Caracterización morfométrica y genética de stocks de tilapias (Cichlidae: Tilapiini) para un efectivo manejo de sus pesquerías en dos presas mexicanas

Several tilapia species were introduced to the Infiernillo Dam during the 1960s. Following this introduction of tilapia, the dam has been an important fish production site in Mexico. However, recent decreases in tilapia catches suggest that fish management strategies and tilapia exploitation practices need to be revised. To date, management practices are limited by the lack of methods to evaluate the status of these introduced species. Here we morphometrically characterized two genera and three species from two sites in the Infiernillo Dam and a site in the Zicuiran Dam. The samples were characterized for 14 allozyme loci and two mitochondrial DNA-RFLP markers, r16S and cytochrome b. Based on these morphological and genetic markers, we identified Tilapia rendalli and Oreochromis aureus in the Infiernillo Dam, and Oreochromis mossambicus at the Zicuiran reservoir. These species were separated into genera based on differences in the number of predorsal scales and the pharyngeal teeth morphology. For Oreochromis, they were further classified into species using six morphometric variables. The allozyme and mtDNA-RFLP results are concordant with the morphological differences. Furthermore, two populations of O. aureus in the Infiernillo Dam appear genetically and morphologically distinct. The levels of genetic variability (He = 0.0567-0.2299 and h = 0.0000-0.4848) are low compared to properly managed tilapia populations. Given the levels of variation in these populations, we suggest sustainable genetic management strategies.Varias especies de tilapias fueron introducidas a la presa El Infiernillo durante los años sesenta del siglo pasado. Posterior a dichas introducciones, la presa ha sido uno de los sitios importantes de producción nacional para peces. Sin embargo, bajas recientes en las capturas, sugieren que las estrategias de manejo y las prácticas de explotación requieren de ser revisadas. Hasta ahora, dichas prácticas de manejo están limitadas por la falta de métodos para evaluar el status de dichas especies introducidas. En éste trabajo se caracterizan morfométricamente dos géneros y tres especies de dos sitios en la presa El Infiernillo y de un sitio de la presa Zicuirán. Las muestras fueron caracterizadas con 14 loci aloenzimáticos y dos marcadores mitocondriales ADN-RFLP, r16S y citocromo b. Basados en estos marcadores morfológicos y genéticos, se identificó a Tilapia rendalli y Oreochromis aureus en la presa El Infiernillo y a Oreochromis mossambicus para Zicurán. Las especies se separaron en dos géneros en base a diferencias en el número de escamas predorsales y a la morfología del diente faríngeo. Para Oreochromis, las especies se separaron con seis variables morfométricas. Los resultados de aloenzimas y PCR-RFLP del mtADN concuerdan con estas diferencias morfológicas. Además, dos poblaciones de O. aureus en la presa El Infiernillo parecen morfológica y genéticamente diferentes. Los niveles de diversidad genética (He = 0.0567-0.2299 y h = 0.0000-0.4848) son bajos comparados con los reportados para poblaciones manejadas adecuadamente. Dados los niveles de variación de estas poblaciones, sugerimos estrategias de manejo adecuadas

ANÁLISIS ESTRUCTURAL DEL GEN MITOCONDRIAL CITOCROMO B Y DE LA REGIÓN CONTROL DE CYNOMYS MEXICANUS Y SPERMOPHILUS SPILOSOMA (RODENTIA: SCIURIDAE)

The nucleotide sequences of the cytochrome b gene and of the control region are described for Cynomys mexicanus and Spermophilus spilosoma. The cytochrome b gene was characterized by the presence of eight non-synonymous substitutions at the inter-generic level, presented mainly in the transmembrane zone (87%). The control region was characterized by the presence of the conserved blocks, ETAS1 and CSB1; by the absence of repetitive sequences and by the conserved blocks, ETAS2, CSB2 and CSB3. Most of the inter-generic variation (47.9%) was observed in the ETAS domain. The structure of the control region was similar to that of phylogenetic related species.The nucleotide sequences of the cytochrome b gene and of the control region are described for Cynomys mexicanus and Spermophilus spilosoma. The cytochrome b gene was characterized by the presence of eight non-synonymous substitutions at the inter-generic level, presented mainly in the transmembrane zone (87%). The control region was characterized by the presence of the conserved blocks, ETAS1 and CSB1; by the absence of repetitive sequences and by the conserved blocks, ETAS2, CSB2 and CSB3. Most of the inter-generic variation (47.9%) was observed in the ETAS domain. The structure of the control region was similar to that of phylogenetic related species

Extreme genetic divergence in the endemic fish Chirostoma humboldtianum: implications for its conservation

Chirostoma humboltianum is an endemic species widely distributed in isolated basins of Central México. However, habitat alteration had reduced the range of distribution and led to the local extinction of the species in some basins. During the Miocene these basins were connected, allowing dispersal and colonization of new hydrological systems. Later on, tectonic, volcanic and climatic events of the Plio-Pleistocene promoted continuous periods of isolation and reconnection allowing the species evolve through continuous cycles of expansion and contraction of its distribution. Therefore it is expected that these events have left signals in the geographical distribution and genetic diversity and divergence of existing populations. Although the analysis of genetic diversity and genetic structure in the population becomes an important factor for the conservation of a species, few studies have been made in this taxon. In this study we used a 341pb segment of the domain I of the hypervariable region of the mitochondrial control region to analyze the genetic diversity and their distribution in 20 individuals of each one of six lakes located in central México. The values of haplotypic (0 - 0.938) and nucleotide (0 - 0.0352) diversity suggested continuous periods of expansion and population contraction related with the formation of the lakes during the Pleistocene which is supported by the BSP and mismatch analysis, and recent anthropogenic factors. In addition, the large number of exclusive haplotypes (66%) and the highly significant genetic differentiation among populations suggests that each one of the population must be conserved because each one is an important component in the evolutionary legacy of the species

Intraspecific karyotypic variation in the silverside fish Chirostoma humboldtianum (Atheriniformes: Atherinopsidae)

Within its genus, Chirostoma humboldtianum is one of the species with the widest distribution, inhabiting lake and pond environments along the Lerma-Santiago basin in the Mexican Plateau. Although the species is of great ichthyological, economic, and cultural relevance, factors related to human activity such as habitat loss, pollution, overfishing, and introduction of non-native fish have played important roles in the decline and disappearance of populations. With the aim of describing the karyotype of the species, 22 specimens of C. humboldtianum were collected and their chromosomes obtained from gills based on Denton (1973). Here we reveal intraspecific chromosome variation, characterized by five cytotypes found in four studied populations: 1) Las Tazas, Tiacaque dam (2n = 48, FN = 58) with chromosome formula 6m + 4sm + 38t; 2); Villa Victoria dam (2n = 48, FN = 54) 2m + 2sm + 2st + 42t; 3) Tepuxtepec dam, with two cytotypes (2n = 48, FN = 50) 8m + 2sm + 38t and (4n = 96, FN = 116) 8m + 2st + 38t; 4) and San Pedro Lagunillas lagoon (2n = 48, FN = 58) 8m + 2sm + 38t. We observed chromosome variation in the morphology of pairs 1, 2, 4, and 5. Results allow us to suggest that pericentric inversions are the source of intraspecific chromosome variation. Comparative analyses support the hypothesis that the karyotype of the population from Villa Victoria dam represents the primitive form for the species

An integrative taxonomic approach reveals Octopus insularis as the dominant species in the Veracruz Reef System (southwestern Gulf of Mexico)

The common octopus of the Veracruz Reef System (VRS, southwestern Gulf of Mexico) has historically been considered as Octopus vulgaris, and yet, to date, no study including both morphological and genetic data has tested that assumption. To assess this matter, 52 octopuses were sampled in different reefs within the VRS to determine the taxonomic identity of this commercially valuable species using an integrative taxonomic approach through both morphological and genetic analyses. Morphological and genetic data confirmed that the common octopus of the VRS is not O. vulgaris and determined that it is, in fact, the recently described O. insularis. Morphological measurements, counts, indices, and other characteristics such as specific colour patterns, closely matched what had been reported for O. insularis in Brazil. In addition, sequences from cytochrome oxidase I (COI) and 16S ribosomal RNA (r16S) mitochondrial genes confirmed that the common octopus from the VRS is in the same highly supported clade as O. insularis from Brazil. Genetic distances of both mitochondrial genes as well as of cytochrome oxidase subunit III (COIII) and novel nuclear rhodopsin sequences for the species, also confirmed this finding (0–0.8%). We discuss our findings in the light of the recent reports of octopus species misidentifications involving the members of the ‘O. vulgaris species complex’ and underscore the need for more morphological studies regarding this group to properly address the management of these commercially valuable and similar taxa

Morphological and genetic variation in seven species of the endangered Chirostoma “humboldtianum species group” (Atheriniformes: Atherinopsidae)

The Chirostoma “humboldtianum” group includes seven silverside species considered as a monophyletic assemblage because of their high genetic and morphological similarities. The group includes five moderately large species, “peces blancos” (117 - 300 mm standard length - SL) and two smaller species, “charales” (70 - 142 mm SL). These species are of great economical, cultural and ichthyological interest for local populations, and their management practices are controversial. We investigated the morphometric, meristic and allozyme variations of the seven species (13 populations) and related the variations with life history, habitat and management procedures. Nineteen morphometric variables, eight meristic variables (by multivariate analysis) and 23 allozyme loci of the seven species and populations of Chirostoma were compared. Principal component analysis (PC) of morphometric and meristic data indicate that both sets of data provided information to differentiate among the seven species. The variables that accounted for most of this differentiation were head length (HL), predorsal 1 length (P1L) and length of pelvic fin base (PfbL). PC and Discriminant Analysis (DA) with morphometric data also suggested the differentiation of populations within C. grandocule (83% correctly classified organisms), whereas PC and DA with meristic data differentiated populations of C. humboldtianum (80% correctly classified organisms). The most important morphometric variables for the differentiation were anal fin height (AfH), length of anal fin base (AfbL) and predorsal 2 length (P2L) and the meristic variables D2fR, PdS and AfR. The genetic variability data indicate changes in values of some of the species in relation to previously reported data. The present populations of C. grandocule show a reduction in He (0.002 vs. 0.009). Other species showed an increase; for instance, C. consocium consocium, C. humboldtianum, C. lucius, C. promelas and C. sphyraena averaged He = 0.069 vs. 0.027. θ indicated significant genetic differentiation among the analysed species (0.247, S.D. 0.159) and θS supported the morphological data that suggest intra-specific differentiation (0.360, S.D. 0.154).El grupo Chirostoma “humboldtianum” incluye siete especies de peces considerados como un conjunto monofilético por sus altas similaridades genéticas y morfológicas. El grupo incluye cinco especies moderadamente grandes, “peces blancos” (117 – 300 mm longitud estándar – SL) y dos especies más pequeñas, “charales” (70 – 142 mm SL). Estas especies son de gran interés económico, cultural e ictiológico para las poblaciones locales y sus prácticas de manejo son controversiales. Nosotros investigamos las variaciones morfométricas, merísticas y de isoenzimas para las siete especies (13 poblaciones) y relacionamos las variaciones con la listoria de vida, el hábitat y los procedimientos de manejo. De las siete especies y poblacines de Chirostoma, se compararon 19 variables morfométricas, ocho variables merísticas (por análisis multivariado) y 23 loci de isoenzimas. El análisis de componentes principales (PC) de los datos morfométricos y merísticos indica que ambos juegos de datos da información para diferenciar entre las siete especies. Las variables que cuentan por casi toda esta diferenciación fueron longitud de la cabeza (HL), longitud predorsal 1 (P1L) y longitud de la base de la aleta pélvica (PfbL). Los análisis discriminantes (DA) y de PC con los datos morfométricos también sugieren la diferenciación de poblaciones dentro de C. grandocule (83% organismos correctamente clasificados), mientras que los análisis DA y PC con los datos merísticos diferenciaron poblaciones de C. humboldtianum (80% organismos correctamente clasificados). Las variables morfométricas más importantes para la diferenciación fueron el alto de la aleta anal (AfH), la longitud de la base de la aleta anal (AfbL) y la longitud predorsal 2 (P2L), y las variables merísticas D2fR, PdS y AfR. Los datos de variabilidad genética indican cambios en los valores de algunas de las especies en relación a datos informados previamente. Las poblaciones presentes de C. grandocule muestran una reducción en He (0.002 vs. 0.009). Otras especies mostraron un incremento; por ejemplo, C. consocium consocium, C. humboldtianum, C. lucius, C. promelas y C. sphyraena promediaron He = 0.069 vs. 0.027. q indicó una diferenciación genética significante entre las especies analizadas (0.247, S.D. 0.159) y qs apoyó los datos morfológicos que sugieren diferenciación intraespecífica (0.360, S.D. 0.154)

Performance of Brooders, Fry and Growth of the Nile Tilapia (Oreochromis niloticus) Cultured in an Experimental Recirculating Aquaculture System

We present results of a long-term study aimed to optimize Nile tilapia O. niloticus production in a recirculating aquaculture system (RAS) in México City. Three experiments were evaluated: 1) fry production; 2) production of masculinized fries; and 3) assessment of growth under three different densities (10, 30 and 75 fish/m3). The broodstock produced on average 2400 ± 600 fry every 15 days during six months, with a total production of 28,800 ± 2000. One hundred percent males were produced in 274-L raceways in an eight-week period. The obtained results in fish production in the RAS system indicated variations related to density. A daily growth rate of 3.6 g/day was registered with a density of 10 fish/m3, 0.9 g/day in 30 fish/m3 and 0.4 g/day in 75 fish/m3. This information could be useful for production purposes in this type of systems.Presentamos los resultados de un estudio a largo plazo dirigido a optimizar la producción de tilapia del Nilo O. niloticus en un sistema de acuicultura recirculante (RAS) en la ciudad de México. Se evaluaron tres experimentos: 1) producción de alevines; 2) producción de papas fritas masculinizadas; Y 3) evaluación del crecimiento bajo tres densidades diferentes (10, 30 y 75 peces / m3). Los reproductores produjeron en promedio 2400 ± 600 alevines cada 15 días durante seis meses, con una producción total de 28.800 ± 2000. Ciento por ciento de los machos fueron producidos en 274-L en un período de ocho semanas. Los resultados obtenidos en la producción de peces en el sistema RAS indicaron variaciones relacionadas con la densidad. Se registró una tasa de crecimiento diario de 3,6 g / día con una densidad de 10 peces / m3, 0,9 g / día en 30 peces / m3 y 0,4 g / día en 75 peces / m3. Esta información podría ser útil para fines de producción en este tipo de sistemas

Role of oceanography in shaping the genetic structure in the North Pacific hake <i>Merluccius productus</i>

<div><p>Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (<i>Merluccius productus</i>) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of <i>M</i>. <i>productus</i> in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (F_ST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.</p></div