Ž. A spectrophotometric nitroblue tetrazolium NBT reduction assay was used to demonstrate the Ž y . production of superoxide anions O by haemocytes of the white shrimp Penaeus Õannamei. It 2 was found that haemocytes, without receiving an experimental stimulant, showed a rather high Ž background activity. Therefore, optimal parameters number of haemocytes, type of incubation . medium, type and concentration of stimulants were first established, in order to obtain a reliable and reproducible quantitative assay. With this optimized assay, and using specific inhibitors, it was shown that it is indeed the production of O y that was measured. Activities varied strongly 2 among individual shrimp specimens. Live bacteria, among these Vibrio strains, induced O y 2 production in the haemocytes, in a dose-dependent manner. Whereas Vibrio anguillarum and a probiotic strain of V. alginolyticus evoked clear reactions, a pathogenic strain of V. harÕeyi failed to elicit O y production in the haemocytes. It is discussed that this may explain this strain's 2 capability of evading the host's oxidative microbicidal activity, which would be a virulence factor in these bacteria. Heat-killed bacteria hardly induced NBT reduction in the cells. The fungicide propiconazole or Tilt w , found as a pollutant in the aquatic environment where the shrimp are reared, was tested for its effect on NBT reduction by the haemocytes. In haemocytes that did not receive an experimental stimulant, Tilt w induced the reduction of NBT in a dose-dependent manner. In experimentally stimulated haemocytes, however, Tilt w strongly reduced the reaction upon the stimulant PMA. Probable explanations for these seemingly controversial effects of Tilt w are discussed, as are possible consequences of this sort of pollutants for shrimp aquaculture. This easy to perform and relatively cheap and simple quantitative assay for measuring the activity of an oxidative microbicidal mechanism in shrimp haemocytes, appears quite reliable and may therefore prove to be a valuable tool for monitoring shrimp health and immunologic status. q

Aquaculture is a productive activity in economic growth due to market productivity which supports many Ecuadorian communities. However, exotic species has been the basis of this activity without considering the endemic and mega-diverse component of Ecuador. On the other hand, current aquaculture systems use a lot of water, generating discharge of nitrogen and phosphorus, causing a negative impact on natural watersheds. The present investigation focused on the diversification of aquaculture production and environmental care, through the polyculture of tilapia and river prawn, in a Biofloc system, which allows reducing the use of water, space, and food, taking advantage of all the nutrients of the aquatic environment without generating pollutant residues, from a carbon-nitrogen ratio of 20:1. The research project was developed under laboratory conditions at 2.728 amsl, for 8 weeks in pre-breading stages. Two factors were established in the study: type of culture (monoculture and polyculture) and production systems (traditional and biofloc), with three replicates. In the Biofloc system, the environmental variables such as temperature, pH, and oxygen did not show any significant differences between treatments (p≤0.05), while conductivity and total suspended solids increased during the test, and the nitrification processes stabilized at day 28 with values of 0.06±0.01 and 0.35±0.09 ppm in ammonium and nitrite respectively. The bacterial load was higher in the Biofloc system (113.66x103 CFU/ml) with predominance of Bacillus sp. and Pseudomonas sp. The bioflocs showed greater volume in polyculture (17.62 ml/L) and 26% of protein. Under these considerations, the best productive performance was detected in the Biofloc polyculture with a total productivity of 142.86g/m2 (p≤0.05). Therefore, diversification of species, types and culture systems are viable for aquaculture in Ecuador, generating an interaction between the chemical and biological components, allowing productive processes to be sustainable.