Aires Oliva-Teles

Effect of dietary lipid level on growth performance and feed utilization by European sea bass juveniles (Dicentrarchus labrax)

Abstract A study was undertaken to determine the effect of the dietary lipid level on growth and feed efficiency of European sea bass juveniles. Four isonitrogenous diets (48% crude protein) with increasing dietary lipid levels (12, 18, 24 and 30% DM) were fed to satiety to triplicate groups of 25 fish (IBW=7 g) for 8 weeks. Final body weight of fish fed the 24% lipid diet was significantly higher than that of fish fed the 12 and 30% lipid diets, although no significant differences in SGR were observed among groups. Feed efficiency values for the 30% lipid diet were significantly lower than those for the other diets. Feed intake of the 12, 18 and 24% lipid diets seemed to be regulated more by protein intake rather than by energy intake. With the 30% lipid diet, both protein and energy intake (g kg−1 day−1) were significantly higher than with the other diets. At the end of growth trial, protein content was significantly higher in fish fed the 12% lipid diet, and lipid and energy content were significantly lower in fish fed the 12 and 18% lipid diets than in the other groups. Liver lipid content was significantly higher in fish fed the 24% lipid diet than in the other groups. Muscle lipid content was unaffected by dietary lipid level. Nitrogen and energy retention (percentage intake) values were significantly lower in fish fed the 30% lipid diet than in the other groups. Energy retention (percentage intake) increased as dietary lipid level increased from 12 to 24%. Lipid retention (percentage intake) decreased as dietary lipid level increased. The apparent digestibility coefficients (ADC) of dry matter and protein were not affected by diet composition, while ADC of lipid and energy were significantly higher in the 24 and 30% lipid diets. The results of this trial indicate that an increase of dietary lipid level from 12 to 24% did not improve growth performance and feed efficiency of sea bass juveniles. The increase of dietary lipid level had no protein sparing effect. Although, the inclusion of 30% of dietary lipid did not depress growth rate, it significantly reduced protein and energy retention efficiencies. It may be concluded that, under the experimental conditions, the increase of dietary lipid level beyond 12% had no beneficial effects.

Nutrition and health of aquaculture fish

Under intensive culture conditions, fish are subject to increased stress owing to environmental (water quality and hypoxia) and health conditions (parasites and infectious diseases). All these factors have negative impacts on fish well-being and overall performance, with consequent economic losses. Though good management practices contribute to reduce stressor effects, stress susceptibility is always high under crowded conditions. Adequate nutrition is essential to avoid deficiency signs, maintain adequate animal performance and sustain normal health. Further, it is becoming evident that diets overfortified with specific nutrients [amino acids, essential fatty acids (FAs), vitamins or minerals] at levels above requirement may improve health condition and disease resistance. Diet supplements are also being evaluated for their antioxidant potential, as fish are potentially at risk of peroxidative attack because of the large quantities of highly unsaturated FAs in both fish tissues and diets. Functional constituents other than essential nutrients (such as probiotics, prebiotics and immunostimulants) are also currently being considered in fish nutrition aiming to improve fish growth and/or feed efficiency, health status, stress tolerance and resistance to diseases. Such products are becoming more and more important for reducing antibiotic utilization in aquafarms, as these have environmental impacts, may accumulate in animal tissues and increase bacterial resistance. This study reviews knowledge of the effect of diet nutrients on health, welfare and improvement of disease resistance in fish.

Nutritional regulation of hepatic glucose metabolism in fish

Glucose plays a key role as energy source in the majority of mammals, but its importance in fish appears limited. Until now, the physiological basis for such apparent glucose intolerance in fish has not been fully understood. A distinct regulation of hepatic glucose utilization (glycolysis) and production (gluconeogenesis) may be advanced to explain the relative inability of fish to efficiently utilize dietary glucose. We summarize here information regarding the nutritional regulation of key enzymes involved in glycolysis (hexokinases, 6-phosphofructo-1-kinase and pyruvate kinase) and gluconeogenesis (phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase) pathways as well as that of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. The effect of dietary carbohydrate level and source on the activities and gene expression of the mentioned key enzymes is also discussed. Overall, data strongly suggest that the liver of most fish species is apparently capable of regulating glucose storage. The persistent high level of endogenous glucose production independent of carbohydrate intake level may lead to a putative competition between exogenous (dietary) glucose and endogenous glucose as the source of energy, which may explain the poor dietary carbohydrate utilization in fish.

Partial replacement of fishmeal by brewers yeast (Saccaromyces cerevisae) in diets for sea bass (Dicentrarchus labrax) juveniles

Abstract A trial was conducted to test the effect of partial replacement of fishmeal (Danish LT fishmeal—the only protein source in the control diet) by brewers yeast, in isonitrogenous (48% CP) and isoenergetic (22 MJ kg−1) diets for sea bass juveniles with an initial average weight of 12 g. Diets were formulated to include 0%, 10%, 20%, 30% or 50% of dietary N from yeast (diets D0, D10, D20, D30, D50, respectively); another diet supplemented with methionine (diet D50M) was also prepared. Each diet was distributed by hand to satiation to duplicate groups of 25 fish and the growth trial lasted 12 weeks. During the trial, feed intake (g kg−1 day−1) was identical in all groups. At the end of the trial growth rate was not significantly different among groups, except for the D50M diet, which was significantly lower than diet D30. Feed conversion was better for diets D10, D20 and D30, containing yeast than for the control diet. N retention (% N intake) was significantly higher in fish fed diets containing yeast (except for the D50M diet) than in those fed the control diet. There were no significant differences among groups in energy retention (% E intake). The protein content of the fish was significantly higher in fish fed diets containing yeast (except for the D50M diet) than in those fed the control diet. Apparent digestibility of the diets was determined in a separate trial with fish weighing 62 g. Feces collection was performed according to the Guelph system. Apparent digestibility coefficients of dry matter and energy significantly decreased with the increase of dietary yeast level. ADC of protein was significantly lower for the D50 diet than for the other diets. Results of this trial indicate that brewers yeast can replace 50% of fishmeal protein with no negative effects in fish performance. Moreover, the inclusion of up to 30% brewers yeast in the diet improved feed efficiency. There was no beneficial effect of supplementing the brewers yeast diets with methionine.

Utilization of raw and gelatinized starch by European sea bass (Dicentrarchus labrax) juveniles

Three isonitrogenous (48% protein) and isolipidic (12% lipids) diets were formulated to contain 25% raw starch (RS), 25% gelatinized starch (GS) or 12.5% raw+12.5% gelatinized starch (RS/GS). Another diet was formulated with no carbohydrates (HP) containing 63% protein and 18% lipid. Each experimental diet was fed to triplicate groups of 25 fish (IBW=6 g) for 10 weeks. The reduction of dietary protein level from 63% to 48%, by starch incorporation, did not affect growth rate or protein and energy retention. For the diets containing starch, specific growth rate of fish fed the GS diet and feed efficiency for the RS diet were significantly lower than values obtained for the other diets. Protein digestibility was independent of diet composition. Energy and starch digestibility significantly increased with the increase in dietary gelatinized starch. At the end of the growth trial there were no significant differences in whole body composition between groups. Hepatosomatic and visceral indices of fish fed the RS and HP diets were significantly lower and the hepatic lipid content of fish fed the GS diet was significantly higher than in the other groups. Muscle lipid content was unaffected by diet composition. After 16 hours of fasting, the plasma glucose level was identical for all dietary treatments. Nitrogen (g kg−1 day−1) and energy retention (kJ kg−1 day−1) were unaffected by dietary treatment. However, a trend towards increased nitrogen and energy retention (% N or E intake) was observed with the increase of dietary gelatinized starch. Ammonia excretion (mg kg−1 day−1) and heat increment (kJ kg−1 day−1) were significantly lower for sea bass fed the GS diet. In conclusion, the total replacement of raw starch by gelatinized starch significantly reduced growth and feed intake, while improving feed efficiency. Overall, the best results were achieved with the diet RS/GS.

Influence of temperature on protein utilization in juvenile European seabass (Dicentrarchus labrax)

Abstract The aim of this trial was to study the utilization of dietary protein by seabass juveniles with 5.5 g mean body weight, at two water temperatures: 18°C and 25°C. For that purpose, the fish were fed for 12 weeks, four isoenergetic diets with different protein levels (36, 42, 48, and 56%). At the end of the trial, growth rate and feed utilization were significantly better at the higher water temperature. Within each temperature, specific growth rate and feed efficiency were significantly higher with the 48 and 56% protein diets than with the other diets. At 25°C, feed efficiency was also significantly better with the 56% than with the 48% protein diet. N retention (g kg average body weight −1 day −1 ) was higher at 25°C than at 18°C but, as a % N intake the inverse was true. Although at 25°C N retention (% N intake) was not different among groups, retention in g kg ABW −1 day −1 was significantly higher with the 56% protein diet than with 36 and 42% protein diets. On the contrary, at 18°C N retention (g kg ABW −1 day −1 ) was similar among groups while as a percentage of N intake it was inversely related to the dietary protein level. Regarding energy utilization, at each temperature, there were no differences among dietary treatments on energy retention (g kg ABW −1 day −1 ). As a % of energy intake, energy retention significantly increased with the increase of dietary protein level at 25°C, while at 18°C, there were no significant differences among groups. Within each temperature, at the end of the trial, there were no differences among groups in proximate composition of whole fish. Apparent digestibility coefficients of dry matter, protein and energy significantly improved with the increase of water temperature but, within each temperature, there were no significant differences among groups. The results of this study indicate that, regardless of water temperature, the dietary protein requirement for growth seems to be satisfied with a diet containing 48% protein. Growth and feed efficiency were significantly higher at the higher temperature, however, protein utilization was more efficient at the lower temperature.

Glucose tolerance in gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax)

Abstract Glucose tolerance tests were performed with seabream and seabass. The fish were adapted to a practical diet (50% protein; 12% lipid) for three weeks and then, after being fasted for 24 h, injected intraperitoneally with 1 g glucose/kg body weight. Blood, liver and muscle samples were collected before and 1, 3, 6, 12, 24, 48 and 72 h after injection. In both species, an increase in plasma glucose level was observed after injection. In seabream, plasma glucose level reached a peak 1–3 h after injection, while in seabass the peak was reached 3–6 h after injection. The peak value was significantly higher in seabream than in seabass. In both species, plasma glucose levels returned to the initial values within 12 h after injection. In seabream, plasma triacylglyceride peaked 1 h after injection and thereafter started to decrease to the initial levels that were reached within 6 h after injection. In seabass, plasma triacylglyceride levels decreased after injection, starting to increase 3 h later. The peak value was attained 6–12 h after injection and the basal values were reached within 24 h after injection. During the first hour after injection liver glycogen content of seabream significantly decreased, while in seabass it significantly increased. In both species, 6 h after injection liver glycogen content started to increase to a peak value, which was reached 12 h and 24 h after injection in seabream and in seabass, respectively. The results of this study indicate that seabream and seabass were able to restore glucose levels within 12 h after being injected with 1 g glucose/kg body weight. These data also suggest that plasma triacylglyceride concentrations and liver glycogen content may be related to the mechanism of glucose regulation in both species. Glucose injection seemed to enhance catabolism of body stores in seabream and to stimulate anabolism in seabass.

Influence of supplementation of practical diets with vitamin C on growth and response to hypoxic stress of seabream, Sparus aurata

Abstract Gilthead seabream were fed a fish meal based diet, supplemented with graded amounts of ascorbyl polyphosphate equivalent to 0, 25, 50, 100 and 200 mg of l -ascorbate (AA)/kg, for 12 weeks. Although there were no significant differences between growth rates of each group, the feed gain ratio and voluntary feed intake were significantly lower, and the protein efficiency ratio was significantly higher for the fish fed 200 mg AA/kg, when compared with the group fed 0 mg AA/kg. An increase of the ascorbate concentration within the liver and spleen occurred with the increasing vitamin supplementation. After 12 weeks, the fish were subjected to hypoxia for 24 h to determine the influence of AA supplementation on the physiological response to this stressor. A significant hyperglycaemia occurred in fish fed all the diets 3 h after the onset of stress, although a significantly higher resting plasma glucose was observed in fish fed the AA free diet. No significant difference was found in plasma cortisol concentration with stress, with the exception of fish fed the 100 mg of AA/kg diet, where a significantly lower cortisol level was found after 9 h of hypoxia. Fish fed the non-supplemented diet showed wider variation and a tendency to increase this variable, having significantly higher levels at 9 h and 24 h of stress then all the other groups and than fish fed the 200 mg AA/kg diet, respectively. Stress had no detectable effect on liver AA concentration in all groups. However, spleen AA showed significantly increased levels between 3–6 h of hypoxic stress in fish fed 25 and 200 mg AA/kg diet and a further increase after 9 h in fish fed the 200 mg of AA/kg diet. These results suggest that the ascorbic acid requirements for seabream is less than 25 mg/kg diet based on a 12-week growth study and that it requires about a four-field increase in weight before signs of deficiency can be observed. Also, the fact that no variation in liver vitamin C concentration was be detected as a response to stress, suggests that this kind of stress does not significantly increase the utilization of this vitamin. However, a possible relation between dietary ascorbate and the physiological response to hypoxia was found, since the fish receiving the non-supplemented diet showed increased plasma glucose and a tendency to have wider plasma cortisol variations than the fish fed the supplemented diets.

Protein and arginine requirements for maintenance and nitrogen gain in four teleosts

Besides being an indispensable amino acid for protein synthesis, arginine (Arg) is also involved in a number of other physiological functions. Available data on the quantitative requirement for Arg in different teleosts appear to show much variability. So far, there are very limited data on the maintenance requirements of indispensable amino acids (IAA) in fish. In the present study, we compared N and Arg requirements for maintenance and growth of four finfish species: rainbow trout (Oncorhynchus mykiss), turbot (Psetta maxima), gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). Groups of fish having an initial body weight close to 5-7 g were fed semi-purified diets containing graded levels of N (0 to 8 % DM) and Arg (0 to 3 % DM) over 4 to 6 weeks. For each species, N and Arg requirements for maintenance and for growth were calculated regressing daily N gain against daily N or Arg intakes. N requirement for maintenance was estimated to be 37.8, 127.3, 84.7 and 45.1 mg/kg metabolic body weight per d and 2.3, 2.2, 2.6 and 2.5 g for 1 g N accretion, in rainbow trout, turbot, gilthead seabream and European seabass respectively. The four species studied appear to have very low or no dietary Arg requirements for maintenance. Arg requirement for g N accretion was calculated to be 0.86 g in rainbow trout and between 1.04-1.11 g in the three marine species. Turbot required more N for maintenance than the other three species, possibly explaining its reputedly high overall dietary protein requirement. Data suggest a small but sufficient endogenous Arg synthesis to maintain whole body N balance and differences between freshwater and marine species as regards Arg requirement. It is worth verifying this tendency with other IAA.

Recent advances in European sea bass and gilthead sea bream nutrition

European sea bass (Dicentrarchus labrax) and gilthead sea bream(Sparus aurata) are amongst the most important finfish speciescultured in the Mediterranean region. Production of these species isnowadays a well-controlled process, but knowledge of their nutritionalrequirements is still very limited. Nevertheless, a considerable amountof data has been accumulated in recent years, and the purpose of thispaper is to review the recent advances on the nutritional requirementsof sea bass and sea bream. The optimum protein to energy ratio of thediets of sea bass and sea bream seem to be higher than for salmonids,and there is some evidence that high dietary lipid levels have nobeneficial effects on fish performances. Although the essential aminoacid requirements were estimated by the ideal protein method, data basedon the dose-response method is only available for a few amino acids.Essential fatty acid requirements were estimated for sea bream juvenilesbut data is lacking for sea bass. Vitamin and mineral requirements ofthese species are practically unknown. Although the importance ofbroodstock nutrition on gonadal development, spawning and egg quality isrecognized, few studies were done to elucidate these aspects. The recentdevelopment of microparticulate diets for larvae will contribute to theaccurate evaluation of their nutritional requirements.