No abstract

We analyzed the combined effects of population density and presence or absence of shelters on growth and physiological performance of the crayfish Cambarellus montezumae. Three different densities-64, 144, and 208 crayfish per m 2 -with and without shelters were used. Growth; survival; metabolic rate; tissue glucose; and total lipid, triglyceride, nitrogen, and energy content were measured. Animals stocked at 64 and 144 per m 2 with shelter reached the highest body weight; those in groups without shelter had elevated levels of glucose (p < .05). Animals stocked at 144 per m 2 retained the most nitrogen and energy (p < .05). Overall, the combination of medium density with shelters produced the best performance.

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...

The protected natural area (ANP), Ejidos de Xochimilco and San Gregorio Atlapulco (SGA), is a priority area of ecological conservation in Mexico City (CDMX), that still have remnants of the ancient lake system of the Valley of Mexico watershed that have been modified for decades due to the impact of human activities and that threaten their continuity, despite been declared as a RAMSAR site and historical and cultural heritage of CDMX. Given the above, the present study aimed to compare the spatial-temporal variability of physical-chemical factors and phytoplankton as indicators of anthropogenic impact to diagnose the current state of this locality and propose possible alternatives for sustainable management in the study area. The research design considered comparing the area of channels and lagoons of the SGA wetland in two contrasting climatic seasons: dry and rainy. Eleven sampling stations were delimited: three in the channels area and eight in the lagoons, during the months of March and July. Nine physical-chemical variables were measured: temperature, pH, total solids, conductivity, dissolved oxygen, as well as the concentrations of ammonium, nitrites, nitrates, and soluble phosphorus in surface and bottom samples from each sampling station. The statistical design took into account a factorial design of fixed effects (epochs - locations and strata), with Tukey's "post hoc" test to delimit subsets and various multivariate analysis techniques. Phytoplankton samples were taken in both localities, which were identified down to the genus level, evaluating the relative frequency of the various taxa, as well as their association through the saprobity and diversity indexes. The water quality variables indicated that both the area of channels and the lagoons of the wetland are sites with hypereutrophic characteristics, but the wetland due to its semi-isolation is an area that presents on average levels of nitrates 2.4 times lower than in the channel zone, nitrite concentrations are almost imperceptible, and ammonia is within tolerable limits for the existing biota. It also presents space-time homogeneity in its physical-chemical dynamics, in contrast to the area of channels. The composition of species indicating saprobity also differed between both sites, denoting a lesser impact on the wetland area, so it is suggested to use this site for reintroduction activities of species removed from the channel area and preserve the remaining biota in the lake system.