even though they are close from each other.

Resumen: Se sabe que los parásitos son útiles como marcadores biológicos en la distinción de stocks de peces, aunque el método de la parasitofauna ha recibido un uso limitado en México. Se determinó la composición y los niveles de infección de la parasitofauna en poblaciones de Caranx caballus de 3 localidades del Pacífico mexicano. Se capturaron y examinaron 388 peces entre diciembre del 2009 y febrero del 2012, identificándose 24 especies de parásitos: 2 monogéneos, 6 digéneos, un cestodo, 5 nematodos, 8 copepodos y 2 isopodos. A nivel de comunidad componente, el número de especies de parásitos varió significativamente de 9 a 18 (en el 2011 y 2012, respectivamente, para la bahía de Acapulco), siendo similar a los registros previos obtenidos para otras especies de Carangidae. Las comunidades componentes, al igual que las infracomunidades de C. caballus presentaron un patrón similar: bajo número de especies, poca diversidad y dominancia de una sola especie. Los análisis multivariados utilizados para diferenciar poblaciones de C. caballus indicaron que cada localidad puede ser considerada como un stock de peces diferente y que por lo tanto C. caballus no realiza migraciones entre las localidades estudiadas, aunque sean cercanas una de otra.

Denarycotyle gardneri n. gen., n. sp. (Monogenea: Monocotylidae) is described from the gills of the stingray, Rhinoptera steindachneri (Myliobatidae), collected in marine waters off Acapulco, Guerrero, Mexico. The genus is assigned to Euzetiinae because it has a haptor with one central loculus, one additional loculus on either side of the central loculus and 10 peripheral loculi. However, the genus described herein can be distinguished from Euzetia , the only genus currently assigned to Euzetiinae, by the presence of two accessory structures on the dorsal surface of the haptor and hamuli with a sclerotized accessory piece on each hamulus. Specimens of D. gardneri n. gen., n. sp. were found on the gills of 4 of 18 individuals of R. steindachneri (22%) but were not present on Rhinobatos glaucostigma Jordan and Gilbert (1 individual), Urotrygon rogersi (Jordan and Starks) (2), Narcine entemador Jordan and Starks (3), Aetobatus narinari (Euphrasen) (1) or Dasyatis longa (Garman) (3). This is the third genus and the fourth species of a monogenean recorded from Rhinoptera and the second member of Euzetiinae from Mexico and from the neotropics. Keys to the subfamilies of Monocotylidae and to the species of Euzetiinae, as well as a hypothesis of phylogenetic relationships between Heterocotylinae, Decacotylinae, and Euzetiinae are provided.

Se describe Denarycotyle gardneri n. gen., n. sp. (Monogenea: Monocotylidae) parásito de las branquias de la raya, Rhinoptera steindachneri (Myliobatidae), de Acapulco, Guerrero, México. El género se incluyó en Euzetiinae por presentar un haptor con 1 lóculo central, 1 lóculo adicional en cada lado del lóculo central y 10 lóculos periféricos. Sin embargo, el género que se describe ahora se distingue de Euzetia -único género incluido hasta ahora en Euzetiinae- por la presencia de 2 estructuras accesorias en la superficie dorsal del haptor, y hamuli con una pieza accesoria esclerotizada presente en cada uno de los hamulus. Los ejemplares de Denarycotyle gardneri n. gen., n. sp. fueron recolectados de 4 de 18 ejemplares de R. steindachneri (22%), pero no se encontraron en Rhinobatos glaucostigma Jordan y Gilbert (1 ejemplar), Urotrygon rogersi (Jordan y Starks) (2), Narcine entemador Jordan y Starks (3), Aetobatus narinari (Euphrasen) (1), ni en Dasyatis longa (Garman) (3). Este es el tercer género y cuarta especie de un monogéneo registrado para Rhinoptera y es el segundo miembro de Euzetiinae en México y el neotrópico. Se presentan una clave para las subfamilias de Monocotylidae y las especies de Euzetiinae, y una hipótesis de las relaciones filogenéticas entre Heterocotylinae, Decacotylinae y Euzetiinae.

A total of 141 highland swordtails, Xiphophorus malinche, were collected from 2 localities in the Pánuco river drainage (Chicayotla and Malila) from Hidalgo, México. The parasite community structure of the 2 localities was examined and compared. Five taxa of helminths were recovered: 2 digeneans, adults of Paracreptotrema sp. and metacercariae of Uvulifer sp.; an adult monogenean, Urocleidoides vaginoclastrum; an adult cestode, Bothriocephalus acheilognathi, and an adult nematode, Rhabdochona xiphophori. Among them, Ur. vaginoclastrum was the most frequent and abundant species. The remaining species were rare and found at low mean abundance. Only 2 species of helminth were found at both localities. The observed species richness, individual abundance, and diversity were low at component community and infracommunity levels. Abundance of helminths and fish standard length were correlated. Uvulifer sp. was more abundant in small fish, but Ur. vaginoclastrum showed the opposite pattern, high abundance in larger fish. Differences observed in this study can be attributed to abiotic and biotic environmental factors resulting from the geographic separation of these localities during to the orogeny of the Sierra Madre Oriental that restricted fish to isolated headwaters.

Se compararon y examinaron las comunidades de helmintos de peces de Xiphophorus malinche de 2 localidades de la cuenca del río Pánuco (Chicayotla y Malila), Hidalgo, México. Se registraron 5 especies de helmintos: 2 digéneos, Paracreptotrema sp. y metacercarias de Uvulifer sp.; 1 especie de monogéneo adulto, Urocleidoides vaginoclastrum; 1 céstodo adulto, Bothriocephalus acheilognathi, y 1 nemátodo adulto Rhabdochona xiphophori. La especie de monogéneo resultó ser la más frecuente y abundante en las comunidades. Las demás especies se encontraron en baja abundancia. Sólo 2 especies de helmintos fueron encontradas en ambas localidades. La riqueza de especies, la abundancia y la diversidad se analizaron tanto a nivel de componente de comunidad como de infracomunidad. La abundancia de helmintos y la longitud patrón de los peces están correlacionadas. Uvulifer sp. fué más abundante en peces pequeños, pero Ur. vaginoclastrum fue más abundante en peces de talla grande. Las diferencias observadas en este estudio pueden ser atribuidas a factores bióticos y abióticos resultado de la separación geográfica de las localidades durante la orogenia de la sierra Madre Oriental, que restringió a los peces a cuerpos de agua aislados.

The objective of this work was to determine by PCR the presence of Salmonella Enteritidis FT-13A (SE) and Salmonella Issatschenko (SI) in different samples of organs from 4 days old chicks experimentally infected. Four days old chicks were inoculated with SE and SI and their organs were frozen for DNAextraction to perform classic and nested PCR. It was possible to demonstrate the presence of SE and SI after 6 hours after experimental infection (AEI), but as time passed AEI positive results were inconsistent, obtaining negative results until 174 hours AEI. PCR is useful for detecting SE and SI in the early hours AEI. It is recommended to use pre-enrichment of the samples, in order to facilitate the DNA extraction and the detection of Salmonella by PCR.

El objetivo del presente trabajo fue determinar por medio de esta prueba, la presencia de Salmonella Enteritidis FT-13A (SE) y de Salmonella Issatschenko (SI), en diferentes muestras de órganos de pollitos de 4 días de edad infectados experimentalmente. Se emplearon órganos congelados de pollitos de 4 días de edad inoculados experimentalmente con SE y SI, para extraer el ADN y realizar la PCR clásica y anidada. Se logró detectar SE y SI desde las 6 horas posinfección experimental (PIE), pero conforme pasó el tiempo PIE, los resultados positivos fueron inconsistentes, obteniendo resultados negativos hasta las 174 horas PIE. Se concluyó que la PCR es útil para detectar SE y SI en las primeras horas PIE. Se sugiere utilizar pre-enriquecimiento de las muestras, para facilitar la extracción de ADN y la detección de Salmonella por medio de la PCR.

During an ongoing study of the helminths of stingrays (Elasmobranchii), 12 stingrays were collected from 3 localities in the state of Veracruz, Mexico: Laguna de Tamiahua, Laguna de Tampamachoco, and a costal reef in the Gulf of Mexico. Metacercarias were collected from the spiral valves of Dasyatis say (bluntnose stingray), Gymnura micrura (lesser butterfly ray), and Rhinobatus lentiginosus (Atlantic guitarfish). The metacercarias, accidental parasites, were assigned to type Paramonilicaecum (Digenea: Didymozoidae). Material (Didymozoidae) previously deposited in the Colección Nacional de Helmintos, Instituto de Biología, Universidad Nacional Autónoma de México, was re-identified. This is the first report of a species in larval phase of the "Type" Paramonilicaecum from the Gulf of Mexico, Veracruz, and the first report from a Mexican stingray.

Como parte de un estudio sobre los helmintos parásitos de rayas (Elasmobranchii), se colectaron 12 ejemplares en 3 localidades del estado de Veracruz, México: Laguna de Tamiahua, Laguna de Tampamachoco y un arrecife de la costa del golfo de México. Se encontraron metacercarias identificadas como parásitos accidentales del tipo Paramonilicaecum (Digenea: Didymozoidae) en la válvula espiral de Dasyatis say (raya látigo chata), Gymnura micrura (raya cola de rata) y Rhinobatus lentiginosus (guitarra diablito). De manera complementaria, se actualizó la identificación de material perteneciente a Didymozoidae depositado en la Colección Nacional de Helmintos en el Instituto de Biología, Universidad Nacional Autónoma de México. Éste es el primer registro para México de metacercarias del tipo Paramonilicaecum en rayas.