Biologists often face the challenge of scaling, whether it's allometric scaling, population-level scaling, or global scaling of elemental fluxes. To understand how individual excretion scales up to population-level nutrient recycling, we need to know the population's demographic structure, including age, sex ratio, and size. For example, the size of zooplankton affects the size of phytoplankton they consume, which in turn affects nutrient uptake and storage. In guppies, females grow indeterminately, impacting nutrient recycling differently than males. Moreover, early-stage or fast-growing organisms consume more phosphorus to produce P-rich ribosomal RNA for protein synthesis. As they grow, their phosphorus needs decrease, shifting from biomass accumulation to maintenance. Metabolic Theory of Ecology suggests a universal allometric scaling coefficient of ~0.75 for physiological rates with body mass, though some argue that it is species-specific. Despite the importance of allometric scaling and debates over scaling coefficients, few studies have examined intraspecific differences in stoichiometric trait scaling. This question is particularly relevant for species with evolved differences in growth rates. Trinidadian guppies (Poecilia reticulata), in their native range, are found in environments with varying predation and resource levels, with high-predation (HP) guppies maturing faster and producing more and smaller offspring than low-predation (LP) guppies. To test how growth rate variations affect stoichiometric traits, I will breed second-generation HP and LP guppies, collecting babies at weeks 0, 1, 3, and 5 to measure body tissue stoichiometry and excretion rates. I expect HP guppies to show a faster decrease in body C:P and excrete less phosphorus during early development than LP guppies. Integrating ontogeny and stoichiometry is crucial for understanding ecosystem nutrient dynamics, given that nutrient needs and management strategies change during development. This study will be among the first to explore how stoichiometric traits change through ontogeny in a rapidly evolving species.