ABSTRACT Short-tailed pipe fish (Microphis brachyurus) is a freshwater organism with high economic potential for the aquarium hobby, so it is necessary to implement methods to promote its culture through studies of digestive physiology. General activities of acid and alkaline proteases were evaluated, as well as the effect of pH, temperature and inhibitors. The optimal pH of stomach proteases was 2, while the optimal pH of intestinal proteases was 10. Optimal temperature for the acidic proteases was 35 ºC, while for alkaline proteases it was 45 ºC. Thermal stability showed high resistance at 35 ºC for both acid and alkaline proteases (above 100% residual activity). Acid proteases are resistant at pH 2 (50% of residual activity), meanwhile alkaline proteases were highly resistant at pH 10 (90% of residual activity). Acid proteases were inhibited by 80% with pepstatin A and alkaline proteases were inhibited with TLCK and TPCK for trypsin (75%) and chymotrypsin (80%), respectively. Finally, metallo-proteases were 75% partially inhibited some serine proteases by 75% with EDTA. In conclusion, M. brachyurus has a good digestive capacity, since they can degrade a wide variety of proteins due to their greater proteolytic activity.

RESUMEN El pez pipa (Microphis brachyurus) es un organismo dulceacuícola con alto potencial económico para la acuarofilia; sin embargo, es necesario implementar su cultivo a través de estudios de fisiología digestiva. Se evaluó el efecto del pH, temperatura e inhibidores sobre las actividades enzimáticas de proteasas ácidas y alcalinas. El pH óptimo de proteasas estomacales es de 2, mientras que el de proteases intestinales es de 10. La temperatura óptima de proteasas ácidas es de 35 ºC y las alcalinas de 45 ºC. La estabilidad térmica para proteasas ácidas y alcalinas es a los 35 ºC (más de 100% de actividad residual). La estabilidad a los diferentes pH de las proteasas ácidas es en 2 (50 % de la actividad residual), mientras que para las proteasas alcalinas es en 10 (90 % de la actividad residual). Las proteasas ácidas fueron inhibidas en 80% con pepstatina A y las proteasas alcalinas fueron altamente inhibidas con TLCK para tripsina (75%) y TPCK quimitripsina (80%). Finalmente, las metaloproteasas fueron inactivadas con EDTA en 70%. En conclusión, M. brachyurus tiene una buena capacidad digestiva al degradar una amplia variedad de proteinas debido a su alta actividad proteolítica.

Abstract Background: The structure of benthic diatom assemblages (diversity, equitability, dominance) may be useful in assessing their ecological status in natural protected areas. Goals: To describe the structure of epipelic diatom assemblages from Laguna Guerrero Negro (LGN), a protected coastal lagoon, and test the hypothesis that H´diversity values would be higher for diatom assemblages in LGN sediments than in typical benthic diatom assemblages. Methods: Sediment samples were collected in the lagoon on November 2013, and January, March, and July 2014. Diatoms were mounted on perma nent slides and examined at 1000x using phase contrast microscopy. In each slide, 500 valves were counted to compute relative abundances of each taxon, and species diversity, equitability, and dominance, using Shannon (H´), Pielou (J´), and Simpson (λ) indices, respectively. Likewise, similarity between samples was measured. The calculated median value of H´ from LGN was compared to previously recorded median values to test the hypothesis that significant differences exist. Results: A total 225 diatom taxa were counted. With few exceptions, the similarity between samples was <60%. Relative abundances depict typical benthic diatom assemblages, with an average H´= 4.96 bits/taxon, and corresponding values of equitability and dominance. The median value of H´ (Md = 4.9) was significantly higher than the median value (Md = 3.7) found in previous studies. Conclusions: The structure of the epipelic diatom assemblages from LGN and their patchy distribution are similar to that of typical diatom assemblages, but with unusually high values of H´ that lead us to reject the statistical null hypothesis and thus sustain our research hypothesis.

Resumen Antecedentes: La estructura de asociaciones de diatomeas bentónicas (diversidad, equidad, dominancia) puede servir de referencia para evaluar su estado ecológico en áreas naturales protegidas. Objetivos: Describir la estructura de asocia ciones de diatomeas epipélicas de Laguna Guerrero Negro (LGN), una laguna costera protegida,contrastando la hipótesis de que la diversidad (H´) sería más alta que en asociaciones típicas de diatomeas bentónicas. Métodos: Se recolectaron sedimentos de LGN en noviembre, 2013, enero, marzo, y julio, 2014. Las diatomeas se montaron en preparaciones per manentes y se examinaron bajo microscopía concontraste de fases a 1000x. Por muestra se contaron 500 valvas para estimar abundancias relativas de los taxa y calcular diversidad de especies, equidad y dominancia,utilizando los índices de Shannon (H´), Pielou (J´) y Simpson (λ). Asimismo, se midió la similitud entre muestras. El valor mediano calculado de H´ para LGN se comparó con la H´ mediana de estudios previos contrastando la hipótesis de que existirían diferencias significativas entre estas. Resultados: Se contaron 225 tasa de diatomeas para LGN. Salvo excepciones, la similitud entre muestras fue <60%. Se describen asociaciones de diatomeas bentónicas con diversidad promedio de H´ =4.96 bits/taxón, y equidad y dominancia correspondientes. El valor mediano de H´ (Md = 4.9) fue significativamente mayor que el valor mediano (Md = 3.7) de estudios previos. Conclusiones: La estructura de asociaciones de diatomeas epipélicas de LGN es similar a la de asociaciones típicas de diatomeas bentónicas y su distribución en parches, pero con valores inusualmente altos de H´ que rechazan la hipótesis nula estadística, y respaldan la hipótesis de investigación.

Wild populations of the green mojarra Cichlasoma beani, are being pressured by anthropogenic activities. It is possible to mitigate the deterioration of native species populations by developing culture techniques. Environmental factors such as light intensity and photoperiod may affect the development of fish under culture conditions. Therefore, the aim of the present study was to examine the effect of these factors on growth, survival, and condition of C. beani cultured in different light intensities and photoperiods. Light intensities of 1000, 1500 and 2000 lux and photoperiod 24:00, 16:08 and 08:16 Light:Dark (L:D) were tested in 40 L tanks (10 fish per tank, three replicates per treatment) during eight weeks. There were no significant differences in light intensity or photoperiod, which was associated with the natural adaptation of the species to these factors. The results also suggested the favorable overall growing conditions during the trial and he response of the life cycle stage of the specimens used in this study. The results of the present study indicate that the natural adaptations of C. beani, allow the favorable culture in various light conditions in juveniles, which can be advantageous for commercial culture as may imply low energy costs.

Recently Bacalar lagoon,Quintana Roo has received much attention because of its high eco-touristic and scientific potential due to the presence of microbialites (thrombolites and stromatolites). Nonetheless, the surrounding tourist and agricultural activities represent potential pollution risks that deserve our concern. Opportune ecological monitoring represents an alternative for the adequate managing of these ecosystems. A reliable floristic basis of diatoms renders an effective reference for the detection of environmental contingencies. Thus an exploratory study of benthic diatom associations that live on the microbialites was undertaken. Sixty eight diatomtaxa were identified and floristic and iconographic references for most of these are provided. Eleven taxa are recorded for the first time in Mexican fresh-water bodies.The observed species richness suggests a high diversity. However, the frequency and abundance of widely distributed diatom taxa such as Denticula elegans, D. kuetzingii and Nitzschia amphibia could have hindered the appreciation of said diversity. The diatoms here recorded represent solely a non-living microbialithic substrate. It is thus necessary to widen the inventory to include taxa living in other substrata and in the cyanobacterial mats related to the microbialites.

Recientemente, la laguna Bacalar, Quintana Roo ha sido objeto de creciente interés por su elevado potencial ecoturístico y científico, debido a la presencia de microbialitos (trombolitos y estromatolitos). Sin embargo, las actividades turísticas y agrícolas circundantes representan potenciales riesgos de contaminación que ameritan atención. El monitoreo ecológico oportuno representa una alternativa para el adecuado manejo de estos ecosistemas. Una base florística confiable de diatomeas ofrece un punto de referencia efectivo para la detección de contingencias ambientales. Con base en esta premisa se emprendió este estudio exploratorio de las asociaciones de diatomeas bentónicas que habitan sobre los microbialitos. Se identificaron 68 taxa de diatomeas epilíticas y se proporciona una referencia florística e iconográfica de la mayoría de éstas. Once taxa son los primeros registros para aguas continentales de México. La riqueza de especies observada sugiere una alta diversidad. No obstante, la frecuencia y abundancia de taxa de diatomeas de amplia distribución, como Denticula elegans, D. kuetzingii y Nitzschia amphibia quizá dificultó apreciar dicha diversidad. Las diatomeas registradas en nuestro estudio representaron solamente parte de un sustrato microbialítico no vivo, es necesario ampliar la labor de inventario haciendo muestreos en otros sustratos, incluyendo los tapetes de cianobacterias relacionados con los microbialitos.

The ecology and floristics of the marine benthic diatoms are barely studied in Mexico. For the Yucatán Península, there are practically no studies dealing with these topics. The objective of this study is to present new records of benthic diatoms and their distribution in the northern coast of the Yucatán Península; descriptions based on light and electron microscopy are also provided. In order to achieve this, we examined phytoplankton samples from various localities and from Thalassia testudinum blades on Dzilam de Bravo. With the exception of Synedrosphenia cuneata and Cocconeis maxima the remainder species were found both on phytoplankton and T. testudinum samples, thus suggesting that re-suspension processes of benthic diatoms are occurring in the area. The most abundant species was Climaconeis aff. coxii. The number of new records from a few samples emphasizes the need to continue and intensify the study of benthic diatoms in the Yucatán Península.

En México la florística y ecología de las diatomeas bentónicas marinas han sido escasamente estudiadas. Para la Península de Yucatán prácticamente no existen trabajos que aborden dichos tópicos. El objetivo de este estudio es dar a conocer nuevos registros de diatomeas bentónicas y su distribución en la costa norte de la Península de Yucatán, proporcionando sus descripciones con base en observaciones de microscopía óptica y electrónica. Para ello, se revisaron muestras de fitoplancton costero obtenidas en diez localidades, así como de diatomeas epífitas sobre Thalassia testudinum en Dzilam de Bravo. Con excepción de Synedrosphenia cuneata y Cocconeis maxima, que solo aparecieron sobre T. testudinum, las especies se encontraron tanto sobre T. testudinum como en la columna de agua. Esto sugiere que ocurren procesos de resuspensión de diatomeas béntonicas en el área. La especie con mayor abundancia fue Climaconeis aff. coxii. La cantidad de nuevos registros en este trabajo a partir de un reducido número de muestras, enfatiza la necesidad de continuar e intensificar el estudio de las diatomeas bentónicas de la Península de Yucatán.