Helena Peres

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.

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.

Nutritional value of heat-treated soybean meal for channel catfish (Ictalurus punctatus)

A study was undertaken to evaluate the effect of heat treatment of defatted raw soybean meal (RSBM) on the growth performance, hematology, immune response and resistance of channel catfish to Edwardsiella ictaluri challenge. Six practical-type diets were formulated to be isocaloric (2.8 kcal DE/kg diet) and isonitrogenous (34% crude protein). A diet containing 45% of commercial soybean meal (CSBM) served as the control. RSBM, non-heat treated (RSBM0) and heated in an autoclave using the dry cycle at 130 °C and 22 psi for 5 (RSBM5), 10 (RSBM10), 20 (RSBM20), and 40 min (RSBM40), was used to isonitrogenously replace the CSBM in the control diet. Each diet was fed to juvenile catfish (4.98 g) in triplicate aquaria twice daily to apparent satiation for 10 weeks. Another batch of diets containing 1% of chromic oxide was used for measurement of apparent digestibility coefficients. Heating RSBM for 20 min or longer lowered trypsin inhibitor (TI) content and increased the apparent protein digestibility (APD). The protein dispersibility index (PDI) decreased with an increase in the duration of heat treatment. Fish fed CSBM and RSBM40 diets had similar weight gain, protein efficiency ratio and apparent protein utilization which were significantly higher than those of fish fed the other diets. Feed intake significantly increased when RSBM was heated for 20 min or longer. Fish fed the RSBM40 diet had significantly lower feed intake but higher feed efficiency than those fed the CSBM diet. Whole-body protein was highest for fish fed the RSBM40 diet but did not differ from that of fish fed the CSBM diet. Hepatosomatic and visceral indices (HSI and VI) of the groups fed CSBM and RSBM40 diets were significantly lower than those fed other diets. Total cell count, red blood cell count, hematocrit and hemoglobin were not significantly affected by dietary treatment. Plasma lysozyme activity and protein of fish fed the CSBM and RSBM40 diets were similar and significantly higher than those of fish fed the other diets. Cumulative mortality 14-day post challenge with E. ictaluri was significantly lower for fish fed the RSMB5 and RSBM10 diets but significantly increased when heating time was increased to 40 min. Macrophage chemotaxis in the presence of exoantigen and antibody titer against E. ictaluri was higher for the groups fed the RSBM containing diets than those fed the CSBM diet, although the differences were not always significant. Results of this study indicate that autoclaving the RSBM for 40 min lowered the TI and PDI, improved the nutritional value of RSBM and increased plasma lysozyme and protein. However, this level of heat treatment significantly decreased macrophage chemotaxis, antibody titer and resistance of fish to E. ictaluri challenge.

Effect of water temperature and dietary starch on growth and metabolic utilization of diets in gilthead sea bream (Sparus aurata) juveniles.

We evaluated the effect of dietary starch level on growth performance, feed utilization, whole-body composition and activity of selected key enzymes of intermediary metabolism in gilthead sea bream juveniles reared at 18 and 25 degrees C. A diet was formulated to contain 48% crude protein, 12% lipids and 30% gelatinized maize starch (diet 30GS). Two other diets were formulated to include the same level of ingredients as diet 30GS except for the gelatinized starch, which was included at 20% (diet 20GS) or 10% (diet 10GS). No adjustment to diet composition was otherwise made. Each diet was fed to triplicate groups of gilthead sea bream (30 g initial mass) for 8 weeks, on a pair-feeding scheme. The higher temperature improved growth performance but the opposite was true for feed efficiency and protein efficiency ratio. Independently of temperature, growth performance, feed efficiency and protein efficiency ratio were lower in fish fed diet 30GS. No effect of temperature or dietary starch level on whole-body composition was noticed. Hepatosomatic index and liver glycogen were higher at 18 degrees C and, within each temperature, in fish fed diet 30GS. Glycemia was not affected by temperature, but was lower in fish fed diet 10GS. Data on enzyme activities showed that increasing water temperature enhances liver glucokinase (GK) and pyruvate kinase (PK) activities, suggesting that gilthead sea bream is more apt to use dietary starch at higher temperatures. No effect of temperature was noticed on hexokinase (HK), fructose-1,6-bisphosphatase (FBPase), glucose-6-phosphate dehydrogenase (G6PD) and glutamate dehydrogenase (GDH) activities. Dietary starch enhanced PK and FBPase activities while depressed GDH activity, suggesting a lack of significant regulation of hepatic glucose utilization and production in this species. HK, GK and G6PD activities were unaffected by dietary composition. Irrespectively of water temperature, gelatinized starch may be included up to 20% in diets for gilthead sea bream juveniles; at higher dietary levels, growth and efficiency of feed utilization are depressed.

Effect of fishmeal replacement by soy protein concentrate with taurine supplementation on hepatic intermediary metabolism and antioxidant status of totoaba juveniles (Totoaba macdonaldi).

The effect of dietary incorporation of soy protein concentrate (SPC) and the concomitant supplementation with taurine on hepatic intermediary metabolism and antioxidant status of totoaba (Totoaba macdonaldi) juveniles was assessed. Four isoproteic and isolipidic diets were formulated containing either 30 or 60% of SPC (diets SP30 and SP60), supplemented or not with 1% of taurine (diets SP30T and SP60T). A fish meal (FM) based diet, without SPC and taurine supplementation, was used as a control. Triplicate groups of 32 totoaba juveniles (average body mass=7.5g) were fed these diets over 45days. Results revealed that dietary FM replacement by SPC depressed the overall intermediary metabolism. Activity of key enzymes of amino acid catabolism and gluconeogenesis was significantly reduced and a trend to reduce glycolysis and glucose-6-phosphate dehydrogenase activity was observed. The incorporation of the highest level of SPC also significantly increased hepatic lipid peroxidation and the activity of superoxide dismutase. Concomitant taurine supplementation restored the activity of amino acid catabolic and gluconeogenic enzymes and hexokinase to levels similar of those of the control diet. Taurine supplementation also led to a significant increase of glucose-6-phosphate dehydrogenase and catalase activity, as well as to a significant reduction of liver lipid peroxidation. These results suggest that taurine may play an important metabolic modulation action on totoaba fed SPC based diets, contributing to the enhancement of the overall metabolism and to the reduction of liver oxidative damage.

The effect of hypoxia on intermediary metabolism and oxidative status in gilthead sea bream (Sparus aurata) fed on diets supplemented with methionine and white tea.

The present study evaluates the influence of previous nutritional status, fish fed on diets supplemented with tea and methionine, on acute hypoxia tolerance and subsequent recovery of Sparus aurata juveniles. Four isonitrogenous (45% of protein) and isolipidic (18% lipid) diets were formulated to contain 0.3% methionine, 2.9% white tea dry leaves or 2.9% of white tea dry leaves+0.3% methionine. An unsupplemented diet was used as control. Hepatic key enzymes of intermediary metabolism and antioxidant status, superoxide dismutase isoenzyme profile, glutathione (total, reduced and oxidized) and oxidative damage markers were determined under normoxia, hypoxia challenge and during normoxia recovery. Dietary white tea inclusion decreased plasma glucose levels under normoxia and seemed to induce an increase in anaerobic pathways as showed by enhanced liver lactate dehydrogenase activity. Hypoxia challenge reversed some of the responses induced by diet tea supplementation. Hypoxia decreased plasma glucose levels, increased glucose 6-P-dehydrogeanse activity, decreased superoxide dismutase activity (especially Mn-SOD and CuZn-SOD isoforms) and increased glutathione peroxidase activity in all dietary treatments. Catalase activity during hypoxia varied with dietary treatments and glutathione reductase was not modified. Antioxidant defenses were insufficient to avoid an oxidative stress condition under hypoxia, independently of dietary treatment. In general, pre-challenge values were recovered for almost all parameters within 6 h recovery time.

Effects of temperature and dietary protein level on hepatic oxidative status of Senegalese sole juveniles (Solea senegalensis)

Effects of 55 and 45% dietary protein levels (55P and 45P diets, respectively) and temperature (12 and 18 °C) on hepatic activity of superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione reductase (GR), glucose-6-phosphate dehydrogenase and lipid peroxidation (LPO) levels of Solea senegalensis juveniles were studied. Further, effects of acute thermal shocks provoked by a drop (18 °C to 12 °C) or a rise (12 °C to 18 °C) of water temperature on sole oxidative state was also evaluated. Dietary protein reduction increased LPO levels though no major alterations were found on antioxidant enzyme activities between dietary treatments. At 12 °C GR activity was higher and SOD activity was lower than 18 °C but LPO levels were not affected. In both thermal shock cases, LPO levels increased in 55P group, probably due to insufficient antioxidant enzyme activation. In contrast, fish of 45P group under acute exposition to warmer and colder temperature exhibited no substantial changes and a significant decrease on LPO levels, respectively, along with no major changes in antioxidant enzymes. Overall, results suggest that independently of rearing temperatures 45P group was more susceptible to oxidative stress than 55P group. Thermal shock either due to rise or drop of temperature seemed to induce oxidative stress in 55P group.

Dietary tryptophan and methionine as modulators of European seabass (Dicentrarchus labrax) immune status and inflammatory response.

Amino acids regulate key metabolic pathways important to immune responses and their nutritional supply may increase synthesis of immune-related proteins. The present study aimed to evaluate the effects of dietary supplementation of tryptophan and methionine on European seabass (Dicentrarchus labrax) cellular and humoral status. The immunomodulatory effects of tryptophan and methionine during an inflammatory insult was also evaluated after intraperitoneal injection with inactivated Photobacterium damselae subsp. piscicida (Phdp). A practical isonitrogenous (45% crude protein) and isolipidic (16% crude fat) diets was formulated to include fish meal and a blend of plant feedstuffs as protein sources and fish oil as the main lipid source (CRL diet). Two other diets were formulated similar to the control but including L-tryptophan or L-methionine at ×2 the requirement level (diets TRP and MET, respectively). European seabass weighing 275 g were fed the experimental diets for a period of 15 days before being sampled (trial 1). Then, fish were subjected to a peritoneal inflammation by intraperitoneally injecting UV killed Phdp (10(6) colony forming units ml(-1)) and sampled following 4 and 24 h post-injection (trial 2). Fish injected with a saline solution served as control. The haematological profile, peripheral cell dynamics and several plasma immune parameters were determined in trials 1 and 2, whereas cell migration to the inflammatory focus was also determined in trial 2. MET positively affected European seabass immune status by improving the peripheral leucocyte response, complement activity and bactericidal capacity, a stronger cellular recruitment to the inflammatory focus, and higher plasma peroxidase and bactericidal activities. TRP also seemed to improve immunostimulation, as there was a trend to augment both cell-mediated immunity and humoral capacity. However, TRP failed to improve an inflammatory response, verified by a decrease in blood phagocyte numbers and lack of immune cells recruitment. In summary, it is confirmed that MET has a pronounced influence on the innate immune response to inflammation, which is more evident than TRP, and raises its potential to incorporate in functional feeds to be used in prophylactic strategies against predictable unfavourable events.