Browsing by Issue Date, starting with "2024-08-10"
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- Coupled quintessence inspired by warm inflationPublication . Sá, PauloWe investigate a coupled quintessence cosmological model in which a dark-energy scalar field with an exponential potential interacts directly with a dark-matter fluid through a dissipa tive term inspired by warm inflation. The evolution equations of this model give rise to a three dimensional dynamical system for which a thorough qualitative analysis is performed for all values of the relevant parameters. We find that the model is able to replicate the observed sequence of late-time cosmological eras, namely, a long enough matter-dominated era followed by a present era of accelerated expansion. In situations where there is a significant transfer of energy from dark energy to dark matter, temporary scaling-type solutions may arise, but, asymptotically, all solutions are dominated by dark energy.
- Optimising sperm quality in flatfish through algae blend fish feed supplementationPublication . Parente, Pedro; Cabrita, Elsa; Oliveira, CatarinaFlatfish production is a growing sector in the Atlantic region, with turbot (Scophthalmus maximus) and Senegalese Sole (Solea senegalensis) being two important species with high market value in southern European countries. However, reproductive dysfunctions like the inability of captive bred individuals spawning spontaneously, poor sperm quality and quantity, still affect the obtention of progeny. Broodstock nutrition impacts reproductive performance, determining gonadal maturation, fecundity and larval survival. Sustainable supplements like micro and macroalgae, rich in essential compounds like vitamins and carotenoids are used in aquafeeds as they are known to enhance sperm quality and antioxidant defences. This study aimed to determine the effects of an algae blend supplementation on turbot and sole breeders’ diet, particularly on sperm quality. Two broodstocks of each species were fed either a control or an algae-supplemented diet for 3 months. For turbot, the algae diet was supplemented with 1% Laminaria digitata and 5% Arthrospira platensis, whereas sole’s diet was supplemented with 3% of Gracilaria birdiae and 3% of Phaeodactylum tricornutum. Sperm quality was evaluated through the analysis of motility, DNA fragmentation and lipid peroxidation (MDA). Total antioxidant status and the circulating levels of sex steroids were assessed in blood plasma samples. The algae diet improved sperm quality in turbot by decreasing DNA fragmentation and enhancing curvilinear and straight-line velocity. However, total motility and 11-ketotestosterone levels decreased, with an increase in malondialdehyde levels, indicating a possible shortening of the spawning cycle. In S. senegalensis the supplemented diet positively affected oxidative stress markers and showed normal oscillations of sperm kinetic parameters and DNA fragmentation. Nonetheless, testosterone levels decreased in the algae group, suggesting a shortening of the steroid cycle. Further studies should perform a deeper analysis by increasing the number of samplings, analyse antioxidant enzymes and algae’s specific compounds effects on each species.