Emídio Gomes

Replacement of fish meal by plant proteins in the diet of rainbow trout (Oncorhynchus mykiss): digestibility and growth performance

Abstract The study was undertaken (1) to obtain apparent digestibility coefficient (ADC) values for a number of ingredients of plant or animal origin, (2) to formulate diets based on ADC values of ingredients, and (3) to evaluate growth performance of trout fed four diets in which fishmeal was gradually replaced by a mixture of other ingredients, but having the same digestible protein (DP) and digestible energy (DE) levels. ADC values of the ingredients tested were generally high, specially for animal proteins. A co-extruded plant protein (rapeseed and peas), “Colzapro”, full-fat toasted soybean, maize gluten and full-fat micronized soybean were the best vegetable proteins tested. No significant differences were observed for weight gain and specific growth rate (SGR) among trout fed diets C0, C33 and C66 (containing only animal protein, 33% and 66% of vegetable protein, respectively). These values were significantly higher than those observed for fish fed a diet containing 100% vegetable protein (C100). The same relationship was observed for voluntary intake with a significant reduction in trout fed diet C100. Based on data obtained, the possibility of partial replacement of brown fish meals by vegetable proteins up to 66% without negative effects was well demonstrated. Further work is necessary in order to understand the factors governing or affecting feed intake in trout fed a fish-meal-free diet.

Effect of dietary non-protein energy levels on condition and oxidative status of Senegalese sole (Solea senegalensis) juveniles

The effects of dietary non-protein energy levels on growth, oxidative status and condition were studied in juveniles of Senegalese sole (Solea senegalensis). Four isonitrogenous diets with four energy levels were used: A-low (11% lipid, raw carbohydrate); B-intermediate (11% lipid, digestible carbohydrate); C-intermediate (21% lipid, raw carbohydrate); and D-high (21% lipid, digestible carbohydrate). Survival, relative growth rate (RGR) and feed conversion rate were not significantly affected by the dietary treatments. The fatty acid composition of the fish muscle varied little among the treatments, but trans 18:2n - 6, total n - 6 and EPA/DHA ratio, tended to be higher in fish fed diets with low lipid level. Cellular energy allocation (CEA) results (indicative of metabolic status and net energy budgets) showed significant differences in liver, but not in muscle samples. Livers of fish fed diet C contained the lowest carbohydrate, protein and CEA values, but the highest cellular energy consumption. Fish fed diet A had the highest CEA for growth, followed by fish fed diets B and D and then diet C. The liver and muscle peroxidation and antioxidant activity were measured by thiobarbituric acid reactive substances (TBARS) test and the enzymatic activities levels of catalase (CAT) and superoxide dismutase (SOD). TBARS values were higher for fish fed diets with high lipid content. However, no clear relation was found between HUFA level and TBARS value. The activity levels of the antioxidant enzymes CAT and SOD were higher in livers of fish fed diets with a high lipid level. Furthermore, CAT and SOD activity and TBARS values were influenced by the type of dietary starch in the diet. Higher oxidation rates were observed in fish fed diets containing raw carbohydrate. These data suggest that lipid and carbohydrate energy sources affect the oxidative status of Senegalese sole. Diets containing low levels of lipid and digestible starch reduce the susceptibility of the fish to oxidation and may enhance growth rate

Effects of dietary incorporation of a co-extruded plant protein (rapeseed and peas) on growth, nutrient utilization and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss)

Abstract Four experimental diets (diets CP0, CP5, CP10 and CP15) containing 42% crude protein were formulated to contain graded levels of colzapro, a co-extruded product of rapeseed and peas, by replacement of protein from fishmeal. Another diet (CPE) with a lower protein (34%) and higher fat content was formulated to contain a high level (45%) of colzapro. A 12-week growth trial was conducted with rainbow trout (initial body weight 40 g; 18°C) to evaluate the potential use of this plant protein in trout diets. Growth performance, digestibility of nutrients, and ammonia nitrogen excretion were measured. The effects of dietary colzapro on the fatty acid composition of trout muscle were studied. Compared to the control group, fish fed diets in which 5, 10 and 15% of protein was replaced by protein of colzapro showed equivalent or slightly betten growth performance. Increasing the dietary colzapro level to 45% (diet CPE) led to a significantly lower final weight, specific growth rate and an increase in feed to gain ratio when compared with the other groups. No significant differences were observed in the digestibility of protein and fat, regardless of dietary treatment, while those of dry matter and energy were affected by colzapro incorporation. Non-faecal nitrogen loss showed a decreasing trend with increasing levels of dietary colzapro. In the muscle, n−6 fatty acids increased with increasing levels of dietary colzapro, mainly due to a rise in linoleic acid levels, while the levels of 20: 4 n−6 did not vary much between treatments. Although the levels of 22: 6 n−3 fatty acids remained stable, a decreasing trend for the total percentage of n−3 fatty acids was observed, thus affecting the n−3 n−6 ratios. Histological observations did not reveal any significant difference in thyroid cells between dietary treatments. The results obtained showed that colzapro can be utilized in rainbow trout diets at levels of up to 20% without negative effects on growth, nitrogen or energy utilization and muscle fatty acid composition.

Utilisation of diets supplemented with microbial phytase by seabass (Dicentrarchus labrax) juveniles

A trial was carried out to compare the growth performance, body composition and apparent digestibility coefficients (ADC) of diets by seabass, with an initial weight of 13.5 g, fed diets including fish meal (68.6 % of the dietary protein) or soybean meal (65.6 % of the dietary protein) as the main protein sources. Microbial phytase was added to the soybean meal based diet (1 000 and 2 000 IU·kg−1) and to the fish meal based diet (2 000 IU·kg−1) in order to study its effect on phosphorus utilisation. Results of this trial showed that growth rate, feed conversion and nitrogen retention were significantly better in fish fed the fish meal based diet. Energy retention was similar in both groups. ADC of protein were similar among groups. ADC of phosphorus was significantly higher in the fish meal based diet (63 %) than in the soybean meal based diet (25 %). Supplementation of the fish meal based diet with microbial phytase did not improve the ADC of phosphorus, while in the soybean meal based diet the inclusion of 1 000 and 2 000 IU·kg−1 of microbial phytase significantly increased the ADC of phosphorus to 71.5 % and 79.8 %, respectively. It is concluded that for practical purposes supplementation of diets with microbial phytase may prove valuable in diets including high levels of plant feedstuffs.

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.

The effect of different processing treatments on soybean meal utilization by rainbow trout, Oncorhynchus mykiss

A 12-week feeding trial was conducted with 38 g rainbow trout to evaluate the effect of 20% dietary protein replacement of brown fish meal in a control diet (diet C) by commercially full-fat soybean meal (diet S1), full-fat extruded soybean meal (diet S2), solvent-extracted soybean meal (diet S3), and solvent-extracted soybean meal, treated by infrared radiation (diet S4). In a separate trial the apparent digestibility of the diets was measured in triplicate groups of rainbow trout, using an automatic faeces collector. Growth rate, feed conversion ratio and nitrogen retention (%NI) of fish fed diets S1, S3 and S4 were better than in fish fed S2 and the diet based on brown fish meal. The poorest results were observed in trout fed the diet S2. Energy retention (%EI) was not significantly different among the dietary treatments. At the end of the trial there were no significant differences in body composition, hepatosomatic and visceral indexes among experimental groups. Apparent protein digestibility coefficients of the experimental diets were significantly (P < 0.05) higher than that of the control diet. There were no differences among experimental groups in apparent dry matter and energy digestibilities, except in trout fed diet S2 which had an apparent energy digestibility significantly lower than in trout fed the fish meal based diet. It is concluded that at the 20% dietary replacement level of brown fish meal by soybean meal improves the growth performance of rainbow trout. However, the commercially extruded full-fat soybean meal did not seem to improve the nutritional value of this plant protein source for rainbow trout.

Effect of frequency of feeding on nitrogen and energy balance in rainbow trout under maintenance conditions

Abstract Three groups of rainbow trout were fed at maintenance level (daily, or once every 2 or 4 days) for a period of 4 weeks. Changes in the individual body weights and in body composition at the end of the trial were recorded. Patterns of nitrogen excretion and of oxygen consumption rates after a meal were followed in these groups, based on which some characteristics of protein utilization for energy purposes under routine and under postprandial conditions were calculated. Trout fed a ration to cover the maintenance needs once every 2 days showed significant conservation of body protein compared to other groups.

Feed intake and growth of fast and slow growing strains of rainbow trout (Oncorhynchus mykiss) fed by automatic feeders or by self-feeders

Abstract Rainbow trout (8.5–9.5 g) of two strains (C and M) differing in growth potential were compared with respect to feeding motivation and feeding rhythms, over a 65-day experimental period, employing self-feeding or automatic feeding. Growth rate, feed gain ratio, feed intake and pattern of feeding activity of fish fed with self-feeders, were recorded, as was body composition of both strains. The final weight of fish of the fast-growing strain, strain C, fed using self-feeders, was significantly higher (82.6 g) than that observed for fish of the slow-growing strain, strain M (69.3 g). When the automatic feeders were used, no significant differences were found between the strains in terms of body weight gain (65 g). Results observed for feed gain ratio were also similar between the two strains. Although the voluntary feed intake (VFI) did not vary significantly with the genetic origin of the fish, strain C displayed a consistently higher VFI compared to strain M. The retention efficiency of nutrients and energy were similar between strains but significantly different between feeding systems. With regard to body composition, when fish were fed by means of self-feeders, no significant differences were found between the two rainbow trout strains. However, when fed automatically, dry matter and lipid content were highest in the strain M fish. The energy and protein content of the whole fish were not significantly influenced either by the feeding system or by the strain of the fish used.

Potential use of a microalga (Chlorella vulgaris) in the pigmentation of rainbow trout (Oncorhynchus mykiss) muscle

The main purpose of this work was to evaluate the colouring effect of carotenoids present in dry biomass obtained from stressed cells ofChlorella vulgaris. Total carotenoids represented only 0.2% of dry algal biomass and consisted mainly of canthaxanthin, lutein, astaxanthin and their esters. — A rainbow trout feeding trial was conducted in order to investigate the effects of dietary algal incorporation as a pigment source, in comparison to that obtained with synthetic pigments, both astaxanthin and canthaxanthin. — The colour intensities measured in muscle were compared, in each case, with those which constitute the Salmonids Roche Colour Card, and proved similar after both 3 and 6 weeks feeding, with a significant increase detected, but at the end of experiment (9 weeks) the increase was shown only in spectrophotometric (quantitative) results.Chlorella vulgaris biomass, which is storable without any special precautions, thus appears to be a promising source of carotenoids to use in commercial fish finishing diets, quite comparable in efficiency with the existing synthetic pigments. Algal biomass micronization, which was also tried out, was not found to be advantageous for the efficiency of colouring, no evidence having been found of any difference in its absorption and in the distribution of pigment through muscle, even if a 150-g rainbow trout, which has a rather short digestive tract, was used.

Use of Chlorella vulgaris as a carotenoid source for rainbow trout: effect of dietary lipid content on pigmentation, digestibility and retention in the muscle tissue

Apparent digestibility, deposition and retention of carotenoids in the muscle of rainbow trout, Oncorhynchus mykiss, were investigated comparing the feeding of pigments from Chlorella vulgaris against commercially available pigments at two different total lipid contents (15% and 20% lipid). Algal biomass (ALG) was included in rainbow trout diets and muscle pigmentation was compared to that obtained in trout fed diets containing a 5:3 mixture of canthaxanthin and astaxanthin (MIX) (reflecting the relative concentrations of these carotenoids in the dry alga) or those fed a diet containing astaxanthin only (AST). Apparent digestibilities of pigments and nutrients were determined by the indirect method, using Cr2 O3 as indicator, and the colour intensity and pigment concentration were assessed in the muscle, using the Roche colour card for salmonids and UV-vis spectrophotometry. After 6 weeks feeding, colour intensity was similar for the various pigment sources, achieving levels 12 to 13, yet significantly higher in fish fed the diet with the higher lipid content (≈ 20%) (p<0.05). Pigment concentration in the muscle was also higher in the fish fed the high-fat diet. Muscle pigment concentrations were similar for fish fed diets ALG and MIX, and over 1.5 times higher than for diet AST (p<0.05) after 6 weeks. Apparent digestibility of dry matter, crude protein, lipid, total energy and specific carotenoid concentrations were also measured. Increased dietary fat content was shown to increase the deposition and the retention of carotenoids in muscle, and the difference increased with time (deposition increase of 10–20% at week 3 and 30–40% at week 6 and retention increase of 10–15% at week 3 and 30% at week 6). Pigment digestibility also apparently increases (10–20%) under those conditions despite the fact that no significant effects in terms of apparent digestibility increase were found for dry matter, protein, lipids or energy.