Variability in the composition of lupin (Lupinus angustifolius) meals influences their digestible nutrient and energy value when fed to rainbow trout (Oncorhynchus mykiss)

Over a series of seven separate experiments 76 different lupin (Lupinus angustifolius) meals were assessed for their digestible dry matter, protein, amino acid and energy characteristics when fed to rainbow trout. Two reference diets (a common basal diet and a reference lupin meal) were also included in each experiment. Minimal variance in the digestibility parameters of both reference diets was observed among the experiments ensuring that there was a high degree of robustness in the across-experiment evaluations. Using simple and multiple-regression techniques, principal diet and ingredient composition factors affecting diet and ingredient digestibilities and ingredient digestible values were explored within the dataset. Using simple linear regression, it was shown that nitrogen digestibility of the lupin meals was negatively influenced by ingredient lignin content, but positively affected ingredient protein (N × 6.25) content. The energy digestibility of the lupin meals was positively affected by a range of compositional features including protein, sum of amino acids and negatively affected by carbohydrate content. The digestible nutrient and energy content of the meals reflected the combined effects of both ingredient digestibilities and ingredient composition. The digestible nitrogen content of the lupin meals was positively affected by protein (N × 6.25), sum of amino acids and energy content, but was negatively affected by lignin and carbohydrate content. The digestible sum of amino acids was also positively affected by protein, sum of amino acids, but only negatively affected by carbohydrate content, not lignin content. The digestible energy content of the lupin meals was also positively affected by protein, sum of amino acids and their own energy density, but only negatively affected by carbohydrate content. Multiple linear regression modelling supported that together ingredient protein and lignin content were the strongest predictors of digestible protein value, explaining close to 60% of the variability in this parameter. Discrete reassessment of these relationships using non-linear analysis methods provided a stronger interpretation of the ingredient composition effects. In recognition of this, a functional model including terms for ingredient protein and lignin content on the digestible protein value was defined. This study demonstrates that within one raw material type that not only does significant variability in the digestible value of the raw materials exist, but that it is possible to identify compositional features of that raw material that are intrinsically influencing their own digestible value.     

Apparent Digestibility of Gross Nutrients from Feedstuffs in Extruded Feeds for Rainbow Trout,Oncorhynchus mykiss

Abstract.— The current experiment was performed to determine apparent protein and energy digestibility coefficients of feed ingredients by the fecal stripping technique using extruded diets. The ingredients tested included five fish meals, three terrestrial animal by‐products, five plant protein concentrates, four plant meals, and seven low‐protein plant ingredients. Protein digestibility differed among fish meals and ranged from 90% for fair and average quality menhaden meal to 97% for anchovy meal. Protein apparent digestibility coefficients (ADCs) in plant concentrates ranged from a low of 89% for rice protein concentrate to a high of 100% for wheat gluten meal. Apparent protein digestibility was lower in plant meals than fish meals with a low of 70% for flaxseed meal to a high of 89% for soybean meal. Low‐protein plant meals had generally lower protein ADC from 64% for rice bran to 85% for whole wheat. A similar pattern for energy ADCs was observed; ADCs ranged from 106% for anchovy meal to 32% for whole wheat. In the current trial, divergent protein and energy ADC values were obtained most notably in ingredients known to be high in fiber or have very high starch content. The comparability of ingredients/diets processed by cold pelleting or extrusion thus appears questionable at this juncture.     

Nutrient Digestibility of Common Feedstuffs in Extruded Diets for Sunshine Bass Morone chrysops♀×M. saxatilis ♂

The digestibility of nutrients and energy in various ingredients to fish is affected by a variety of factors including ingredient quality and processing. Limited information is available regarding the digestibility of nutrients in feedstuffs for sunshine bass Morone chrysops♀×M. saxatilis♂. This information is particularly needed to improve the accuracy of diet formulations and allow appropriate substitution of feedstuffs. Therefore, a study was conducted with advanced sunshine bass fingerlings (50–75 g) to determine the apparent digestibility coefficients (ADCs) for protein, lipid, carbohydrate, gross energy, and organic matter in a variety of feedstuffs in extrusion‐processed diets. Included in the study were low‐temperature processed menhaden fish meal (Select®), meat and bone meal, fish meal analog (PROPAK?) dehulled soybean meal, cottonseed meal, corn grain, sorghum, wheat flour, wheat middlings, and rice bran. Test diets consisted of a 70:30 mixture of reference diet to test ingredient with chromic oxide (0.8%) as the inert marker. Reference and test diet ingredients were mixed in a commercial ribbon blender, preconditioned and extruded on a Wenger X‐20 to produce a neutrally buoyant pellet (5 mm). The digestibility trials were conducted in six 600‐L rectangular tanks connected as a closed recirculating brackish (5–7 ppt) water system. Diets were randomly assigned to tanks of 45–50 sunshine bass and fed twice daily to satiation. Feedstuffs of high‐protein and high‐lipid content were better digested by sunshine bass than feedstuffs of high carbohydrate or high fiber content. Organic matter digestibility ranged from 42% for both sorghum and corn to 96% and 98% for meat and bone meal and Select? menhaden fish meal, respectively. Select? menhaden fish meal and meat and bone meal appeared to be the best Ingredients for sunshine bass diets in terms of overall nutrient profiles and digestibility of nutrients. The fish meal analog did not perform as favorably as the other two animal products. Protein and lipid of cottonseed meal were highly available to sunshine bass with ADCs of 85% and 92%, respectively. Protein digestibility was high for soybean meal (77%), whereas the digestibility of organic matter (51%), lipid (54%), carbohydrate (25%) and energy (56%) in this feedstuff was moderately low. Energy in wheat middlings and wheat also was moderately available at 67% and 59%, respectively. Energy in sorghum and corn was much less available at 44% and 40%, respectively. Digestibility of nutrients and energy in rice bran exceeded 90%. Use of this information should aid the development of more efficient and economical diet formulations for sunshine bass.     

Proteolysis by juvenile sea bass (Dicentrarchus labrax) gastrointestinal enzymes as a method for the evaluation of feed proteins

Protein digestibility by gastrointestinal homogenates of Dicentrarchus labrax, was investigated in 5 feeds in relation to their amino acids composition and their ability to sustain growth of D. labrax post larval juveniles. Gastric proteolysis was found to contribute <25% of the total proteolytic capacity. Correlation was found between intestinal proteolytic capacity and the feed protein content of three pairs of amino acids. The sum of basic amino acids, arginine + lysine in the feed protein exhibited a positive correlation with susceptibility to proteolysis. The sum of the acid amino acids glycine and proline showed a negative correlation.Comparison of the intestinal proteolytic enzymatic activities in 3 growth stages of this species revealed similar profiles. Post larval and large juveniles had similar proteolytic capacities when compared on the basis of equal activity on an artificial substrate of Trypsin. Specific growth rates of post larval fish fed on these 5 feeds correlated positively with their protein digestibility as measured with large juvenile's intestinal homogenates. The results suggest that in this species, the efficiency of feeds in sustaining growth at the post larval stage can be estimated by measuring the feed protein digestibility by the proteolytic system of larger sized juveniles.     

Carbohydrate and lipid digestibility of animal and vegetal ingredients and diets for juvenile Australian redclaw crayfish, Cherax quadricarinatus

Carbohydrate and lipid digestibility of three vegetal and four animal ingredients, and diets in which they were included, were evaluated for juvenile Australian redclaw crayfish, Cherax quadricarinatus. The ingredients were: soy paste, textured wheat, sorghum meal, sardine meals (67% and 58% crude protein), squid meal and red crab meal. A basal diet was formulated, and then seven experimental diets were created, including 150 g kg^?1 of each ingredient in the reference diet. Digestibility was measured in vivo, using chromic oxide as marker. A single‐factor, completely randomized experimental design with three replicates per treatment was performed. Mean carbohydrate digestibility of vegetal ingredients and the corresponding diets was better than carbohydrate digestibility of animal ingredients. Sorghum meal had a carbohydrate digestibility over 94%, and the diet in which it was included over 92%. Soy paste and wheat meals also presented excellent carbohydrate digestibility (around 88% for ingredients and over 90% for diets). Mean carbohydrate digestibility of animal ingredients and their corresponding diets were very poor (from 18% to 32%) and this affected the carbohydrate digestibility of diets in which they were included (87–89%). Lipid digestibility was also better for vegetal ingredients. Soy paste and wheat meal recorded values over 93% and their diets over 94%. Sorghum lipid presented slightly lower digestibility. Some of the animal ingredients, especially red crab, had an excellent lipid digestibility (92.1%).     

Apparent digestibility coefficients of feed ingredients and their prediction in diets for tilapia Oreochromis niloticus×Oreochromis aureus (Teleostei, Cichlidae)

Apparent digestibility of crude protein (CP), lipid, carbohydrate, energy and fatty acids was measured in various feed ingredients fed to hybrid tilapia (Oreochromis niloticus×Oreochromis aureus) including fish and poultry meals, corn gluten, soybean meal, rapeseed meal, sunflower seed meal, wheat, corn, sorghum, barley and wheat bran. Chromic oxide was used as a non‐absorbed marker. A diet compounded from a mixture of these ingredients was then used to examine the possibility of predicting the digestibility of formulated diets. In addition, the effect of pelleting or extrusion on digestibility of a compound diet was examined. Apparent digestibility of CP ranged from 75% to 97%, lipids from 72% to 90% and energy from 39% to 89% in the different ingredients. Apparent digestibility of carbohydrates was lower and ranged from 32% to 80%. Digestibility of fatty acids ranged from 75% to 90% with saturated fatty acids exhibiting digestibilities lower than unsaturated fatty acids. In a full‐fat soy diet containing 19% fat, digestibility of lipids did not decrease. There were no significant differences in digestibility between a diet that was either pelleted or extruded. Tests conducted using a compound diet indicated that ingredient digestibility was additive for protein, lipids carbohydrates and energy. Diets for the hybrid tilapia may thus be formulated on the basis of digestibility of individual ingredients, for the nutrients examined in this study.     

Apparent digestibility coefficients of selected feed ingredients for juvenile snakehead,Ophiocephalus argus

Apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid, gross energy, phosphorus and amino acids in Peruvian fish meal, poultry by‐product meal, meat and bone meal, spray‐dried blood meal, hydrolysed feather meal, corn gluten meal, soybean meal, peanut meal, cottonseed meal and rapeseed meal were determined for juvenile snakehead (Ophiocephalus argus) with initial mean body weight of 78.1 g. A reference diet and test diets that consisted of a 70 : 30 mixture of the reference diet to test ingredient were used with 5 g kg^?1 Cr₂O₃ as an external indicator. Fish meal, poultry by‐product meal and corn gluten meal had higher ADCs of dry matter, crude protein, and gross energy among ingredients tested. Dry matter ADCs ranged 61.9–81.5% for animal ingredients and corn gluten meal and ranged 52.2–68.0% for soybean meal, peanut meal, cottonseed meal and rapeseed meal. Energy ADCs of ingredients followed similar trends to differences in dry matter digestibility. Protein ADCs of animal and plant ingredients ranged 73.6–92.8% and 75.3–85.6%, respectively. Amino acid ADCs generally reflected protein digestibility. Lipid ADCs were relatively high for the ingredients tested. Phosphorus ADCs of animal and plant ingredients ranged 39.5–65.2% and 38.7–57.1%, respectively.     

Effect of protein source and nutrient density on growth efficiency, histology and plasma amino acid concentration of rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of protein source and nutrient density on growth efficiency, nutrient digestibility and plasma amino acid concentrations of rainbow trout were evaluated. A 3 by 2 factorial treatment design with three protein sources, fish meal–barley (F–B), plant concentrates (PC) and plant meals (PM), and two nutrient densities were used. A commercial reference diet was also fed. Triplicate tanks of 30 fish (initial wt. 28 g) were fed each diet, and the final weight averaged 240 g fish⁻¹. Protein source and nutrient density affected feed intake, weight gain and feed conversion ratio. Weight gain of trout fed the PC and PM diets was approximately 10% less than fish fed the F–B diets. Protein retention was affected by protein source, but not nutrient density, and was the highest for the fish fed diets containing fish meal and the lowest for the fish fed PM diets. Apparent digestibility coefficients and apparent amino acid availabilities of the diets corresponded with differences in weight gain. This study provides further evidence that growth rates of trout fed fish meal‐free diets, using conventional and concentrated plant protein ingredients, are good but some limitation to growth exists in the fish meal‐free diets.     

Apparent digestibility of alternative plant‐protein feedstuffs for channel catfish,Ictalurus punctatus (Rafinesque)

A study was conducted with channel catfish, Ictalurus puntatus to determine apparent digestibility/availability coefficients of protein, amino acids, lipid and energy for alternative plant‐protein feedstuffs: corn gluten feed, corn germ meal, distillers dried grains with solubles, and canola meal, compared with those for soybean meal. A 32%‐protein, chemically defined diet containing 8% fish meal was used as the reference diet. Test diets consisted of 70:30 ratio of reference diet to test ingredient with chromic oxide (0.75% of the diet) as an inert indicator. Apparent digestibility/availability coefficients of protein, essential amino acids and energy in alternative protein feedstuffs tested were generally lower than those in soybean meal by channel catfish. Apparent digestibility coefficients of protein ranged from 75 to 87% and those of energy ranged from 52 to 59% for alternative feedstuffs. Lysine in alternative feedstuffs was 67–79%, methionine was 69–85% and cystine was 73–82% available to channel catfish. There were no significant differences in lipid ADCs among test feedstuffs (91.9–96.8%). Results from the present study can be useful in formulating cost‐effective catfish feeds using these alternative feedstuffs.     

Apparent digestibility coefficients of feed ingredients and their predictability in compound diets for gilthead seabream, Sparus aurata L.

Apparent digestibility of crude protein, amino acids, lipid, carbohydrate and energy was measured for a range of feed ingredients fed to gilthead seabream, Sparus aurata L. — fish meal, poultry meal, meat meal, blood meal, squid meal, extracted soyabean and wheat flour. Chromic oxide was used as a non-absorbed reference substance and faeces were collected by stripping. Diets compounded from mixtures of these ingredients were then used to examine the possibility of predicting the digestibility of formulated diets.
Apparent digestibility of crude protein ranged from 79% to 90%, lipids from 83% to 95% and energy from 72% to 88% in the different ingredients. Apparent digestibility of carbohydrates was lower and ranged from 49% to 77%. Apparent digestibility of amino acids was higher than that of crude protein and differences were found among digestibilities of individual amino acids.
Tests conducted using five compound diets indicated that ingredient digestibility was additive for protein, amino acids, lipids and energy, whereas the digestibility of carbohydrates in the compound feeds was slightly lower than predicted.
Diets for Sparus aurata may thus be formulated on the basis of digestibility of individual ingredients.     

Apparent digestibility coefficients of nutrients in brewer's and rendered animal by-products for rainbow trout (Oncorhynchus mykiss (Walbaum))

Two experiments were conducted to measure the apparent digestibility coefficients (ADCs) of nutrients, dry matter, and energy in by‐products of the brewing industry and in selected animal protein ingredients for rainbow trout. In experiment 1, 500 rainbow trout (average body weight 170.8±5.5 g) were stocked in ten 140‐L digestibility tanks with 50 fish per tank and two tanks per diet. Yttrium oxide was used as an inert marker in the diets. The high fibre content of brewer's dried grains (BDG) affected the ADCs of dry matter but not of protein or amino acids. Brewer's dried yeast had a higher protein content than BDG, but ADC values for protein and amino acids were significantly lower. The ADCs of phosphorus were similar among brewer's dried products. The BDG high‐protein, fraction had marginally higher ADC values for dry matter, protein and amino acids than regular BDG. Conditions in experiment 2 were similar to those in experiment 1. ADC values for spray‐dried porcine plasma were over 98% for dry matter, crude protein, crude fat, and gross energy. ADC values for spent hen meal were higher than those of poultry by‐product meal or feather meal, with the exception of gross energy. However, spent hen meal was unpalatable. The ADCs in these ingredients were variable, and this variability must be taken into account when these ingredients are formulated into feeds for fish.     

Apparent digestibility of selected feed ingredients in diets for juvenile hybrid tilapia,Oreochromis niloticus×Oreochromis aureus

The apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid, ash, phosphorus, gross energy and amino acids of 10 selected ingredients for juvenile hybrid tilapia (7.05 ± 0.09 g) were determined using 0.5% Cr₂O₃ as an inert indicator. The feed ingredients tested in this study were corn gluten meal (CGM), corn byproduct, corn germ meal (CG), soybean meal (SBM), fermented soybean meal (FSM), soy protein concentrate (SPC), soy protein isolate, malt sprouts (MS), fish meal (FM) and earthworm meal (EM). The test diets were prepared by incorporation of 30% test ingredients into the reference diet. Reference and test diets were fed to the fish and the faecal samples were collected using a faecal collection column attached to the fish‐rearing tanks. The ADCs for dry matter, crude protein, crude lipid, ash, phosphorus and gross energy were 41.7–98.9%, 90.6–99.6%, 73.1–98.8%, 34.1–98.6%, 49.5–99.6% and 45.4–99.7% respectively. Soy protein isolate, FM and EM had higher dry matter, crude protein and gross energy ADCs. Corn byproduct and EM had higher crude lipid ADCs, and CG and EM had higher phosphorus ADCs. Corn germ meal had the highest ash ADC, while CGM had the highest value for gross energy. The lowest dry matter, crude protein, lipid and gross energy ADCs occurred in MS, while the lowest ash and phosphorus ADCs occurred in SPC. The amino acid ADCs ranged from 83.3% to 100%, exhibiting a positive correlation with crude protein digestibility for a given test ingredient. The feed ingredient digestibility of this study may provide useful information about nutrient and energy utilization to facilitate formulation of least‐cost practical diets for hybrid tilapia.     

Response of Pacific White Shrimp,Litopenaeus vannamei,to Three Sources of Solvent Extracted Soybean Meal

Three sources of soybean meal (SBM) were biochemically characterized and evaluated in diets for juvenile Litopenaeus vannamei. Three biological techniques were utilized to evaluate the nutritional quality of the meals including an outdoor growth trial as well as determination of in vivo apparent digestibility and in vitro digestibility including pepsin digestibility (0.0002%), pH Stat degree of hydrolysis, and immobilized digestive enzyme assay (IDEA). The growth trial was conducted over a 10‐wk period using soybean meal as the primary protein source with each meal being included at 54–58% of the diet based on an equal protein inclusion. At the conclusion of the growth trial there were no significant differences between the test diets indicating equivalent biological availability under practical conditions. The in vivo digestibility trial utilized chromic oxide as the inert marker and 70:30 replacement techniques resulted in typical results. Apparent protein digestibility (APD) and apparent energy digestibility (AED) of the diets ranged from 66.8 to 80.2% and 65.4 to 74.7%, respectively. Ingredient digestibility values for protein and energy ranged from 78.8 to 93.5% and 60.5 to 85.0%, respectively. One of the three SBM evaluated had numerically lower protein digestibility and significantly lower energy digestibility than the other two meals .     

Apparent digestibility of Asian carp‐ and common carp‐derived fish meals in feeds for hybrid striped bass Morone saxatilis ♀ × M. chrysops ♂ and rainbow trout Oncorhynchus mykiss

Apparent digestibility coefficients (ADCs) of nutrients (crude protein, amino acids, crude lipid, fatty acids, and minerals) were determined for fish meals derived from menhaden, Asian carp (combination of silver and bighead carps), and common carp in feeds for hybrid striped bass and rainbow trout. Extruded test diets were formulated to contain a 70 : 30 mixture of reference diet and test ingredient with yttrium oxide (1 g kg^?1) serving as the inert marker. Diets were randomly assigned to triplicate tanks and fish were fed once per day at 2% body weight. Fecal samples were collected by manual stripping. The ADCs were calculated according to standard procedures. The composition and digestibility of Asian carp and common carp meals was broadly similar to menhaden meal. Protein digestibility ranged from 86.5% (Asian carp meal) to 93.1% (common carp meal). Lipid was highly digestible with ADCs >100% for all ingredients. Although the Asian carp meal was less digestible than the other two fish meals, it was still a highly digestible ingredient. Our data suggest that fish meals derived from Asian or common carp would be valuable feedstuffs in diets for hybrid striped bass, rainbow trout, and possibly other cultured fishes.     

A comparison of the digestibility of lupin (Lupinus sp.) kernel meals as dietary protein resources when fed to either, rainbow trout, Oncorhynchus mykiss or red seabream, Pagrus auratus

The nutritional value of the kernel meals of three species of lupin (Lupinus albus, L. angustifolius and L. luteus) was compared against each other and solvent extracted soya bean meal and wheat gluten, when fed to either rainbow trout or red seabream. The digestible nutrient and energy values were determined for each ingredient, based on the diet substitution digestibility method. Each test ingredient was included in test diets at 300 g kg^?1. As different faecal collection methods were used on each species, only ingredient comparisons within each fish species study are valid. Protein digestibility for all lupin kernel meals was significantly better than for soya bean meal when fed to red seabream, although only numerically so when fed to rainbow trout. The highest protein digestibility in both fish species was that from the wheat gluten (100.0% for both rainbow trout and red seabream). Energy digestibility for each of the lupin kernel meals (range 62.4%–64.9% in rainbow trout and 60.9%–69.5% in red seabream) was less than that obtained from soya bean meal (75.1% and 81.0% for rainbow trout and red seabream, respectively). However, the higher gross energy content of the lupin kernel meals still resulted in both L. albus and L. luteus providing equivalent levels of digestible energy as that of soya bean meal. Organic matter digestibility was generally poorer for each of the lupin kernel meals relative to that for the soya bean meal and particularly compared with the wheat gluten. Phosphorus digestibility was significantly better in all lupin kernel meals than that from both the soya bean meal and wheat gluten. Highest phosphorus digestibility was that obtained from L. albus kernel meal (100.0% for both rainbow trout and red seabream) although notably the phosphorus digestibility of all lupin kernel meals when fed to rainbow trout was determined at 100%. Similarly the digestibility of phosphorus from lupin kernel meals fed to red seabream was also very high. This study supported the good nutritional value to both rainbow trout and red seabream of kernel meals of all three species of lupin, although the digestible nutrient attributes of kernel meal from L. luteus were particularly favourable.     

Effects of the protein/carbohydrate ratio of extruded diets on protein synthesis, protein growth and body composition in juvenile brown trout (Salmo trutta)

High levels of protein in fish feeds result in higher costs and nitrogen waste. Therefore, studies focused on protein substitution by alternative energy sources are necessary. Here we examine whether the protein:carbohydrate ratio in extruded diets affects protein-turnover parameters and the main tissue components in brown trout. Juvenile fish were adapted to two extruded diets: one higher in protein and lower in carbohydrate, C: 45/28 and the other higher in carbohydrate and lower in protein, HC: 37/40. Gross energy was 19 MJ kg⁻¹ DM in both diets. Protein and lipid digestibility were high and similar in both groups (≈90%), whereas total and carbohydrate digestibility and digestible energy were lower in the HC-fed group than in the C-fed group. Consequently, when fish were adapted to the diets, plasma levels of glucose and insulin differed between diets. HC-group presented higher plasma glucose levels and lower plasma insulin levels than C-group. Protein synthesis rates in white muscle, liver and whole body did not differ significantly between diets. In contrast, protein accretion rate of white muscle and whole body were significantly lower in the HC group, indicating an increase of protein degradation in these tissues and a decrease of synthesis retention efficiency. In spite of the daily protein intake of HC group was lower than C-group, the anabolic stimulation efficiency was increased by 34% in HC group. Protein and lipid contents in white muscle and liver were stable throughout the experiment. No hepatomegalia or increased fat deposition was observed in fish fed HC. Differences in specific growth rates (C: 0.88%; HC: 0.77%) were associated more with the lower protein consumption rate and the lower level of digestible energy in fish fed HC than with the higher dietary carbohydrate content of the diet.     

Evaluation of the feed value of a transgenic strain of the narrow‐leaf lupin (Lupinus angustifolius) in the diet of the marine fish,Pagrus auratus

This study assessed the nutritional and biological value of a noncommercial, transgenic line of the Australian sweet lupin, Lupinus angustifolius, (cv. Warrah), produced to increase the methionine content of the seed. An initial experiment demonstrated that differences in the methionine content of the transgenic and nontransgenic control lupins had no apparent influence on the growth of juvenile red seabream fed practical diets. Re‐evaluation of the nutritional characteristics of the lupin meals with subsequent digestibility studies allowed the determination of the digestible value of the protein and energy content of each of the varieties. The digestible protein content of either variety was similar, however significant differences in the digestible energy value of each variety existed (56.3% cf. 64.0%). This re‐evaluation of the nutritional value of the genetically manipulated (GM) and non‐GM lupin varieties enabled the reformulation of diets on a digestible protein and energy basis. A second growth trial was undertaken using sub‐satietal pair‐feeding regimes, with the experiment also involving protein‐restrictive diets to allow expression of the differences in the methionine content of the transgenic and nontransgenic lupin meals. A significant benefit of the enhanced methionine level in the transgenic lupin was observed. It is argued that in the high‐protein fish diets used, the importance of amino acid composition is relatively limited. Economic modelling of the potential value of the increased methionine in the transgenic lupin suggests that this will have limited benefit for aquaculture industries, and that greater value would be attributable to higher protein and energy levels in ingredients.     

Apparent digestibility of soybean coproducts in extruded diets for Nile Tilapia,Oreochromis niloticus

Soybean coproducts are important protein sources in aquaculture because of their amino acid profile. Tilapia can be reared on soybean coproducts as the only source of dietary protein without compromising growth. This study estimated apparent digestibility coefficients for five soybean coproducts for juvenile Nile tilapia, Oreochromis niloticus, fed with extruded diets. A reference diet and test diets consisting of 70% reference diet and 30% coproduct ingredient were formulated, along with 5.0 g kg^?1 chromic oxide (Cr₂O₃) as a marker. Apparent digestibility coefficients (ADC) for dry matter (ADCDM), gross energy (ADCGE) and crude protein (ADCCP) for soybean coproducts were estimated as 84.2–88.4%, 86.9–91.1% and 96.8–97.9%, respectively. ADCDM and ADCCP values did not vary among the ingredients, but low‐protein soybean meal exhibited lower ADCGE values than did soybean protein concentrate. ADCs of all amino acids were >95%, and mean ADCs for amino acids were similar to the values observed for ADCCP. Soybean coproducts had good nutritional value in extruded diets fed to tilapia. Methionine, histidine and valine were the limiting amino acids in all evaluated ingredients.     

Apparent digestibility coefficients of selected feed ingredients for juvenile hybrid tilapia,Oreochromis niloticus×Oreochromis aureus

The apparent digestibility coefficients (ADCs) of dry matter, crude protein, crude lipid, gross energy, phosphorus and amino acids in local fish meal (LFM), Peruvian fish meal (PFM), poultry by‐product meal (PMM), meat and bone meal (MBM), tilapia by‐product meal (TM), fermented soybean meal (FSBM), soybean meal (SBM), peanut meal, canola meal (CM), cottonseed meal (CSM) and de‐gossypoled cottonseed meal were determined for juvenile hybrid tilapia (7.18 ± 0.2 g, mean ± SD). A reference diet (RF) and test diets (consisting of 70% RF and 30% of the feedstuff) were used with 0.5% chromic oxide as an external digestibility marker. The juvenile hybrid tilapias were stocked in 500‐L fibreglass tanks at a density of 20 fish per tank. Faeces were collected from triplicate groups of fish using a faecal collection column attached to the fish‐rearing tank. The results indicated that the ADCs of dry matter for juvenile hybrid tilapia ranged 71.88–89.53% for animal products and 65.89–79.98% for plant products. For crude protein, apparent digestibility coefficients of protein (ADCp) exceeding 90% were observed for FSBM, SBM and PFM, and ADCp of MBM was the lowest among all the treatments. Apparent digestibility coefficients of lipid in all the treatments were above 90%; the results indicate that lipids from both animal and plant sources were well digested by hybrid tilapia. The ADCs of phosphorus of animal and plant feedstuffs ranged between 58.04–74.44% and 52.65–64.23% respectively. The lowest ADC of phosphorus was observed in CSM among plant ingredients and in MBM among animal ingredients. The ADCs of energy were similar to those of dry matter and protein; the highest and lowest ADCs of energy were found in PFM and CM respectively. In general, the amino acid availability coefficients tended to reflect the ADCp among highly digestible ingredients. For the animal products, the availabilities of amino acids in PFM, LFM and PMM were generally higher than that in TM and MBM; among all the plant products, the availabilities of amino acids in FSBM and SBM were higher than in CM. These results indicated that juvenile hybrid tilapia is able to utilize different feedstuffs efficiently.     

Apparent digestibility coefficients of fungal fermented plant proteins in two different penaeid shrimps—A comparative study

Using the 70:30 replacement method and chromium as an inert marker, the digestibility of four fermented oilseed meals/cakes (soybean meal (FSBM), groundnut oil cake (FGNC), rapeseed meal (FRSM), and sunflower oil cake (FSFC)) were determined in Penaeus monodon and Penaeus indicus. Apparent dry matter digestibility (ADMD) of fermented ingredients was ranked as FSBM > FGNC > FRSM > FSFC. The critical variations in apparent protein digestibility (APD) in P. monodon (0.816%) and P. indicus (0.608%) were lower than the ADMD. Appaprent amino acid digestibility (AAD) was >90% in FSBM for both the species and was lower for other ingredients. Protein had a higher digestibility than total amino acids and was in the range of 0.69%–2.71% in P. monodon and 0.32%–2.75% in P. indicus. A correlation between the ADC of total amino acids and protein was found to be r = 0.8229 in P. indicus and r = 0.7447 in P. monodon. Data were further subjected to two way analysis of variance for assessing the digestibility variations between the species. It was observed that P. indicus had higher values of ADMD than P. monodon in FSBM (2.97%) and FRSM (1.22%) and the reverse was true in FGNC and FSFC. The APD was high in P. indicus for FSBM, FGNC and FRSM but not for FSFC. However, significant variations could be noticed in AAD between the species.