Resumen. Se estudiaron 13 localidades de las cuencas Copalita, Zimatán y Coyula, Oaxaca. En 4 muestreos se capturaron más de 3 200 crustáceos decápodos representando 3 familias, 4 géneros y 13 especies, y 3 posibles nuevas especies de los géneros Atya y Pseudothelphusa. Las especies se analizaron de acuerdo con su abundancia, frecuencia de aparición y distribución en las cuencas, y se comparó la composición de especies y distribución altitudinal de las localidades. La familia mejor representada fue Palaemonidae con 1 género y 8 especies, le siguieron Atyidae con 2 géneros y 3 especies y Pseudothelphusidae con 1 género y 3 especies. Potimirim glabra y Atya sp. 1 fueron las especies más abundantes; A. margaritacea y P. glabra las más frecuentes, pues se detectaron en 10 de 13 estaciones; Macrobrachium michoacanus se detectó en 9, y M. americanum y M. occidentale en 8 estaciones. Los juveniles de langostino tuvieron una alta frecuencia en 9 de las localidades. La riqueza y el índice de diversidad de especies se incrementaron hacia la porción baja de los ríos; en la porción alta, los valores fueron bajos y en la media de moderados a altos. Las localidades de muestreo se asociaron en 3 grupos de acuerdo con su altitud.
Resumen. Dentro de los macroinvertebrados que habitan los ambientes dulceacuícolas, los insectos son el grupo biológico más idóneo para determinar la calidad del agua de los ecosistemas, ya sean lénticos o lóticos. Considerando la sensibilidad y la tolerancia intrínsecas de los insectos acuáticos, en este estudio se aplicó el índice biótico de Hilsenhoff (IBH, 1988) en las porciones alta, media y baja de 3 ríos perennes: Copalita, Zimatán y Coyula, Oaxaca. El IBH mostró en los 3 casos una calidad del agua de buena a muy buena.
The routine metabolic rate (QO 2 in mg O 2 g −1 DW h −1 ) was measured in juveniles of the brown shrimp, Farfantepenaeus aztecus (Ives, 1891) at salinity and temperature ranges prevailing during the cold and warm seasons at the coastal lagoon of Tamiahua, Veracruz, Mexico. A semiclosed respirometer was employed, with eight 4-L experimental chambers, each containing two shrimp of similar size and sex. The shrimp were fasting and in the intermoult stage, and acclimated to the chambers for 12 h prior to determining oxygen consumption. Oxygen measurements were taken every two hours with a partial replacement of water and aeration of one hour between readings. In a 24 h cycle, 6 to 8 measurements were made. Relations between QO 2 and DW, for the different salinity and temperature conditions tested, were calculated and adjusted to the equation: QO 2 = αDW β . Two-way ANOVA was applied to analyse the effect of salinity, temperature, time of day, and body weight on F. aztecus QO 2 . Salinity had no significant (p > 0.05) effect upon the shrimp's routine metabolic rate at intervals of 26 to 34 psu and 22 to 36 psu, typical of the cold and warm seasons, respectively. However, seasonal temperature variation did significantly affect the shrimp's QO 2 , thus suggesting the existence of a different "pattern of acclimatization" in the energy requirements of the individuals from both seasons. The results indicate that the population of F. aztecus from this area of the Gulf of Mexico may represent a "cline", the physiological response of the components of which differs from that of other brown shrimp populations distributed over a wide geographical range in the western tropical Atlantic. RESUMENSe midió la tasa metabólica de rutina (QO 2 : mg O 2 g −1 PS h −1 ) en camarones juveniles de la especie Farfantepenaeus aztecus (Ives, 1891), en regímenes de salinidad -temperatura típicos de
The effect of saUnity and temperature regimes, typical of most contrasting periods of the annual cycle (warm and cold) at Tamiahua lagoon, Veracruz, Mexico, on food consumption, body composition and allometdc relationships of juveniles of the brown shrimp Farfantepenaeus aztecus (Ives, 1891) were examined. The following morphometric and tissue composition parameters were measured: total length (TL), céphalothorax length (CL), wet weight (WW), dry weight (DW), % body water content, organic matter (OM), total minerals (TM) and energy content (EC). The digestive tract of shrimps collected from both warm and cold periods was analysed determining its composition, quantity, and caloric content of the ingested food. AUometric relationships were calculated among: DW-WW, WW-TL and CL-TL. OM and TM content were correlated with the shrimp's body weight. During the cold and warm seasons, salinity fluctuated between 24 and 36 psu and 12-36 psu, and average temperatures between 25 and 30°C, respectively. WW-TL and CL-TL relationships were statistically different among shrimps from both seasons. Body water content varied significantly, altering the DW-WW relationship, being higher in the warm season. No significant seasonal variation was detected in the shrimp's OM, TM and EC. A shift in shrimp feeding habits was distinguished in the two seasons examined. Carnivorous habits prevail in winter whilst herbivory is more frequently observed during the warm season. However, the food energy remained relatively stable in both seasons, indicating that shrimp consume available resources in the lagoon in order to compensate for the absence of other food components and thus to maintain a constant energy flow independent of the season.Se evaluó el efecto de los regímenes de salinidad-temperatura, propios de las épocas más contrastantes del ciclo anual (cálida-fría) de la laguna de Tamiahua, Veracruz, México, sobre la ingestión de alimento, composición corporal y relaciones alométricas de camarones juveniles de ambos sexos de la especie Farfantepenaeus aztecus (Ivés, 1891). Los índices morfométricos y de composición del tejido medidos fueron: longitud total (LT), longitud del cefalotórax (LC), peso húmedo (PH), peso seco (PS), % de agua corporal, materia orgánica (MO), minerales totales (MT) y contenido de energía (CE). Se analizó el tracto digestivo en camarones colectados en ambas épocas, midiendo el tipo, cantidad y contenido calórico del alimento ingerido. Se calcularon las relaciones alométricas: PS-PH, PH-LT y LC-LT. La MO y el contenido de minerales se correlacionaron con el peso corporal de los camarones. Durante la época fria la salinidad fluctuó entre 24-36 ups, en la época cálida se registró entre 12-36 ups, las temperaturas promedio de cada época fueron 25° y 30°C respectivamente. Las relaciones PH-LT y LC-LT, resultaron estadísticamente diferentes entre camarones de ambas épocas. El contenido de agua corporal varió significativamente, alterando la relación PS-PH, siendo superior en organismos de época cálida. La MO, MT y el CE d...
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