Domenico Voltolina

Growth of Scenedesmus sp. in artificial wastewater

The microalga Scenedesmus sp. was grown in artificial wastewater with 30 and 50% daily replacements of the culture volume and under continuous lighting. The biomass per unit volume was higher with the 30% dilution, but daily yields were better with 50%. In 24 h, phosphate removal was more than 50% in both cases. The total nitrogen removed, most of which was ammonia, was approximately 50 and 66% of the initial concentration for the 30 and 50% dilutions, respectively, and a nitrogen budget calculated using the total daily removal and the average algal protein harvested gave an imbalance of close to 65 and 75%, showing that ammonia stripping due to high pH values and aeration might play an important role in the biological tertiary treatment of wastewater with photosynthetic organisms.

Nitrogen budget in Scenedesmus obliquus cultures with artificial wastewater

Semicontinuous cultures of Scenedesmus obliquus in artificial wastewater, recycled into proteins about 33% and 25% of the dissolved nitrogen missing from the medium 24 h after harvesting 50% and 70% of the culture, and replacing the volume harvested with fresh medium. The residual dissolved nitrogen concentrations were 25% and 43% of the initial, respectively, with an imbalance in the mass budget close to 17 and 20 mg N l(-1) d-1. Most or all the nitrogen missing was found in an ammonia trap located at the air vent of the closed cultures, showing that an important role of microalgae in wastewater treatment is that of favouring NH3 stripping due to the photosynthesis-induced pH increases.

Effect of blue-green light on growth rate and chemical composition of three diatoms

The diatomsChaetoceros sp.,Skeletonema costatum andThalassiosira pseudonana were grown with different irradiances of white and of blue-green light, and with a mixture of blue-green plus 6.5 μmol m−2 s−1 of white light. Exponential growth rates were higher in mixed blue for the first two, whileT. pseudonana grew faster in white light but, in all cases, mean cell division rates did not differ with increasing irradiances. Harvesting in stationary, rather than in late exponential growth phase, resulted in higher protein contents forChaetoceros sp. andS. costatum, but forT. pseudonana the highest value was in the exponential phase. The highest protein content was in blue-green light for the three species and it increased with irradiance. As to other fractions, the three strains showed different responses, related to quality and quantity, as well as to culture ages.

Histological effects of a combination of heavy metals on Pacific white shrimp Litopenaeus vannamei juveniles

Exposure to different levels of a mixture in equitoxic concentrations of Cd, Cu, Fe, Hg, Mn, Pb and Zn, equivalent to between 5 and 0.5% the individual respective 96-h median lethal concentrations (0.05-0.005AF: application factors) caused dose- and time-dependent damages to the hepatopancreas, gills, epipodites and midgut tissues of Litopenaeus vannamei juveniles. After between 1 and 3-4 weeks, there was between 50 and 100% loss of the hepatopancreas R cells and of the tubules regular structure. Gill alterations were observed between 2 and 3 weeks with 0.05-0.025 and 0.005AF, respectively. Epipodites showed time- and dose-dependent increasing degrees of melanization, and hemocytic enteritis was observed with 0.025 and 0.01AF. Exposure to 0.05 and 0.025AF caused also 50 and 12% mortalities after 2 and 3 weeks respectively, showing that even at these low levels the mixture of these metals may have a mid-term lethal effect. For this reason, the assessment of risk and of safe levels of toxic substances added to any natural environment through human or natural sources, should not neglect the effects on biological systems caused by the interaction of minute amounts of toxicants, which would be harmless unless present in combination.

Toxic effect of the harmful dinoflagellate Cochlodinium polykrikoides on the spotted rose snapper Lutjanus guttatus

The dinoflagellate Cochlodinium polykrikoides isolated from Bahía de La Paz, Gulf of California, showed an important short‐term toxic effect on the spotted rose snapper Lutjanus guttatus. This microalga was able to decrease fish liver catalase activity and lipid peroxidation. Fish exposed to live dinoflagellates developed an abnormal mucus secretion on the gills that was directly related to algal cell concentration. Hepatic catalase inhibition and an increase in mucus secretion on the gills occurred when fish were exposed to 2 × 106 cells L–1 of C. polykrikoides. Lipid peroxidation was significantly different at 4 × 106 cells L–1 and the hepatosomatic index decreased at 3 × 106 cells L–1. Our results suggest that oxidative stress contributes, at least in part, to the ichthyotoxic effect of C. polykrikoides from the Gulf of California.

Nitrogen budget in intensive cultures of Litopenaeus vannamei in mesocosms, with zero water exchange and artificial substrates

After 29 days without water exchanges, 55% of the total nitrogen (N) inputs were retained as shrimp biomass in 1 m3 cultures of juvenile Litopenaeus vannamei with artificial substrates (Aquamats®), in comparison to 37.2 to 44.8% without Aquamats. The N discharged with the effluent was 1.8-2.3% of the inputs, and the sediments contained 35.9-37.3% of the N inputs without Aquamats and 14.7 to 13.6% with Aquamats. In these, close to 16% of the N inputs were in the periphyton, indicating that additional substrates are an attractive alternative for nutrient recycling in shrimp farms operating as closed systems.

Cadmium, Copper, Lead and Zinc Concentrations in Female and Embryonic Pacific Sharpnose Shark (Rhizoprionodon longurio) Tissues

In this work we compared the cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) contents of muscle, liver and placenta of gestating females of the viviparous shark Rhizoprionodonlongurio and of muscle, liver and umbilical cord of their respective embryos. The higher values of the essential Cu and Zn were in embryonic or embryo-related tissues (placenta and umbilical cord). Maternal muscle and liver had the highest values of Pb and Cd, respectively. There were significant direct correlations between the Zn and Cd concentrations of placenta and umbilical cord, as well as between maternal muscle and embryonic livers for Pb and Cd, but the relation between these tissues was inverse in the case of Zn. All correlations between the metal content of embryonic tissues and size of the embryos were negative, suggesting an inverse relation between the rate of mother-to-embryo metal transfer and embryonic growth.

Humoral and Haemocytic Responses of Litopenaeus vannamei to Cd Exposure

White shrimp, Litopenaeus vannamei, subadults were exposed to four dilutions of the 96 h cadmium LC50 reported for postlarvae (PL12) of this species, and the effects were evaluated after 5, 48, and 96 h of exposure. While treatments did not affect survival and hemolymph clotting time increased with time, but not as a response to Cd exposure, the intensity of other responses was related to concentration, to time of exposure, and to their interaction. Hemocyanin decreased with time in all metal concentrations but increased in the control treatment, and an almost similar trend was observed with hemocyte numbers. As an initial response, phenoloxidase activity decreased with all metal concentrations, but it increased later to values similar or higher than the control treatment.

Efecto de la densidad de siembra sobre el crecimiento y supervivencia larval del pargo lunarejo Lutjanus guttatus

The effect on growth and survival of the initial stocking density (30, 20 and 10 eggs L-1) in larval rearing of spotted rose snapper (Lutjanus guttatus) was evaluated. The eggs were incubated in nine black fibreglass tanks with three replicates for treatment. Larvae were cultured in the same tanks using the green water technique. Larvae were harvested at 45 days post-hatch (DDE). Total length (LT), weight (PH) and survival rate (S) were determined. Initial stocking density did not affect growth and survival rates. Therefore, it is advisable to carry out larval culture of the spotted rose snapper using 30 eggs L-1 to maintain good growth levels.

The Effect of Initial Cell and Nutrient Concentrations on the Growth and Biomass Production of Outdoor Cultures of Dunaliella sp.

The final concentrations of non-axenic outdoor mass cultures of Dunaliella sp. grown for two or three days in f/2 and 2f media were found to be dependent on the initial cell concentration, since the cultures started with 80 × 103 cells ml-1 gave better yields than those started with 40 × 103 cells ml-1. There was a correlation between nutrient availability and cell yields: the two and three days-old cultures started with 40 × 103 cells ml-1 and grown in medium f/2 had lower concentrations than those grown in 2f medium, whereas in cultures with 80 × 103 cells ml-1 inoculum the yield was significantly higher only after three days. The lowest dry biomass yields after two and three days were with the inoculum of 40 × 103 cells ml-1 and medium f/2.