Stable carbon (δ13C) and nitrogen (δ15N) isotopes as natural indicators of live and dry food in Piaractus mesopotamicus (Holmberg, 1887) larval tissue

This study proposed the use of the stable isotope technique to track the type of food utilized by pacu Piaractus mesopotamicus larvae during their development, and to identify the moment when the larvae start using nutrients from the dry diet by retaining its carbon and nitrogen atoms in their body tissues. Five-day-old pacu larvae at the onset of exogenous feeding were fed Artemia nauplii or formulated diet exclusively; nauplii+formulated diet during the entire period; or were weaned from nauplii to a dry diet after 3, 6 or 12 days after the first feeding. δ13C and δ15N values for Artemia nauplii were −15.1‰ and 4.7‰, respectively, and −25.0‰ and 7.4‰ for the dry diet. The initial isotopic composition of the larval tissue was −20.2‰ and 9.5‰ for δ13C and δ15N respectively. Later, at the end of a 42-day feeding period, larvae fed Artemia nauplii alone reached values of −12.7‰ and 7.0‰ for δ13C and δ15N respectively. Larvae that received the formulated diet alone showed values of −22.7‰ for δ13C and 9.6‰ for δ15N. The stable isotope technique was precise, and the time at which the larvae utilized Artemia nauplii, and later dry diet as a food source could be clearly defined.