Density-dependent condition of juvenile penaeid shrimps in seagrass-dominated aquatic vegetation beds located at different distance from a tidal inlet.

Seagrasses are critical habitats for the recruitment and growth of juvenile penaeid shrimps within estuaries and coastal lagoons. The location of a seagrass bed within the lagoon can determine the value of a particular bed for shrimp populations. Consequently, differences in the abundance of shrimp can be found in seagrasses depending on their location. As shrimp density increases, density-dependent effects on biological parameters are more likely to occur. However, knowledge about density-dependent processes on shrimp populations in nursery habitats remains limited. The present investigation was undertaken to examine the effects of population density on shrimp condition in two selected seagrass beds, located at different distance from a tidal inlet, one 25 km away (distant) and the other 1 km away (nearby), in a subtropical coastal lagoon. The study was based on monthly samplings during one year in Laguna Madre (Mexico), performing a total of 36 shrimp trawls (100 m2 each one) within each seagrass bed (n = 3 trawls per bed per month for 12 months). Shrimp density was related to the proximity to the tidal inlet (higher density was consistently observed in the nearby seagrass bed), which in turn adversely affected the condition of both species studied (Penaeus aztecus and P. duorarum). In this regard, the present study provides the first evidence of density-dependent effects on shrimp condition inhabiting a nursery habitat. Both shrimp species exhibited a negative relationship between condition and shrimp density. However, this pattern differed depending on the proximity to the tidal inlet, suggesting that shrimp populations inhabiting the nearby seagrass bed are exposed to density-dependent effects on condition; whereas, such effects were not detected in the distant seagrass bed. Shrimp density within the distant seagrass bed was probably below carrying capacity, which is suggested by the better shrimp condition observed in that area of the lagoon. Intra and interspecific competition for food items is surmised to occur, predominantly within seagrass beds near the tidal inlet. However, this hypothesis needs to be tested in future studies.

Effect of Propolis, a Honeybee Product, Against a Parasite (Ligictaluridus floridanus) from Catfish (Ictalurus punctatus) Gills.

PURPOSE: The aim of this study was to evaluate the in vitro and in vivo efficacy of propolis against Ligictaluridus floridanus on Ictalurus punctatus gills. METHODS: This study used an ethanol extract of propolis at a concentration of 300 mg mL-1, with a total polyphenol concentration of 2.77 mg mL-1 as determined by chromatography. In vitro trial used propolis concentrations at 5, 30 as well as 60 mg L-1 and a 70% ethanol control group to treat naturally infected catfish. The in vivo experiment was 16 weeks in duration, consisting of seventy-two fish infected by cohabitation and subjected to one-hour baths every 72 h during the trial. RESULTS: In vitro studies showed that parasites exposed to 60 mg L-1 of propolis displayed a significant reduction (p < 0.05) in their survival time. In vivo studies confirmed the reduction of intensity and abundance of Ligictaluridus floridanus on the gills of channel catfish. CONCLUSION: This study has provided the first challenge of propolis against L. floridanus on I. punctatus gills and shows that propolis has an anthelmintic effect.

Spatial Analysis of Metal Profiles in Sediments in a Tropical Estuary: A Geostatistical Approach.

The spatial structure and distribution of heavy metals [cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), and nickel (Ni)] in sediments were geostatistically analyzed along the estuarine ecosystem of Tigre River-San Andres Lagoon (Tamaulipas, Mexico). In most cases, heavy-metal concentrations exhibited a strong spatial autocorrelation along the estuary as indicated by variogram analysis. Heavy-metal concentrations were found to be higher in the middle estuary, close to the mouth of the Tigre River, and declined as distance from the mouth increased. Metal mean levels at the middle estuary were 2.41 mg/kg Cd, 4.80 mg/kg Cu, 172.36 mg/kg Fe, 5.22 mg/kg Pb, and 2.10 mg/kg Ni. The spatial distribution of heavy metals suggests the existence of a common heavy-metal source located in this area of the estuary. The importance of wastewater discharges and open dumping in the town of El Moron, adjacent to the mouth of the Tigre River, is highlighted; these are believed to be the anthropogenic sources for heavy metals in this estuarine ecosystem.

Cadmium and lead levels along the estuarine ecosystem of Tigre River-San Andres Lagoon, Tamaulipas, Mexico.

Cadmium and lead levels were evaluated in water and sediment along the estuarine ecosystem of Tigre River-San Andres Lagoon (Gulf of Mexico) during September to December 2009. Significant highest metal concentration in water (0.45 mg L(-1) Cd and 3.94 mg L(-1) Pb) and sediment (2.83 mg kg(-1) Cd and 6.61 mg kg(-1) Pb) were found at the mouth of the Tigre River, where the fishing town of El Moron is located. Cadmium levels in sediment were above limits associated with adverse biological effects on aquatic fauna, so negative impacts on natural populations of aquatic organisms would be expected to occur. This in turn could affect the fishery resources inhabiting this ecosystem.

Cadmium, lead and zinc concentrations in water, sediment and oyster (Crassostrea virginica) of San Andres Lagoon, Mexico.

The spatial distribution of cadmium, lead and zinc concentrations in water, sediment and oysters from San Andres Lagoon was evaluated. Significantly higher cadmium (0.33 mg L(-1)) and lead (0.70 mg L(-1)) concentrations in water were observed in front of the mouth of Tigre river, whereas, zinc concentration (5.0 mg L(-1)) was significantly higher in the south part of the lagoon. Similarly, lead and zinc values in sediment (1.01 and 9.29 µg g(-1), respectively) and oyster tissue (0.86 and 3.19 µg g(-1), respectively) were significantly higher in the south part of the lagoon. Levels of cadmium and lead in oyster tissue were positively related to those found in sediment. However, concerning zinc no evident relationship was found. Such differences in regression analyses may be explained by differential bioaccumulation of xenobiotic (cadmium, lead) and essential (zinc) metals.