Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Background: Prebiotics are polysaccharides that cannot be digested by the host; however, they generate benefits by stimulating the activity of beneficial microorganisms in the digestive system, which can maximize weight gain, feed conversion, and stimulate the immune response. Mannan oligosaccharides (MOS) have been evaluated in several fish species of commercial importance. Goals: Determine inclusion effects of diffe­rent MOS levels in balanced diets for juveniles of Atractosteus tropicus on the growth, productive parameters, survival, somatic indexes, and activity of digestive enzymes. Methods: Six experimental diets including MOS (0.0, 0.2, 0.4, 0.6, and 0.8%) and a trout control diet (DC) were designed, manufactured, and evaluated in triplicate during 62 days. A hundred and eighty juveniles (5.11 ± 0.08 g) were distributed in a recirculation system with 18 tanks of 70 L with a flow of 10 L min-1. Results: The 0.2% MOS diet produced the highest va­lues in weight gained (WG), specific growth rate (SGR), and protein efficiency rate (PER) and the lowest value in feed conversion rate (FCR). Survival in all treatments was greater than 96%. The hepatosomatic index was higher for the 0.4% treatment, while the viscerosomatic index was higher for the 0.4% and 0.6% treatments. All the enzymatic activities (acid protease, alkaline protease, trypsin, chymotrypsin, leucine aminopeptidase, carboxypeptidases, lipases, α-amylase, acid phosphatases, and alkaline phosphatases) showed significant differences by the inclusion of MOS in the diet. Conclusions: Supplementation of 0.2% MOS in diets for juveniles of A. tropicus, generates benefits in growth and productive performance. The inclusion of MOS in diets for juveniles of A. tropicus modifies somatic indices and the activity of digestive enzymes of juveniles.

Background. The presence of Thysanoteuthis rhombus Troschel, 1857 in the eastern Pacific Ocean was estimated based on the geographic range of the species constructed from scattered locations of adults, juveniles, and egg masses. Goals. This note describes morphometric characteristics of the southernmost registry of the diamond squid T. rhombus in Mexican waters of the Gulf of Tehuantepec (16°N-95°W). Methods. In January 2015 we found a stranded adult female weighing a total of 12.5 kg, with a total length of 92 cm, and a mantle length of 45.5 cm. Results. This was a mature female, with oocytes inside the oviducts that averaged 1.2 mm in diameter, and seven attached spermatophores on the buccal membrane of the female, as evidence of mating. Conclusions. This late registry in the Gulf of Tehuantepec could simply be due to their relative scarcity in the eastern Pacific Ocean.  

Background. Originally, there was a single lake in the Mexico Basin known as Texcoco Lake, which was separated by an levee constructed by the Aztecs to prevent salt water from the north from mixing with fresh water of Tenochtitlan. Goals. The objective of this work was to determine if the absence of the brine productive layer in the southern zone of Lake Texcoco is caused by faults or changes in facies. A study of lithological correlation was carried out using cores with continuous recovery of sediments. Methods. Five cores were made with a rotary machine in order to define the lithology in an N-S cross section along the Lake of Texcoco, by means of a detailed lithological description. Results. We determined that the brine productive hard layer was not affected by faults, but rather changed in the meridional lake zone due to muddy facies. The presence of volcanic ash, sometimes pumitic, was useful for the lithological correlation. Sediments are corrosive due to their salinity concentrations. Reducing greenish muds and oxidant red muds were found with frequent ostracods intercalations. There is a non-homogeneous medium with depths from 37 m to 60 m. The muds may amplify seismic waves. Conclusions. Lacustrine sediments in the subsoil of Texcoco Lake are a heterogeneous media and the subsoil is highly corrosive due to its salinity levels. The first hard layer was successfully defined and a second hard layer was found under the first hard layer. There are diverse lithological facies with interbedded volcanic ashes.  

Background. Tropical mountain rivers are strategic sources of water for human development while biological communities are indicators of the status of these ecosystems. However, volcanic basins close to large urban areas are affected by increasing human pressures that threaten the future of these ecosystems and their benefits to society. Goals. This paper analyzes the evolution of the responses of the aquatic macroinvertebrate assemblages in the face of increasing pressures in the Birrís River basin, which is essential for providing food and energy for the Greater Metropolitan Area of Costa Rica. The hypothesis that volcanic headwater communities are highly vulnerable to human impacts was tested. Methods. Composition and structure of aquatic macroinvertebrate assemblages were assessed along main river channels over two years. Results. The spatial variability of assemblages was related to organic pollution and the self-purification capacity of the river. Temporal variability was mainly explained by the intra-annual climate variability (seasonality). Macroinvertebrate assemblages were dominated by Chironomidae (Diptera), Simuliidae (Diptera), and Baetidae (Ephemeroptera) throughout the year. High flows during the rainy season (May to December) reduced density while diversity peaked at the end of that season. Ephemeroptera and Trichoptera reached their maximum abundance during the dry season, while Diptera showed maximum richness at the end of the rainy season. Conclusions. Biological communities showed spatial and temporal adaptations to the main environmental stresses, including high levels of organic pollution. However, the high slope of river channels favors the self-purification processes, which offer an opportunity for the recovery of ecological integrity combined with control of the organic discharges. More information is needed on taxonomy and autoecology of aquatic fauna and flora in these fragile volcanic environments that are strategic for the protection of water resources in the tropics.

Background. La Escobilla is a sandy beach and the main nesting site of the Olive Ridley turtle, Lepidochelys olivacea, (golfina in Spanish), from the southern Mexican coast. Studies related to the habitat of these organisms suggest conservation strategies that lead us to examine the physical parameters that affect the arribazones [i.e., coastal abundance of fish, off-shore shoals, and, by extension, abundance of turtles]. Goals. The aim of this study was to investigate the textural characteristics of coastal sediments and morphology of the beach in order to determine their possible relation with the nesting of this species. Methods. Sediment samples were collected along 15 km of infra-, meso-, an supra-beach, topographic surveys of beach profiles were made, and some sedimentological parameters were obtained, i.e., Mzf (size grain) and sf (sediment classification). Results. Meso-beach and supra-beach areas with a gentle slope (from 2° to 4°), grain size medium sands (1f to 2f), and the opening of the sandbar at the mouth of the Cozoaltepec River during rainy season appear to favor nesting. Conclusions. Areas with major nesting sites are located at a distance of 2.3 km to the east of the Cozoaltepec River, where apparently the morphology of the beach is more adequate because its slope is not so high and the beach is wide enough for nesting. We also know that the largest observed turtle arribazones occur in this area.  

Background: Sphyrna lewini, is a semi-oceanic and cosmopolitan species globally distributed throughout tropical and warm temperate seas. In the northeastern tropical Pacific, this specie represents an important contribution to the biomass of artisanal and small-scale fisheries. Goals: In this study the aim was to obtain information about length frequency distribution and reproductive aspects of S. lewini, in Oaxaca, Mexico. Methods: Samples were taken from August 2001 to December 2007 in four landing sites of the artisanal fleet on the coast of Oaxaca. Results: Samples were collected 388 females and 434 males. Total length ranged from 44-308 cm for males and from 44-332 cm for females. The catches were made up of neonates (24.3%, 44-74 cm), juveniles (42.2%, 75-170 cm) and adults (33.5%, > 170 cm). The sex ratio shows differences by size, and season. The greatest catches were recorded in the rainy season (85.5%), with a predominance of juveniles and adults, and a higher proportion of males. In the dry season (15.5%) were recorded with a predominance of larger sizes >100 cm in both sexes. The females reached sexual maturity (TL50) at 198.8 cm and the males at 181 cm, based on characteristics and measurements of reproductive organs. A total of 37 gravid females with sizes between 175 and 281 cm were registered, from April to August. Gravid females had between 15-42 embryos, varying from 44-54 cm. Conclusion: S. lewini was present year round in the study area with the greatest catch from April to September, the season when pregnant females were present. 

Background. Wetlands are heterogeneous and dynamic ecosystems, very susceptible to invasions or local extinctions by the effects of invasive or over-dominant plant species. Resistance to invasion in wetlands that suffer disturbances such as fires has not been thoroughly studied. When Phragmites australis (common read) is present, its interaction with disturbance factors has led to local extinction of many native species. In a previous study, it was determined that harvesting is an effective control method for this species. But removal of aerial parts of this species generates many fragments that might propagate the species. Goals. Evaluate under controlled conditions the invasive potential of fragments of Phragmites australis in plant communities dominated by native plant species that are subjected to frequent human-made disturbances, such as fire, under controlled conditions. Methods. We carried out an experiment that consisted of two assays in 36 mesocosms with canopies of Schoenoplectus americanus. Results. Phragmites australis was practically not able to establish itself after the loss of the S. americanus canopy following fires, because the canopy of this last species recovered rapidly. Survival and growth were slightly higher in mesocosms with low disturbance (27.7% and 55.9 cm in the first assay, and 9.4%, and 60.6 cm in the second assay), when compared with controls (8.5% 35.3 cm, and 7.4% and 86.7 cm), because in control units the canopy of S. americanus was a permanent barrier to the development of P. australis. Height differences among burned and control mesocosms after the first fire event were significant (p =0.002) but not after two consecutive years of burning (p =0.085), because the few plants that survived in control units reached considerable height. Conclusions. The risk of establishment of the fragments of Phragmites australis that are generated during harvesting is low even after major disturbances of native vegetation cover.

Background. This study of feeding provides biological information on the species and its ecosystem function. Species of the family Bothidae are characterized by their demersal habits and are part of the accompanying fauna of shrimp. Goals. This study quantified and described the diet and trophic ontogenetic variation of Trichopsetta ventralis (Pleuronectiformes: Bothidae) collected at 20 locations with a shrimp trawl in the southern portion of the Gulf of Mexico at depths between 41 and 355 m. Methods. Prey were analyzed using area (volumetric), gravimetric (weight), occurrence frequency, and Relative Importance Index (RII) methods. The number of size intervals required to evaluate ontogenic trophic variation was obtained by considering the maximum size minus the minimum, number of intervals, and total samples. Results. Trophic analysis was realized in 167 specimens between 5.5 to 14.8 cm standard lengths. We identified 46 food items, grouped in six trophic categories. Within these categories, fish were the principal trophic component (RII: 76.4%), a preference that remained constant through the ontogeny, but in different proportions among the size classes recorded. The standardized Levin index showed that T. ventralis has a tendency toward specialization (0.07). Conclusions. The results obtained provide information about the function of this sole in the food web of the southern Gulf of Mexico and contribute to the knowledge of the trophic dynamics of this species.

Background. Myriophyllum aquaticum has a high phenotypic plasticity and its plant dispersion is a function of its fast vegetative reproduction; its submerged leaves possess structural characteristics that allow the release of organic compounds, among them phenolic compounds. Goals. Under laboratory conditions, this study analyzed the development of Myriophyllum aquaticum (Vell.) Verdc. cultures associated with the release of phenolic compounds and evaluated the effect of these compounds on germination and root elongation of Lactuca sativa L. Methods. Under laboratory conditions, we cultivated emerging shoots of M. aquaticum to evaluate their growth and the production of phenolic compounds. We evaluated their effect using bioassays with L. sativa and applying phytotoxicity indices to the phenolic compounds released. Results. Our evaluation of the production of phenolic compounds found a direct relationship between this plant species and its behavior under cultivation; cultivation caused a quicker release of phenols during the first days of development. These compounds released by M. aquaticum on L. sativa, as measured by the IGN and IER index comparison, were found to have caused lower toxicity. Conclusions. The bioassay application with the evaluation of early development endpoints of L. sativa plantlets allowed us to confirm the effect of phenolic compounds released by the M. aquaticum submerged plants and characterize them as bioactive compounds.  

Reseña de la monografía incluida en el título.