Seasonal dynamics of biochemical composition and fatty acids of swordfish (Xiphias gladius) in the Southeast Pacific Ocean off the coast of Chile

Bioenergetic status of swordfish (Xiphias gladius) during the El Niño 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 Niño Southern Oscillation (ENSO): warm phase "El Niño" in 2015 to the cold phase "La Niña" 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 ω3/ω6 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 ω3/ω6 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.

Variability in the energy reserves of swordfish (Xiphias gladius) of the southeastern Pacific Ocean: A temporal and intra-individual perspective

The temporal dynamics of energy reserves are associated with the physiological processes (i.e., reproduction) in marine fishes, in which storage organs play a key role for efficient energy investment. We evaluated the temporal (i.e., seasons) and intra-individual (i.e., organs) dynamics of adult female swordfish (Xiphias gladius) during its feeding period off the Chilean coast in the southeastern Pacific Ocean (SEPO). The biochemical composition (i.e., lipids, proteins, and glucose), energy content and fatty acid profile of the muscle, liver and gonad were evaluated during the austral autumn, winter, and spring. Our results showed principally an intra-individual effect in both the muscle and liver in the autumn and spring. Herein, a trend of higher amounts of lipids and total energy were found in the muscle, while the liver showed greater protein and glucose contents. Consequently, the muscle showed a higher saturated, monounsaturated, and polyunsaturated fatty acid contents than the liver. Although the gonad showed no significant temporal effect in the lipids and proteins contents, an increasing trend of each biochemical constituent, fatty acid group and gonadosomatic index were found from autumn to winter. Consistently, the glucose and total energy content as well Fulton's condition factor were significantly higher in winter. These findings reflect the spatial-temporal physiological dynamic of swordfish based on the storage of energy reserves in different organs during its feeding period. In this way, the products obtained from swordfish could have an added value depending on the season and capture zone, which could benefit the exploitation and regulation measures of this resource under an ecological approach of conservation and sustainability in the SEPO.

Temporal and inter-individual changes in the integrated biochemical condition of the gonads of female swordfish (Xiphias gladius) from the Southeastern Pacific Ocean

The integrated biochemical condition (IBC) of gonads is closely related to the reproductive success of highly migratory marine species. The IBC of gonads can be influenced not only by size and/or age, but also by environmental conditions. Here, female swordfish, Xiphias gladius, that migrate to temperate regions with a marked seasonality (e.g., the Southeastern Pacific Ocean, SEPO) were compared in relation to the IBCs (lipids, proteins, glucose and, fatty acid profiles) of their gonads; individuals with two body size ranges and distinct degrees of sexual maturity were evaluated, and considered as: small and/or virginal (SV: <170 cm lower jaw fork-length (LJFL), oocyte size (OS) <0.08 mm) vs large and/or maturing females (LM: >190 cm LJFL, OS >0.133 mm). This comparison was conducted in two environmentally contrasting seasons (winter vs spring). Our results showed that the gonadosomatic index (GSI) was significantly higher in LM than SV. Lipid contents varied significantly between seasons and body sizes. The highest lipid concentrations were recorded in the spring in large females. No significant differences were found when comparing the protein and glucose contents of the two evaluated seasons or body size ranges of the studied females. In turn, the fatty acid (FA) profiles of female gonads significantly varied for both seasons and body size ranges. A high content of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs) were recorded in female gonads in the spring. The SFAs C16:0 and C18:0, the MUFA C18:1n9, and the essential PUFA C22:6n3 were the main contributors to the observed differences between spring and winter. These results could be used as indicators of the nutritional condition and health status of swordfish individuals. Hence, the IBC of female swordfish gonads have great potential to aid in estimating survival rates and stock abundances of this species. The integration of this information constitutes an asset in fishery management models with an ecosystem approach.

The influence of upwelling on key bivalves from the Humboldt and Iberian current systems

Eastern Boundary Upwelling Systems (EBUS) deliver cold, nutrient-rich waters, influencing coastal biota from the molecular to the ecosystem level. Although local upwelling (U) and downwelling (DU) conditions are often known, their influence on body attributes of relevant species has not been systematically compared within and between EBUS (i.e., below and above regional scales). Hence, we compared the physical-chemical characteristics of U and DU sites in the Humboldt Current system (Chile) and the Iberian Current system (Portugal). We then assessed the influence of U and DU upon eight body attributes in purple mussels (Perumytilus purpuratus) and Mediterranean mussels (Mytilus galloprovincialis), from the Humboldt and Iberian systems, respectively. We hypothesized that bivalves from U sites display better fitness, as measured by body attributes, regardless of their origin (EBUS). As expected, waters from U sites in both systems showed lower temperatures and pH, and higher nitrite concentrations. We also found that mussels from U sites showed better fitness than those in DU sites in 12 out of 16 direct U vs DU comparisons. Shell length, shell volume, organic content of soft-tissues, and mechanical properties of the shell averaged consistently higher in mussels from U sites in both Current systems. In addition, total weight, soft-tissue weight, shell weight and shell thickness were all higher in the U site at the Humboldt system but had less consistent differences at the Iberian system. Altogether, most results supported our working hypothesis and indicate that U conditions support better fitted mussels. The few attributes that did not exhibit the expected U vs DU differences in the Iberian system suggest that local and species-specific differences also play a role on the attributes of these species. These results may also serve as a reference point for further studies addressing the influence of upwelling in these productive, critically important systems.

Changes in lipid and fatty acid contents of gonad during the reproductive cycle of the Mediterranean swordfish Xiphias gladius

Swordfish Xiphias gladius is a large pelagic fish distributed worldwide and exploited for human consumption, however there is limited knowledge about its reproductive biology, especially regarding lipid dynamic in gonads. In teleost fish, reproductive success and offspring survival are associated to lipid availability for gamete synthesis. This study investigated the lipid composition, including lipid classes and fatty acids (FA) of cell membrane and reserve lipids (i.e., polar and neutral lipids, respectively; PL and NL), along female and male gonad development of a swordfish population from waters surrounding Corsica Island in the Mediterranean Sea. Overall, swordfish gonads contained <2% wet weight of total lipids, with testes and ovaries having similar fat content. Lipid classes and FA concentrations remained unchanged during testes maturation. However, concentrations of phosphatidyl choline (PL), triacylglycerol (NL), and some FA (16:0, 18:1n-9, and 22:6n-3) followed an "inverted U-shaped" relationship with the ovarian maturation. In both PL and NL, 22:6n-3 was the main polyunsaturated FA (>20% of total FA), while 20:5n-3 and 20:4n-6 were minor (3-6% of total FA) and varied little with maturation. 22:6n-3 and 18:1n-9 were selectively allocated to the ovarian maturation (increased in concentration and in proportion with maturation) until spawning. Finally, swordfish gonads might represent a good food source for humans given that 150 g of swordfish ovaries can cover the daily requirements in omega-3 for humans, but research on pollutants should also be conducted to evaluate their implications on the reproduction output of this species, and on the safety of swordfish gonads for human consumption.