Isotopic discrimination factors and nitrogen turnover rates in reared Atlantic bluefin tuna larvae (<em>Thunnus thynnus</em>): effects of maternal transmission

Abstract

Summary:The use of stable isotope analysis to study animal diets requires estimates of isotopic turnover rates (half time, t 50 ) and discrimination factors (Δ) for an accurate interpretation of trophic patterns. The stable isotopes of carbon and nitrogen were analysed for eggs and reared larvae of Thunnus thynnus, as well as for the different diets supplied during the experiment. The results showed high values of δ 15 N in eggs and larvae (n=646) until 4 DAH. After this time lapse, the stable isotope values declined progressively until 12 DAH, when notochord flexion began. The δ 13 C showed an inverse trend, suggesting that maternal inheritance of the stable isotopes is evident until pre-flexion stages. This study proposes a model for estimating maternal isotopic signatures of bluefin broodstock. After notochord flexion, larvae were fed with aquaculture-bred gilthead seabream, which resulted in a rapid increase of bluefin larvae δ 15 N values together with a rapid decrease in δ 13 C values. The estimated nitrogen half-time to reach the steady state from the diet was 2.5±0.3 days and the discrimination factor was 0.4±0.3(‰). These results represent the first data set that has allowed isotopic nitrogen turnover rates and discrimination factors of the larval stages of bluefin tuna to be estimated.Keywords: bluefin tuna larvae; stable isotopes; maternal transmission; discrimination factors; nitrogen turnover ratio. Factores de discriminación y tasas de renovación isotópica de nitrógeno en larvas de atún rojo de cultivo (Thunnus thynnus): efectos de la transferencia maternaResumen: El análisis de isótopos estables para estudiar la dieta de los animales requiere estimaciones de las tasas de rotación isotópicas (tiempo medio, t 50 ) y factores de discriminación (Δ) para una correcta interpretación de los patrones tróficos. Los isótopos estables de carbono y nitrógeno se analizaron en los huevos y larvas criadas de Thunnus thynnus, así como para las diferentes dietas suministradas durante el experimento. Los resultados mostraron altos valores de δ 15 N en huevos y larvas (n=646) hasta cuatro días después de eclosionar. Después de este lapso de tiempo, los valores de los isótopos estables disminuyeron progresivamente hasta el día 12, cuando se inició la flexión de la notocorda. El δ 13 C mostró una tendencia inversa, lo que sugiere que la herencia materna de los isótopos estables es evidente en la etapa de pre-flexión. Este estudio propone un modelo para estimar las firmas isotópicas maternas de reproductores de atún rojo. Después de la flexión de la notocorda, las larvas se alimentaron con larvas recién eclosionadas de dorada, lo que dio lugar a un rápido aumento de los valores de δ 15 N en las larvas de atún rojo, junto con una rápida disminución del δ 13 C. El tiempo medio de nitrógeno para alcanzar el equilibrio con la dieta fue de 2,5±0,3 días y el factor de discriminación fue de 0,4±0,3(‰). Estos resultados representan el primer conjunto de datos que permitió la estimación de la tasa de renovación isotópica de nit...

Stable isotope analysis indicates resource partitioning and trophic niche overlap in larvae of four tuna species in the Gulf of Mexico

“…Δ 15 N bulk values of T. thynnus during the early larval stage were higher than those of tuna species at the same stage. We applied the maternal isotopic transmission model to these preflexion larvae to estimate maternal isotopic signatures (Uriarte et al 2016) and found the N isotopic values estimated (mean ± SD: 12.11 ± 1.83 ‰) were similar to those reported for adult T. thynnus in the GOM spawning area (approx. 11 to 13 ‰; see Butler et al 2015, Logan et al 2011.…”

“…Similarly, ontogenetic differences in SIA bulk values between pre-and postflexion tuna larvae are likely a result of maternal transmission of isotopes (Uriarte et al 2016). Δ 15 N bulk values of T. thynnus during the early larval stage were higher than those of tuna species at the same stage.…”

“…Anchoa mitchilli, Engraulidae) (McBride et al 2015). Recent studies using SIA bulk in tuna larvae in the Mediterranean Sea revealed differences between preflexion and postflexion ontogenetic stages as a consequence of the maternal transmission of their isotopic signature (Uriarte et al 2016, García et al 2017. This finding allowed for the development of a maternal isotopic transmission model of T. thynnus using preflexion isotopic signatures, which reveals information on trophic dynamics of the breeders (Uriarte et al 2016).…”

“…A mean nitrogen isotopic discrimination factor (δ 15 N) of 1.64 ‰ was used, as proposed by Varela et al (2011) for T. thynnus juveniles. Only postflexion tuna larvae were used for the comparative TP, isotopic niche width, and overlap analyses to avoid influence of maternally transmitted isotopes in preflexion and flexion tuna larvae (Uriarte et al 2016, García et al 2017).…”

“…Recent studies using SIA bulk in tuna larvae in the Mediterranean Sea revealed differences between preflexion and postflexion ontogenetic stages as a consequence of the maternal transmission of their isotopic signature (Uriarte et al 2016, García et al 2017. This finding allowed for the development of a maternal isotopic transmission model of T. thynnus using preflexion isotopic signatures, which reveals information on trophic dynamics of the breeders (Uriarte et al 2016). Conversely, based on diet-switching feeding experiments, Tanaka et al (2016) successfully demonstrated that Japanese anchovy Engraulis japonicus were income breeders because the δ 15 N bulk and δ 13 C bulk ratios in eggs closely followed the isotope ratios of the food of adult fish.…”