Nematodes as indicators of shrimp farm impact on an amazonian estuary (Curuçá, Pará, Brazil)

Abstract Shrimp farming reduces demand on wild fishery stocks and avoids environmental damage resulting from fishing practices, however, it has the potential to affect the water quality if not properly managed. In this study the impacts of a shrimp farm in an Amazonian estuary were evaluated, focusing on changes in nematodes regarding taxonomic composition, richness, density and diversity. Sampling was conducted in August 2004 (dry season) and January 2005 (rainy season) in the river at stations situated upstream and downstream at different distances from the main source of farm effluent discharge. Thirty-eight genera were recorded with Terschellingia dominating in the dry season and Terschellingia, Daptonema, Ptycholaimellus and Gomphionema in the rainy season. Abundances were within the range recorded in other estuaries and together with genera richness and diversity showed a strong temporal pattern with significantly higher values in the rainy season. No clear patterns of changes were observed at the stations. Some signs of organic enrichment were detected but they were not yet intense, probably a consequence of the strong local hydrodynamics and the age of the shrimp farm, which was just starting its operation. We recommend that in future studies on farming impacts a combination of factors, beyond the physical and chemical parameters of the water and sediments or taxonomic refinement, should be taken into account - such as the duration of the operation of the farm, the area occupied by ponds and the farm's production. Furthermore, we also believe that nematodes are a useful tool for evaluating aquaculture impacts due to the ease of sampling and because they are organisms at the base of marine food chain

Heavy metals in fishes from Culiacan Valley, Sinaloa, Mexico

Levels of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were evaluated in edible muscle, gill and viscera of the fishes Mugil curema and Tilapia mossambica, collected in April 1988 from the Chiricahueto and Bataoto lagoons and Culiacán River, on the northwestem coast of Mexico. In general, the highest concentrations were found in the fishes from Chiricahueto lagoon and the lowest in fishes from the Culiacán River. The levels observed were compared with those reported for other areas in the same species or genus. The Cu concentrations in the edible muscle of T. mossambica for this study (5.6 µg/g) were twofold than the levels found in Mexicali Valley, Baja California, Mexico (2.6 µg/g). The Cu levels in edible muscle of M. curema (6.3 µg/g) were threefold than the Cu levels of Mugil cephalus (1.9 µg/g) reported for the Miami coast. Although the Cu levels were relatively high, they did not exceed those established by the Intemational Public Health Legislation

Diet and trophic level of scalloped hammerhead shark (Sphyrna lewini) from the Gulf of California and Gulf of Tehuantepec, Mexico

We examined the diet and trophic level of Sphyrna lewini in the Gulf of California (GC) during 2001 and in the Gulf of Tehuantepec (GT) during 2005 using data from stomach content and stable isotope analysis of δ15N and δ13C. S. lewini diet was represented by pelagic and benthic prey species where the most important in weight was Scomber japonicus (27.70±4.54%) in GC, while in GT it was Auxis spp. (26.19±4.14%). There were differences for δ15N and δ13C between group sizes, showing a difference in the use of area and resources, while the differences for δ15N and δ13C between areas were related to changes in the isotopic signal from the base of the food web in each region. Based on δ13C and δ15N variability, diversity values (GC=3.69; GT=3.17) and diet breadth (GC=0.006; GT=0.002), we propose that S. lewini is an opportunistic predator. The trophic level of S. lewini was above four in all categories, which indicates that S. lewini is a tertiary consumer. We may conclude that S. lewini plays an important functional role as top predator within areas of Mexico.</p

Arsenic and Arsenic Species in Cultured Oyster (Crassostrea gigas and C. corteziensis) from Coastal Lagoons of the SE Gulf of California, Mexico.

The aim of this study was to evaluate the bioavailability of arsenic (As) through cultured oyster Crassostrea gigas and Crassostrea corteziensisfrom four coastal lagoons (SE Gulf of California). Organisms were collected in two seasons (rainy and dry season), and they were analyzed for total arsenic and chemical speciation of this element. The concentrations of As in oyster soft tissue fluctuated between 5.44 and 9.56 μg/g for rainy season and 6.46 and 8.33 μg/g for dry season (dry weight) in C. gigas. In C. corteziensis, the As concentrations were <5 μg/g for both seasons (dry weight). Arsenic speciation indicated arsenobetaine as the major arseno-compound accounting for 43.2–76.3 % of total content of As. Lower contributions were obtained for non-extractable As (11.3–17.5 %) and other molecules such as arsenocholine and methyl-arsonate (<5 %). Inorganic arsenic was detectable in only two samples, at concentrations lower than <0.1 μg/g. These As data are the first generated for these mollusks in NW Mexico and indicate that C. gigas and C. corteziensis farmed in this area are safe for human consumption in terms of arseno-compounds