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Formation water (FoW) is a by-product from oil and gas production and usually has high concentrations of soluble salts and metals. Calcium (Ca) and magnesium (Mg) have been shown to reduce the toxicity of metals to aquatic animals, and previous study showed that high waterborne Ca exerts mild effect against disturbances on Na+ regulation in Amazonian armored catfish tamoatá (Hoplosternum littorale) acutely exposed to high Fe, Mn, and Ba levels. Here, we hypothesized that high Mg levels might also reduce the toxic effects of these metals on Na+ regulation of tamoatá. The exposure to 5% FoW promoted an increase in Na+ uptake and a rapid accumulation of Na+ in all tissues analyzed (kidney+-ATPase in fish. High waterborne Mg lowered Na+ efflux rates and markedly inhibited Na+ uptake, and also reduced both NKA activity and newly Na+ accumulation in gills of fish. High Fe levels increased Na+ net losses and inhibited Na+ uptake in tamoatá. The diffusive Na+ losses and the newly accumulated Na+ in gills were reduced in fish exposed to high Mn and Ba. High waterborne Ba also inhibited NKA in gills, while both high Mn and Ba inhibited v-type H+-ATPase in kidney of tamoatá. High Mg did not lessen the toxic effect of Fe on Na+ net fluxes, and reduced even more Na+ uptake and the newly Na+ accumulation in gills and plasma, and did not prevent the inhibition of both NKA and v-type H+-ATPases in kidney. Furthermore, Mg did not attenuate the effect of Mn on inhibition Na+ uptake, keeping the activity of v-type H+-ATPase in kidney significantly lowered. High Mg levels mildly attenuated the effects of Ba in Na+ balance by increasing the new accumulation of Na+ in liver, and restore the activity of both NKA and v-type H+-ATPase in gills of tamoatá. Overall, high waterborne Mg does not have a strong contribution to, or have only minor effects, in protecting tamoatá against disruptions in Na+ regulation mediated by high Fe, Mn, and Ba levels. [ABSTRACT FROM AUTHOR]

Cage fish farming in natural and artificial lakes has become increasingly popular in recent years in tropical countries. The most commonly farmed tropical fish species is the Nile tilapia ( Oreochromis niloticus L.). The aim of this study was to characterize the concentration of phosphorus, total ammonia nitrogen and chlorophyll a from existing fish farms ( FF) in Lake Palminhas, located in Linhares/ ES, Brazil. Three transects were drawn from 0 to 500 m from each of the four FF ( FF1 to FF4) in the lake during six trials (three in the rainy season and three in the dry season). The lake presented a monomictic-hot pattern, with stratification during the rainy season. Dilution of the monitored parameters did not occur sufficient over a distance of up to 500 m from the FF. The location of the FF in the lake and the input of N and P were critical to ensure optimal mixing conditions because the worst results was observed for the fish farm ( FF1) located on a finger of the lake, where the highest concentrations of total phosphorus and chlorophyll a occurred. It was also noted that there was possible total phosphorus interference between FF3 and FF4. The results of this study demonstrate that Lake Palminhas had a low dilution power, and these findings may inform environmental assessments of cage fish farming in this region, providing instruments that may support environmental control of cage fish farming. [ABSTRACT FROM AUTHOR]

The article provides information on a study which examined ammonia excretion in fat snook (Centropomus parallelus) at different salinities. Topics addressed include the problems for fish caused by high concentration of ammonia, relationship between the ammonia excretion and salinity, and the average values of water quality variables during the ammonia excretion experiment in fasting and fed fish.

Silver catfish, Rhamdia quelen, is widely distributed in rivers and lakes of Brazil and used in fish culture. The objective of this study was to determine the lower and the upper lethal temperatures for fingerlings of this species. Fishes were acclimated to temperatures of 16, 21, 26, and 31°C for 22 days. Experiments increasing or decreasing water temperature of the tanks were carried out to obtain 0 and 100% mortality. The mean lethal temperature (LT50) was calculated by nonlinear, sigmoid regression. The lower LT50 values were 7.71, 9.87, 10.97, and 14.22°C, and the upper values were 33.5, 33.55, 34.5, and 34.5°C for acclimation temperatures of 16, 21, 26, and 31°C, respectively. The area of the thermal tolerance polygon (expressed as °C2) for fingerlings of silver catfish was 804, indicating that this species is eurythermal. [ABSTRACT FROM AUTHOR]

The effect of different salt concentrations (0, 1, 3, or 6 g/L table salt) in the water for transport on survival and on Na+ and K+ body levels of fingerlings of the freshwater silver catfish, Rhamdia quelen, was analyzed. Mortality increased with time of transport and salt concentration, with a significant correlation between these parameters. The water containing 6 g/L salt increased body levels of Na+, compared to other treatments from 6 to 12 hours. Body levels of K+ of fingerlings transported in water with 1, 3, and 6 g/L salt decreased from 6 to 12 hours, compared to the treatment without the addition of salt. These results indicate that the water for transport of silver catfish fin-gerlings should not contain salt. Since dissolved oxygen levels decreased to low levels, it is suggested that time of transport should not exceed 12 hours. [ABSTRACT FROM AUTHOR]