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.     

Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

Amino acid availability from selected animal‐ and plant‐ derived feedstuffs for market‐size sunshine bass (Morone chrysops × Morone saxatilis)

A study was conducted with market‐size (867 g) hybrid striped bass to determine the nutrient digestibility and apparent amino acid availability of six common feedstuffs. The animal‐protein feedstuffs tested were menhaden fish meal (MEN), anchovy fish meal (ANCH), pet‐food grade poultry by‐product meal (PBM‐pet), and feed‐grade poultry by‐product meal (PBM‐feed), while the plant‐protein feedstuffs were dehulled solvent extracted soybean meal (SBM) and distiller’s dried grains with solubles (DDGS). Test diets consisted of a 70 : 30 mixture of reference diet to test ingredient with chromic oxide (10 g kg^?1%) as the inert marker. Diets were randomly assigned to triplicate tanks of fish that were fed their respective diets for 7 days prior to fecal collection by stripping. Two feeding trials were conducted sequentially to determine the digestibility of the six test ingredients. In trial 1, the three ingredients evaluated were MEN, PBM‐feed, and PBM‐pet. In trial 2, the three ingredients evaluated were ANCH, SBM, and DDGS. Apparent digestibility coefficients of protein (ADC‐CP) were significantly (P < 0.05) different among test ingredients in trial 1 as protein digestibility of MEN (86%) was significantly higher (P < 0.05) than that of PBM‐feed (75%), but was not significantly different from that of PBM‐pet (78%). Protein digestibilities in trial 2 were not significantly different among test ingredients and averaged 76% for ANCH, SBM, and DDGS. Some apparent amino acid availability coefficients differed among feedstuffs for both trial 1 and trial 2. MEN provided higher amino acid availabilities for alanine, aspartic acid, glutamic acid, lysine, valine, and tryptophan (99%, 98%, 94%, 96%, 99%, and 108%, respectively) when compared to PBM‐feed (73%, 50%, 69%, 80%, 77%, and 91%, respectively) and PBM‐pet (79%, 66%, 81%, 81%, 78%, and 99% respectively). Glycine, histidine, leucine, and proline availabilities in MEN (95%, 96%, 100%, and 98%, respectively) were significantly (P < 0.05) higher than those of PBM‐feed (64%, 82%, 82%, and 57%, respectively), but were not significantly different from PBM‐pet (85%, 92%, 89%, and 80%, respectively). For trial 2, apparent amino acid availabilities for cystine, isoleucine, lysine, and tyrosine were significantly higher (P < 0.05) among treatments fed SBM (100%, 87%, 93%, and 97%, respectively) and ANCH (37%, 95%, 92%, and 84%, respectively) compared to treatments fed DDGS (?13%, 52%, 62% and 62%, respectively). Overall, amino acid availability in SBM and the two PBM’s appear comparable to MEN and ANCH and corroborate their high value as potential replacements for fish meal in sunshine bass diets. However, DDGS provided the lowest availabilities for several amino acids and should be used with caution.     

Different utilization of plant sources by the omnivores jundiá catfish (Rhamdia quelen) and Nile tilapia (Oreochromis niloticus)

Plant sources are receiving special attention as feedstuffs in aquafeeds because of fish meal and oil shortage. However, studies about the effects of dietary fibre in fish are scarce. The inclusion of plant ingredients containing different levels of dietary fibre – broken rice (BR), ground corn (GC), wheat bran (WB), citrus pulp (CP) and soybean hulls (SH) were evaluated for the omnivores jundiá catfish and Nile tilapia. Tilapia is a typical omnivore with long intestines, whereas jundiá has short intestines and no pyloric ceca. Fibrous sources (CP, WB and SH) were less digestible for both species than the starchy ones (BR and GC). However, jundiá presented less ability to utilize the starch and protein from plant sources than tilapia. Growth of tilapia followed plant sources digestibility but no significant differences were detected for jundiá, probably because of its slower growth rate. Muscle layer was thicker in the distal intestine of jundiá fed CP diet, which possibly indicates an adaptation to propel the large volume of viscous digesta along the intestine. Therefore, despite its lower ability to utilize starchy plant sources, jundiá showed an adaptive capacity to utilize fibrous diets, which is in agreement with its omnivorous feeding habit.     

Evaluation of soybean meal in the formulated diets for juvenile Pangasianodon hypophthalmus (Sauvage, 1878)

The influence of soybean meal (SBM) on the growth and feed utilization of juvenile sutchi catfish (Pangasianodon hypophthalmus, Sauvage, 1878) was investigated. Eight isonitrogenous (300 g kg^?1 CP) and isoenergetic (18 MJ kg^?1) diets were formulated incorporating Argentine SBM to replace fish meal at 0, 150, 300, 450, 600, 750, 900 and 1000 g kg^?1 dietary protein. Each diet was fed to three replicate groups of fish with an initial weight 6.0–6.2 g for twelve weeks. Growth performance decreased, and feed utilization was worsened with the increase in SBM inclusion in the diets. Final weight and relative growth rate (RGR) of fish fed control diet (0 SBM) were significantly higher than those fed test diets (P < 0.05). However, there were no significant differences in the final weight and RGR between the fish fed on 15 SBM, 30 SBM, 45 SBM and 60 SBM diets. Specific growth rate of fish fed 0 SBM, 15 SBM, 30 SBM and 45 SBM diets was significantly higher than those fed other diets. Feed conversion ratio of fish fed 0 SBM, 15 SBM, 30 SBM, 45 SBM and 60 SBM diets was significantly lower than those fed other diets (P < 0.05). The dry matter and protein digestibility were lesser in all the diets in comparison with the control diet. Hepatosomatic index and viscerosomatic index increased with increasing SBM in diet. This present trial indicated that fish meal can be replaced by SBM in the diet of juvenile sutchi catfish only up to 45% of fish meal protein without any adverse effect on growth, feed utilization and body composition.     

Growth and body composition of rohu (Labeo rohita) fed diets containing oilseed meals: partial or total replacement of fish meal with soybean meal

A 56‐day feeding trial was conducted to evaluate growth, feed utilization and body composition of fingerling rohu, Labeo rohita (4.5 ± 0.2 cm; 2.58 ± 0.04 g), fed five isonitrogenous (350 g kg^?1 crude protein) and isoenergetic (15.7 kJ g^?1 metabolizable energy) diets in which the main protein contributors were: diet I, fish meal (FM); diet II, soybean meal (SBM); diet III, groundnut meal (GNM); diet IV, equal amounts of SBM, GNM and canola meal (CM); diet V, equal amounts of FM, SBM, GNM and CM. Fish were stocked in triplicate groups of 25 fish held in 70 L flow‐through tanks (water volume 55 L) and fed twice daily (0900 and 1700 hrs) to apparent satiation. Fish fed diet I exhibited the highest (P < 0.05) values for live weight gain and specific growth rate (% per day). Feed conversion and protein efficiency ratio were better (P < 0.05) in fish‐fed diets I and II. Fish‐fed diet II exhibited lower (P < 0.05) fat and ash contents in carcass. Based on these findings, a 70‐day trial (Experiment II) was conducted with six diets fed under the same conditions where FM was incrementally replaced with SBM. Fingerling L. rohita (6.7 ± 0.4 cm; 4.07 ± 0.02 g) were used for the study. Crystalline l ‐methionine was added to diets containing more than 250 g kg^?1 SBM. This second study showed no significant (P > 0.05) variation in growth, feed utilization and carcass composition for fish fed the different diets. In conclusion, SBM was more effective than GNM or CM, as FM was replaced in feeds for fingerling L. rohita and could completely replace FM when supplemented with methionine and fortified with minerals under the conditions of this study.     

The in vitro efficacy of oxytetracycline against re‐isolated pathogenic Aeromonas hydrophila carrying the cytolytic enterotoxin gene through hybrid catfish,Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) in Thailand

Aeromonas hydrophila is a pathogen infecting farmed hybrid catfish, Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) which incurs substantial economic losses in Thailand. The study aimed at a genetic tracking of A. hydrophila infection and the in vitro assessment of the efficacy of antibiotics against its virulent strains. Five clinical strains from catfishes and Nile tilapia were employed. They were 3‐passage re‐isolated through healthy hybrid catfish and the cytolytic enterotoxin gene (AHCYTOEN) of individuals was traced. Each of the re‐isolates at a dose of ~6.67 × 10⁵ CFU/g was intraperitoneally injected into ~15 g‐healthy hybrid catfish and their pathogenicity were observed for 7 days. It was found that AHCYTOEN was carried over whereas typical signs of motile aeromonas septicaemia were found in the specimens. The bacterial strains of Nile tilapia origin did not induce mortality but those of catfish origins (80%–100% rate of mortality). The strains were susceptible to the tetracycline antibiotics, and oxytetracycline produced MIC₅₀ and MBC as low as 0.007–0.031 μg/ml and 1–8 μg/ml respectively. As oxytetracycline specifically inhibited pathogenic A. hydrophila in vitro, it is recommended that an appropriate dosage regimen of the drug should be established.     

Digestibility of dietary components and amino acids in animal and plant protein feed ingredients in striped catfish (Pangasianodon hypophthalmus) fingerlings

The apparent digestibility (AD) of dietary components, energy and essential amino acids (EAA) of selected locally available animal and plant protein feed ingredients in striped catfish (Pangasianodon hypophthalmus) fingerlings was studied. The AD of the test ingredients (ADi) differed (P < 0.05) and ranged from 81.1% to 90.8%, for ADi_DM, from 84.0% to 95.0% for ADi_CP, from 78.4% to 86.9% for ADi_OM and from 79.0% to 87.8% for ADi_GE. The highest ADi_DM, ADi_CP and ADi_OM in the test ingredients were found for shrimp head meal, catfish by‐product meal, golden apple snail and groundnut cake, while the lowest values were obtained for earthworm meal and rice bran. The highest ADi_GE was found in rice bran, followed by golden apple snail and catfish by‐product meal, while there were no differences (P < 0.05) between the other test ingredients, except for earthworm meal. The AD of total and individual EAA was high in catfish by‐product meal and shrimp head meal, followed by decreasing AD in golden apple snail, groundnut cake, rice bran and earthworm meal ingredients (P < 0.05). The low AD of earthworm meal may limit its potential to be used as replacement for fish meal in the feed.     

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.     

Effect of phytic acid on growth and nitrogen retention in tilapia Oreochromis niloticus L.

Two experiments were conducted to determine the effect of phytic acid on nitrogen retention in tilapia (Oreochromis niloticus). The first experiment utilized graded levels of soybean meal (SBM) with or without hydrolysis of phytic acid. The second experiment utilized diets containing graded levels of purified phytic acid. In the first experiment, weight gain was inversely related to SBM inclusion beyond 250 g kg^?1 of the crude protein (CP). Broken‐line and quadratic models were applied to the growth data. The models suggest limiting inclusion to 380 and 170 g kg^?1 CP for untreated and phytase treated SBM, respectively. The two SBM treatments exhibited similar trends in efficiency parameters. However, significant differences (P < 0.05) within treatments appeared when phytase treated SBM surpassed 250 g kg^?1 CP, but not until 750 g kg^?1 CP with untreated SBM. At similar rates of SBM incorporation, apparent net protein utilizations with untreated SBM were significantly higher beyond 250 g kg^?1 CP (P < 0.05). In the second experiment, phytic acid did not affect efficiency parameters until the concentration was twice that in diets incorporating SBM as 1000 g kg^?1 CP in a 330 g kg^?1 CP diet. Phytic acid does not reduce nitrogen retention in tilapia, and its removal from SBM may decrease nitrogen retention.     

The source of dietary non‐protein energy affects in vivo protein digestion in African catfish (Clarias gariepinus)

The development of chyme characteristics and the in vivo digestion of crude protein (CP) were assessed in response to different dietary sources of non‐protein energy. African catfish (Clarias gariepinus) were fed a starch or fat diet for 28 days, and faecal CP apparent digestibility coefficient (ADC) was determined by a marker method. After the consumption of a single meal, chyme was collected from four compartments of the gastrointestinal tract and viscosity, dry matter (DM), CP and marker concentration were measured. Replacing dietary fat by starch resulted in a lower faecal CP ADC (P < 0.05), even though CP originated from the same dietary ingredients. A higher inclusion level of starch led to a higher viscosity of chyme in the stomach, but a lower DM content, compared to the fat diet (P < 0.05). Gastric evacuation was delayed in starch fed fish, likely due to the high viscosity of chyme. After evacuation of chyme into the proximal intestine, no significant differences in chyme characteristics were observed between diets (P > 0.05). Changes in macronutrient composition can alter the environment in which CP digestion takes place. We suggest that for the formulation of highly digestible diets, the entire feed matrix needs to be considered, rather than single ingredients.     

Digestibility of dietary components and amino acids in plant protein feed ingredients in striped catfish (Pangasianodon hypophthalmus) fingerlings

The apparent digestibility (AD) of dietary components, energy and essential amino acids (EAA) of selected locally available plant protein feed ingredients in striped catfish (Pangasianodon hypophthalmus) fingerlings was studied. The AD of the test ingredients (ADi) differed (P < 0.05) and ranged from 66.2 to 89.6% for ADi_DM, from 63.6 to 91.3% for ADi_CP, from 65.4 to 85.3% for ADi_OM and from 69.8 to 89.3% for ADi_GE. The highest ADi_DM, ADi_OM and ADi_GE in the test ingredients was obtained for broken rice, maize meal and soybean meal, while the lowest values were obtained for duckweed meal. Soybean meal and duckweed meal had the highest ADi_CP, while there were no differences (P > 0.05) between the other test ingredients. The AD of total and individual EAA was higher in soybean meal, duckweed meal and broken rice than in the other test feed ingredients (P < 0.05). The lowest AD of individual EAA was found in maize meal, followed by cassava leaf meal and sweet potato leaf meal (P < 0.05). The low AD of individual plant feed ingredients may limit their potential to be used as replacement for fish meal in the feed.     

Evaluation of Distiller's Dried Grains with Solubles from Different Grain Sources as Dietary Protein for Hybrid Tilapia,Oreochromis niloticus (♀) × Oreochromis aureus (♂)

The effects of distiller's dried grains with solubles (DDGS) from different sources on growth performance, hematology, and immunity of hybrid tilapia, Oreochromis niloticus × Oreochromis aureus, were evaluated. Sex‐reversed, all‐male hybrid tilapia (3.72 ± 0.08 g initial weight) were fed diets in which 30% of protein in the control diet, supplied by a combination of soybean meal (SBM) and corn meal (CM) (SBM : CM ratio = 1.8), was replaced by wheat DDGS (WtDDGS), sorghum DDGS (SDDGS), whiskey DDGS (WkDDGS), or one of three corn DDGS (CDDGS 1–3) sources (control and six experimental diets) for 10 wk. Tilapia were stocked at 30 fish per aquaria (three aquaria per diet). Growth of tilapia fed diets containing DDGS sources was similar to or better than the control diet, and no nutritional deficiencies were observed. Tilapia fed the CDDGS 2 and 3 sources showed superior weight gain. Improved growth appeared to be caused by an increase in feed intake and not due to improvements in dietary nutritional value. Hematology and immunity were not affected by DDGS source. It is concluded that DDGS from all the sources examined can be included in the diet of juvenile hybrid tilapia at about 30% as a replacement of one‐third protein from SBM‐CM mixture without adverse effects.     

Total replacement of fish meal by soy bean meal, with various percentages of supplemental L-methionine, in diets for blue catfish, Ictalurus furcatus (Lesueur)

A 12-week feeding trial was conducted in aquaria with juvenile (8.9 g) blue catfish, Ictalurus furcatus (Lesueur), to examine effects of totally replacing fish meal with a high (65%) percentage of soy bean meal (SBM) in prepared diets. Five isonitrogenous (35% protein) and isocaloric (10.5 kJ digestible energy g^?1 of diet) diets were formulated. Diet 1 was similar to a high-quality commercial channel catfish diet, containing 15% fish meal and 42% SBM. Diets 2-5 contained 0% fish meal and 70% SBM with various amounts (0.0%. 0.3%, 0.6% and 0.9%) of L-methionine added. After 12 weeks, individual weight, weight gain, survival, specific growth rate, feed conversion ratio, protein efficiency ratio and food intake were not significantly different (P > 0.05) among treatments and averaged 36 g, 302%, 100%, 1.6% day^?1. 2.4,1.3, and 3.4% body weight, respectively. Whole-body compositions of fish were not significantly different (P > 0.05) among treatments and averaged 75%, 61% and 27% for percentage moisture, protein and fat, respectively. These data suggest that a diet with an all-plant protein source (SBM) can totally replace fish meal in a diet for blue catfish, without adverse affects on weight gain or body composition, when the dietary protein level is 35% and fish are fed to satiation.     

Utilization of genetically modified soybean meal in Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> diets

The utilization of genetically modified soybean meal (GM SBM) was compared with that of non-GM SBM in Nile tilapia. Four experimental diets were formulated to include either non-GM or GM SBM at 34 or 48%, respectively. These diets were fed to juvenile Nile tilapia (49.5 g average weight) for 12 weeks. The uptake of the cauliflower mosaic virus 35S promoter fragment of the GM SBM in fish muscle was examined at 8th and 12th week. After 12th week, fish were fed the non-GM SBM diets to determine the residual span of the incorporated promoter fragment. There was no significant difference in specific growth rate or feed efficiency between GM and non-GM groups at the same inclusion level. A small number of muscles from fish receiving both levels of GM SBM diet were positive for the promoter fragment. Additionally, the promoter fragment was not detected by the second day after changing to the non-GM SBM diets. These results indicate that the utilization of GM SBM was similar to that of non-GM SBM and the promoter fragment was rarely found in fish muscles, suggesting that suitability and safety of GM SBM in Nile tilapia diet were similar to those of non-GM SBM.     

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 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.     

Amino acid availability and protein digestibility of several protein sources for Nile tilapia,Oreochromis niloticus

Apparent amino acid availability coefficients and protein digestibility of four animal products [fish meal (FM), meat and bone meal (MBM), poultry by‐product and feather meal] and four plant protein‐rich products [soybean meal (SBM), cottonseed meal‐28, cottonseed meal‐38 and corn gluten meal (CGM)] were determined for Nile tilapia, Oreochromis niloticus. Ingredients were incorporated to a practical reference diet at a 7 : 3 ratio (70% of reference diet and 30% of test ingredient). Chromic oxide was used as external digestibility marker. Among animal products poultry by‐product meal (PBM; 89.7%) and FM (88.6%) presented the highest apparent protein digestibility (APD) while MBM (78.4%) and feather meal (78.5%) presented the lowest APD. Among plant protein‐rich products CGM (91.4%) and SBM (92.4%) presented the highest APD values while cottonseed meal‐28 presented the lowest APD (78.6%). Average apparent amino acid availability of feed ingredients was similar to protein digestibility with 92.3%, 89.6%, 73.4%, 80.7%, 88.9%, 84.4%, 91.2% and 79.7% values for SBM, CGM, cottonseed meal‐28 and 38, FM, MBM, PBM and feather meal respectively. These results indicate that O. niloticus is able to utilize efficiently different feedstuffs.     

Effect of DL‐methionine supplementation on the success of almost total replacement of fish meal with soybean meal in diets for hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

This study evaluated the effects of increasing levels of methionine (Met) supplementation on the success of almost total replacement of fish meal (FM) with soybean meal (SBM) in diets for hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus). Fish were fed for 70 days a FM‐based diet (Diet1‐positive control) or SBM‐based diets supplemented with graded levels of DL‐methionine (Diet2 to Diet7). Contrast in dietary Met, concentration was created by supplementing Diet2‐negative control with 1.2 (Diet3), 2.4 (Diet4), 3.6 (Diet5), 4.8 (Diet6) or 6.0 g kg^?1 (Diet7) of DL‐Met. Specific growth rate (SGR), feed conversion ratio (FCR), and protein gain and retention efficiency (PER) improved significantly with increasing levels of dietary DL‐Met supplementation. Moreover, nonlinear regression analysis of the effects of supplementing SBM‐based diet with graded levels of DL‐Met indicated that a dietary Met + Cys level of 15.7 and 12.5 g kg^?1 diet (as fed) was required to reach 95% of maximum weight and protein gain, respectively. Supplementation of SBM‐based diet with graded levels of DL‐Met proved an effective strategy in reducing FM content in practical diets for hybrid tilapia. Data also indicate that adjustment of dietary formulas according to currently recommended Met or Met + Cys dietary concentrations is probably limiting maximum growth potential of hybrid tilapia.     

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.