To assess to what extent addition of phytase to a plant-based diet results in spatio-temporal changes of phytate, available P, soluble protein, total amino acids and the activity of the main digestive proteases in gilthead sea bream, fish were fed two plant-based diets with or without phytase. Stomach, proximal intestine and distal intestine contents were monitored for these parameters at 0, 1, 2, 4 and 6 h after feeding. A reduction (P < 0.0001) of the soluble P–IP6 in the stomach when phytase was added to the diet was observed. Within stomach, most of the total P–IP6 was precipitated (86%), possibly due to the low acidification capacity of the sea bream (pH > 4), but 57% of the dietary P–IP6 was dephosphorylated, suggesting that phytase could have the capacity to dephosphorylate insoluble IP6 at such pH. An increment (60%) (P < 0.01) in total gastric protease activity was observed by phytase addition, this being the first demonstration of the in vivo effect of IP6 on the pepsin activity in fish stomach. Gastric pH and residence time of the digesta inside the stomach are critical factors for an efficient phytase action and improve P and N bioavailability in plant-based diets used in fish aquaculture.Fil: Morales, Gabriel Alejandro. Universidad de Almería; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marquez, L.. Universidad de Almería; EspañaFil: Saenz de Rodrigañez, M.. Universidad de Almería; EspañaFil: Bermúdez, L.. Fundación Centro Tecnológico de Acuicultura de Andalucía; EspañaFil: Robles, R.. Fundación Centro Tecnológico de Acuicultura de Andalucía; EspañaFil: Moyano, F. J.. Universidad de Almería; Españ

Postlarvae of tiger shrimp, Penaeus monodon (Fabricius), were fed semipurified diets supplemented with various levels of astaxanthin (AX) and ascorbic acid‐polyphosphate (ApP): three groups were fed 230 mg AX kg⁻¹ diet combined with 100, 1700 and 3400 mg ascorbic acid (AA) kg⁻¹ diet, respectively; two diets contained 810 mg AX kg⁻¹ mixed with 200 and 1700 mg AA kg⁻¹, respectively. Each treatment was run in four replicates. Incorporated levels of AA and AX, production output, and physiological condition were recorded after 4 weeks of feeding. Whole‐body AA (21‐47 μg g⁻¹) and AX, concentrations (19‐35 μgg⁻¹) were linked to dietary ApP and AX supply, respectively, although not significantly for the latter. The biomass of the group receiving the lower dietary ApP‐AX combination was significantly lower than for all other treatments, i.e. 3.1 versus 3.9 g, respectively. In the groups fed 230 mg AX kg⁻¹ diet, significant differences in stress resistance were observed according to the dietary ApP level, i.e. raising the vitamin C content in the feed from 100 to 3400 mg AA kg⁻¹ resulted in a concomitant drop in mortality after an osmotic shock. For the treatments receiving 810 mg AX kg⁻¹ diet, the beneficial effect of extra dietary vitamin C was not significant. An increase in the dietary AX for shrimp fed comparable ApP levels resulted in a significant drop of the stress index from 56 to 33 (cumulative mortality index). An increased resistance to salinity shock was demonstrated in association with supplementation of high dietary AA or AX levels. No conclusive results regarding possible improved disease resistance could be made since no mortality was observed after a disease challenge with Vibrio harveyi.

With the intensification of aquaculture production systems, mass mortality of fish and shellfish caused by bacterial infections is not unusual. Chemotherapy (treatment of infection with antimicrobial compounds) and inimunoprophylaxis (vaccination and imniunostiniulation), are tlie common methods applied to treat bacterial infections. In search of an efficient and cost‐effective delivery route for antimicrobial agents and/or immuno‐prophylactics to treat fish and shrimp larvae, the use of live prey organisms bioen‐capsulated with drugs has been explored. This article provides an update on the use of the bioencapsulation technique in aquaculture.