Isotopic turnover dynamics in larval pacú (Piaractus mesopotamicus): bridging the gap between maternal transmission and trophic ecology

Carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes (SI) serve as natural markers for evaluating fish food sources. However, interpreting SI isotope values in newly hatched fish becomes intricate due to the transfer of maternal resources during early development (egg, larvae). This research investigates maternal influences on neotropical freshwater fish larvae growth through SI analysis, focusing on the pacú fish (Piaractus mesopotamicus). The study utilizes a commercial inert feed to assess carbon and nitrogen contributions to larval tissue growth while evaluating the turnover rate, providing valuable insights into early-life nutritional dynamics. Both SI exhibit variations during larval development, following a chronological pattern corresponding to ontogeny, with a significant shift at 13 days after hatching (DAH). Maternal transmission significantly influences isotopic signatures in early larval stages, showing linear correlations between isotopic ratios and standard length (SL) until 15 DAH. C:N ratios decrease from 6.3 ± 0.1 at 0 DAH to 4.2 ± 0.1 at 13 DAH. The isotopic composition of maternal origin aligns with egg stage values, emphasizing the stability of maternal transmission. Under experimental conditions, elemental carbon half-life in tissue (t₅₀) is 6.44 days, and nitrogen t₅₀ is 3.82 days. Maternal isotopic ratios in initial larval development stages offer a potential method for estimating nutritional tracers in field-collected eggs, contributing to understanding the role of freshwater nurseries in comprehending migratory routes, critical hatchery areas, and stock assessment of neotropical migratory fishes. This research provides valuable insights for fisheries management of continental fish species, emphasizing the efficiency of using maternal transmission as an indicator for estimating contributions from nurseries to fish stock recruitment.