Acid and Fermented Silage Characterization and Determination of Apparent Digestibility Coefficient of Crude Protein for Pacu Piaractus mesopotamicus

Three types of raw materials including commercial waste from saltwater (SW), freshwater fish (FW) and tilapia fillet residue (FR) were used to produce fish silage by either acid digestion (2% formic acid and 2% sulfuric acid) or anaerobic fermentation (5% of Lactobacillus plantarum and 15% sugar cane molasses). Six test diets were used in digestibility trials prepared with 70% reference diet and 30% of each experimental silage. These diets were fed to juvenile pacu Piaractus mesopotamicus (146 g average weight) in triplicate. Fish were kept in 500-L tanks and feces collected by manual extrusion. It was observed for both processes that SW waste always had the highest moisture content and lowest fat and ash. Highest crude protein levels were found in silages from commercial fish waste (SW and FW) made from whole fish unfit for human consumption. However, apparent digestibility coefficients did not vary among diets ( P > 0.05). Although values did not differ statistically, fermented silage consistently displayed higher digestibility coefficients compared to acid silage. The silages exhibited relatively high protein digestibility (72.5–80.0%), thus suggesting the feasibility of using fish industry by-products in aquaculture feeds.     

Apparent Digestibility Coefficients of Various Feed Ingredients for Grouper Epinephelus coioides

Apparent digestibility coefficients (ADC) of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in white fish meal, brown fish meal, soybean meal, peanut meal, and yeast were determined for grouper Epinephelus coioides. Apparent digestibility was determined using a reference diet with 0.5% chromic oxide indicator and test diets that contained 70% reference diet and 30% of the feed ingredient being evaluated. The fish, averaging 12.0 g, were held in 250-L tanks at a density of 30 fish per tank. Feces were collected from three replicate groups-of fish. Apparent dry matter digestibility of ingredients was 78.85 ± 2.43, 79.11 ± 0.61, 69.85 ± 3.60, 73.67 ± 2.30 and 57.70 ± 4.69% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent gross energy digestibility of ingredients was 93.27 ± 2.90, 89.48 ± 1.78, 70.52 ± 4.01, 73.13 ± 2.41 and 51.67 ± 2.01% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. Apparent protein digestibility of ingredients was 89.82 ± 1.24, 87.34 ± 1.25, 83.97 ± 1.92, 80.79 ± 1.95, and 61.14 ± 0.54% for white fish meal, brown fish meal, soybean meal, peanut meal, and yeast, respectively. White fish meal and brown fish meal showed higher protein digestibility among ingredients tested (P ± 0.01). Lipid digestibility of ingredients was high (90.66-94.48%) and not significantly different except for yeast. Amino acid availability values for test ingredients were similar to values of protein digestibility. Amino acid availability values of white fish meal and brown fish meal were higher than other ingredients. Fatty acid availability values for test ingredients were similar to values of lipid digestibility. In general, the digestibility of most fatty acids was over 80% in all ingredients, except for 14:0 in yeast and 18:0 in peanut meal, PUFA + HUFA > MUFA > SFA. Longer-chain saturated fatty acids were less digestibility, except for 14:0, with digestibilities diminishing as fatty acid chain length increased. Apparent digestibility of dry matter, crude protein, lipid, gross energy, amino acids, and fatty acids in yeast was the lowest among the ingredients.     

Effect of Oxygen Saturation in Water on Reproductive Performances of Pacu Piaractus brachypomus

Broodstock pacu Piaractus brachypomus as well as their eggs during their embryonic development were exposed to either normoxia (5.5–7.5 mg O₂/L) or hypoxia (2.0–4.5 mg O²/L) conditions. The plasma concentrations of 11-ketotestosterone in males and estradiol-17β in females, as well as that of their precursor testosterone (T) were significantly ( P < 0.01) higher in fish maintained under normoxic conditions than in fish exposed to hypoxia. After ovulation and spermiation induced by hormonal treatments, the plasma concentrations of T and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) significantly ( P 0.05) increased in both sexes under both normoxic and hypoxic conditions. The plasma levels of T and 17,20βP achieved under normoxic conditions were higher than the ones recorded under hypoxia, except for those of 17,20βP in males. Males responded positively to the hormonal treatments, and the concentration of spermatozoa was 10.5 ± 0.8 10⁹/mL under both oxygen conditions. Hypoxia resulted in significantly lower survival of embryos (17.3 ± 28%) in comparison to normoxic conditions (68.5 ± 25%). Moreover, larval deformities were found when exposed to hypoxia (91.6 ± 6%). During embryonic development of this species 4 mg/L of oxygen is tolerated at 26–27 C without negative impact. We conclude that despite the highly adaptable nature of adult pacu to environmental hypoxia, oxygen concentrations below 4 mg/L severely impacted survival of embryos.     

Apparent Digestibility Coefficients of Selected Feed Ingredients for Yellowfin Seabream, Sparus latus

The apparent digestibility coefficients (ADC) of dry matter (DM), crude protein (CP), gross energy (GE), and amino acid in seven feed ingredients were determined with juvenile yellowfin seabream (initial body weight, 41 ± 2 g; means ± SD) through two digestibility trials. The ingredients consisted of white fish meal (WFM), Peruvian fish meal (PFM), brown fish meal (BFM), rapeseed meal (RM), soybean meal (SBM), extruded soybean meal (extruded SBM), and peanut meal (PM). In each of the two trials, a casein–gelatin reference diet was mixed with test ingredients in a ratio of 70:30 to produce a series of diets, and yttrium oxide was used as the inert marker. The reference and test diets were fed to yellowfin seabream reared at 27.5 ± 1 C, and fecal samples were collected by siphoning. The derived DM, CP, and GE ADCs (means ± SD) for the test ingredients were, respectively, WFM – 72.3 ± 3.87, 86.4 ± 1.06, and 93.6 ± 2.63; PFM – 54.1 ± 15.45, 80.5 ± 7.81, and 77.4 ± 11.9; BFM – 57.7 ± 2.34, 82.8 ± 3.07, and 84.5 ± 5.77; RM – 33.5 ± 5.50, 84.7 ± 2.83, and 56.3 ± 9.87; SBM – 58.7 ± 4.42, 92.6 ± 3.94, and 58.1 ± 2.91; extruded SBM – 65.1 ± 16.52, 89.7 ± 1.68, and 64.8 ± 6.23; and PM – 70.6 ± 1.43, 97.3 ± 3.52, and 59.8 ± 4.78. The ADC of CP of both plant and animal feed ingredients was high, whereas DM and GE values varied greatly. Apparent DM digestibility coefficients of ingredients decreased as ash or fiber contents of ingredients increased, and the variation of apparent GE digestibility coefficients of ingredients is similar to that in DM, with the exception of the value for PM.     

Apparent Digestible Energy Coefficients and Associative Effects in Practical Diets for Red Swamp Crayfish

Adult red swamp crayfish ( Procambarus clarkii ) were held in fecal collection chambers and fed common feedstuffs in two different types of diets, as the sole feedstuff and as a 30% substitution in a reference diet. Feedstuffs tested were soybean meal, peanut meal, wheat shorts, cooked corn, menhaden fish meal, and shrimp-head meal. Feed consumption, apparent digestible dry matter, and energy coefficients were determined for feedstuffs when fed in both diets. Addition of menhaden fish meal, shrimp-head meal, and peanut meal in the reference diet resulted in decreased consumption, and menhaden fish meal was poorly digested when incorporated at 30% in the reference diet. Apparent dry matter and energy digestion coefficients Indicated that plant feedstuffs have greater potential as ingredients in crayfish diets than feedstuffs of animal origin. Differences in consumption and digestibility between the two types of diet were observed. Therefore, it appears that the associative effects of additions of feedstuffs in diets should be considered when formulating crayfish feeds.     

中华鳖日本品系对6种饲料蛋白原料表观消化率的研究

研究了中华鳖日本品系(Pelodiscus sinensis,Japanese strain)幼鳖对蝇蛆蛋白粉、虾壳粉、发酵豆粕、豌豆浓缩蛋白、大豆浓缩蛋白以及玉米蛋白粉的干物质、粗蛋白质、氨基酸、粗脂肪和总能的表观消化率。试验饲料由70%基础饲料和30%待测饲料原料组成,并以0.5%的三氧化二铬(Cr2O3)为外源指示剂。选取平均体重为(14.69±0.55)g的中华鳖日本品系幼鳖180只,随机分成6组,每组3个重复,每个重复10只,投喂试验饲料养殖4周,采用虹吸法收集粪便进行表观消化率测定。结果表明,6组饲料的干物质、粗蛋白质、粗脂肪以及总能表观消化率范围为77.8%~85.6%、73.2%~83.7%、81.2%~91.1%和78.8%~85.6%,其中蝇蛆蛋白粉和发酵豆粕的干物质表观消化率较高,大豆浓缩蛋白的粗蛋白、粗脂肪及总能表观消化率较高;各原料总氨基酸表观消化率在75.8%~86.1%,最高值和最低值分别出现在大豆浓缩蛋白和虾壳粉。     

Apparent Digestion Coefficients and Metabolizable Energy of Feed Ingredients for Rainbow Trout Oncorhynchus mykiss

More than 50 feedstuffs used or of potential use in diets for rainbow trout Oncorhyndus mykiss were compared through metabolism chamber trials. Testing included determination of apparent digestibility and metabolic energy for a wide variety of ingredients, including fish and animal meals, vegetable proteins, and single cell protein products. Testing involved feeding individual 200–300-g fish contained in replicate chambers, from which feces, urine, and gill excreta were collected seg arately and analyzed for residual nitrogen and energy. For comparison, several products previously tested at this or other laboratories were re-evaluated at dietary concentrations of 25, 50, or 100%.     

Effect of Diets Formulated with Native Peruvian Plants on Growth and Feeding Efficiency of Red Pacu (Piaractus brachypomus) Juveniles

We evaluated the effects of casein‐based semipurified diets, alone or supplemented with native Peruvian plants, on growth, feed efficiency, and histology of the digestive tract of red pacu, Piaractus brachypomus, juveniles over an 8‐wk feeding trial. Three tanks were randomly assigned to one of four casein–gelatin (40:8) diets containing a supplement of 15% wheat meal (control) or an identical level of substitution of three South American native plant as follows: camu‐camu fruit (Myrciaria dubia), aguaje fruit (Mauritia flexuosa), or maca tuber meal (Lepidium meyenii). The fish (initial weight, 2.04 ± 0.06 g) were fed experimental diets at decreasing feeding rates from 4 to 2.6% of body weight. After 8 weeks of feeding, fish fed a diet supplemented with maca meal showed significantly higher (P < 0.05) weight gain, specific growth rate, protein efficiency ratio (PER), apparent net protein utilization (NPU), and instantaneous feed intake than fish fed other diets. Feed conversion ratio (FCR), PER, and NPU in fish fed the casein–gelatin diet supplemented with maca meal were among the best ever reported in the scientific literature, 0.64 ± 0.03, 3.13 ± 0.15 and 23.8 ± 2.0, respectively. The camu‐camu meal had a negative impact on diet palatability and utilization, which resulted in slower growth. The stomach, intestine, pancreas, and pyloric caeca at the start and end of the experiment showed normal differentiation and appearance of cells and tissues. The liver parenchyma showed lipid infiltration and pigment accumulation in all samples at the initiation of the experiment and may be attributed to the period of decreased feed intake prior to the study. At the end of the study, similar histopathologies were recorded in all samples from the control and camu‐camu groups. Normal liver histology (polyhedral hepatocytes with centrally located nuclei) was observed in two of three samples from the maca group and all the samples from the group that was fed the aguaje‐supplemented diet.     

Apparent Digestibility of Different Ingredients in Diets for Bullfrog Rana catesbeiana Tadpoles

The objective of this study was to determine apparent digestibility of protein and energy of ingredients commonly present in rations fed to bullfrog tadpoles Rana catesbeiana such as corn, soybean meal, wheat meal, rice bran, poultry by-product meal, blood meal, fish meal, corn starch and soybean oil.
A completely randomized design was used to test ten experimental diets with four replicates. About 30% of the reference diet was replaced by the test ingredients, except for soybean oil that was used at 10% ratio and 0.5% of chromium oxide as inert marker. The values of apparent digestibility coefficient of crude protein (ADC_CP) and gross energy (ADC_GE) of the protein ingredients were, respectively: fish meal, 81 and 95%; poultry byproduct meal, 82 and 87%; blood meal, 64 and 53%; and soybean meal, 93 and 90%. While for the energetic ingredients, ADC_CP and ADC_GE, were, respectively: wheat meal, 100 and 72%; rice bran, 57 and 24%; and corn, 84 and 92%. Soybean oil and cornstarch ADC_GE values were 70 and 96%, respectively; cornstarch digestibility is highly dependent on feed processing technique.
The results showed that the ingredients of plant origin, except for rice bran, had good digestibility, thus indicating that tadpoles can effectively use plant protein. In this trial, the least digestible ingredients were blood meal and rice bran, thus indicating that the use of such ingredients in bullfrog tadpole diets should be limited.     

Co-Feeding of Pacu,Piaractus mesopotamicus Holmberg (1887), Larvae with Artemia Nauplii and a Microencapsulated Diet

Abstract

Aiming at a precocious substitution of live prey by artificial diet, a 20-day experiment with pacu, Piaractus mesopotamicuslarvae using co-feeding and abrupt weaning strategies was set up. At the end of the experiment, larvae fed Artemia showed the best results (P < 0.05) in weight, total length and biomass, compared with other treatments. Larvae fed exclusively a microencapsulated diet never ingested the diet. Diet ingestion in co-fed and abrupt-weaned larvae was low, but did increase during the experiment; however, Artemia influenced diet ingestion on co-fed larvae. Careful considerations should be given to diet processing and formulation to ensure survival and growth of larvae fed exclusively on prepared diets.     

Effects of Carbohydrate‐Rich Alternative Feedstuffs on Growth,Survival, Body Composition,Hematology, and Nonspecific Immune Response of Black Pacu,Colossoma macropomum,and Red Pacu,Piaractus brachypomus

To facilitate economical culture of black pacu, Colossoma macropomum, and red pacu, Piaractus brachypomus, in the Amazon region of South America, we assessed locally available alternative energy sources for practical diets. We tested the effects of control diets (containing wheat products) versus diets with different Amazonian feedstuffs (yucca, Manihot sculenta, plantain, Musa paradisiaca, or pijuayo, Bactris gasipaes) on the performance of the pacus in three feeding trials. Black pacu (22.5 ± 0.03 g; Trial 1) or red pacu (2.56 ± 0.01 g; Trial 2) were fed diets containing 30% wheat bran (control) or cooked or uncooked yucca, plantain, or pijuayo for 12 wk. In Trial 3, larger black pacu (86.9 ± 6.4 g) were grown to market size in 24 wk on similar diets. Weight gain, feed conversion, survival, alternative complement activity, and lysozyme were similar among diets. Hepatosomatic index, liver glycogen, and dry matter were affected by diet in Trials 1 and 2, but effects were not consistent among trials. In Trial 3, protein efficiency ratio was lower in fish fed the diet containing wheat middlings. However, relative to wheat bran or wheat middlings, all feedstuffs tested were effective energy sources for juvenile black pacu and red pacu.     

The Apparent Digestibility Coefficients of 13 Selected Animal Feedstuff for Cobia,Rachycentron canadum

The apparent digestibility coefficients (ADCs) of crude protein, lipid, phosphorous, and amino acids, as well as energy, of 13 animal feedstuffs were determined for cobia, Rachycentron canadum (initial weight 130.0 g). The feedstuffs tested included five types of fishmeal, two of blood meal, one of poultry meat meal, two of meat‐and‐bone meal, two of feather meal, and one type of shrimp meal. A reference diet was formulated and the test diets contained 70% of the reference diet and 30% of each feedstuff. The ADCs of crude protein, lipid, energy, phosphorous, and amino acids of the test ingredients ranged from 68.97 to 92.5%, 69.3 to 95.7%, 77.5 to 98.3%, 58.2 to 80.1%, and 72.5 to 97.0%, respectively. The ADCs of crude protein of white fishmeal, steam‐dried brown fishmeal, imported flame‐dried fishmeal, spray‐dried blood cells, poultry byproduct meal, meat‐bone meal, and meat meal were significantly higher than those of dried blood meal, fermented feather meal, and hydrolyzed feather meal (P < 0.05). The ADCs of lipid of dried blood meal and hydrolyzed feather meal were significantly lower than those of other feedstuffs (P < 0.05). The ADCs of energy of fermented feather meal and hydrolyzed feather meal were significantly lower than those of other feedstuffs (P < 0.05) and the ADCs of phosphorus of white fishmeal, steam‐dried brown fishmeal, and imported flame‐dried fishmeal were significantly higher than those of the other ingredients (P < 0.05).     

Apparent Digestibility Coefficients and Amino Acid Availability of Cricket Meal,Gryllus bimaculatus,and Fishmeal in African Catfish,Clarias gariepinus,Diet

A study was conducted on African catfish, Clarias gariepinus, to examine the apparent digestibility coefficient (ADC) of protein, dry matter, lipid, and energy, and the apparent availability coefficient (AAC) of essential amino acid (EAA) for a cricket meal (CM) diet, Gryllus bimaculatus, and fishmeal (FM). Both diets consisted of 30% isonitrogenous levels with a 70:30 ratio of basal diet to test ingredient. Chromic oxide (0.5%) was added to the diet as an inert marker. The ADCs of crude protein (CP) in CM (81.21%), lipid (89.82%), gross energy (64.42%), and dry matter (73.97%) was significantly higher (P < 0.05) than the value of CP (78.22%), lipid (82.03%), gross energy (56.52%), and dry matter (62.26%) in FM. All EAAs were present in both diets. The AACs for both diets ranged from 0.906 to 0.961 and 0.812 to 0.938 for the CM and FM diets, respectively. The growth performance of fish fed with CM exhibited significantly higher (P < 0.05) weight gain, feed conversion ratio, and protein efficiency ratio compared with FM. Overall, the results suggest that CM could be included in the African catfish diet without affecting their nutrient and amino acid digestibility as well as growth performance.     

花鱼骨 鱼种对11种蛋白质饲料原料的消化率

为获得花(鱼骨)对常用蛋白源的可消化性数据,按照"70%基础饲料+30%被测原料"的饲料配制方法,用三氧化二铬指标物,测定了花(鱼骨)鱼种对白鱼粉、褐鱼粉、四海豆粕、加佳豆粕、血粉、蚕蛹粉、啤酒酵母、菜籽粕、棉籽粕、花生粕、玉米蛋白粉等11种蛋白原料干物质和粗蛋白的表观消化率.结果表明:花(鱼骨)对11种原料的干物质和蛋白质表观消化率分别为54.84%～86.96%和69.17%～96.77%.其中自鱼粉、褐鱼粉、血粉以及豆粕、啤酒酵母等的干物质消化率较高,白鱼粉、褐鱼粉及豆粕、花生粕等的蛋白质消化率较高.     

Effect of dietary carbohydrates and lipids on growth in cachama (Piaractus brachypomus)

The effects of diets with three contents of carbohydrates and lipids were evaluated on the growing performance of cachama Piaractus brachypomus juveniles (initial weight 7.8 ± 0.49 g). The experiments were performed a 3 × 3 factorial design (200, 280 and 360 g of carbohydrates and 40, 80 and 120 g of lipids kg^?1). Protein content was kept constant in 320 g kg^?1 and digestible energy between 11.3 and 16.1 MJ kg^?1. Simple effects and interaction of factors on growth performance varied significantly (P < 0.05) indicating dependence among them. The maximum weight gain was observed in fish fed 200 and 280 g kg^?1 carbohydrates and 40 g kg^?1 lipids. Increase of lipids from 80 to 120 g kg^?1 reduced growth significantly. Protein efficiency rate and percentages of protein retention and energy were positively correlated with carbohydrate levels and no significant differences (P > 0.05) were observed with the lipid levels. Results indicate that cachama utilizes carbohydrates as energy source more efficiently than lipids; likewise, lipid levels over 40 g kg^?1 depress growth at any carbohydrates level.     

青鱼配合饲料中可消化能需要量的研究

以精制配合饲料投喂青鱼夏花鱼种,饲料中醣含量为30%固定值,改变蛋白质和脂肪含量,设计一个两因素、三水平的正交试验,研究青鱼配合饲料的可消化能(digestible energy)最适需要量。结果得出,每公斤饲料可消化能为3560～3911千卡,饲料可消化能量·蛋白比(DE/P)为9.77～11.8千卡/克蛋白最适宜;试验还证明,适当提高饲料中脂肪的含量,可获得节约饲料蛋白质的效果。     

Effects of Dietary Carbohydrase Supplementation on Performance and Apparent Digestibility Coefficients in Pacific White Shrimp,Litopenaeus vannamei

A growth trial and a digestibility trial were conducted to evaluate the efficacy of carbohydrase supplemented to practical shrimp feeds. The 5‐wk growth trial investigated the effects of carbohydrase supplementation at 0, 0.01, 0.02, 0.03, 0.04, and 0.05% in soybean‐based diets on the performance of juvenile Pacific white shrimp, Litopenaeus vannamei. No significant differences were observed in final biomass, final mean weight, weight gain, feed conversion ratio, and survival across all treatments. The digestibility trial was conducted to evaluate the effects of carbohydrase supplementation at 0.02%, which is the recommended dose by the company that developed the carbohydrase on apparent digestibility coefficients of dry matter, protein, and energy of Pacific white shrimp. Protein digestibility was significantly improved when fed diets contained 0.02% carbohydrase in contrast with the basal diet. No significant differences were found in apparent digestibility coefficients of dry matter and energy. Based on the positive results on protein digestibility, further research regarding the efficacy of exogenous enzymes and their application is warranted.     

Effects of Feeding Frequency on Apparent Energy and Nutrient Digestibility/Availability of Channel Catfish,Ictalurus punctatus,Reared at Optimal and Suboptimal Temperatures

This study examined the effects of feeding frequency (daily versus every other day [EOD]) on nutrient digestibility/availability of channel catfish, Ictalurus punctatus, reared at optimal (30 C) and suboptimal (24 C) temperatures. A 28% protein practical diet was used as the test diet, and chromic oxide was used at 0.75% of the diet as a maker. Twenty channel catfish of a mean weight of 141 g/fish were stocked into 12 flow‐through aquaria (110 L). Fish were fed daily or EOD to apparent satiation for 7 d before fecal samples were collected by the dissection method. Fish fed EOD to apparent satiation consumed more diet on days fed than those fed daily, and fish reared at 30 C consumed more diet than those reared at 24 C. Neither feeding frequency nor water temperature significantly affected apparent digestibility coefficients for energy and protein and apparent availability coefficients for total amino acids. Results show no advantage by feeding EOD over feeding daily on nutrient digestibility and diet utilization efficiency.     

Apparent Digestibility Coefficients of Nutrients and Nutritional Value of Poultry By-product Meals for Rainbow Trout Oncorhynchus mykiss Measured in vivo Using Settlement

Fish meal production is not growing worldwide, therefore, it is important to search for alternative protein sources. Three types of poultry by-product meals (feed grade, prime, and refined) and two fish meals (herring and menhaden) were mixed into a casein-gelatin purified reference diet at 30% to measure apparent digestibility coefficients (ADCs) for rainbow trout Oncorhynchus mykiss . A total of 90 fish (initial mean body weight 294.6 ± 10.7 g) were stocked into six 140-L fiberglass digestibility tanks at 15 fish per tank. Individual tanks were assigned randomly to each of the five experimental diets and the reference diet. Fecal collection by settlement lasted for 2 wk. Feces collected in each week represented a replicate, and they were analyzed separately. The ADCs of nutrients for herring meal, menhaden meal, feed grade poultry by-product meal, prime poultry by-product meal, and refined poultry by-product meal were: dry matter, 81.3, 70.9, 70.9, 71.5, and 74.5%, respectively ( P = 0.0168); crude protein, 89.8, 85.8, 83.1, 84.8, and 87.1%, respectively ( P = 0.0032); crude fat, 91.5, 90.7, 79.7, 82.7, and 79.9%, respectively ( P = 0.0004); ash, 76.6, 66.2, 74.1, 77.4, and 79.6%, respectively ( P = 0.2880); phosphorus, 58.2, 46.9, 49.4, 45.8, and 56.0%, respectively ( P = 0.0143); gross energy, 88.2, 84.0, 81.9, 83.4, and 79.8%, respectively ( P = 0.2466). Significant differences in ADCs of essential amino acid existed only for arginine, leucine, and tryptophan when comparing refined poultry by-product meal with herring meal. Results showed that refined poultry by-product meal had similar ADC values to herring meal, thus, it has a similar nutritional value and can replace portions of herring meal in rainbow trout feeds. Furthermore, differences exist in ADC values among grades of poultry by-product meals that should dictate appropriate use levels in rainbow trout feeds.