Bioenergetic status of swordfish (Xiphias gladius) during the El Nino Southern Oscillation (ENSO) in the Southeast Pacific Ocean: An interannual scale

The bioenergetic status of fishes has been used to study their physiological responses to temporal changes at interannual scales. We evaluated the physiological responses of swordfish at an interannual scale from the El Nin similar to o Southern Oscillation (ENSO): warm phase "El Nin similar to o" in 2015 to the cold phase "La Nin similar to a" in 2017 and under neutral conditions as well in 2019. Herein, muscle samples from females and males were analyzed to evaluate the bioenergetic status from their biochemical constituents (L: lipids, P: proteins and G: glucose, E: total energy, and FAs: fatty acid profile), elemental composition (C: carbon, N: nitrogen, H: hydrogen), and nutritional indices (L:P, C:N, DHA/C18:1n-3, DHA/C16:0 and omega 3/omega 6 FAs). The physiological response of swordfish showed an interaction between the year and sex. Herein, the L and E showed similar trends, with the lowest female values found in 2015 and the highest in 2019. Contrary, males showed their highest values in 2015 and lowest in 2019. FA profile differed among years and highlighted significant differences between females and males in 2019. Although the female L:P and C:N ratios were lower in 2015 than in 2017, a decreasing trend in these ratios was found from 2017 to 2019. Moreover, DHA/C18:1n-3, DHA/C16:0 and omega 3/omega 6 showed higher ratios in females than males in 2019. Our results coincide with the beginning of the ENSO phases; it is therefore likely that the swordfish diet changed in response to the disturbances in environmental conditions. Furthermore, the degree of individual dietary specialization found under the neutral conditions could indicate differences in the feeding behaviors of males vs. females, which may be an adaptive strategy in this species. These findings will aid in understanding the bioenergetic status of swordfish under different climatic scenarios and the current global warming, providing relevant information for the management of this resource.