Effects of Microalgae Addition and Fish Feed Supplementation in the Integrated Rearing of Pacific White Shrimp and Nile Tilapia Using Biofloc Technology.

This study aims to evaluate a Pacific white shrimp and Nile tilapia integrated system using biofloc technology with or without the addition of the microalgae Scenedesmus obliquus and with or without fish feed supplementation in a two-factor 62-day experiment. The shrimp (2.16 ± 0.01 g) were reared under a density of 400 shrimp m−3 and the fish (1.53 ± 0.12 g) were reared under a density of 522 fish m−3. The microalgae was added to the culture water two times a week. Growth performance, sludge production, and water microbiology were evaluated. Fish feed and the microalgae addition improved fish final biomass in 58% and 14%, respectively (p < 0.05). Fish survival was significantly higher when microalgae was added (93.9 ± 1.8%) compared with the treatments without microalgae addition (86.2 ± 7.6%) (p < 0.05). The yield of the overall system was higher in the treatments with fish feed supplementation (4.2 ± 0.2 kg m−3) compared with no addition (3.9 ± 0.2 kg m−3) (p < 0.05). These results suggest that fish feed supplementation at the rate of 1% of the biomass and microalgae inoculation can improve fish growth performance and system yield, without affecting sludge production and water microbiology. This work is an expansion of a conference paper with the same title.

Synergistic effect of growth conditions and organic carbon sources for improving biomass production and biodiesel quality by the microalga Choricystis minor var. minor.

In the search for microalgae species with potential for biodiesel production, Choricystis minor var. minor has been seen as a promising source of biomass due to its high lipid content and the satisfactory characteristics of its fatty acid methyl esters (FAMEs). For this reason, the objective of this study was to investigate the synergistic effect of growth conditions and organic carbon sources on cultivation of this microalga. To do so, experimental cultivations were conducted in photoautotrophic, heterotrophic and mixotrophic metabolisms using glucose, fructose, glycerol or sucrose - in growth conditions that use organic carbon. Thus, growth parameters of the cultures were evaluated and at the end of the cultivations, FAMEs yield and profile were determined by gas chromatography, the efficiency of carbon conversion into biomass was evaluated and a microbial analysis was conducted. Regarding growth conditions, the findings have confirmed that, regardless of the organic carbon source used, the heterotrophic and mixotrophic metabolisms can present advantages over the photoautotrophic one. In addition, biomass production was higher with the use of glucose than with other organic carbon sources, regardless of growth condition (heterotrophic or mixotrophic). Moreover, cultivations with the addition of CO2 have converted carbon into biomass less efficiently. On the other hand, photoautotrophic cultures presented the lowest bacterial load. In comparison to photoautotrophic and mixotrophic, heterotrophic cultures have led to lower FAMEs content and higher yields of unsaturated fatty acids. The most satisfactory FAMEs profile for biodiesel production was obtained with mixotrophic growth using fructose.

Growth modeling of the green microalga Scenedesmus obliquus in a hybrid photobioreactor as a practical tool to understand both physical and biochemical phenomena in play during algae cultivation.

In recent years, numerous studies have justified the use of microalgae as a sustainable alternative for the generation of different types of fuels, food supplementation, and cosmetics, as well as bioremediation processes. To improve the cost/benefit ratio of microalgae mass production, many culture systems have been built and upgraded. Mathematical modeling the growth of different species in different systems has become an efficient and practical tool to understand both physical and biochemical phenomena in play during algae cultivation. In addition, growth modeling can guide design changes that lead to process optimization. In the present work, growth of the green microalga Scenedesmus obliquus was modeled in a hybrid photobioreactor that combines the characteristics of tubular photobioreactors (TPB) with thin-layer cascades (TLC). The system showed productivity greater than 8.0 g m-2 day-1 (dry mass) for CO2 -fed cultures, and the model proved to be an accurate representation of experimental data with R2 greater than 0.7 for all cases under variable conditions of temperature and irradiance to determine subsystem efficiency. Growth modeling also allowed growth prediction relative to the operating conditions of TLC, making it useful for estimating the system given other irradiance and temperature conditions, as well as other microalgae species.

Spatial distribution of digestive proteinases in the midgut of the Pacific white shrimp (Litopenaeus vannamei) indicates the existence of endo-ectoperitrophic circulation in Crustacea.

The effect of dietary protein concentration on the spatial distribution of digestive proteinases in the shrimp Litopenaeus vannamei indicates the existence of endo-ectoperitrophic enzyme circulation in this species. Samples recovered from the midgut gland tissues, stomach contents, three different portions of the midgut and feces were used for quantitative and qualitative analyses of the composition and distribution of the digestive proteinases. Animals were divided into three different groups: (1) animals (controls) fed with a commercial 35% protein diet, (2) animals fed with a commercial diet supplemented with ovalbumin to a final protein concentration of 60%; (3) animals fed with an 80% protein diet. Quantitative determinations using different substrates and zymograms showed that increasing protein concentration in the diet alters the distribution of proteinases along the digestive tract. Composition of proteinases in the midgut gland, stomach contents, midgut sections and feces were similar, but not identical. Chymotrypsin and trypsin paralogues were identified in all enzyme sources in a concentration gradient along the midgut in the control shrimp, the expected distribution supporting the existence of a recycling mechanism. The occurrence of a peritrophic membrane in other Decapoda suggests that endo-ectoperitrophic circulation of digestive enzymes and nutrients may also occur in other crustaceans and also extends beyond the Insecta.