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This work evaluates the effects of the dietary inclusion of crude or hydrolysed Arthrospira platensis (Cyanobac- teria) biomass on growth, muscle composition, digestive functionality and immune activities in gilthead seab- ream (Sparus aurata) fry (20.32 mg mean body weight). A 40-day feeding trial was conducted, aimed at assessing four experimental diets that included 5 or 10% (w/w) A. platensis, either crude or hydrolysed, plus a microalgae- free diet as control batch. Overall, none of the dietary treatments caused negative impacts on fish growth, body composition, muscle fatty acid profile, or innate immune response. Thus, the dietary inclusion of both crude and hydrolysed A. platensis reduced significantly the oxidation of muscle lipids, especially when using hydrolysed biomass, regardless of the dietary inclusion level. In relation to digestive enzymes, significantly higher levels of trypsin, chymotrypsin and leucine aminopeptidase activities were measured in fish fed on A. platensis-supple- mented diets compared to control fish. In addition, within each inclusion level (5 or 10% w/w), those animals fed with diets that included the hydrolysed biomass yielded consistently higher digestive enzyme activities than those receiving the crude biomass. Microalgae dietary inclusion also induced favourable changes in fish gut morphology, according to the increase in microvilli length and diameter observed. This fact might well have contributed to reinforce the role of the intestinal mucosa as a protective barrier against microorganisms, as well as to enhance the absorptive capacity of the intestinal mucosa. Finally, 10% inclusion of microalgae hydrolysate enhanced lysozyme activity in liver, this fact suggesting improved protection against infectious diseases. In conclusion, the positive effects observed in fish fed with the diets including A. platensis up to 10% (not least the hydrolysed biomass) with regard to the different parameters assessed (digestive enzyme activities, intestinal epithelium ultrastructure, muscle lipid oxidation, and lysozyme activity) suggest the benefits of including this product in starter feeds for gilthead seabream fry., Evaluación de los efectos de las microalgas, incluidas en dietas de dorada, sobre el crecimiento, supervivencia y resistencia a infecciones., ALGAFISH, SI

The development of non-parenteral delivery systems allowing efficient intestinal absorption in fish is a current research topic drawing much interest. Different aspects would benefit from such oral delivery, especially those related to immunization, owing to the convenience of this route in terms of time saving, safety, and lack of stressful effects among others. In the last years, DNA vaccines are evidencing their suitability for fish immunization, although commercial preparations currently available require parenteral administration. In this regard, this work was aimed at assessing a chitosan-based oral delivery system for plasmid DNA (pDNA) in fish. Plasmid pCMVβ was encapsulated in chitosan nanoparticles with the aim of evaluating the ability of inert capsules to retain and protect pDNA from in vitro conditions mimicking the fish gut environment. Furthermore, the feasibility of in vivo oral gene delivery was also assessed in fish by administrating pDNA nanoparticles comparing oral and intramuscular routes. The results indicated that lacZ gene expression (β-galactosidase activity) could be detected in fish tissues following both oral and i.m. administration of pDNA-chitosan nanoparticles up to 60 days. However, organ distribution of the reporter gene expression was more evident after oral (β-gal activity measured in gut, liver and muscle) than after parenteral administration (mostly restricted to adjacent tissues). The results suggest that chitosan nanoparticles enabled efficient oral delivery of pDNA, followed by organ migration and further sustained expression of the reporter gene encoding for β-galactosidase. The intensity of such expression was similar to that obtained by intramuscular injection, a fact that might suppose valuable practical applications in terms of on-farm administration of DNA-based vaccines to fish.

The rising costs of fishmeal worldwide promote great research effort aimed to find alternative and renewable ingredients for aquafeeds. In the last years considerable attention has been paid to the use of algae as a potential ingredient for fish feeds. The objective of this work was to evaluate the effects of the microalgae Scenedesmus almeriensis incorporated to diets intended to feed sea bream (Sparus aurata) juveniles in a 45-day trial. Growth, body composition, and intestinal functionality of fish were studied. Microalgae meal was tested in triplicate at different inclusion levels (0%, 12%, 20%, 25% and 39%). At the end of the trial, individual body weight was recorded for evaluation of growth and nutrient utilization, and biological samples were obtained for proximate analysis, determination of digestive enzyme activities, intestinal histology, and microvilli morphological evaluation. Results indicated that S. almeriensis did not cause negative effects on fish growth or nutrient utilization efficiency. Growth rate and protein utilization in fish fed on a diet with 20% Scenedesmus meal tended to be higher, although not significantly different from those fed on control diet. None of the treatments caused adverse effects on body composition. Fish fed 12% S. almeriensis showed higher trypsin than animals fed on control diet. Leucine-aminopeptidase and alkaline phosphatase activities showed a quadratic response with increasing levels of Scenedesmus biomass. Ultrastructural study revealed that the dietary inclusion of algal biomass, especially at 20% level, significantly increased the absorptive capacity of intestinal mucosa in both the anterior and posterior intestinal regions. This study confirmed the usefulness of S. almeriensis to partially replace fishmeal in practical diets for gilthead sea bream juveniles.

Four lots of sea bream were fed with different ration levels (R100, R75, R50, and R25, corresponding to 100, 75, 50 and 25%, respectively, of the standard ration fed in the fish farm), in order to assess the effects of a 30-day pre-slaughtering period of feed restriction on the textural characteristics of the edible muscle of farmed sea bream (Sparus aurata). Results showed that food restriction over 50% influenced negatively total body and individual organ weights. Fish in a good nutritional condition presented lower muscle pH and poorer muscle characteristics, showing soft texture and decreased water holding capacity (WHC). When the intake was moderately restricted (R75), a positive influence on pH and WHC of muscle was found. A 50% reduction of the ration size also delayed muscle softening during cold storage; whereas, a more severe restriction (R25) did not improve this parameter. Electrophoretic studies showed minor changes in the relative optical density of sarcoplasmic and myofibrillar protein fractions attributable to the different ration sizes assayed. These results suggest that the main contributing factor to the observed enhancement in muscle texture due to feed restriction is likely the decrease of lipid deposits in the structural components of the muscle.