Julián Gamboa-Delgado

Assessment of Nutrient Allocation and Metabolic Turnover Rate in Pacific White Shrimp Litopenaeus vannamei Co-Fed Live Macroalgae Ulva clathrata and Inert Feed: Dual Stable Isotope Analysis

ABSTRACT The current study quantified the relative contribution of dietary carbon and nitrogen supplied by live biomass of the green macroalgae Ulva clathrata and a commercial inert feed to the growth of juvenile shrimp Litopenaeus vannamei. The stable isotope ratios of carbon and nitrogen (&dgr;13C and &dgr;15N) were analyzed in both food sources, whole bodies, and muscle tissue of shrimp reared on co-feeding regimes where 75%, 50%, and 25% of daily consumed macroalgal biomass was substituted by inert feed (regimes 75F/25U, 50F/50U, and 25F/75U, respectively). Higher growth rates were observed in shrimp fed regime 75F/ 25U (k = 0.062), followed by shrimp fed only inert feed (100F, k = 0.060). Animals reared only on U. clathrata (100U) showed minimal growth (k = 0.008) and very high metabolic turnover rates of carbon and nitrogen. Isotopic values measured in inert feed (&dgr;13C = -23.0‰, &dgr;15N = 9.1‰) and macroalgae (&dgr;13C = -13.1‰, &dgr;15N = -3.5‰) were highly contrasting and both had a rapid influence on the isotopic values of shrimp. Animals reached full isotopic equilibrium through growth and fast metabolic turnover in only 2 wk, except shrimp fed macroalgae only. At the end of the experiment, &dgr;13C and &dgr;15N values in shrimp reared on all cofeeding regimes were strongly biased toward the isotopic values of U. clathrata. Total dry matter contributions to growth were estimated using an isotope mixing model, and considered the elemental concentration of both nutritional sources. Results indicated that shrimp in the co-feeding regimes incorporated significantly higher amounts of dietary carbon and nitrogen from the macroalgal biomass. Shrimp in treatment 75F/25U incorporated 52% of carbon from the inert feed and 48% from the macroalgae. Animals under feeding regimes 50F/50U and 25F/75U incorporated higher amounts of dietary carbon from U. clathrata (65–89%) when compared with carbon proportions supplied by both co-feeding regimes (33-70%), and also incorporated the majority of nitrogen from the macroalgae. However, a high incorporation of nitrogen was not reflected in larger growth in the latter treatments because metabolic turnover rates were very high. Estimated turnover rates ranged from 0.049–0.191/day for carbon and from 0.013–0.100/day for nitrogen, and values followed an increasing trend as a function of macroalgae consumption. Nitrogen halftimes in tissue consistently decreased throughout the different treatments from 9.5 days (100F) to 6.4 days (100U). Proportions of incorporated nutrients in muscle tissue followed similar patterns as those observed in whole bodies.

Effect of different diets on proteolytic enzyme activity, trypsinogen gene expression and dietary carbon assimilation in Senegalese sole (Solea senegalensis) larvae

The effect of diet on larval growth, anionic trypsinogen gene expression (ssetryp1), and trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) activities was assessed in Solea senegalensis. Changes in larval carbon stable isotope (δ(13)C) composition were used to estimate carbon assimilation. Diets were supplied for 20days to fish held in larval rearing tanks and consisted of live rotifers, Artemia sp. nauplii, rotifers followed by Artemia sp., rotifers co-fed with inert diet and inert diet alone. Growth was significantly faster in larvae fed only Artemia and those fed rotifers and Artemia (k=0.381-0.387day(-1)). Trypsin and chymotrypsin activities increased from 3 to 4days after hatching (DAH) in all dietary treatments, while ssetryp1 transcripts increased at 4-5 DAH only in larvae fed live prey. ssetryp1 gene expression was activated later in larvae fed only Artemia and this corresponded with Artemia δ(13)C values being reflected in larval tissue. Larval δ(13)C values also indicated greater selection and/or assimilation of rotifers in relation to the inert diet. Results demonstrate that during early larval development of sole, diet modulates ssetryp1 gene expression. The rapid and intense response to diets that promoted different growth and survival suggests the suitability of this biomarker as a nutritional status indicator in early sole larvae.

Nutritional contribution of fish meal and microalgal biomass produced from two endemic microalgae to the growth of shrimp Litopenaeus vannamei

Different sources of microbial biomass have drawn attention as novel ingredients for aquaculture feeds. In the present study, isotopic measurements were applied to determine the contribution of dietary nitrogen supplied by two sources of microalgal biomass and fish meal, to the growth of shrimp Litopenaeus vannamei . Microalgae Schizochytrium sp. and Grammatophora sp. were isolated from the Sea of Cortez and massively cultured to obtain sufficient biomass. Experimental diets were formulated with low levels of microalgal biomass replacing 5 and 10% of fish meal nitrogen. Nitrogen stable isotope values were determined in ingredients, diets and shrimp to estimate the relative contributions of the dietary nitrogen and dry matter supplied by these ingredients to the somatic growth. At the end of a feeding trial, significant differences were observed in mean final weight gain. Dietary nitrogen contributions from microalgae were similar to established dietary proportions, but when estimated on a dry matter basis, nutritional contributions were different for a diet containing 10% of Schizochytrium , whcih contributed 24 % of dry matter to growth. Results demonstrate that low dietary inclusion levels of microalgal biomass elicit similar or higher growth rates than diets based on fish meal only. Isotopic data indicated that microalgae actually contributed protein to tissue accretion.