The Effect of Different Levels of Krill Meal Supplementation of Soybean-based Diets on Feed Intake, Digestibility, and Chemical Composition of Juvenile Nile Tilapia Oreochromis niloticus, L

Abstract— The main objective of this study was to determine the effect of different levels of krill meal (KM) as a feed attractant in juvenile Nile tilapia fed soybean (SBM) diets on growth performance, feed utilization, and body composition. Fish of an initial average weight 0.8 × 0.01g were stocked in 18 glass aquaria (80 L each) at a rate of 25 fish per aquarium. Fish meal (FM 20% of the diet) was used as the sole source of animal protein in the control (Diet 1). Diets 2 to 6 had (SBM) protein with various levels of krill meal (0.0,1.5,3.0,4.5, and 6.0%, diets 2-6 respectively). Test diets were fed to satiation to triplicate groups of Nile tilapia four times daily for 20 wk. Fish fed krill meal supplemented diets had significantly ( P < 0.05) better growth performance compared with fish fed the unsupplemented and FM control diets. The krill meal increased growth of Nile tilapia by 31.9% compared to control diets (average Anal wet weight, 14.15 × 0.95 g and 10.72 × 0.2 g, respectively). Moreover, weight gains were not significantly different for fish fed diets with different levels of krill meal. Feed utilization parameters such as feed intake, feed conversion ratio, protein efficiency ratio differed significantly for fish fed krill meal diets compared with control. Digestibility of nutrient and energy of diets increased with increasing levels of krii meal. The incorporation of krill meal in diets significantly affected the protein, fat, ash, and energy of whole body composition. These results suggest that supplementation of krill meal at 1.5% in the diets of Nile tilapia as attractant or stimulant may lead to increased feed intake, growth performance, and feed utilization. Soybean meal can completely replace fishmeal in diets for juvenile tilapia.     

Nutritional value of animal by-product meal in practical diets for Nile tilapia Oreochromis niloticus (L.) fry

Animal by-product meals (ABM) were substituted for fish meal in five experimental diets for Nile tilapia fry, Oreochromis niloticus (L), with 25%, 50%, 75% and 100% substitution. Two diets with 100% ABM were tested, one with 50:50 animal lipid:soybean oil, and the other with 100% fish oil as attractant. In general, the best growth and feeding performance was obtained with a control diet based on fish meal as the sole protein, but the results were not statistically different from those obtained with 75% and 100% ABM with soybean oil. A simple cost analysis suggested better economic efficiency when tilapia were fed with 100% ABM. It was concluded that animal by-product meal can be used as a sole protein source in commercial diets for Nile tilapia fry, without affecting growth and food utilization of the fish, improving the economics of feeding in comparison with fish meal.     

Effects of dietary protein on growth and body composition of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein (25%, 30%, 35%, 40% and 45%) on growth, survival, feed conversion ratio (FCR), protein efficiency ratio (PER) and body composition were investigated for four sizes (0.51, 45, 96 and 264 g) of Nile tilapia, Oreochromis niloticus L. In all four experiments, there was a progressive increase in growth with increasing dietary protein. In fry (0.51 g), significantly higher growth, survival and feed conversion were recorded for fish fed 40–45% rather than 25–35% protein diets. Similar trends for growth and FCR were also noted in 45 g fish. For larger (96 and 264 g) tilapia, significant differences in growth and FCR were found only between fish fed 25% and 30–45% protein diets. FCR and PER decreased with increasing weight of fish, and both were found to be negatively correlated with dietary protein level. Whole-body composition of the smallest fish was significantly influenced by dietary protein content. Percentage body protein of the fish fed 40–45% protein was higher than that of fish fed 25–35% protein diets, whereas lipid content decreased with increasing dietary protein level. In 45 g fish, both protein and lipid contents were higher in fish fed 25% and 30% protein diets than in those fed 35–45% protein diets. In larger tilapia, no significant influence of dietary protein level on body protein content was found. Percentage lipid decreased with increasing dietary protein level, and no definite trends in ash content were found. The results of these studies indicate that O. niloticus fry (0.51 g) should be reared on a practical diet containing 40% protein, and larger tilapia (96–264 g) on a diet containing 30% protein.     

Evaluation of Cow Pea Seed Meal,Vigna sinensis,as a Dietary Protein Replacer for Nile tilapia,Oreochromis niloticus (L.), Fingerlings

The main objectives of this study were to evaluate the effect of partial and total replacement of fish meal (FM) protein by cow pea seed meal (CPSM) protein in practical diets on growth performance, feed utilization, and body composition of Nile tilapia, Oreochromis niloticus (L.). Fish of an average initial weight of 4.6 ± 0.2 g were stocked in 15 glass aquariums (80 L each) at a rate of 15 fish per aquarium. FM protein (30% of the diet) was used as the sole source of animal protein in the control diet. Percent replacement of FM by CPSM on the basis of crude protein were as follows: 0% (control diet A), 25% (diet B), 50% (diet C), 75% (diet D), and 100% (diet E). Diets were fed to fish at a rate of 4% of the total fish biomass daily, for a period of 16 wk. The results of this study revealed that the fish fed control diet A (100% FM) had the best average final body weight, specific growth rate (SGR %/d), weight gain (g/fish), weight gain %, while the poorest results for all parameters were obtained with fish fed diet E (100% CPSM). The same parameters of fish fed diets B (25% CPSM) and C (50% CPSM) were not significantly different (P > 0.05) from those of fish fed the control diet A. Feed utilization parameters of fish fed diets A, B, C, and D were better than for diet E. Proximate composition of whole‐body moisture and ash contents were not significantly different (P > 0.05) among all experimental diets and control diet. Whole‐body protein contents for fish fed diets B and C were superior to the control diet A. Incorporation of CPSM in the diets significantly increased whole‐body fat content. Incorporation of CPSM in the diets significantly decreased apparent digestibility coefficient of crude protein crude fat and energy. Diets B and C were not significantly different from control diet A. Therefore, these findings suggest that up to 50% of FM protein can be replaced by CPSM protein in Nile tilapia diets without any adverse effects on growth performance, feed utilization, body composition, and digestibility.     

Use of cottonseed meal supplemented with iron for detoxification of gossypol as a total replacement of fish meal in Nile tilapia, Oreochromis niloticus (L.) diets

The objective of this study was to determine the effect of total replacement of fish meal by cottonseed meal (CSM) supplemented with various levels of iron in practical diets on growth performance, feed utilization, body composition and some biological and haematological parameters of Nile tilapia, Oreochromis niloticus (L.). Juvenile fish (average weight 3.78±0.1 g) were stocked in 18 glass aquariums (80 L each) at 25 fish per aquarium. Fish meal (50% of the diet) was used as the sole source of animal protein in the control diet 1. Diets 2–6 had 100% CSM (0.145% free gossypol) protein with various levels of supplemented iron (86, 486, 972, 1458 and 1944 mg Fe kg diet^?1) in diets 2–6 respectively. Diets were fed to fish twice daily at a rate of 3% of body weight during the first 12 weeks then 2% of the total fish biomass daily until the end of the experiment (30 weeks). The results of this study revealed that, groups of fish fed diets 1, 4, 5 and 6 had significantly (P≤0.01) the higher average body weight and specific growth rate than those of fish fed diet 2 (100% CSM without iron supplementation) and diet 3 (100% CSM plus 486 mg Fe kg diet^?1). The best values for feed conversion ratio, protein efficiency ratio and condition factor (K) were recorded with groups of fish fed diet 4 (100% CSM plus 972 mg Fe kg diet^?1). Red blood cell count, haematocrit and haemoglobin were increased with increasing levels of iron and significantly affected by dietary iron. Hepatosomatic index for diets 3–6 were not significantly different (P>0.05) and superior to that of diet 1 control [100% fish meal (FM)]. The gonadosomatic index of males of Nile tilapia was not influenced by CSM diets with or without iron, while females of Nile tilapia were significantly influenced with iron and the lowest values were recorded with groups of fish fed diet 2 (100% CSM without iron supplementation). Apparent digestibility coefficients of protein, fat dry matter and energy were relatively high for most diets supplemented with iron and increased by increasing iron supplementation. There were no significant differences between groups of fish fed diet 1 (100% FM) and diets 5 and 6 which contained 100% CSM with additional 1458 and 1944 mg Fe kg diet supplemental iron^?1 respectively. Proximate composition of whole body was not influenced by diet. Adding 972 mg Fe kg diet^?1 from ferrous sulphate to the CSM‐based diets that contained 972 mg free gossypol (1:1 iron to free gossypol ratio) for Nile tilapia reduce the negative effects of gossypol and improved growth performance, feed utilization and blood parameters and can totally replace fish meal in tilapia diets.     

Use of duckweed, Spirodela polyrrhiza L. Schleiden, as a protein feedstuff in practical diets for tilapia, Oreochromis niloticus L.

The use of solar-dried duckweed, Spirodela polyrrhiza L. Schleiden, as a dietary protein component for tilapia, Oreochromis niloticus L., reared in glass tanks was evaluated. Six isonitrogenous diets (30% crude protein) were fed to all-male tilapia fingerlings for 56 days. The fish meal protein in the diets was substituted at a rate of 5%, 10%, 20%, 30% and 100% with duckweed. A diet without the duckweed served as a control. Growth performance and nutrient utilization of fish were based on daily weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio and protein productive value. There were no significant differences (P > 0.05) in growth performance and nutrient utilization of fish fed on diets containing up to 20% duckweed inclusion and the control. However, increases in dietary duckweed inclusion resulted in progressively reduced growth performance and nutrient utilization of fish. Diet without fish meal (100% duckweed) gave the poorest result. The most cost-effective diet in terms of cost per unit gain in weight of fish was obtained with 30% duckweed dietary inclusion. The result showed that solar-dried up to 30% duckweed dietary inclusion as a replacement for fishmeal in practical diets supported fish growth and was cost-effective.     

Partial and complete replacement of fish meal with gambusia meal in diets for red tilapia 'Oreochromis niloticus × O. mossambicus'

A 12‐week experiment was conducted to evaluate the suitability of gambusia (Gambusia affinis) fish meal (GFM) as a partial and complete substitute for the protein supplied by herring fish meal (HFM) in diets for red tilapia fingerlings (mean weight 0.42 g). Seven isonitrogenous (35% crude protein), isolipidic (9% fat) and isoenergetic (15.9 kJ DE‐g^?1 diets were formulated in which GFM replaced 0.0, 10, 25, 50, 75, 90 and 100% of the protein supplied by HFM. In general, GFM exhibited good potential as a substitute for HFM in red tilapia diets with no adverse effects on growth, feed efficiency, body composition, blood parameters or apparent digestibility of dry matter, protein and gross energy compared with the HFM‐based control diet. Growth performance (in terms of final weight, weight gain, per cent increase in weight and growth rate) of fish fed diets containing GFM at 25 or 50% level of replacement for HFM‐protein (diets 3 and 4) was statistically higher than for fish fed diets containing GFM at replacement levels >50%. Diet 4 had the best economic efficiency of fish weight gain. Partial or complete substitution of GFM for HFM did not affect feed utilization efficiency (in terms of FCR, FER, PER and APU) or digestibility coefficients of dry matter, protein and gross energy compared with those of the HFM‐based diet. Apparent protein digestibility varied little between diets, ranging from 84.2 to 87.3% with no significant differences. Survival of fish fed all the experimental diets (except for fish fed GFM at 90 or 100% level of replacement for HFM‐protein) was comparable with that of fish fed the control diet and ranged from 91.7 to 98.3%.     

Evaluation of growth, feed utilization, and economics of hybrid tilapia, Oreochromis niloticus×Oreochromis aureus, fed diets containing different protein sources in combination with distillers dried grains with solubles

A feeding trial was conducted in aquaria with juvenile hybrid tilapia (Oreochromis niloticus×Oreochromis aureus) to evaluate the use of different protein sources in combination with distillers dried grains with solubles (DDGS). Twelve 110‐L glass aquaria were stocked with 28 juvenile (2.7±0.5‐g) hybrid tilapia per aquarium. Three replicate aquaria were randomly assigned to each of the four dietary treatments. Diets were isonitrogenous and isocaloric. The control diet contained 12% fish meal and 41% soybean meal as the primary protein sources (Diet 1). Each experimental diet contained 30% DDGS by weight, in combination with 8% fish meal and 34% soybean meal (Diet 2), 26% meat and bone meal (MBM), and 16% soybean meal (Diet 3), or 46% soybean meal alone (Diet 4). Fish were fed to apparent satiation twice a day for 10 weeks. There were no significant differences (P>0.05) in average weight gain, specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER) among tilapia fed Diets 1, 2, and 3. Fish fed Diet 4 had significantly lower (P<0.05) average weight gain, SGR, and PER than fish fed Diets 1 and 3. Relative cost per unit weight gain for Diets 1, 2, and 3 were statistically similar (P>0.05), while cost per unit weight gain for Diet 4 was significantly higher (P<0.05) than other diets. Diet 3 represented approximately a 20% cost savings compared with the control diet, with no reduction in growth. This study indicates that diets without fish meal containing 30% DDGS in combination with MBM and soybean meal provide good growth in tilapia. A diet without animal protein did not support acceptable growth.     

Evaluation of Gambusia, Gambusia affinis, Fish Meal in Practical Diets for Fry Nile Tilapia, Oreochromis niloticus

This study was conducted to evaluate the use of gambusia, Gambusia affinis, fish meal (GFM) in practical diets for fry Nile tilapia, Oreochromis niloticus (2.11 ± 0.11 g). Six isonitrogenous diets (35%) were formulated in which GFM replaced 0.0, 10, 25, 50, 75, or 100% of the protein supplied by herring fish meal (HFM). Fish were fed one of the test diets at a feeding rate of 4% of the fish body weight 6 d a week, 2 times a day for 13 wk. Results demonstrated that fish growth increased with increasing GFM up to 75%, which produced the highest growth of the treatments. The lowest fish growth was obtained at 100% GFM. Feed intake (FI), protein efficiency ratio (PER), and apparent protein utilization (APU) increased significantly, while feed conversion ratio (FCR) decreased significantly with increasing GFM up to 75%. FI, PER, and APU decreased significantly, while FCR increased significantly for diets containing 100% GFM. There were no significant differences in moisture, protein, lipid, or ash contents in final fish body following inclusion of GFM in fish diet. There was no significant difference in the digestibility coefficient of dry matter. The digestibility coefficients of protein and gross energy for diets containing 100% GFM replacement were the lowest as compared with other GFM levels. The present study recommended that GFM is a suitable protein source in practical diets for fry Nile tilapia and could replace HFM up to 75%.     

Complete Replacement of Fish Meal by Soybean Meal with Dietary L-Lysine Supplementation for Nile Tilapia Oreochromis niloticus (L.) Fingerlings

The effect of complete replacement of fish meal by soybean meal (SBM) with the dietary L-lysine supplementation in prepared diet was studied in Nile tilapia fingerlings. Five isonitrogenous (33.2% crude protein) and isocaloric (4.8 kcal gross energy/g of diet) diets were formulated. Diet 1 was similar to a high quality commercial tilapia diet, containing 20% fish meal and 30% SBM. Diets 2–5 contained 55%, 54%, 53%, and 52% SBM and 0.5%, 1.0%, 1.5%, and 2.0% L-lysine supplementation, respectively. After 10 wk, there was a significant difference in the final individual weight, final body length (cm), weight gain (%), specific growth rate (SGR), feed conversion ratio (FCR), protein effkiency ratio (PER), and food intake among flsh groups ( P ≤ 0.05). The best bal individual weight, final individual length (cm), weight gain (%), specific growth rate, feed conversion ratio, protein efficiency ratio (PER), and food intake were recorded in fish fed diet 2, which contained 55% SBM and 0.5% L-lysine. There was a significant difference between it and diet 1 (control). Moisture in fish flesh was not significantly different ( P > 0.05) among treatments and averaged 75.13%, while percentage protein was significantly dltrerent ( P ≤ 0.0% and the best result was achieved in flsh fed diet 2 and diet 1 (control). The highest values of digestibility coefficients of protein, fat and energy were recorded in groups of fish fed diet 2. These suggest that a diet with 55% SBM supplemented with 0.5% L-lysine can totally replace fish meal in a diet for Nile tilapia fingerlings, without adverse effect on fish performance.     

Effect of soybean meal diets on the growth performance,ammonia excretion rates,gut histology and feed cost of Nile tilapia (Oreochromis niloticus) fry

Aquaculture development in Ghana is currently limited by inadequate supply of fingerlings and prohibitive cost of commercial feeds among other challenges. This study tested the feasibility of using low‐cost feeds containing soybean meal instead of fishmeal for nursing Nile tilapia (Oreochromis niloticus) fry. Three isonitrogenous (~48% crude protein) and isoenergetic (~17 kJ/g) diets with increasing inclusions of soybean meal as partial replacements for fishmeal were formulated. A commercial fishmeal‐based fry feed served as the control diet. Triplicate groups of 225 fish per tank (average initial weight: 2.09 ± 0.14 g) were stocked in a recirculating aquaculture system and fed the experimental diets for 21 days. Afterwards, we investigated the postprandial metabolism, nutrient digestibility, growth and gut histology in Nile tilapia fry. Simple economic analyses were also conducted to assess the cost‐effectiveness of the diets used in the feed trial. The dietary inclusions of the soybean meal significantly reduced feed cost by ~43% relative to the control diet. The growth performance and feed utilization parameters did not vary significantly among the different treatments. The soybean diets elicited significant reductions in villi heights and goblet cell numbers, which corresponded with increasing dietary levels of soybean meal. This study confirms the potential of soybean meal as a partial replacement for fishmeal in Nile tilapia fry diets in terms of lower feed costs, fish growth performance, nutrient digestibility and postprandial nitrogenous excretions. The inclusion of soybean, however, affected negatively the gut integrity of the fry.     

Evaluation of different protein sources in fingerling grey mullet <Emphasis Type="Italic">Mugil cephalus</Emphasis> practical diets

An eight-week experiment was carried out to evaluate the effects of different protein sources (fish and haemoglobin meal, soybean meal and torula yeast), in practical diets, on growth, body composition and gut morphology of fingerling grey mullet (Mugil cephalus). Weight gain (%), SGR, FCR, N retention, PER, PGR, FDR and carcass composition of fish were not significantly affected by the dietary protein source. Fish fed the torula yeast based diet showed reduction in growth performance. Histological examinations performed on the alimentary tract of the fish showed a normal structural pattern in the experimental groups, as fundamental histological and histochemical aspects were similar if compared to the control group. The lower growth performance observed in fish fed a torula yeast based diet may be tentatively correlated with the presence of some detrimental morpho-functional aspects in the gut of these fish if compared to fish fed the other diets. Further studies are necessary to confirm this hypothesis.     

Complementary responses between hydrolyzed feather meal,fish meal and soybean meal without amino acid supplementation in Nile tilapia Oreochromis niloticus diets

The purpose of this study was to evaluate hydrolyzed feather meal (HFM) as a substitute for fish meal (FM) or soybean meal (SBM) in Nile tilapia fry diets. Triplicate groups of fish (initial body weight 2.30 g ± 0.01) were fed seven isonitrogenous and isocaloric diets formulated to contain 30 % crude protein and 19.70 kJ g^?1 gross energy for 8 weeks. The control diet (CD) contained 22 % local FM and 30 % SBM, whereas in the other six diets, HFM replaced 33, 66 or 100 % of FM or SBM. The best weight gain (11.46), specific growth rate (3.14) and feed conversion ratio (1.24) of tilapia fry fed SBM_33%, CD, FM_33% and SBM_66% diets were exhibited. Final body weight and protein retention increased in a linear pattern with increasing amino acids in the experimental diets with the exception of leucine and valine. The results indicated that good-quality HFM can successfully replace FM or SBM by up to 33 and 66 %, respectively, in Nile tilapia fry diets without compromising growth and protein utilization. The results also support the benefits of combining different sources of plant and animal proteins in Nile tilapia diets.     

Effect of replacing soybean meal with canola meal on growth,feed utilization and haematological indices of juvenile hybrid tilapia,Oreochromis niloticus×Oreochromis aureus

An 8‐week feeding trial was conducted to evaluate the effects of replacing soybean meal (SBM) with canola meal (CM) on growth, feed utilization, body composition and haematological indices of juvenile hybrid tilapia (Oreochromis niloticus×Oreochromis aureus). Six isonitrogenous diets containing graded levels of CM (0, 95, 190, 285, 380 and 634 g kg^?1 of diet corresponding to 0%, 15%, 30%, 45%, 60% and 100%, respectively, of protein from SBM) to replace SBM on an equal protein basis were fed to triplicate groups of juvenile fish (initial weight=6.3 g). The results indicated that up to 30% of SBM could be replaced by CM without causing a significant reduction in growth performance. Fish fed with diets in which CM replaced over 45% of SBM had a significantly lower protein efficiency ratio and a significantly higher feed conversion ratio than fish fed with other diets. The apparent digestibility coefficients (ADC) of dry matter, protein and phosphorus were lowest for fish fed the CM100 diet. Significant differences in haemoglobin, haematocrit and white blood cell concentration were found in fish fed diets with different CM levels. It is concluded that up to 19.02% CM can be used to replace 30% of SBM in diets for juvenile hybrid tilapia without compromising growth, feed conversion and protein utilization.     

The Effects of Plant-protein-based Diets Supplemented with Yucca on Growth, Digestibility, and Chemical Composition of Nile Tilapia (Oreochromis niloticus, L) Fingerlings

Replacement of fish meal (FM) protein with dehulled and solvent‐extracted plant by‐products, soybean meal, cottonseed meal, sunflower meal, and linseed meal was tested in diets for juvenile Nile tilapia, Oreochromis niloticus. Fish averaging (±SD) 14.2 ± 2.9 g were divided into 18 groups and fed for 6 mo on pelleted feed containing each of the plant protein meal supplemented with Yucca schidigera powder extract at 750 mg/kg. Methionine (1%) and lysine (0.5%) were added to each diet except the control diet (FMC), while diet FMC + Y was supplemented with yucca only. Three groups of fish were fed each of six isonitrogenous (25% crude protein) and isocaloric (4.3 kcal/g) diets replacing 100% of FM protein and performance compared against a nutritionally balanced control and a commercial tilapia feed. After 6 mo of feeding, the fish fed plant protein diets supplemented with yucca exhibited growth performance not differing significantly from that of fish fed FMC + Y, while differing significantly from the control FMC and diet linseed meal (LSM). The highest apparent protein digestibility coefficient was observed for diets treated with yucca, which was significantly higher than that observed for the control diet FMC. No significant differences were found in whole‐body moisture of fish fed different experimental diets. An increase in the whole‐body protein content was observed in fish fed diets supplemented with yucca, which was significantly different from that of the diet FMC. The whole‐body fat content of Nile tilapia was low and showed significant differences among treatments supplemented with yucca compared with the control diet FMC. The whole‐body energy content showed the same trend as whole‐body fat content.     

Growth performance and feed utilization of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) and tilapia galilae Sarotherodon galilaeus (Linnaeus, 1758) fingerlings fed plant protein-based diets

This study was designed to determine the effect of complete substitution of fish meal (FM) by three plant protein sources including extruded soybean meal (SBM), extruded full‐fat soybean (FFSB) and corn gluten meal (CGM) on growth and feed utilization of Nile tilapia Oreochromis niloticus and tilapia galilae Sarothrodon galilaeus. Four isonitrogenous of crude protein (ca. 28.0%) and isocaloric (ca. 19 MJ kg⁻¹) experimental diets were formulated. The control diet (diet 1) was prepared with FM as the main protein sources. Diets 2–4, each FM control diet, were completely substituted with SBM (diet 2), FFSB (diet 3) and CGM (diet 4). l ‐lysine and dl ‐methionine were added to plant protein diets to cover the nutritional requirements of tilapia. Each treatment was allocated to three net pens and fed for 17 weeks. Nile tilapia fed the control diet showed significantly higher (P≤0.05) values for final body weight (FBW), feed intake (FI), weight gain (WG) and specific growth rate (SGR), whereas fish fed the diet with CGM achieved the lowest values. Tilapia galilae fed SBM diet recorded the highest (P≤0.05) values for growth performance. Better feed conversion ratio (FCR) for both Oreochromis niloticus and Sarothrodon galilaeus was observed when fish were fed SBM diet, whereas the worse FCR was recorded for FFSB diet. Feed utilization parameters including protein productive value (PPV), fat retention (FR) and energy retention (ER) showed significant differences (P≤0.05) for both the species fed different dietary protein sources. The present results suggest that, for Nile tilapia, both SBM and FFSB supplemented with dl ‐methionine and l ‐lysine can completely replace dietary FM. Meanwhile, S. galilaeus fed SBM diet exhibited comparable growth and feed utilization with those fish fed a fish‐meal‐based diet.     

Growth and Body Composition of Nile Tilapia,Oreochromis niloticus,Fry Fed Organic Diets Containing Yeast Extract and Soybean Meal as Replacements for Fish Meal,with and without Supplemental Lysine and Methionine

Quantities of fish meal (FM) have remained level for the past several decades; however, demand has dramatically increased because of its inclusion in all animal production as a high‐quality protein source. Soybean meal (SBM) is the most widely used plant‐protein ingredient for replacing various proportions of FM in aquatic animal diets. However, use of SBM as the sole protein source has often resulted in reduced fish growth. There is a growing segment of consumers who desire organically grown seafood, and tilapia is one of the most‐cultured fish in the world. As tilapia have herbivorous/omnivorous feeding habits, tilapia fed organic diets may allow producers to enter this rapidly developing market. A feeding experiment was conducted to evaluate the combination of organic SBM and an organic yeast extract (YE) as complete replacements for FM in Nile tilapia, Oreochromis niloticus, fry diets. Nine diets were formulated to contain various percentages of organic YE (0, 15, 30, and 45%) in combination with organic SBM (84–34%) with and without amino acid (methionine and lysine) supplementation. At the conclusion of the study, fry fed a control diet containing 20% FM and fry fed a diet containing 45% YE/36%SBM with amino acid supplementation showed no significant differences (P > 0.05) in final weight, weight gain, and specific growth rate (SGR) compared to those fed all other diets. On the basis of these data, an organic diet which replaces FM with a combination of SBM and YE with added methionine and lysine is commercially feasible and further investigation into the increased use of these two ingredients as protein sources in aquaculture diets is warranted.     

Replacement of Fish Meal by Plant Proteins in the Diet of Nile Tilapia: Digestibility and Growth Performance

Apparent digestibility coefficient (ADC) values for a number of ingredients of plant or animal origin were obtained in order to formulate diets based on such values and to evaluate growth performance of Nile tilapia Oreochromis niloticus fed four experimental diets in which fish meal was gradually replaced by a mixture of other ingredients.The digestibility of various diet components was measured by using an inert marker in the feed and by using the Guelph faeces collecting system. ADC values of the ingredients tested were generally high, especially for fish meal. It was found that extruded pea seed meal (92.6%), defatted soybean meal (94.4%), full-fat toasted soybean (90.0%) and micronized wheat (88.6%) were the best vegetable proteins tested. Lupin seed meal and faba bean meal had similar ADC values for protein and energy.Groups of tilapia, initial mean body weight (SD) 6.7 (0.1) g, were fed experimental diets with the same digestible protein (DP) and digestible energy (DE) containing graded levels of a mixture of vegetable ingredients as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks as partial or total replacement of fish meal protein. A growth trial was conducted over 12 weeks at a water temperature of 25 °C. Significant differences were observed for weight gain among tilapia fed diets D0, D33, D66 and D100 (containing only animal protein, 33, 66, and 100% of plant protein, respectively). No significant differences were observed for voluntary intake among tilapia fed diets D0, D33 and D66. These values were significantly lower than those observed for tilapia fed plant protein based diet (D100) and suggest the possibility of partial replacement of fish meal by vegetable proteins without negative effects.     

Interactive effects of dietary protein and live bakery yeast, Saccharomyces cerevisiae on growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection

Yeasts used as a probiotic in fish diets could stimulate fish resistance against bacterial infection and could enhance the activities of digestive enzymes in fish guts. In addition to yeast importance, dietary protein is another important part in fish diets that should be carefully optimized to meet fish requirement. It is proposed that the yeast supplementation may enhance the dietary protein turnover and reduce the protein requirement for fish. Therefore, the interactive effects of dietary protein and yeast levels on the growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection was evaluated. In the present study, ten experimental diets were formulated to contain either 35% or 45% crude protein (CP). For each protein level treatment, bakery yeast (Saccharomyces cerevisiae) was supplemented at 0.0, 0.50, 1.0, 2.0, or 5.0 g/kg diet. Fish (0.25–0.48 g) were distributed at a rate of 25 fish per 140-L aquarium. For each diet, triplicate aquaria were fed twice a day, 5 days a week for 12 weeks. Fish growth and feed utilization were significantly affected by either dietary protein or yeast levels alone, while no significant effect of their interaction was observed. The highest fish growth was obtained at 1.0–5.0 g yeast/kg diet at both protein levels; however, the fish performance at 45% CP was better than that fed on 35% CP diets. The optimum feed conversion ratio (FCR) was obtained when fish fed on 1.0–5.0 and 2.0–5.0 g yeast/kg diet at 35 and 45% CP, respectively. The cumulative fish mortality, after interperitoneal injection with A. hydrophila for 10 days, and bactericidal activity was significantly higher in fish fed 35% CP diets than those fed 45% CP diets. Both variables decreased significantly with the increase in yeast levels. The lowest bacterial count and bactericidal activity were obtained in fish fed 5.0 g yeast/kg diet irrespective to dietary protein levels. It could be concluded that the inclusion of live bakery yeast in practical diets could improve the growth performances, feed utilization, and physiological status of Nile tilapia fry and their challenge against A. hydrophila infection. Moreover, fish performance when fed 45% CP diet was better than those fed 35% CP diet. Based on these results, the most suitable yeast level for maximum Nile tilapia growth was determined to be 2.0 g yeast/kg diet with 45% CP diet; however, this level was recommended to stimulate their productive performance and enhances their resistance against A. hydrophila infection.     

Sunflower seed meal as a protein source in diets for Tilapia rendalli (Boulanger, 1896) fingerlings

This study tested the use of sunflower seed meal as a dietary protein replacement for fishmeal in practical diets for tilapia fingerlings. In order to determine the optimum substitution level for this species, sunflower seed meal was used to replace 10%, 20%, 30%, 40% and 50% of the fishmeal protein in diets containing 40% protein overall. During a 70‐day feeding period, diets containing 10% and 20% plant protein provided the best growth and feeding efficiency results, with values statistically similar to those of the control diet based on fishmeal as the sole protein. The unitary feeding cost index showed the highest profit with diets containing 20% sunflower seed meal. Growth depletion observed with diets containing higher sunflower seed meal percentages is explained by increasing Phe and Met deficiencies, and high non‐digestible fibre content. It was concluded that sunflower seed meal is a suitable feed ingredient for tilapia complete diets when it constitutes up to 20% of the dietary protein.