Planktonic crustacean assemblages of three reservoirs from the Mexican Central Plateau: relationships with biotic and abiotic factors

The reservoirs Trinidad Fabela (TF), Ignacio Ramírez (IR) and Tepuxtepec (T) are located along an altitude gradient in the upper Lerma Basin of the Mexican Central Plateau. Between July 1993 and June 1994, the planktonic crustacean assemblages of these systems were dominated by seven cladoceran species and five copepod species. Specific richness ranged from 13 species in TF to 16 species in T, out of a total 20 species. Nine species were common to all three systems, while the rest were absent from at least one reservoir. Canonic correspondence analysis showed that the structure and seasonal variation of these assemblages are regulated by factors directly related (transparency and dissolved oxygen) or inversely related (turbidity, temperature, mineralization and eutrophication) to the altitude at which the reservoirs are located. TF had the lowest levels of mineralization and the lowest specific richness, as well as the highest plankton diversity and mean density, while T had the highest mineralization and highest specific richness, but showed the lowest density. Crustacean mean size was smaller in T than in TF, possibly due to predation by fish in the former system and the presence of fish predators (waterfowl) in the latter, as well as the impact of the different hydrological regime and release schedules of the reservoirs

Removal of suspended solids from the effluents of a shrimp farm by the Blood Ark Anadara tuberculosa (Sowerby, 1833)

The potential of Anadara tuberculosa for bioremediation of shrimp farm effluents was evaluated in five field experiments performed in a semi-intensive shrimp farm in Sonora (NW Mexico), and yielded mean filtration, clearance and biodeposition rates of 33.10 mg/h/g, 0.41 L/h/g and 31.19 mg/h/g, respectively. This study demonstrates that A. tuberculosa adults can remove the particulate matter of a semi-intensive shrimp farms effluents

Removal of epiphytes of the kelp Macrocystis pyrifera (L.) Agardh using different biocides

The aim of this work was to evaluate the effectiveness of some biocides for the removal of epiphytes from the blades of the kelp Macrocystis pyrifera. The lowest initial removal was with 1% KMnO4 and with the water purifier Fit®, but both gave better results in the long term. The treatments with distilled and tap water, which avoid the use of biocides, gave a better than 75% reduction of the epiphytes and had a long-lasting effect. In addition, the photosynthetic activity of the controls was similar to that of these two treatments. This confirms that a simple immersion in freshwater may achieve a good initial removal of epiphytic diatoms and prevent their subsequent growth

Intensive culture of Litopenaeus vannamei without water exchange and with an artificial substrate

Aiming to determine the effect of the periphyton growing on artificial substrates, juveniles (3 g initial weight and 440 g m-3 stocking biomass) of the whiteleg shrimp Litopenaeus vannamei (Boone, 1931) , were grown during 32 days in eight 1 m3 cylindrical tanks with 3.7 m2 of total submerged surface. Two culture treatments (with and without artificial substrate or control) were tested with four replicates each. Artificial substrate (Aquamats) provided an additional surface area of 7.2 m2 . The mean dissolved ammonium (NH4 +) and ammonia (NH3) concentrations for the Aquamats group were 39 and 22% lower than the respective values obtained for the control cultures. The artificial substrate stimulated nutrient recycling among the biological components (shrimp, biofilm, bottom microfauna, etc.) since mean shrimp biomass yield was 13% higher for the Aquamats group, and it contained a significantly higher percentage of the total nitrogen and phosphorus inputs than the control treatment. The protein content of shrimp cultured with Aquamats was 21.4% higher than that obtained for the control group, which is explained by the higher availability (and diversity) of the natural food of the periphyton. In view of these results, the use of closed cultures added this artificial substrate seems a viable alternative for shrimp culture

Nitrogen Recycling in Closed Cultures of Litopenaeus vannamei (Boone 1931) with Different Artificial Substrates

Abstract Litopenaeus vannamei juveniles (5.6±0.6 g), at an initial density of 152 individuals/m 2 , were grown for 28 days in 12 cylindrical 1,000-l tanks with no water exchange. Three tanks had 7.1 m 2 Aquamats® to promote periphyton growth, and six had 7.1 m 2 geotextile fabric or mosquito net (three for each substrate). The remaining three served as controls. The shrimp were fed 35% protein shrimp feed, twice daily, supplied on demand. There were no differences in dissolved TAN or unionized ammonia (NH 3 ) concentrations between treatments with substrates, but they were significantly lower than in the control. N-NO 3 -values were higher in tanks with substrates, possibly indicating faster nitrification rates. These tanks produced shrimp with higher mean individual weights and growth rates than the control, but the final yield in tanks with mosquito netting was intermediate between the control and the remaining treatments. The highest feed and economic feed conversion indices, and the lowest nitrogen utilization and protein efficiency ratio, were in the control, and there were no differences between the three treatments with added substrates, showing that the less expensive geotextile fabric and mosquito net may be used with the same efficiency as Aquamats® in periphyton-based aquaculture

Budget and discharges of nutrients to the Gulf of California of a semi-intensive shrimp farm (NW Mexico)

A previous study conducted in 1998 assessed yearly nutrient discharge by the Sinaloa and Sonora shrimp farms to the coastal areas of the Gulf of California (1,509.4 and 438.7 tons of N and P corresponding to 2.1 and 1.05% of the total nutrient discharges to the Gulf along those two states coastlines). However, that estimate did not take into account other nutrient sources, nor the high daily water exchanges of the farms of Sonora, that are likely to increase the calculated amount of nutrients discharged. The evaluation of the nutrient budget of one semi-intensive shrimp farm of Sonora, including the nutrient sources not measured in other studies, showed that during one production cycle this farm discharged 547 kg N·ha-1 and 73 kg P·ha-1, with respective net exports of 122 kg N·ha-1 and 14 kg P·ha-1. Based on the results of this study, the recalculated totals for Sinaloa and Sonora, including rivers, agricultural runoff, and urban wastewater were 77,007.7 and 38,108.3 tons of N and P, and those of shrimp farms 3,556 tons of N and 620.7 tons of P (4.8 and 1.6%). The total discharges of 2003 may be estimated at 78,798.2 and 38,874.1 tons of N and P. In view of its high groth rate, the contributions of shrimp culture would be 10.1% and 3.3%

Cadmium, Copper, Lead, and Zinc Contents of Fish Marketed in NW Mexico

To assess if they were within the safety limits for human consumption, the Cd, Cu, Pb, and Zn contents of fish muscles, bought from separate stalls of the fish markets of nine cities of NW Mexico, were determined by atomic absorption spectrophotometry. Considering all fish and markets, the mean contents were Zn: 23.23±5.83, Cu: 1.72±0.63, Cd: 0.27 ± 0.07, and Pb: 0.09 ± 0.04 µg/g (dry weight). Cu, Zn, and Pb did not reach levels of concern for human consumption, but the high Cd values determined in Mazatlán (Mugil cephalus: 0.48±0.15; Diapterus spp.: 0.57±0.33; Lutjanus spp.: 0.72±0.12; small shark: 0.87±0.19 µg/g dry weight) indicate that this was the only metal of concern for human health because the daily individual consumption of fish muscle to reach the PTDI would be within 0.27 and 0.41 kg

Growth of Synechococcus sp. immobilized in chitosan with different times of contact with NaOH

The thickness of the walls of the capsules of chitosan-immobilized Synechococcus cultures was dependent on the time of contact with NaOH and was directly related to culture growth. After an initial lag phase, probably caused by cell damage, the capsules obtained after 80 s in a 0.1 N NaOH solution showed better growth than that of free cell cultures (6.9 and 5.2 divisions in 10 days, respectively)

Test of quality of shrimp postlarvae in commercial hatcheries: a case study

Three characteristic of postlarvae of Litopenaeus vannamei Boone which are used as indicators of postlarvae quality, were evaluated and compared as tools for internal quality control at a commercial hatchery in Ecuador, using organisms of four successive ages from each of forty different larval cultures. The results indicated that Vibrio concentration and resistance to withstand osmotic stress at any given age were not relayed, and provided little or no information to evaluate future quality in terms of survival to the point of sale test of resitance to osmotic stress. Low size variability may be used as indicative of a probable better survival to the osmotic stress test but cannot be used quantitatively as a predictive tool

Filtration and clearance rates of Anadara grandis juveniles (Pelecypoda, Arcidae) with different temperatures and suspended matter concentrations

The mangrove cockle Anadara grandis (Broderip and Sowerby, 1829) is a potential candidate for aquaculture and for bioremediation of aquaculture effluents in the tropical and subtropical coastal areas of the eastern Pacific Ocean. Laboratory-produced spat are available, but there is no information on their responses to the range of environmental conditions to which they might be subject during the growth cycle. The aim of this study was to evaluate the filtration and clearance rates of A. grandis spat (shell length 9.50±0.37 mm) with a food concentration (7.5 mg/L)at four different temperatures (22. 25. 28. 31º C) with pH= 7.5± 2.2 and O2 concentration of 6.4±0.5 mg/L; experiment one); and with a temperature (25º C) and five concentrations of suspended matter (from 7.5 to 29 mg/L and pH and O2 values of 7.9± 0.2 and 6.8± 0.4 mg/L; experiment two). Filtration and clearance rates were highest at 25 ºC and significantly different (p<.05) from those obtained at 22, 28 and 31 ºC; the clearance rates had the same tendency but the differences were not significant (p >.05). In the second experiment filtration increased according to the amount of food available, but there were no significant differences (p>.05) between 7.5 and 11 mg/L and from 22.4 to 29 mg/L. The trend was similar for clearance and in this case significant differences were found (p<.05) between 7.5, 22.4 and 29 mg/L. Filtration at 31 ºC was close to 80% at the optimum temperature of 25 ºC, which indicates that A. grandis is a good candidate for tropical aquaculture. Clearance increased with high concentrations of suspended solids, but the production of biodeposits could be a source of environmental concern. Therefore, the possibility of using this species for bioremediation of aquaculture effluents should be studied with larger specimens and at higher seston concentrations.La almeja Anadara grandis (Broderip and Sowerby, 1829) es un candidato potencial para la acuicultura y la biorremediación de efluentes acuícolas en las áreas costeras tropicales y subtropicales del océano Pacífico oriental. Se dispone de semilla producida en laboratorio, sin embargo no hay información sobre sus respuestas a los intervalos de las condiciones ambientales a las cuales puede estar sujeta durante el periodo de crecimiento. El objetivo de este estudio fue evaluar las tasas de filtración y de clarificación de semilla de A. grandis (largo de la concha= 9.50±0.37 mm) con una concentración de alimento (7,5 mg/L) y cuatro diferentes temperaturas (22, 25, 28 y 31 ºC con pH= 7.5±0.2, concentración de O2 de 6.4±0.5 mg/L; experimento uno); y con una temperatura (25 º C) y cinco concentraciones de material suspendido (de 7.5 a 29mg/L y niveles de pH y O2 de 7.9±0.2 y 6.8±0.4 mg/L, experimento dos). Las tasas de filtración y de clarificación fueron máximas a 25 ºC y significativamente diferentes (p<.05) de las obtenidas a 22, 28 y 31 ºC; la tasa de clarificación presentó la misma tendencia, pero las diferencias no fueron significativas (p>.05). En el segundo experimento, se registró un incremento de la filtración, de acuerdo a la concentración de alimento, pero sin diferencias significativas (p>.05) en los intervalos 7.5 a 11 mg/L y 22,4 a 29 mg/L. La clarificación mostró la misma tendencia y en este caso se encontraron diferencias significativas (p<.05) entre 7.5, 22.4 y 29 mg/L. La cantidad de sólidos ingeridos a 31 ºC representó más del 80% de la filtración a 25 ºC, que indica que A. grandis es un buen candidato para la acuicultura tropical. Con altas concentraciones de sólidos la clarificación aumentó, pero se notó una producción de pseudoheces que pudieran ser fuente de problemas ambientales, por lo cual se sugiere que la posibilidad de utilizar esta especie para la biorremediación de efluentes debería ser investigada con especímenes de mayores dimensiones y con concentraciones de seston más altas