Loading...
20 results
Search Results
Now showing 1 - 10 of 20
- Changes in plasma amino acid levels in a euryhaline fish exposed to different environmental salinitiesPublication . Aragão, C.; Costas, B.; Vargas-Chacoff, L.; Ruiz-Jarabo, I.; Dinis, Maria Teresa; Mancera, J. M.; Conceição, L. E. C.Previous studies have shown that Senegalese sole is partially euryhaline in the juvenile phase, being able to adapt to a wide range of salinities in a short-time period, due to changes at the osmoregulatory and metabolic level. This study aimed to assess the effects of acclimation of sole to a wide range of salinities, with a special emphasis on the role of plasma amino acids during this process. Sole juveniles were acclimated for 2 weeks to different salinities: 5, 15, 25, 38, and 55 g L−1. Plasma levels of cortisol, glucose, osmolality, and free amino acids were assessed at the end. Changes in plasma levels of cortisol, glucose, and amino acids indicate that fish reared at 5 and 55 g L−1 were facing extra energy costs. Amino acids seem to play an important role during salinity acclimation, either as energy sources or as important osmolytes for cell volume regulation.
- Can dietary aromatic amino acid supplementation be beneficial during fish metamorphosis?Publication . Pinto, W.; Rodrigues, V.; Dinis, Maria Teresa; Aragão, C.Aromatic amino acids (AA, phenylalanine and tyrosine) are the precursors of thyroid hormones, which regulate metamorphosis in all vertebrates. In fish, this is a critical developmental stage where physiological requirements for aromatic AA may increase. Therefore, it is possible that dietary aromatic AA supplementation may be beneficial to accomplish a successful transition from larvae to the juvenile stage. This work aimed to assess the effect of dietary aromatic AA supplementation on tyrosine metabolism in species with an accentuated (Senegalese sole, Solea senegalensis) and a less marked (gilthead seabream, Sparus aurata) metamorphosis. For this purpose, either species were fed Artemia and subsequently received or not an aromatic AA supplement through tube-feeding, together with a L-[U-14C] tyrosine marker, throughout metamorphosis. Tyrosine was elected as a tracer since the metabolic fate of this aromatic AA is directly linked to the production of thyroid hormones and metamorphosis. Results showed that dietary phenylalanine supplementation did not increase tyrosine retention in Senegalese sole larvae during metamorphosis, suggesting that this species may not be able to biosynthesise tyrosine from phenylalanine at a sufficient rate to supply its physiological requirements until after metamorphosis. Furthermore, dietary tyrosine supplementation effectively increased tyrosine availability in Senegalese sole body fluids at metamorphosis, most likely for coping with metamorphosis-related processes, such as production of thyroid hormones. Therefore, dietary tyrosine supplementation may be beneficial for Senegalese sole during metamorphosis. On the other hand, results indicated that gilthead seabream larvae do not seem to require an additional supply of aromatic AA during metamorphosis, probably because the physiological requirements for tyrosine do not increase during this developmental stage. The different results observed for Senegalese sole and gilthead seabream are probably related to the complexity of metamorphosis that each species undergoes and to the needs for production of thyroid hormones, which seems to affect aromatic AA requirements during this critical stage of development. These findings may be important for physiologists, fish nutritionists and for the flatfish aquaculture industry.
- Different environmental temperatures affect amino acid metabolism in the eurytherm teleost Senegalese sole (Solea senegalensis Kaup, 1858) as indicated by changes in plasma metabolitesPublication . Costas, B.; Aragão, C.; Ruiz-Jarabo, I.; Vargas-Chacoff, L.; Arjona, F. J.; Mancera, J. M.; Dinis, Maria Teresa; Conceição, L. E. C.Senegalese sole (Solea senegalensis) is a eurytherm teleost that under natural conditions can be exposed to annual water temperature fluctuations between 12 and 26C. This study assessed the effects of temperature on sole metabolic status, in particular in what concerns plasma free amino acid changes during thermal acclimation.
- High stocking density induces crowding stress and affects amino acid metabolism in Senegalese sole Solea senegalensis (Kaup 1858) juvenilesPublication . Costas, B.; Aragão, C.; Mancera, J. M.; Dinis, Maria Teresa; Conceição, L. E. C.; Refojos, B. C.Fish held at high stocking densities are generally exposed to chronic stress situations that impose severe energy demands and may predispose the ¢sh to infection. Senegalese sole Solea senegalensis (Kaup) juveniles (78.8 18.9 g body weight) were maintained at low (LSD; 4 kg m2 at the end of the experiment), medium (MSD; 9 kg m2 ) and high (HSD;14 kg m2 ) stocking densities during a period of 63 days. Although disease outbreaks were observed in ¢sh reared at HSD, growth and food consumption did not vary among di¡erent treatments. Results from plasma cortisol and free amino acids (FAAs) showed signi¢- cant di¡erences among di¡erent rearing densities pointing to HSD as stressful rearing condition.
- Free amino acids are absorbed faster and assimilated more efficiently than protein in postlarval Senegal sole (Solea senegalensis)Publication . Rønnestad, I.; Conceição, L. E. C.; Aragão, C.; Dinis, Maria TeresaTo improve the formulation of diets for the early stages of marine fish, assimilation rates of free amino acids (FAA) and protein in postlarval Senegal sole (Solea senegalensis) were determined. Fish (2.45 ± 0.87 mg dry weight) were tube fed 36 nL of a diet of FAA containing L-[35S] methionine (FAA diet) or bovine serum albumin, containing L-[methylated-14C]bovine serum albumin (Prot-diet), both at a concentration of 4.08 g/L. A time series was performed, and the amounts of label in incubation water, liver, gut and body carcass were quantified. The FAA diet was absorbed with a 3.5-times-higher transfer rate (P < 0.001) from the gut into the larval body tissues compared with the Prot-diet. The FAA diet also was assimilated with greater efficiency than the Prot-diet (80% versus 58%, P = 0.001). If we assume that the label present in the gut represents amino acids incorporated into the intestinal tissue, the assimilation efficiencies for the two diets were 89 and 64%. Therefore, FAA seems to be superior to protein as a dietary source of amino acids in Senegal sole postlarvae. However, because the absorption dynamics of protein and FAA differ, care should be taken when using the sources together to avoid amino acid imbalance.
- Stress response and changes in amino acid requirements in Senegalese sole (Solea senegalensis Kaup 1858)Publication . Aragão, C.; Corte-Real, Joana; Costas, B.; Dinis, Maria Teresa; Conceição, L. E. C.Fish in aquaculture are often exposed to various stressors that may change their ability to survive or limit growth. Amino acids are used for processes other than growth, including stress response. This study intended to analyse how repeated acute handling stress can affect growth and amino acid requirements in fish. Senegalese sole juveniles were weekly held in the air during 3min (Handling) for 9 weeks; Control groups were left undisturbed. Growth and plasma levels of stress indicators and of free amino acids were assessed at the end of the experiment. Plasma cortisol and osmolality levels showed that fish in the Handling treatment were stressed, but growth was unaffected. Plasma amino acid concentrations indicate that their requirements in stressed fish were altered, which probably reflects the synthesis of proteins or other specific compounds related to stress response.
- How does fish metamorphosis affect aromatic amino acid metabolism?Publication . Pinto, W.; Figueira, L.; Dinis, Maria Teresa; Aragão, C.Aromatic amino acids (AAs, phenylalanine and tyrosine) may be specifically required during fish metamorphosis, since they are the precursors of thyroid hormones which regulate this process. This project attempted to evaluate aromatic AA metabolism during the ontogenesis of fish species with a marked (Senegalese sole; Solea senegalensis) and a less accentuated metamorphosis (gilthead seabream; Sparus aurata). Fish were tube-fed with three l-[U-14C] AA solutions at pre-metamorphic, metamorphic and post-metamorphic stages of development: controlled AA mixture (Mix), phenylalanine (Phe) and tyrosine (Tyr). Results showed a preferential aromatic AA retention during the metamorphosis of Senegalese sole, rather than in gilthead seabream. Senegalese sole’s highly accentuated metamorphosis seems to increase aromatic AA physiological requirements, possibly for thyroid hormone production. Thus, Senegalese sole seems to be especially susceptible to dietary aromatic AA deficiencies during the metamorphosis period, and these findings may be important for physiologists, fish nutritionists and the flatfish aquaculture industry.
- Amino acid pools of rotifers and Artemia under different conditions: Nutritional implications for fish larvaePublication . Aragão, C.; Conceição, L. E. C.; Dinis, Maria Teresa; Fyhn, H. -J.The rearing of most marine fish species still relies on live food. Amino acids (AA) are the building blocks for protein synthesis, are important energy substrates, and are involved in specific physiological functions. Thus, the AA pools (free and protein-bound) of the rotifer Brachionus rotundiformis and of Artemia parthenogenetica metanauplii were analysed, after enrichment with different diets or at different salinities. The changes in these pools were related to their impact when used as feed for the developing fish larvae. Rotifers and Artemia were enriched for 24 h in microalgae, in commercial diets, or starved for the same time period. The enrichment at different salinities was also tested using Artemia. The free AA (FAA) quantity and quality was strongly affected by the enrichment used, in both rotifers and Artemia metanauplii. The relative FAA content was significantly higher in rotifers and Artemia enriched with microalgae than in the ones enriched with commercial products, and between the different microalgae tested, the enrichment in T. chui resulted in the highest FAA content for both preys. Differences regarding the FAA quantity and quality were also found between rotifers and Artemia. With the exception of the starved preys, a higher relative FAA content was found in rotifers than in Artemia metanauplii and while the FAA pool of the rotifers was dominated by alanine, taurine was the dominant AA in the FAA pool of Artemia. Salinity had only a small effect on the FAA pool of Artemia. Concerning the protein fraction, starvation increased the relative protein content in the rotifers. Among the metanauplii, the relative protein content was affected neither by the enrichment nor by salinity, except for a significantly lower content found when the microalgae Nannochloropsis gaditana was used. The quality of the protein pool is affected by the different enrichments, but not by salinity. However, the changes in the protein-bound AA pool were less pronounced than for the FAA pool and reflect differences in the protein content and/or quality of the diet. This study showed that the AA composition of cultured zooplankton is affected by feeding regime and by salinity. The choice of the best zooplankton enrichment and/or mixture of enrichments for the different fish larval stages, should take into account the AA composition, in order to fulfil the energetic and nutritional requirements of the larvae.
- Nutritional physiology during development of Senegalese sole (Solea senegalensis)Publication . Conceição, L. E. C.; Ribeiro, Laura; Engrola, S.; Aragão, C.; Morais, S.; Lacuisse, M.; Soares, Florbela; Dinis, Maria TeresaThe Senegalese sole, a species with a complex metamorphosis, difficulties in weaning and with occasional problems of malpigmentation and skeletal deformities, is a good model species to study larval nutritional physiology. In addition, the early metamorphosis and acquisition of a peculiar non-proactive bottom-feeding behaviour make early weaning an important issue in sole hatcheries. The present work reviews recent findings in different aspects of nutritional physiology during the development of Senegalese sole, in an attempt to optimize the composition of sole diets and to understand what are the limiting factors for weaning sole. Both digestive enzymes activity and tracer studies using 14C-Artemia show that sole larvae, even at young stages, have a high capacity for digesting live preys. This is reflected in a high growth potential and low mortality rates for this species during the larval stage compared to other marine fish species. Based on the observation of the digestive enzymes profile, early introduction of inert microdiets in co-feeding with Artemia does not seem to affect intestinal function. However, when co-feeding is not provided, intestinal activity may be depressed. Furthermore, early introduction of microdiets in co-feeding with Artemia may have a positive effect on survival rates, but at the expense of lower growth rates and higher size dispersal. This may reflect variation in the adaptation capacity of individual larvae to inert diets. High dietary neutral lipid (soybean oil) content results in reduced growth and accumulation of lipid droplets in the enterocytes and affects the capacity of Senegalese sole larvae to absorb and metabolise dietary fatty acids (FA) and amino acids (AA). Through tube feeding of different 14C-lipids and free FA it has been shown that FA absorption efficiency increases with unsaturation and that sole larvae spare DHA from catabolism. In addition, it was demonstrated that absorption efficiency varies according to molecular form, being highest for free FA, lowest for triacylglycerols and intermediate for phospholipids. Live preys commonly used in larviculture do not seem to have a balanced AA profile for sole larvae. Furthermore, the ideal dietary AA composition probably changes during development. Rotifers and Artemia metanauplii are apparently deficient in one or more of the following AA depending on the larval development stage: histidine, sulphur AA, lysine, aromatic AA, threonine and arginine. It has also been demonstrated that balancing the dietary AA profile with dipeptides inArtemia-fed larvae increases AA retention and reduces AA catabolism. When supplementing larval diets with limiting AA it should also be considered that sole larvae have different absorption, and retention efficiencies for individual AA, and that they have the capacity to spare indispensable AA. In addition, the absorption of free AA is faster and more efficient than that of complex proteins. Improvements in biochemical composition of inert microdiets for sole are likely to contribute to the reproducible weaning success of Senegalese sole.
- Growth, stress response and free amino acid levels in Senegalese sole (Solea senegalensis Kaup 1858) chronically exposed to exogenous ammoniaPublication . Pinto, W.; Aragão, C.; Soares, Florbela; Dinis, Maria Teresa; Conceição, L. E. C.Stressful husbandry conditions are likely to a¡ect growth and amino acid metabolism in ¢sh. In this study, chronic ammonia exposure was used to test the e¡ects of a stressor on growth and amino acid metabolism of Senegalese sole juveniles. The ¢sh were exposed for 52 days to 11.6 mg L 1 [low-TAN (L-TAN)] or 23.2 mg L 1 [high-TAN (H-TAN)] of total ammonia nitrogen (TAN), or to 0 mg L 1 (Control). Growth in L-TAN groups was slightly but signi¢- cantly di¡erent from the Control groups [relative growth rate (RGR50.35 0.13 and 0.52 0.23% day 1respectively)]. In H-TAN groups, growth was severely a¡ected (RGR50.01 0.13% day 1 ).