Substitution of fish meal with sunflower seed meal in diets for Nile tilapia (Oreochromis niloticus L.) reared in earthen ponds

This study investigated sunflower seed meal (SSM) as dietary protein replacement of fish meal (FM) for Nile tilapia (Oreochromis niloticus) juveniles (initial mean weight of 19.8 ± 6.3 g) reared in earthen ponds for 210 days. SSM replaced 25%, 50%, 75%, and 100% (i.e., D₂₅, D₅₀, D₇₅, and D₁₀₀, respectively) of FM in an isonitrogenous and isocaloric diet. The optimum FM replacement level of D₂₅ as predicted by the equation y = 177.5 + 26.5x – 7.9x² yielded an optimum weight of about 184 g within 100 days. Thus D₂₅ was the most effective SSM level for Nile tilapia growth in earthen ponds. Fish growth declined as SSM exceeded D₂₅. The length-weight relationship (r ≥ 90%) depicted an isometric fish growth. Nutrient utilization parameters were similar in all the diets except for D₁₀₀. The protein content of fish carcass was highest in the control and D₂₅, while fiber level was highest in D₁₀₀. Amino acids imbalance and high fiber content could have reduced the fish growth at D₅₀, D₇₅, and D₁₀₀.     

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.     

Potential of the use of peanut (Arachis hypogaea) leaf meal as a partial replacement for fish meal in diets for Nile tilapia (Oreochromis niloticus L.)

The rapid growth of tilapia culture has stimulated the expansion of tilapia feed production and a search for novel protein sources to replace fish meal. Vegetable or plant sources are promising alternatives and legumes are both naturally abundant and high in protein content. A study was carried out to evaluate the effects of replacing the protein from fish meal with peanut ( Arachis hypogaea ) leaf meal (PLM) in diets for male tilapia ( Oreochromis niloticus , initial body weight 75.3 g). Four isonitrogenous (35% CP) and isocaloric (18.834 kJ g⁻¹) diets were prepared to include 0% (CON), 10% (PLM10), 20% (PLM20) and 30% (PLM30) of PLM protein. Average fish weights at the end of the 126-day experiment were not statistically different among the fish fed CON, PLM10 and PLM20 diets. The PLM30 diet produced the poorest growth performance. Organic matter and protein contents of fish were similar in the CON, PLM10 and PLM20 diets. Carcass chemical composition showed a decrease in body fat content as PLM replacement levels increased. The high survival ratio in all dietary groups (>97%) suggests that PLM can be used in O. niloticus feeds for long periods without affecting fish growth performance or health.     

Replacement of fish meal with a mixture of different plant protein sources in juvenile Nile tilapia, Oreochromis niloticus (L.) diets

A plant protein mixture (PPM) was tested to replace fish meal (FM) in diets for juvenile Nile tilapia, Oreochromis niloticus. Fish averaging (±SD) 3.7±0.14 g were divided into 15 groups. Three groups were fed each of five isonitrogenous (33.6%) and isocaloric (4.7 kcal g^?1) diets replacing 0%, 25%, 50%, 75% and 100% of the FM protein with similar percentages of PPM (PPM0, PPM25, PPM50, PPM75 or PPM100 respectively). The PPM consisted of 25% soybean meal, 25% cottonseed meal, 25% sunflower meal and 25% linseed meal, and 0.5% of both methionine and lysine were added to each diet except for the control. After 16 weeks of feeding, the fish fed diets PPM75 and PPM100 exhibited growth performance not differing significantly from the fish fed control diet. PPM substitution of up to 75% of the FM protein did not result in differences in the apparent protein digestibility compared with the control, whereas in the PPM100 group digestibility was significantly lower than in the other groups, except for fish fed the PPM75 diet. The incorporation of PPM in diets did not significantly affect whole‐body dry matter, protein, fat or energy compared with the control. The cost–benefit analyses of the test diets indicated that the PPM diets were economically superior to FM. The protein from PPM can completely replace the FM protein in the diets for Nile tilapia, based on the results of this study.     

Effects of substituting fish meal with Azolla pinnata in practical diets for fingerling and adult Nile tilapia, Oreochromis niloticus (L.)

Abstract. Dry and fresh Azolla pinnata were evaluated as feed ingredients for fingerling and adult Nile tilapia, Oreochromis niloticus (L.). Dry Azolla was incorporated into practical diets containing approximately 30% crude protein and 360–400kcal/lOOg of GE lo replace 25,50,75 and 100% of the fish meal (FM) protein in the control diet. Fresh Azolla was also tested as a total diet for these fish. Formulated diets were fed to duplicate groups of fingerling (2–54g ± 0093) and adult (4033g ± 103) fish at a daily rate of 5% and 3% of their body weight respectively for 10 weeks. Growth and feed utilization efficiency of fish fed the control diet were significantly higher than of those fed Azolla-supplemented diets. Fish performance continued to deteriorate with increasing dietary Azolla level in the diets. This reduction was extremely sharp when dry and fresh Azolla were used as total diets. Furthermore, adult tilapia fed fresh Azolla started losing weight from the 7th week. Fish fed fresh Azolla had significantly higher moisture content than those fed formulated diets. Body protein and lipid contents were negatively correlated with Azolla levels in the diets, while body ash content showed a positive correlation. Results of this study indicate that young Nile tilapia utilizes Azolla more efficiently than the adults.     

Salmon testes meal as a functional feed additive in fish meal and plant protein‐based diets for rainbow trout (Oncorhynchus mykiss Walbaum) and Nile tilapia (Oreochromis niloticus L.) fry

Fishery processing by‐products are a large resource from which to produce fishmeal and other products for a variety of uses. In this study, testes meal (TM) produced from pink salmon processing by‐product was evaluated as a functional ingredient in aquafeeds. Nile tilapia and rainbow trout fry were fed five isonitrogenous and isoenergetic experimental diets for 4 and 9 weeks respectively. Two diets were fishmeal‐based (FM) and three were plant protein‐based (PP). Salmon TM was added to the FM and PP diets at 7% to replace 20% of fishmeal protein (FMTM and PPTM respectively). An additional control diet was prepared in which fishmeal was added to the PP diet to supply an equivalent amount of protein as supplied by TM (PPFM). Inclusion of TM in both the FM‐ and PP‐based diets resulted in higher final body weights, although differences were only significant between rainbow trout fed FM or FMTM diets. Similar differences were calculated for other indices of fish performance, e.g. specific growth rate, feed conversion ratio, protein efficiency ratio and protein retention efficiency. Feed intake was significantly higher for fish fed FMTM compared with FM in rainbow trout. For tilapia, final weights were numerically higher, but not significantly different for fish fed diets containing TM compared with non‐TM diets (FM vs. FMTM; PP vs. PPTM). Performance of trout or tilapia fed the PPFM diet did not increase compared with the PP diet. The results indicate that TM addition to both FM and PP diets increased feed intake and also increased metabolic efficiency, demonstrating that TM can be a functional ingredient in aquafeeds.     

Effects of cellulase addition to canola meal in tilapia (Oreochromis niloticus L.) diets

The effects of commercial cellulase enzyme products on the nutritive value of canola meal (CM) were determined in tilapia fry. Nine diets were prepared by adding cellulase enzyme (1–5 g kg^?1) to control diet (containing no canola), low canola (41.7 g kg^?1 CM) and high canola (208.3 g kg^?1 CM). Tilapia fry was fed for 90 days, and growth, feed conversion ratio (FCR), body composition and nutrient digestibility were determined. Fish fed the diets containing the lowest levels of canola meal (41.7 g kg^?1) had similar final weight and FCR relative to the group fed the control diet, and high canola diet showed significantly lower growth than other groups (P < 0.05), irrespective of cellulase enzyme. The addition of canola meal to tilapia diets resulted in lower protein digestibility and cellulose digestibility. There were no significant differences in body compositions in all treatments. Addition of enzymes to canola meal diets had no significant effects on growth performance, body compositions and nutrient digestibility. The results of this study indicate that use in higher level of canola meal in tilapia diet was adversely affected growth parameters and FCR. Adding dietary cellulase enzyme in different rations to diets showed no significant differences in growth parameter.     

Partial and complete replacement of fish meal by broad bean meal in feeds for Nile tilapia, Oreochromis niloticus, L., fry

A 16‐week feeding experiment was conducted to study the feasibility of using broad bean meal (BBM) as a replacement for fish meal (FM) for Nile tilapia Oreochromis niloticus fry, initial average weight 1.9±0.18 g. FM (50% of the diet) was used as sole sources of animal protein in the control diet 1. The replacement levels of BBM in diets (2–5) were 25%, 50%, 75% and 100% of the FM. Methionine (1%) and lysine (0.5%) were added to each diet except the control diet. Three groups of fish were fed each of five isonitrogenous (31.2% CP) and isocaloric (20.1 kJ g^?1), and performance was compared against a nutritionally balanced control diet at the end of the experiment. Nile tilapia fed the diet containing 50% BBM exhibited comparable growth with those fed the FM‐based control diet. Digestibility of protein, energy and lipid decreased with increasing levels of BBM above 50% of total replacement FM into the diet. Incorporation of BBM in the diets significantly affected the moisture, fat and energy of whole fish body. These results suggest that BBM can replace 50% of the FM in diet for Nile tilapia fry, without adverse effects on fish performance.     

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.     

Haematological response and growth performance of Nile tilapia (Oreochromis niloticus L.) fed diets containing folic acid

Haematological response and growth performance over 150 days, and resistance to a low-temperature stress of Nile tilapia fed diets with increasing folic acid (FA) levels were evaluated. The experiment was conducted in a completely randomized design with eight FA levels (0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 mg kg⁻¹ feed) supplemented in purified diets (32.0% CP and 13 398 kj DE kg⁻¹). One hundred and ninety-two fingerlings were randomly assigned to 32 net cages distributed in eight 1000 L aquaria with a physical and biological filter and a temperature control system (26.0 ± 1.0 °C). For cold-induced stress, fish were transferred to 24 30 L-aquaria with individual biofilters and aeration. The water temperature was gradually reduced until it reached 13 °C. Haematological parameters evaluated before and after cold stress were total erythrocytes and leucocytes count, differential leucocyte, haemoglobin, haematocrit, total plasmatic protein and haematometric indices. Growth performance parameters were mean weight gain, feed conversion ratio and survival. Dietary FA supplementation did not influence erythropoiesis under normal temperature conditions; cold stress impaired erythropoiesis, causing hypochromic microcytic anaemia and leucopoiesis, and also neutrophilia. Growth performance is influenced by folate and supplementation between 0.5 and 1.0 mg FA kg⁻¹ diet, which makes up for nutritional demands, guaranteeing production and health under appropriate temperature conditions.     

Effects of stocking density and feeding levels on growth and feed efficiency of Nile tilapia (Oreochromis niloticus L.) fry

The effects of stocking density and feeding levels on larval survival, growth rates, feed utilization efficiency and body composition of Nile tilapia (Oreochromis niloticus L.) fry were investigated in two consecutive experiments. In experiment 1, swimup fry (0.016 g average body weight) were stocked in 20‐L fibreglass tanks, in a closed, recirculating indoor system, at five stocking densities (3, 5, 10, 15 and 20 fry L^?1) and fed a larval test diet (40% crude protein) to apparent satiation, three times a day, for 40 days. Fish survival, percentage weight gain and specific growth rate (% SGR) were negatively correlated with stocking density. The best performance was achieved at 3 fry L^?1. However, no significant differences in growth parameters were found between 3 and 5 fry L^?1. Body composition was not significantly affected by stocking density. In experiment 2, fry (0.016 g average body weight) were stocked at 5 fry L^?1, and fed a larval test diet (40% crude protein) at six feeding levels (10%, 20%, 25%, 30% and 35% BW day^?1) and to satiation, three times a day for 40 days. Fish growth rates and survival were extremely poor at 10% feeding level, and improved significantly with increasing feeding levels up to 30%, and levelled off with further increase in feeding levels. On the contrary, feed conversion ratio (FCR) and protein production value (PPV) were negatively correlated with feeding level. The lowest feeding level (10%) produced significantly lower body lipid and higher protein and ash than other feeding levels. The present results suggest that the optimum stocking density and feeding level of Nile tilapia fry are 5 fry L^?1 and 30% per day respectively.     

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.     

Animal by‐products with or without enzymatic hydrolysis completely replacement of fish meal in genetically improved farmed tilapia diets (Oreochromis niloticus)

An 8‐week feeding trial was performed to examine the potential of total replacement of fish meal with animal by‐products with or without enzymatic components in juvenile genetically improved farmed tilapia (GIFT) diets, Oreochromis niloticus, (mean initial weight, 19.71 ± 0.28 g), reared in RAS system. Five isonitrogenous and isoenergetic diets were formulated with fish meal for the diets with total replacement of the isonitrogenous amounts of enzymatic fish meal (E‐FM), chicken liver meal (CLM), enzymatic chicken liver meal (E‐CLM), dried porcine solubles (DPS) and enzymatic dried porcine solubles (E‐DPS) respectively. The results indicated that the weight gain rate (WGR) and specific growth rate (SGR) in the FM group were significantly higher than the E‐FM and E‐CLM groups (p < .05), but the specific growth rate (SGR) in the E‐CLM group lower than the E‐FM group. The feed conversion ratio (FCR) in FM and CLM was significantly lower than the E‐FM, E‐CLM and E‐DPS groups (p < .05), and no significant difference was observed among the FM, CLM and DPS groups (p > .05). The values of the protein retention efficiency (PRE) and protein efficiency ratio (PER) in FM, CLM and DPS groups were significantly higher than the E‐CLM group (p < .05). The values of feed intake ratio (FIR) in FM and CLM groups were significantly lower than the E‐FM, E‐CLM and E‐DPS groups (p < .05). There was no significant difference in the whole body contents of moisture, crude lipid and crude ash among the FM and E‐CLM groups (p > .05). The whole body contents of crude protein in the FM group were significantly higher than the E‐FM, CLM, E‐CLM DPS and E‐DPS groups (p < .05). The apparent digestibility coefficients (ADC) of dry matter, crude protein and crude lipid in the FM, E‐FM, E‐CLM and E‐DPS groups were not significantly different (p > .05). The serum glucose(GLU), total cholesterol (TCHO) and triglycerides (TG), or the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were not affected by the different treatments (p > .05). There was no significant difference in serum total protein (TP) or albumin (ALB) and between the FM group and other groups (p > .05). There was no significant difference in the serum urea nitrogen (BUN) content in the FM, CLM, E‐CLM and DPS groups (p > .05). Fish fed with the CLM and DPS diets had significantly lower hepatic GHR1, IGF1 and IGF2 gene mRNA expression levels than in fish fed the FM diet (p < .05). The present data showed that 6% of dietary fish meal can be totally replaced by the chicken liver meal and dried porcine solubles with no effect on the growth performance of GIFT strain tilapia.     

Dualistic feeding pattern of Nile tilapia (Oreochromis niloticus,L.) reared under different self‐feeding system conditions

Nile tilapia (Oreochromis niloticus) is one of the most important cultured species worldwide. The research aims to clarify the feeding characteristics, such as daily feeding pattern of Nile tilapia using a self‐feeding technique. The feeding pattern was conducted under two rearing conditions, indoor treatments under a controlled light regime (LD 12:12) and constant water temperature (25°C), and outdoor treatments under natural conditions which consisted of duplicate trials with two periods each. The outdoor treatment was carried out from early summer through late autumn in Mie, Central Japan. Daily self‐feeding activity of Nile tilapia in indoor treatments was nearly daytime feeding pattern, synchronizing with the given photoperiod (24 hr). However, the self‐feeding activity in the outdoor experiments from early summer to early autumn was almost daytime feeding pattern, but it became less clear and shifted to a nighttime feeding profile in late autumn. The results revealed that Nile tilapia has a dualistic capacity for demand‐feeding both in light and dark phases. These results might have been caused by the seasonal change in light intensity and/or water temperature. Information obtained from the self‐feeding experiments enables us to identify the influence of environmental changes on the physiological condition of farmed fish through their expression of appetite.     

Use of ideal protein concept for precision formulation of amino acid levels in fish-meal-free diets for juvenile Nile tilapia (Oreochromis niloticus L.)

This study was undertaken in a closed system with Nile tilapia (Oreochromis niloticus) to examine the effects of total replacement of fish meal (FM) by soybean meal. Nile tilapia fingerlings with an average weight of 5.34±0.08 g were hand‐fed one of the five isoenergetic (≈13.5 MJ digestible energy kg^?1) and isoproteic (≈31% of digestible protein) experimental diets to satiation, six times a day during 85 days in eight replicate fibreglass tanks (six fish per tank). The control diet containing FM was substituted by soybean meal, with and without essential amino acids (lysine, methionine and threonine) or dicalcium phosphate supplementation. The supplemental amino acids were added at levels to simulate the reference amino acid profile of Nile tilapia carcass protein, based on the ideal protein concept. The results showed that soybean meal diet supplemented only with dicalcium phosphate was inferior to the control diet with FM and soybean meal diets supplemented with dicalcium phosphate and essential amino acids. Multiple essential amino acids and dicalcium phosphate incorporation in soybean meal diets was associated with performance, whole‐body composition and carcass yield equal to that of the fish fed with the control diet containing FM. These data suggest that a diet with all plant protein source, supplemented with essential amino acids, based on tissue amino acid profile, can totally replace FM in a diet for Nile tilapia, without adverse effects on the growth performance, carcass yield and composition.     

Growth and economic performance of Nile tilapia (Oreochromis niloticus L.) fed on two formulated diets and two locally available feeds in fertilized ponds

Lack of suitable diets for semi‐intensive production of Oreochromis niloticus in Kenya has necessitated use of expensive diets designed for intensive production. To address this problem, two isonitrogenous (24% protein) diets were formulated and evaluated for production of O. niloticus in fertilized ponds. One diet contained vitamins and minerals premix (CV) while the other had no premix (CW). Growth of fish fed on the formulated feeds was compared with groups of fish fed on commercial pig pellets (PP) and wheat bran (WB). There were significant differences in mean weights, growth rates and feed conversion ratios between the formulated and the other diets. No significant differences in these parameters were observed between CV and CW and also between PP and WB. Fish that fed on the formulated feeds produced significantly lower number of juveniles than those fed on PP and WB. Fish fed on WB gave the best economic returns while those on PP had the least returns. Present results suggest that vitamins and minerals premix may not be necessary in diets for semi‐intensive production of O. niloticus. Present results showed that the formulated feeds produced higher yields than PP and WB, but WB had the best economic returns among the test diets.     

Productive performance of a new synthetic red tilapia population ‘Pargo‐UNAM’ compared with that of wild‐type Nile tilapia (Oreochromis niloticus L.)

A 342‐day trial was conducted comparing productive performance in a synthetic strain of red tilapia Pargo‐UNAM (PU) and in a Nile tilapia Oreochromis niloticus (NT) population during four experimental stages: Is, IIs, IIIs and IVs. In the Is, 900 nonsexually inverted PU and NT fry (0.07 and 0.06 g respectively) were each placed in four plastic tanks per strain. For the IIs [1.59 g (PU) and 1.39 g (NT)], the population in each replicate was reduced to 440. For the IIIs [36.6 g (PU) and 36.5 g (NT)], the tanks were culled to 220 fish and transferred to 1 m³ cages. At the end of IIIs, all the fish were sexed and 40 fish (133.3–231.6 g) of a single sex were placed in a cage, with eight per genetic group. Survival was similar between groups in any stage. Weight gain was similar in Is and IIs, while PU exhibited more growth than NT during the IIIs. At the end of the IVs, weight of males was similar (PU=623.4 g; NT=650.1 g), but PU females had higher weight (435.4 g) than NT females (323.6 g). Fillet rate (>32%) was similar in all groups. Advantages of culturing the synthetic strain ‘PU’ are discussed.     

Effect of using okara meal,a by‐product from soymilk production as a dietary protein source for Nile tilapia (Oreochromis niloticus L.) mono‐sex males

The main objectives of this study was to evaluate the effect of partial and total replacement of fishmeal protein by okara meal (OM) protein in practical diets on growth performance, feed utilization and body composition of Nile tilapia (Oreochromis niloticus L.) mono‐sex males. Fish of an average initial weight of 2.67 ± 0.01 g were stocked in 15 glass aquariums (80 L each) at a rate of 15 fish per aquarium. Fishmeal protein (18% of the diet) was used as the sole source of animal protein in the control diet. Percent replacement of fish meal (FM) by OM on the basis of crude protein was 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 5%, and then gradually reduced to 4% of the total fish biomass daily, for a period of 12 weeks. The results revealed that the fish fed diets A (100% FM control), B (25% OM), C (50% OM) and D (75% OM) had significantly the best average body weight, weight gain g, specific growth rate (SGR % day^?1), weight gain % and feed intake g fish^?1 compared with diet E (100% OM) which had the lowest values. There were no significant differences (P > 0.05) among all experimental diets and control in terms of feed conversion ratio (FCR), protein efficiency ratio (PER) and survival rate %. Whole body protein contents for fish fed diets B, C and D were superior to the control diet. Incorporation of OM in the diets increased significantly whole body fat content. Incorporation of OM in the diets significantly increased apparent digestibility coefficient of crude protein crude fat and energy. Therefore, these findings suggest that up to 75% of FM protein can be replaced by OM protein in Nile tilapia, mono‐sex male diets.     

Sensitivity and specificity of real‐time PCR and bacteriological culture for francisellosis in farm‐raised Nile tilapia (Oreochromis niloticus L.)

Despite the worldwide occurrence of Francisella noatunensis subsp. orientalis (Fno) infection in farmed tilapia, sensitivity and specificity estimates of commonly used diagnostic tests have not been reported. This study aimed to estimate the sensitivity and specificity of bacteriological culture and qPCR to detect Fno infection. We tested 559 fish, sampled from four farms with different epidemiological scenarios: (i) healthy fish in a hatchery free of Fno; (ii) targeted sampling of diseased fish with suggestive external clinical signs of francisellosis during an outbreak; (iii) convenience sampling of diseased and clinically healthy fish during an outbreak; and (iv) sampling of healthy fish in a cage farm without a history of outbreaks, but with francisellosis reported in other farms in the same reservoir. The qPCR had higher median sensitivity (range, 48.8–99.5%) than culture (range, 1.6–74.4%). Culture had a substantially lower median sensitivity (1.6%) than qPCR (48.8%) to detect Fno in carrier tilapia (farm 4). Median specificity estimates for both tests were >99.2%. The qPCR is the superior test for use in surveillance and monitoring programmes for francisellosis in farmed Nile tilapia, but both tests have high sensitivity and specificity which make them fit for use in the diagnosis of Fno outbreaks.