Effect of gelatinization degree and inclusion level of dietary starch on the characteristics of digesta and faeces in Nile tilapia (Oreochromis niloticus (L.))

Higher faeces removal efficiency can help and reduce the negative impact of faecal waste on water quality and on the environment. Physicochemical properties of feed ingredients/nutrients may change the faeces characteristics and the ratio of removed to non-removed solids. The aim of this study was to assess what physicochemical properties of the diet (viscosity, fermentation and dry matter) influence faeces characteristics and faeces removal using Oreochromis niloticus (L.) as the test animal. Four experimental diets were formulated by the addition of two types of starch differing in gelatinization degree (gelatinized and native) and two levels (high and low) of starch to a basal diet according to a 2 × 2 factorial design. The diets were assigned to 16 tanks with 40 fish each, with four replicates for each diet. Replacement of native starch by gelatinized starch improved faeces removal rate, growth and digestibility (P < 0.01), but reduced fermentation (P < 0.05) at the end of the intestine. Addition of gelatinized starch did not change viscosity and dry matter of the digesta at the end of the intestine. A high level of starch in the diet also increased digestibility, growth and faeces removal percentage (P < 0.05). Fermentation and dry matter content at the end of the intestine were not influenced by a high starch diet, but viscosity was higher at the high level of starch inclusion. Volatile fatty acid levels in the stomach of Nile tilapia were high in the treatments with gelatinized starch. In conclusion, intestinal fermentation induced by native starch had a negative impact on faeces removal efficiency. A higher inclusion level of starch resulted in a higher viscosity of the digesta, leading to higher faeces removal efficiency.     

Type of dietary fibre (soluble versus insoluble) influences digestion, faeces characteristics and faecal waste production in Nile tilapia (Oreochromis niloticus L.)

The physico‐chemical properties of nutrients influence the physical characteristics of faeces and thus may affect waste removal efficiency. The aim of this study is to assess the effect of type of non‐starch polysaccharide (NSP) on digesta viscosity, faeces recovery and nutrient digestibility in Nile tilapia. Insoluble (cellulose) and soluble (guar gum) NSPs were included separately and combined at a level of 8%, thereby formulating four experimental diets. The diets were assigned to 16 tanks with 35 fish each, with four replicates for each diet. Cellulose inclusion did not influence digesta viscosity, growth and digestibility of protein and starch and tended to increase faeces recovery (P=0.06). Guar gum inclusion increased digesta viscosity and reduced the growth and digestibility of protein, fat and starch (P<0.01). Faeces recovery was reduced by 42% in diets containing guar gum. There were interaction effects (P<0.05) between cellulose and guar gum for the growth and feed conversion ratio, indicating that cellulose alleviated the negative impact of guar gum. In conclusion, dietary soluble NSPs increase organic matter load in the culture system through a reduction in faeces recovery and nutrient digestibility, whereas insoluble NSPs improve the removal efficiency of particles by increasing faeces recovery.     

Nutrient digestibilities and gut function in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar), kept in saltwater, were fed fish meal based cold-pelleted diets where graded levels of native or extruded non-starch polysaccharides (NSP) from soybeans replaced cellulose, at a total NSP level of 100 g kg^− 1 for 28 days. The study also included a diet where defatted soybean meal (SBM) constituted the NSP at a level of 100 g kg^− 1 and a reference diet without NSP supplementation.The SBM diet resulted in a significant reduction in faecal dry matter content, apparent digestibilities of starch and organic material, and growth, and an increased faecal output of several elements (K, Na, Zn), compared to all the other diets. Morphological changes were only seen in the intestine of the fish fed the SBM, i.e. the diets holding purified soy-NSP did not induce enteritis. When compared to the diet without NSP, cellulose addition increased faecal dry matter, while inclusion of native soy-NSP reduced it. Dry matter in faeces and apparent digestibility of crude protein decreased in a linear manner, while the digestibility of starch and faecal output of K and Na increased linearly when native soy-NSP replaced graded levels of cellulose from 0 to 100 g kg^− 1 feed. When diets with 75 or 100 g kg^− 1 of native NSP and extruded soy-NSP were compared, fish fed native soy-NSP had reduced faecal dry matter, higher digestibility of starch, and increased faecal output of Cu, Fe, and K. Dry matter in faeces and faecal output of Cu was lower for the highest inclusion level, while digestibility of starch and faecal output of Mn and K were higher.In conclusion, soy-NSP was inert compared to the fish meal reference, with respect to nutrient digestibilities and intestinal pathologies, but affected faecal mineral excretion in Atlantic salmon.     

Effects of a dietary organic acids blend and oxytetracycline on the growth,nutrient utilization and total cultivable gut microbiota of the red hybrid tilapia,Oreochromis sp., and resistance to Streptococcus agalactiae

A 20‐week feeding trial was conducted to measure growth, nutrient utilization and faecal/gut bacterial counts in triplicate groups of red hybrid tilapia, Oreochromis sp., when fed diets supplemented with 0.5% organic acids blend (OAB), 1.0% OAB, 0.5% oxytetracycline (OTC) or a control diet (no additives). At the end of the feeding trial, tilapia were challenged with Streptococcus agalactiae for 22 days. Fish fed the OTC diet had significantly higher (P < 0.05) growth than the control treatment, while growth between fish fed the OTC or OAB diets was not significantly different (P > 0.05). Phosphorus, dry matter and ash digestibility were significantly higher in the 1.0% OAB diet than the control diet. Fish fed the OAB diets had significantly lower colony‐forming units of adherent gut bacteria compared to the control or OTC treatments while those fed the 1.0% OAB diet had the lowest total faecal bacterial counts. Tilapia fed the 0.5% OTC or OAB diet had significantly higher resistance to S. agalactiae than those fed the control diet. This study indicates that dietary organic acids can potentially replace OTC as a growth promoter and antimicrobial in tilapia feeds.     

Effect of ingredient particle sizes and dietary viscosity on digestion and faecal waste of striped catfish (Pangasianodon hypophthalmus)

The ingredients’ particle size and dietary viscosity may alter digestion, performance and faecal waste management of fish. This study aimed to assess the effect of grinding screen sizes of feed ingredients and dietary viscosity on digestibility, faecal waste and performance of striped catfish (Pangasianodon hypophthalmus, Sauvage, 1878). The experiment had a 2 × 3 factorial‐design: two feed mesh particle sizes, by grinding ingredient mixtures at two screen sizes (0.8 versus 1.0 mm); and three dietary viscosity levels, created by exchanging carboxymethylcellulose by guar gum (GG) (0, 3 and 6 g of GG/kg of diet). Six diets were assigned to 18 tanks, each connected to three faecal settling tanks. All aquaria were stocked with 20 fish (82 g per fish). After 52 experimental days, dietary viscosity negatively affected both feed digestibility and performance of striped catfish; as a result, the amount of organic matter in the culture system through faeces had increased significantly. The coarse diets significantly increased the digestibility of dry matter and carbohydrate but worsened feed conversion ratio. Increasing dietary viscosity tended to increase the viscosity and moisture content of the faeces, but significantly accelerated the faecal disintegration through the reduction of both faecal recovery and the amount of recovered faeces.     

Cork and guar gum supplementation enhanced the buoyancy of faeces,and protease supplementation alleviated the negative effects of dietary cork on growth and intestinal health of tilapia,Oreochromis niloticus × O. aureus

To evaluate the effects of dietary cork, protease and guar gum on growth, intestinal health and faecal floatability of tilapia, fine or coarse particle cork (0.45–0.60 mm, 0.60–0.83 mm) was included in diets at 0 (control), 20 g/kg, 30 g/kg and 40 g/kg, and then, 0.175 g/kg protease (P) and 3 g/kg guar gum (G) were supplemented to the 40 g/kg coarse particle diet individually or in combination (P + G). Tilapia with an initial body weight of 15.0 ± 0.5 g were fed one of the 10 diets for 60 days. The results showed that weight gain (WG), apparent digestibility coefficient (ADC) of dry matter (DM) and crude protein (CP), intestinal evacuation ratio, intestinal digestive enzyme activity (IDE) and villus height decreased, and floating faeces ratio increased with the increasing cork level in diets. At the same supplementation level, coarse particle groups showed significantly higher floating faecal ratio than fine particle groups (p < .05). Dietary protease increased the WG, ADC of DM, IDE and villus height (p < .05), and guar gum increased floating faecal ratio when compared to 40 g/kg coarse particle group (p < .05). However, the ADC of DM, IDE and villus height of protease group were still inferior to those of control group (p < .05). In conclusion, dietary cork increased the floating faeces ratio, and the coarse particles produced more floating faeces than fine particles. Moreover, the supplementation of guar gum in cork‐supplemented diet further increased the floating faeces ratio. However, dietary cork negatively affected the growth performance of tilapia, which could be partially alleviated by the supplementation of protease.     

The effect of plant protein‐based diets on apparent nutrient digestibility,growth response,egesta quantity,postprandial ammonia excretion rate and serum quality of Nile tilapia

The study assessed the effect of oilseed meal mixtures on the biological value, faecal matter output, ammonia excretion rates and serum biochemistry of Nile tilapia over 63 days. The experimental diets (PPB 1, PPB 2 and PPB 3) were formulated using four selected oilseed meals that were mixed in different protein proportions to contribute 80% of total dietary crude protein. In each diet, either one or two of the oilseed meals were the dominant protein contributor. A commercial tilapia feed was used as the control diet (CTRL). Sex‐reversed Nile tilapia fingerlings (35 g) were stocked at 20 fish per tank in a recirculation system and fed at 3% body weight of their respective diets. At the end of the study, ADCs of dry matter, crude lipid and ash were significantly (p < .05) lower in all the plant‐based diets compared with the control diet. Fish fed the control diet had significantly higher weight gain and SGR compared with the plant‐based diets. Egesta output was 127% higher in the plant‐based diets compared with the control diet. All dietary treatments exhibited a similar trend in changes in ammonia nitrogen. Nevertheless, serum metabolites levels indicated no significant differences among treatments. Although the PPBs did not affect ADC of protein and serum profile, fish growth was reduced while faecal output increased.     

Digestibility of starch in Penaeus vannamei: in vivo and in vitro study on eight samples of various origin

Apparent digestibility coefficients (ADC) of carbohydrate, protein and lipid were investigated in Penaeus vannamei (18–25 g) with diets containing eight starches of various origin. Test ingredients, included at a level of 35% of diet, were native (NC) or gelatinized (GC) corn starch, waxy corn starch, either native (XC) or gelatinized (GX), high amylose corn starch (AC), potato starch, either native (NP) or gelatinized (GP), and native wheat starch (NW). Experimental diets differed only in the type of starch. Chromic oxide was included as a marker. On each starch sample, water solubility index (WSI) was determined and in vitro digestibility assays were carried out with shrimp digestive gland homogenates in order to evaluate correlations between criteria. In vitro digestibility was estimated as the initial rate of hydrolysis (IRH) in micrograms of reducing units per minute per microgram of substrate in glucose equivalents. Starch ADC ranged from 63.1 (AC) to 95.8% (GX), WSI ranged from 0.06 (NP) to 0.69% (XC) for native starch and from 55 (GX) to 85% (GP) for gelatinized starch, while IRH was between 17 (AC) and 89.10⁻⁴ μg min⁻¹ μg⁻¹ (GC). Significant differences (P < 0.05) appeared within each of the parameters depending on the source of dietary starch; in vitro tests were significantly (P < 0.05) correlated with each other as was IRH with starch ADC (y = 8.0 In(10⁴x) + 59.0; R² = 0.81; x representing IRH). IRH appeared to be more suitable than WSI to predict in vivo digestibility for starch. Protein and lipid ADC which ranged from 94.1 to 97.8% and from 76.6 to 84.8%, respectively, were also significantly affected, thus indicating some associative effects.     

The effect of carbohydrate source, inclusion level of gelatinised starch, feed binder and fishmeal particle size on the apparent digestibility of formulated diets for spiny lobster juveniles, Jasus edwardsii

The development of cost-effective and digestible formulated diets is essential for the commercialisation of spiny lobster aquaculture. Large juvenile spiny lobsters, Jasus edwardsii (115 g), were used to measure the apparent digestibility of formulated diets with six different carbohydrate sources, three levels of gelatinised starch, three types of binder, and two ranges of particle size of fishmeal. Carbohydrate source, inclusion level and binder type all had a significant effect on the dry matter digestibility (ranging 61–79%) of formulated diets for J. edwardsii. The digestibility of the carbohydrates included at 35% by dry weight were: dextrin (99%), carboxymethyl cellulose (CMC; ~ 94%), native wheat starch (91%), gelatinised maize starch (84%), native potato (60%) and maize (59%) starches. Gelatinised maize starch inclusion level (ranging from 15% to 55% by dry weight) was negatively correlated with starch digestibility (ranging from 92% to 79% respectively). Dry matter digestibility of the diets was improved by using gelatine (73%) instead of alginate (68%) and agar (61%) as a binder. Nitrogen digestibility (ranging 82–89%) did not differ significantly among diets. Reducing the particle size distribution of the fishmeal from < 500 µm to < 106 µm did not improve digestibility. The results indicate that using digestible carbohydrate sources (dextrin, CMC, and native wheat starch) for energy, reducing the inclusion level of gelatinised starch, and using CMC or gelatine as binders improve the apparent digestibility of formulated diets. Furthermore, the results also indicate that the use of more soluble and pre-hydrolysed protein sources in diets for J. edwardsii may greatly improve digestibility which is critical in these spiny lobsters where overall food intake is limited.     

Availability of minerals in rendered meat and bone meal for Nile tilapia: Preliminary observations

A digestibility trial was conducted with 180 Nile tilapia (32.65 ± 4.52 g) fed a reference diet containing 350 g/kg crude protein and 4,500 kcal/kg gross energy. Five different meat and bone meals (MBMs) were evaluated. The test diets compound by 70% of reference diet and 30% of each MBM were elaborated and classified according to ash content: MBM‐430, MBM‐400, MBM‐370, MBM‐340 and MBM‐310. The apparent availability coefficient (AAC) of minerals and the apparent digestibility coefficient (ADC) of dry matter (DM) were subjected to one‐way analysis of variance (p < .05). Differences among ADC and AAC were determined by Tukey's multiple range test (p < .05). When appropriate, a polynomial regression analysis was performed. Linear correlation analyses between MBM chemical composition and the AAC and ADC were performed (p < .01). Higher values of ADC_DM, AAC_Ca and AAC_P were observed in MBM‐310, while low values were observed in MBM‐430. Quadratic effects of ash, P and Ca contents on AAC_Ca, AAC_P and ADC_DM were observed. The AAC_Ca, AAC_P and ADC_DM indicated a negative correlation with ash, P and Ca contents. MBM‐310 exhibited the highest mineral AAC, which could be used as a mineral source for Nile tilapia.     

Mesquite bean (Prosopis juliflora) meal in diets of Nile tilapia (Oreochromis niloticus): Nutritional value,growth, physiological responses and health

Two experiments were conducted to assess the nutritional value and potential use of mesquite bean (Prosopis juliflora) meal (MBM) to substitute corn in extruded diets for Nile tilapia (Oreochromis niloticus). Digestible energy and the content of protein, soluble carbohydrates and amino acids were measured for 160 Nile tilapia juveniles (average weight 25.58 ± 5.52 g), allocated to eight treatment groups (four fed the experimental diet, and four fed a reference diet). To determine the inclusion potential of MBM, 384 fish (average weight 21.85 ± 1.01 g) were used and allocated to 24 tanks (1,000 L capacity). The experimental design was completely randomized with six levels of substitution (0%, 20%, 40%, 60%, 80% and 100%), and four repetitions. After the feeding experiment, tissue samples (blood, liver, muscle and intestine) were used to analyse metabolic and haematological variables. MBM produced apparent digestibility coefficients (ADC) similar to those of traditional diet ingredients: 81.85% dry matter (DM), 83.02% crude energy, 88.57% crude protein, 82.88% lysine and 82.57% methionine. Differences were observed in the digestibility of soluble carbohydrates (p < 0.05), with MBM having higher levels of starch (72.19%) and sucrose (88.99%). A 20% substitution with MBM produced a decrease in zootechnical performance (p < 0.05). Enzymatic activity of amylase and sucrose seemed to be induced in response to the proportion of their respective substrate in the diets. We observed a reduction in the efficiency of dietary protein utilization, with reduced levels of plasma amino acids (p < 0.05), owing to the increase in the enzymatic activity of muscular alanine and aspartate transaminases (ALT and AST) and the deaminase glutamate dehydrogenase in the hepatic and muscular tissues. Haematological variables did not indicate any adverse effects of MBM on the health status or survival of the fish (100%). Therefore, we conclude that MBM may be a viable alternative to corn meal in the diet, enabling substitution of up to 20%.     

Growth performance, feed utilization, and body composition of Nile tilapia (Oreochromis niloticus L.) fed with differently heated soybean-meal-based diets

This study was undertaken in order to determine the effect of feeding heat-treated, defatted soybean meal (SBM) on growth, feed utilization, and body composition of Nile tilapia (Oreochromis niloticus). A control diet (SBM₀) of 378 g kg⁻¹ crude protein with 18.4 kJ g⁻¹ gross energy was formulated, and three diets identical to the basal diet were autoclaved for 10, 20, or 30 min. The autoclaved diets were named SBM₁₀, SBM₂₀, and SBM₃₀, respectively. Each diet treatment was applied to triplicate groups of 30 fish (2.45 ± 0.03 g) per tank (120 l). The fish were hand fed to satiation four times daily for 45 days. At the end of the feeding trial the fish fed with the SBM₃₀ diet had significantly (P < 0.05) higher weight gain and protein efficiency ratio than those fed with the other diets. No feed-related mortality was observed during the whole experimental period. Heating SBM for 30 min reduced trypsin inhibitor activity (TIA) and increased apparent protein digestibility (APD), and indicated significant differences (P < 0.05) among various treatments. No significant differences were found in carcass moisture, lipid, and ash of fish fed with different experimental diets. An increase in the body protein content of fish fed with diet SBM₃₀ was significantly (P < 0.05) higher than in all other experimental groups. The results of this study seem to indicate that autoclaving the SBM for 30 min improved its nutritional value in practical feeds for Nile tilapia fingerlings.     

Apparent Protein and Energy Digestibility and Amino Acid Availability of Corn and Co‐products in Extruded Diets for Nile Tilapia,Oreochromis niloticus

We assessed the nutritional value of corn in extruded diets for Nile tilapia, Oreochromis niloticus, by determining the apparent digestibility coefficients of dry matter, crude protein, and gross energy, and by measuring the apparent availability coefficients (AACs) of essential and non‐essential amino acids (AAs) in several corn‐based diets. We fed 180 juvenile Nile tilapia a reference diet containing 325.8 g/kg crude protein and 4613 kcal/kg gross energy or a test diet containing a 70:30 mixture of the reference diet and a test ingredient (whole corn, corn germ, corn germ meal, corn gluten feed, or corn gluten meal). The apparent digestibility coefficients ranged from 56.3 to 96.6% (dry matter), 89.4 to 96.8% (crude protein), and 59.0 to 95.4% (gross energy). The AACs of all AAs exceeded 80% for all diets and were >90% for corn gluten meal. All ingredients showed high levels of apparent digestibility for crude protein and high AACs of AAs. Diets based on whole corn or corn gluten meal showed higher digestibility values for dry matter and gross energy, suggesting that they are preferable choices for Nile tilapia.     

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.     

Dietary Oil Sources on the Innate Immunity and Resistance of Nile Tilapia,Oreochromis niloticus,to Streptococcus agalactiae Challenge

The effect of different dietary oil sources on the innate immunity and resistance of Nile tilapia, Oreochromis niloticus, to Streptococcus agalactiae infection were evaluated. Fish were fed with diets containing different lipid sources (soybean oil [SO], corn oil, linseed oil [LO], fish oil [FO], and olive oil [OO]). Fish fed SO presented the highest (P < 0.05) hematocrit and serum protein. LO and FO diets increased (P < 0.05) the erythrocyte resistance to osmotic lysis in comparison with other treatments. Fish fed OO showed the highest (P < 0.05) iron‐binding capacity and the lowest serum lysozyme and bactericidal activities (P < 0.05). No difference (P > 0.05) was found between diets in alternative complement activity. Fish fed the SO diet had the highest (P < 0.05) survival rate against S. agalactiae challenge. In conclusion, diets with LO oil and FO, rich in ω‐3 fatty acids, and OO, rich in ω‐9 fatty acids, have an immunomodulatory effect in Nile tilapia juveniles. The use of SO in the Nile tilapia diet improved immune function and resistance against S. agalactiae.     

Nutrient Digestibility of Reduced‐Soybean‐Meal Diets Containing Moringa or Leucaena Leaf Meals for Nile tilapia,Oreochromis niloticus

Vegetable leaf meals are cheaper feed ingredients than soybean meal (SBM) in developing countries, and leaf meals are less important as human food. We evaluated the nutrient digestibility of practical diets containing reduced levels of SBM in combination with leaf meals made from Moringa oleifera and Leucaena leucocephala in Nile tilapia, Oreochromis niloticus. Five isonitrogenous diets (32% crude protein) were made: the control diet contained 50% SBM, and the test diets were made by substituting 15 or 30% of SBM protein with either Moringa or Leucaena. Dry matter, protein, and lipid digestibility decreased with increasing Moringa or Leucaena in the diet. Protein and lipid digestibility were high across diets (75–90%). Ash digestibility of the control diet was similar to that of both Moringa diets, while the ash digestibility of the Leucaena diets was lower than other diets. Overall, nutrient digestibilities of Moringa diets exceeded those of Leucaena diets. Dry matter, protein, and lipid digestibilities decreased with increasing dietary fiber, which increased with increasing leaf meals. Ash digestibility was generally low for all diets. Better digestibility of practical diets containing Moringa compared to Leucaena indicates greater potential for Moringa to replace SBM in Nile tilapia diets without compromising fish performance.     

Comparison of faecal collection method with high- and low-quality diets regarding digestibility and faeces characteristics measurements in Nile tilapia

The need for unbiased digestibility estimation has led to the development of a number of faeces collection methods. However, there is still a large variation in apparent digestibility coefficient (ADC) of diet/ingredients between these methods. This study investigated the impact of dietary quality on ADC and faeces recovery measurements obtained by two faecal collection methods (Choubert and settling tank). The fish were fed five diets: a control diet as high‐quality diet, two levels of dried duckweed (20% and 40%) and two levels of fresh duckweed (20% and 40%), which were added to the control diet, as low‐quality diets. Apparent digestibility coefficient estimates were highly correlated (r>0.95) between both faecal collection methods. For all diets the ADC estimates were higher when using settling tanks compared with Choubert collectors. For the control diet differences in ADC between two collectors were small, but by inclusion of duckweed these differences increased. The recovery percentage of faeces was not correlated between both faecal collection methods (r=0.22, P=0.41). The estimated recovery percentage of faeces by settling tanks was about three times higher than by Choubert. In conclusion, the differences in ADC and faeces recovery measured by two faecal collection methods depend on diet quality.     

Growth performance,digestibility, and blood biochemical parameters of Nile tilapia (Oreochromis niloticus) reared in floating cages and fed poultry by-product meal

ABSTRACT

A 120-day feeding trial was conducted in floating cages to evaluate growth performance and digestibility of Nile tilapia (Oreochromis niloticus) juveniles fed diets containing different levels of poultry by-product meal (PBM) as a replacement for fishmeal. Nile Tilapia with an average body weight of 56.6 ± 0.28 g were used in this experiment. Five diets were formulated to contain graded levels of PBM at 0%, 5%, 10%, 20%, and 30% poultry by-product meal (PBM) and are referred as PBM0, PBM5, PBM10, PBM20, and PBM30, respectively. Groups of 25 Nile tilapia were fed close to the apparent satiation, three times a day. The results showed that growth performance, survival and whole-body composition for fish fed the experimental diets were not significantly different (P > .05) than fish fed the control diet. Apparent digestibility of dry matter, protein, lipid and amino acids of fish fed the PBM20 and PBM30 were lower compared to the other treatments (P < .05). The PBM dietary levels significantly lowered total protein, high-density-lipoprotein (HDL) and cholesterol concentration. The results of this study indicated that good quality PBM can be used up to 30% in commercial diets for Nile tilapia without any adverse effect.     

Effect of non‐starch polysaccharide composition and enzyme supplementation on growth performance and nutrient digestibility in Nile tilapia (Oreochromis niloticus)

The experiment investigated whether the effect of enzyme supplementation on performance and nutrient digestibility is dependent on type of the ingredient(s) used, by incorporating wheat bran (WB), sunflower meal (SFM) and citrus pulp (CP) to a reference diet (REF). Those ingredients are known to be rich in different types of non‐starch polysaccharides (NSP). Diets were supplemented with and without (control) an enzyme mix (phytase 1,000 FTU/kg and xylanase U/kg) according to a 2 × 4 factorial arrangement. In total, 24 tanks (3 replicates/treatment) were used with 30 fish each (Nile tilapia, Oreochromis niloticus; mean initial body weight 41 g). Fish were restrictively fed the experimental diets for 43 days (80% of expected satiation). Enzyme supplementation affected the absolute growth (g/day) and FCR (p < 0.05), improving the growth of fish fed the WB and SFM diets, while fish fed the REF and CP diets did not benefit. NSP, energy, ash, phosphorous and calcium digestibility improved with enzyme supplementation (p < 0.05). There was an interaction effect on all growth parameters, as well as the digestibility of energy and phosphorus (p < 0.05). This indicates that the effectiveness of the enzymes was dependent on the NSP‐rich ingredient used and thus the composition of the NSP fraction.     

Digestibility, faeces recovery, and related carbon, nitrogen and phosphorus balances of five feed ingredients evaluated as fishmeal alternatives in Nile tilapia, Oreochromis niloticus L.

This study shows that alternatives for fishmeal in a fish diet affect not only fish growth but also faeces stability and nitrogen (N) and phosphorus (P) waste production. Wheat gluten diet (WGD), soybean meal extract diet (SBE), soybean meal diet (SBM), duckweed diet (DWD) and single‐cell protein diet (SCP) were evaluated as a fishmeal replacement on a 15% weight weight^?1 basis in tilapia diets. Fishmeal replacement affected dry matter (dm), protein, ash and P digestibility significantly. Faeces recovery (6.8–11.2%) was not significantly affected, although the amount of non‐recovered faeces and total faeces showed significant differences. Duckweed diet and SCP resulted in the largest amounts of non‐recovered and total faeces (199–210, 224–225 g dm kg^?1 feed dm). Compared with fishmeal diet (FMD), the WGD and SBE resulted in similar growth, but higher non‐faecal N losses (471–495 vs. 416 g N kg^?1 N). Soybean meal diet, DWD and SCP resulted in lower growth but less non‐faecal loss (409–450 g N kg^?1 N). The DWD and FMD had the highest N retention (480 g N kg^?1 N) compared with the other diets (431–451 g N kg^?1 N). Carbon retention, faecal and non‐faecal losses and P retention were similar for all diets (302–358, 142–176 and 489–523g C kg^?1 C, 606–704 g P kg^?1 P). Phosphorus faecal loss was lower for all diets (329–381 g P kg^?1 P) than for the FMD (401 g P kg^?1 P).