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The relative contribution of the dietary nitrogen supplied by fish meal and a biofloc meal to the growth of Pacific white shrimp was evaluated using stable isotope analysis. Biofloculated material was obtained from an experimental tilapia culture system. Five formulated diets were supplied. Two of them consisted in isotopic controls having only fish meal or biofloc meal as protein source. Three mixed diets were formulated with varying proportions of these ingredients on a dietary nitrogen basis (75:25, 50:50 and 25:75). At the end of the trial, survival rates were similar (92-100%) but significant differences in mean final weight were observed and a negative correlation between the inclusion of biofloc meal and weight gain was evidenced. Mean final weight in shrimp fed on diet containing only fish meal was 2.8 g, while mean final weight of animals fed on diet containing 50% biofloc was 1.9 g. Isotopic mixing models indicated that all diets contributed higher proportions of dietary nitrogen from fish meal than from biofloc meal. Dietary nitrogen available in diets containing 25%, 50% and 75% of biofloc meal was incorporated in muscle tissue as 5%, 41% and 64% respectively. Diet supplying 25% of nitrogen from biofloc was the only mixed diet eliciting growth comparable to diet containing only fish meal. Lower growth and nitrogen deposition in shrimp fed on diets containing high proportions of biofloc meal were possibly associated to the use of only two protein sources and a restriction of essential amino acids. [ABSTRACT FROM AUTHOR]

Stable isotope analyses were applied to explore the relative dietary nitrogen contributions from fish meal and pea meal ( Pisum sativum) to muscle tissue of Pacific white shrimp postlarvae (141 ± 31 mg) fed low protein diets having different proportions of both ingredients as the sole dietary protein sources. A negative control diet was formulated to contain 100% pea meal and six more isoproteic diets to have decreasing levels of pea meal-derived nitrogen: 95%, 85%, 70%, 55%, 40% and 0% of the initial level. Growth rates were negatively correlated to dietary pea protein inclusion due to progressive essential amino acid deficiencies (sulphur amino acids, threonine, lysine, histidine). The nitrogen turnover rate significantly increased in muscle tissue of shrimps fed diets having high levels of pea meal; however, contrary to observations from a previous study using soy protein, the relative contributions of dietary nitrogen from pea meal to shrimp muscle tissue were equal or higher than expected contributions established by the dietary formulations. Results highlight the effectiveness of stable isotope analysis in assessing the nutritional contributions of alternative ingredients for aquaculture feeds and the potential suitability of pea as a source of protein (provided the diets are nutritionally balanced). [ABSTRACT FROM AUTHOR]

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 Penaeus 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, which 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 a fish meal only. Isotopic data indicated that microalgae actually contributed protein to tissue accretion. [ABSTRACT FROM AUTHOR]

Torula yeast ( Candida utilis ) and fish meal were used to formulate six experimental diets for Pacific white shrimp Litopenaeus vannamei. The dietary nitrogen supplied by fish meal was replaced by increasing dietary proportions of torula yeast (0, 7.5, 15, 30, 60 and 100%). Nitrogen stable isotope values (δ 15 N) were measured in ingredients, diets and muscle tissue of experimental animals in order to estimate the relative contributions of dietary nitrogen and dry matter supplied by both ingredients. At the end of a 29-day bioassay, there were no significant differences in survival rate among treatments. Shrimps fed on all diets containing torula yeast and fish meal had higher growth rates ( k = 0.059–0.064) than the animals fed on diets containing only fish meal or only torula yeast ( k = 0.041–0.054). Incorporation of δ 15 N values of ingredients and muscle tissue into an isotopic mixing model indicated that the relative incorporation of dietary nitrogen and total dry matter from torula yeast to growth consistently increased in relation to increasing proportions of this ingredient in the experimental diets. The only exception was the diet formulated with the highest yeast content (60%, diet 40F/60T) where the fish meal contributed a higher proportion of dietary nitrogen to growth. Dietary nitrogen from torula yeast available in diets 93F/7T, 85F/15T, 70F/30T and 40F/60T was incorporated in muscle tissue at proportions of 6.5, 13.7, 27.1 and 50.5%, respectively. Estimated nitrogen residency time in tissue ( t 50 ) was relatively shorter in shrimps fed on diets 85F/15T and 70F/30T (3 days), indicating higher metabolic turnover rates in these animals than those fed on diet containing only fish meal. Growth and survival rates were statistically similar in shrimp fed on all mixed diets, therefore indicating the suitability of this single cell protein as dietary ingredient in diets containing up to 60% of torula yeast. Statement of relevance The present study applied measurements of nitrogen stable isotopes at natural abundance levels to evaluate the dietary contribution of torula yeast ( C. utilis ) and fish meal to the growth of shrimp L. vannamei . Growth and survival rates were similar in shrimp fed on diets containing varying proportions of both ingredients. The incorporation of dietary nitrogen from torula yeast to growth increased in relation to increasing dietary proportions, indicating the suitability of this ingredient in diets containing up to 60% of torula yeast. [ABSTRACT FROM AUTHOR]

Abstract: The nutritional contribution of the dietary nitrogen, carbon and total dry matter supplied by fish meal (FM), soy protein isolate (SP) and corn gluten (CG) to the growth of Pacific white shrimp Litopenaeus vannamei was assessed by means of isotopic analyses. As SP and CG are ingredients derived from plants having different photosynthetic pathways which imprint specific carbon isotope values to plant tissues, their isotopic values were contrasting. FM is isotopically different to these plant meals with regards to both, carbon and nitrogen. Such natural isotopic differences were used to design experimental diets having contrasting isotopic signatures. Seven isoproteic (36% crude protein), isoenergetic (4.7kcal g−1) diets were formulated; three diets consisted in isotopic controls manufactured with only one main ingredient supplying dietary nitrogen and carbon: 100% FM (diet 100F), 100% SP (diet 100S) and 100% CG (diet 100G). Four more diets were formulated with varying mixtures of these three ingredients, one included 33% of each ingredient on a dietary nitrogen basis (diet 33FSG) and the other three included a proportion 50:25:25 for each of the three ingredients (diets 50FSG, 50SGF and 50GFS). At the end of the bioassay there were no significant differences in growth rate in shrimps fed on the four mixed diets and diet 100F (k =0.215–0.224). Growth rates were significantly lower (k =0.163–0.201) in shrimps grown on diets containing only plant meals. Carbon and nitrogen stable isotope values (δ13C and δ15N) were measured in experimental diets and shrimp muscle tissue and results were incorporated into a three-source, two-isotope mixing model. The relative contributions of dietary nitrogen, carbon and total dry matter from FM, SP and CG to growth were statistically similar to the proportions established in most of the diets after correcting for the apparent digestibility coefficients of the ingredients. Dietary nitrogen available in diet 33FSG was incorporated in muscle tissue at proportions representing 24, 35 and 41% of the respective ingredients. Diet 50GSF contributed significantly higher amounts of dietary nitrogen from CG than from FM. When the level of dietary nitrogen derived from FM was increased in diet 50FSG, nutrient contributions were more comparable to the available dietary proportions as there was an incorporation of 44, 29 and 27% from FM, SP and CG, respectively. Nutritional contributions from SP were very consistent to the dietary proportions established in the experimental diets. [Copyright &y& Elsevier]