Hatchery production of blue tilapia, Oreochromis aureus (Steindachner), in small suspended hapa nets

Abstract Two-year-old blue tilapia, Oreochromis aureus (Steindachner), were stocked into five replicate breeding hapas (1·2 m × 1·2 m × 2·7 m) at a density of six males and six females per hapa. At stocking, males and females averaged 415 and 225g respectively. During the 50-day trial (July-August), 62900 seed (eggs and sac-fry) representing 78 spawns, were collected from 30 females. In comparative treatments, prestocking surgical removal of the male's maxillary bone did not influence hatchery productivity. However, removal of the female's maxillary bone significantly reduced frequency of repeat spawning and clutch size (P < 0·05). Removal of the maxillary bone also influenced weight gain of broodstock. It is hypothesized that these significant responses were due to the surgical removal of the maxillary bone and the subsequent breakdown in dominance hierarchies.     

Genetic improvement of Israeli blue (Jordan) tilapia,Oreochromis aureus (Steindachner), through selective breeding for harvest weight

Genetic parameters and selection responses were obtained for harvest body weight of blue tilapia (Oreochromis aureus) from data collected over three generations in a selected population. A total of 18 194 records representing 186 sires and 201 dams were used in the analysis. Within generation heritability estimates for harvest body weight ranged from 0.18 to 0.58. When data from more than one generation were included in the analysis, heritability estimates became more stable (0.33–0.40) and it was 0.33 when all data were included in the analysis. The common full‐sib effect accounted for 10% of the phenotypic variance in the full data set. Heritability for survival from stocking to harvest was estimated at 0.01 and 0.09 in actual units (fitting an animal model) and in the logit (sire model) scale respectively. The genetic correlation between harvest body weight and survival was 0.22 and not significantly different from zero. The total selection response for harvest body weight over the three generations of selection measured as the difference between least‐squares means of selected and control lines was 17.7%. The corresponding figure when response was measured as the difference between mean breeding values of selected and control lines was 19.6%. The average inbreeding coefficient was 0.003 after three generations of selection. These results indicate that there are good prospects for the genetic improvement of harvest body weight in blue tilapia.     

Ultraviolet-induced androgenesis in Nile tilapia, Oreochromis niloticus (L.), and hybrid Nile × blue tilapia, O. aureus (Steindachner)

Fertilization of ultraviolet (UV) irradiated oocytes of Nile tilapia, Oreochromis niloticus (L.), with sperm from O, niloticus or blue tilapia, O, aureus (Steindachner), and subsequent suppression of the first cleavage of fertilized eggs successfully induced androgenesis in Nile and blue tilapia. The optimal doses of UV irradiation to denucleate a female genome of Nile tilapia prior to androgenesis ranged from 5940 to 6930 erg mm^?2 for 54-63 s at a fixed intensity of 110 erg mm^?2 s^?1. Putative androgenetic fish were created from eggs which were irradiated at various times and several durations of heat-shock. Eggs which were treated for 5 min at 41.6 ^oC at 2 7.5 min after fertilization were the most successful at suppressing the first cleavage and producing viable androgenetic diploids in Nile or hybrid Nile X blue tilapia. The maximal survivals of putative androgenetic diploids in relation to the control were 1.60% and 0.90% in Nile and hybrid Nile X blue tilapia, respectively. The androgenetic offspring established exhibited active feeding and normal growth.     

Induction of apoptosis in tilapia, Oreochromis aureus Steindachner, and in TO-2 cells by Staphylococcus epidermidis

This study describes apoptosis induced in vivo and in vitro in tilapia, Oreochromis aureus Steindachner, by Staphylococcus epidermidis . In an in vivo experiment, tilapia were challenged using viable S. epidermidis and its cultured supernatant, respectively. Apoptosis was predominantly detected in lymphocytes and macrophages in spleen and kidney. Apoptotic figures were observed occasionally in the brain, liver, gonad, mesentery, stomach, intestine and skeletal muscle of infected fish. In an in vitro experiment, TO-2 cells treated with brain heart infusion broth supernatant of the bacteria after 48 h revealed that the supernatant was able to induce the cell apoptosis. Fragmented DNA was also detected 48 h after treatment using 1.5% agarose gel electrophoresis. The smallest multimeric DNA fragment was approximately 180-bp in length. Results of both the in vitro and in vivo experiments showed that products of the bacteria could induce tilapia cell apoptosis.     

Soldier fly, Hermetia illucens L., larvae as feed for channel catfish, Ictalurus punctatus (Rafinesque), and blue tilapia, Oreochromis aureus (Steindachner)

Abstract. Three feeding trials, involving pre-pupal larvae of soldier fly, Hermetia illucens L., grown on poultry manure, were conducted to assess: (1) channel catfish, Ictalurus punctatus (Rafinesque), response to substitution of dried meal larvae for the fish meal component of the catfish diet and (2) if feeding 100% whole or chopped larvae to channel catfish or blue tilapia, Oreochromis aureus (Steindachner), will support normal growth comparable to those fed a commercial diet. Effects on fish quality were also evaluated. Replacement of 10% fish meal with 10% soldier fly larvae resulted in slower growth over a 15-week period for subadult channel catfish grown in cages (trial 1). However, the replacement did not reduce growth rate significantly when channel catfish were grown in culture tanks at a slower growth rate (trial 2). Feeding 100% larvae did not provide sufficient dry matter or protein intake for good growth for either species grown in tanks (trials 2 and 3). Chopping of the larvae improved weight gain and efficiency of the utilization.     

吞噬作用在尼罗罗非鱼抵抗嗜水气单胞菌感染过程中的重要作用

罗非鱼是重要的经济鱼类,而嗜水气单胞菌(Aeromonashydrophila)是其主要病原菌之一,只有充分的掌握该病原菌的感染机制才能提供更好的预防和治疗手段。本研究首先通过转录组筛查尼罗罗非鱼(Oreochromisniloticus)脾脏中与细菌感染相关的基因,然后通过荧光定量PCR证实上述基因的表达变化,最后使用秋水仙素试验和交叉免疫试验进行验证。研究结果显示,尼罗罗非鱼在感染嗜水气单胞菌之后,吞噬作用发生显著增强。秋水仙素试验发现,微管蛋白的功能受到抑制可以显著降低罗非鱼对嗜水气单胞菌的防御能力。交叉免疫试验证实,通过迟缓爱德华菌(Edwardsiella tarda)激活吞噬作用也可以提高罗非鱼对嗜水气单胞菌的防御能力。本研究旨在了解吞噬作用在罗非鱼抵御嗜水气单胞菌感染过程中发挥重要作用,并试图通过交叉免疫试验为细菌疫苗的制备提供新思路。     

Growth, feed utilization and nutrient digestibility in tilapia fingerlings (Oreochromis aureus Steindachner) fed diets containing bacteria-treated coffee pulp

The effectiveness of bacteria treated‐coffee pulp (BT‐CoP) in fish diets was evaluated in a feeding trial with Oreochromis aureus (Steindachner) fingerlings. Five diets were formulated to contain 0%, 6%, 12%, 18% and 24% BT‐CoP, replacing wheat meal. Fish were reared in a recirculating unit consisting of 16 aquaria. Each aquarium was stocked with 10 fish of 1.1–2.4 g. Fish were fed ad libitum twice daily (10 and 15 h) for 4 weeks. Fish fed diets without BT‐CoP and with 6% BT‐CoP showed similar growth (body weight, growth rate: RGR_m) and feed utilization (feed conversion ratio, protein efficiency ratio, apparent net protein utilization). Diets containing 0% and 6% BT‐CoP gave similar dry matter and protein digestibility coefficients, but dietary BT‐CoP levels higher than 6% produced lower digestibility values, except for carbohydrate. It is concluded that O. aureus fingerlings may assimilate only small amounts (6%) of BT‐CoP in the diets without adverse effects on growth and feed utilization parameters. The CoP‐containing diets did not affect fish survival (100%). The depression in tilapia performance may be associated mainly with the high level of fibre present in the CoP diets.     

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) ×Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The effects of four levels of food supply (0.5%, 1%, 2% and 3% body weight daily) were investigated on some reproductive traits and growth of hybrid tilapia in outdoor concrete tanks. Fast-growing fish matured early in the season (March), but spawning started late in May. Smallest size of males and females at first maturity was 8.1 cm. Fish size at maturity appears to be influenced by the feeding level, which affects the growth of fish. For both sexes, no significant difference was found in gonadosomatic index (GSI) among different treatments. Mean percentage of mature fish decreased with decreasing food supply and was found to be significantly different between fishes fed at 3% (46%) and 0.5% (28%) body weight. Fecundity increased with increased feeding levels, although significant differences were found only between 3% and other feeding rates (0.5–2.0%). The fecundity per g female was higher at the lower ration levels (0.5% and 1%) than at the higher feeding levels. Egg quality, with respect to egg size, hatchability. fry length and weight, was not affected by the feeding rates. Final mean weight and food conversion ratios were significantly influenced by feeding rates. Higher increase in ovary weight with increasing body weight of mature females fed at 0.5% body weight than fishes receiving higher food levels suggests that in these fish, more food resources are diverted towards gonad building than to somatic growth.     

Blue tilapia Oreochromis aureus (Steindachner) carcass composition and haematology in relation to the female parent size under recirculated water conditions

The relation between female parent size/age of Oreochromis aureus (Steindachner) and their offspring carcass composition and some haematological parameters was investigated. Blood parameters (glucose, triglycerides, albumin, cholesterol, total lipid, haematocrit, osmolarity), proximate carcass composition (crude protein, crude fat, moisture, ash), and total lipid content of liver were evaluated. No clear differences between populations could be reported regarding carcass composition. However, the offspring of the smallest/youngest female parent gave the highest crude protein and the lowest crude fat levels, while that of the largest/old female parent showed an opposite picture. Results obtained on blood parameters and liver lipid content were not clearly related to the female parent size/age, nor to the final body weight of the populations, despite the statistically significant (P < 0.05) differences observed for glucose, triglycerides and plasma and liver total lipids. It is concluded that more research is needed in order that a clear correlation between the female parent size/age and the investigated biochemical parameters of their progeny to be established.     

Live Spirulina (Arthrospira platensis) as a growth and immunity promoter for Nile tilapia, Oreochromis niloticus (L.), challenged with pathogenic Aeromonas hydrophila

The use of antibiotics to control fish disease is one of the constraints in tilapia farming. Hence, the use of probiotic and live organisms as alternative strategies has received much more attention. This study was undertaken to evaluate the use of Spirulina (Arthrospir platensis) as a growth and immunity promoter for Nile tilapia, Oreochromis niloticus (L.). Fish (1.88 g) were randomly distributed at 20 fish per 100 L aquarium and fed a diet containing either 0.0, 1.25, 2.5, 5.0, 7.5 or 10.0 g Spirulina kg^?1 diet for 12 weeks. After the feeding trial, fish of each treatment were challenged by pathogenic Aeromonas hydrophila, which was given by an interperitoneal injection, and they were kept under observation for 10 days to record any abnormal clinical signs and the daily mortality rate. The growth‐promoting influence of Spirulina was observed with fish, and the optimum growth and feed utilization were obtained at 5.0 g Spirulina kg^?1 diet. No significant changes were observed in fish survival among the different treatments. Spirulina supplementation improved the protein and lipid contents in fish bodies without significant differences among them, especially when fed 2.5–10.0 g kg^?1 diet, but no significant differences in the moisture and ash contents were observed among different treatments. The physiological parameters were improved when fish were fed a Spirulina‐enriched diet. However, the highest red blood cells, white blood cells and nitro blue tetrazolium values were obtained at 5.0–10.0 g Spirulina kg^?1 diet; meanwhile, the lowest value was obtained in the control. Total fish mortality due to A. hydrophila infection decreased with an increase in the Spirulina level in fish diets. These results indicate that Spirulina supplement is promising as an alternative method to antibiotics for disease prevention in tilapia aquaculture, and the optimum level of Spirulina in the fish diet should be 5.0–10.0 g kg^?1 diet.     

Nanoparticles of Arthrospira platensis improves growth,antioxidative and immunological responses of Nile tilapia (Oreochromis niloticus) and its resistance to Aeromonas hydrophila

Several studies investigated the usage of spirulina (Arthrospira platensis) in aquaculture as a functional dietary additive or plant proteins replacers; however, more efforts still needed to test its nano form inclusion in aquafeed. In this study, Nile tilapia (Oreochromis niloticus) fed dietary spirulina (A. platensis) nanoparticles (SNP) at 0 (control), 0.1, 1 and 10 g/kg diet while the fifth diet was mixed with 10 g/kg of the normal form of A. platensis as a positive control. The final weight (FW), weight gain (WG) and feed conversion ratio of fish fed SNP at 10 g/kg displayed improved values comparing with the other groups (p < 0.05). Further, fish fed 1 g SNP had higher FW and WG than the control and 0.1 g SNP and 10 g normal A. platensis. The incorporation of SNP at 1 and 10 g/kg in Nile tilapia diets significantly (p < 0.05) enhanced total protein, albumin, globulin, lowered the values of serum glucose and activities of ALT and AST compared with control and spirulina groups. The SOD, CAT, GPx, lysozyme and respiratory burst activities were meaningfully promoted (p < 0.05) in fish received 1 and 10 g/kg diet concerning the control and spirulina groups. Nile tilapia challenged with Aeromonas hydrophila showed congestion of the kidney, liver and spleen tissues while SNP alleviated the inflammation induced by A. hydrophila. Different levels of SNP-incorporated group showed lower cumulative mortality than the other groups. In conclusion, the obtained results illustrated that spirulina in nano form is recommended to enhance Nile tilapia well-being.     

Aeromonas jandaei and Aeromonas veronii caused disease and mortality in Nile tilapia,Oreochromis niloticus (L.)

Diseases caused by motile aeromonads in freshwater fish have been generally assumed to be linked with mainly Aeromonas hydrophila while other species were probably overlooked. Here, we identified two isolates of non‐A. hydrophila recovered from Nile tilapia exhibiting disease and mortality after exposed to transport‐induced stress and subsequently confirmed their virulence in artificial infection. The bacterial isolates were identified as Aeromonas jandaei and Aeromonas veronii based on phenotypic features and homology of 16S rDNA. Experimental infection revealed that the high dose of A. jandaei (3.7 × 10⁶ CFU fish^?1) and A. veronii (8.9 × 10⁶ CFU fish^?1) killed 100% of experimental fish within 24 h, while a 10‐fold reduction dose killed 70% and 50% of fish, respectively. When the challenge dose was reduced 100‐fold, mortality of the fish exposed to A. jandaei and A. veronii decreased to 20% and 10%, respectively. The survivors from the latter dose administration were rechallenged with respective bacterial species. Lower mortality of rechallenged fish (0%–12.5%) compared to the control groups receiving a primary infection (37.5%) suggested that the survivors after primary infection were able to resist secondary infection. Fish exposed to either A. jandaei or A. veronii exhibited similar clinical signs and histological manifestation.     

Lack of association between Flavobacterium columnare genomovar and virulence in hybrid tilapia Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner)

Columnaris disease can be problematic in tilapia (Oreochromis spp.) production. An understanding of the pathogenesis and virulence of Flavobacterium columnare is needed to develop prevention strategies. The objective of this study was to determine the virulence of genetically defined isolates of F. columnare in sex‐reversed hybrid tilapia, Oreochromis niloticus (L.) × O. aureus (Steindachner). A series of immersion challenge trials were performed using isolates of the five established genomovars of F. columnare: I, II, II‐B, III and I/II. The mean per cent mortality of fish challenged with genomovar I, II and III isolates ranged from 0 to 100, 3.3–78 and 3.3–75%, respectively. The mean per cent mortality of fish challenged with genomovar II‐B ranged from 35 to 96.7%, and the only genomovar I/II isolate tested caused no mortality. Contrary to previous work in other fish species, there did not appear to be an association between F. columnare genomovar and virulence in tilapia. The challenge model used resulted in acute mortality. An alternative challenge model was tested by cohabitating healthy fish with dead fish infected with F. columnare. This method resulted in rapid appearance of clinical signs and mortality, suggesting the potential for F. columnare to increase in virulence upon growth on/in a fish host.     

Natural co‐infection of cultured Nile tilapia Oreochromis niloticus with Aeromonas hydrophila and Gyrodactylus cichlidarum experiencing high mortality during summer

Aeromonas hydrophila and Gyrodactylus cichlidarum are common pathogens that induce significant economic losses in farm‐reared Nile tilapia. Nowadays, the sudden appearance of fish mortalities was exaggerated due to mixed and multiple infections. During summer 2016, mass mortality among earthen pond‐farmed Nile tilapia was reported. Clinico‐pathological, bacteriological and parasitological examinations have been demonstrated. As well, the water quality parameters were assessed. The clinical and histopathological findings of the moribund and recently dead fish were characterized by generalized septicaemic signs. The water quality parameters were significantly elevated over the permissible levels, whereas there was an elevation in nitrite (0.04 mg/L), un‐ionized ammonia (0.8 mg/L), hydrogen sulphide levels (153.1 mg/L) and organic matter content (3.79 mg/L). A. hydrophila was identified based on phenotypic characterization, API 20E features and the homology of 16S rRNA gene sequence analysis. In addition, PCR data confirmed the presence of aerolysin (aerA) and haemolysin (hly) genes in the identified A. hydrophila isolates. Gene sequencing and phylogenetic analysis based on 16S rRNA sequence confirmed that A. hydrophila H/A (accession No. MN726928) of the present study displayed 98%–99% identity with the 16S rRNA gene of A. hydrophila. Furthermore, the monogenetic trematode, G. cichlidarum was identified in the wet mounts from the skin and gills of the examined fish with a high infestation rate. In this context, it was reported that the synergistic co‐infection of A. hydrophila and G. cichlidarum with deteriorated water quality parameters could induce exaggerated fish mortalities during hot weather.     

Structure and function of the small intestine of the tilapia Oreochromis niloticus×Oreochromis aureus (Teleostei, Cichlidae)

This study examined the microscopic structure of the small intestine and digestion and absorption in the hybrid tilapia, Oreochromis niloticus×Oreochromis aureus. The small intestine was lined on the luminal face with villi, which were narrower and more dense in the proximal small intestine and became wider and sparser distally. The columnar epithelial cells lining the villi were predominantly enterocytes containing a brush border, interspersed with mucus containing goblet cells approximately every 4–6 cells. These mucus‐secreting cells contained both acid and basic mucins and increased in density in the distal and the terminal sections of the intestine. Proliferation of enterocytes was observed in the intervillus areas and lower third of the villus. Fish were fed diets of either fish meal or fish meal–wheat to which chromic oxide had been added as a non‐absorbed reference standard. Activity of the pancreatic enzymes, lipase, trypsin and amylase were determined along the small intestine relative to the non‐absorbed marker. Activity of these pancreatic enzymes was maximal in the proximal segments and decreased distally. Changes in the activity patterns of trypsin and amylase were observed with the different diets in the proximal small intestine. Net secretion of both N and fatty acids was found in the hepatic loop and absorption commenced distally decreasing in rate with distance from the pylorus. The pattern of N absorption in the proximal small intestine changed with the different diets. The structure and function of the small intestine of the tilapian omnivore thus are generally similar to mammals and digestion and absorption adapt with diet.     

Digestibility and transit time of Azolla filiculoides Lamarck in Oreochromis aureus (Steindachner)

Azolla, an aquatic fern that is able to fix nitrogen directly from the atmosphere, could represent an interesting low-cost food for tropical fish. In the present study, the authors evaluated the apparent digestibility of Azolla filiculoides Lamarck by Oreochromis aureus (Steindachner), an omnivorous-phytoplankton-ophagous species of tilapia. Two digestibility tests (5 days) were performed in digestibility tanks on adult O. aureus fed only with dried A. filiculoides given ad libitum (2% biomass day^?1). Experiment 1 was made on fish weighing 28-49 g (duplicate) at a water temperature of 29 ± 0.5°C; experiment 2 was made on fish weighing 36-81 g (duplicate) at a water temperature of 27 ± 0.5°C. The transit time in O. aureus (weight: 30-50 g; water temperature: 27 ± 0.5°C) fed only and ad libitum with A. filiculoides was determined with methylene blue as a vital dye. The apparent faecal digestibility coefficients (%) obtained for dry matter and crude protein were 49.0 and 55.4%, respectively, in experiment 1, and 53.5 and 60.9% in experiment 2. The transit time values of 2.5-3.0 h and 3.0-3.5 h were obtained, respectively, for fresh and dried A. filiculoides. Thus, A. filiculoides shows relatively good digestibility values in O. aureus, which are comparable to those obtained with other aquatic plants in tropical fish. However, in order to meet the nutrient requirements of tilapias, Azolla has to be mixed with other foods.     

Juvenile tilapia (Oreochromis niloticus×Oreochromis aureus) requires dietary myo-inositol for maximal growth

An 8-week growth experiment was conducted to estimate the dietary requirement of myo-inositol (MI) for juvenile hybrid tilapia. MI was supplemented at 0, 150, 250, 350, 450, 600, and 1200 mg/kg diet in the basal diet providing 0, 167, 259, 367, 479, 612, and 1253 mg MI/kg diet. Basal diet without MI but with succinylsulfathiazole to suppress MI synthesis by intestinal bacteria was included for comparison. Each diet was fed to triplicate groups of tilapia (mean initial weight 0.51±0.01 g, n=3). Fish fed ≥367 mg MI/kg diet had significantly (P<0.05) higher weight gain, followed by fish fed 259 mg MI/kg diet, and lowest for fish fed the unsupplemented basal diet. Fish fed ≥367 mg MI/kg diet had higher feed efficiency than fish fed the basal diet. Supplementation of dietary inositol did not affect survival of tilapia. The MI concentrations in liver were highest in fish fed the ≥479 mg MI/kg diet, followed by fish fed the 259 and 167 mg MI/kg diets, and lowest in fish fed the basal diet. Hepatic lipid concentrations were higher in fish fed 367 mg MI/kg diet than fish fed ≤259 mg MI/kg diet. Weight gain percentage and MI concentrations in the liver for the different treatments were analyzed by broken-line regression and indicated that the requirement for dietary MI in growing tilapia is about 400 mg/kg diet. Addition of an antibiotic to basal diet did not affect the growth and hepatic inositol concentration of tilapia, suggesting that the intestinal microbial synthesis was not a significant source of inositol for tilapia.     

Effects of Bacillus subtilis strains and the prebiotic Previda® on growth,immune parameters and susceptibility to Aeromonas hydrophila infection in Nile tilapia,Oreochromis niloticus

This study was conducted to evaluate the individual and combined effects of long‐term feeding of diets containing two probiotic Bacillus subtilis group strains (Aqua NZ and AP193) and the prebiotic Previda^®, a commercial hemicellulose extract, on growth performance, immune parameters and Aeromonas hydrophila susceptibility of juvenile Nile tilapia, Oreochromis niloticus. Nile tilapia of average weight 7.47 ± 0.11 g were fed diets formulated with the probiotics and/or the prebiotic, or a control diet for 8 weeks and, subsequently, challenged with A. hydrophila by intragastric gavage at a dosage of 3.9 × 10⁷ CFU per fish. Fish attained a mean weight of 59.5 ± 0.99 g at the end of the growth period. Under the conditions of the present trial, none of the diets significantly improved mean per cent weight gain (P = 0.70), thermal growth coefficient (P = 0.88) or feed conversion ratio (P = 0.87) of Nile tilapia. Except for the diet containing the prebiotic Previda^® only (P = 0.17), all other diets resulted in significantly higher fish survival compared to the control (P < 0.05). The combined effect of the prebiotic and probiotic strains emerged as the most important diet with respect to mortality reduction. The mean lysozyme and respiratory burst activities did not show any significant differences between treatments and control (P = 0.14 and 0.32, respectively). Thus, these probiotic strains used in this study have the potential to prevent disease due to A. hydrophila in O. niloticus.     

Effect of the use of the microalga Spirulina maxima as fish meal replacement in diets for tilapia, Oreochromis mossambicus (Peters), fry

The present study addresses the use of the microalga Spirulina maxima as a protein source in diets for tilapia, Oreochromis mossambicus (Peters), fry. Animal protein was replaced with algae protein at ratios of 20%, 40%, 60%, 80% and 100%, and the substitution effect was compared with a control diet in which fish meal was the sole protein. An additional 100% spirulina protein diet was supplemented with phosphorous to test for possible mineral deficiency in the plant-protein-based diet. The six treatments were tested in triplicate in a closed-recirculating system where the fish were fed by hand at 6% of their body weight. After a 9-week feeding period, the growth rate and protein utilization of fish fed the diet with 20% and 40%Spirulina were elevated and not significantly different (P>0.05) from those fed the control diet. Further increases in the alga protein content significantly decreased the growth and feeding performance. The addition of P to the 100%Spirulina diet slightly improved performance in comparison to the same diet without P. None of the treatments produced any clear adverse effects on carcass composition. It is observed that Spirulina can replace up to 40% of the fish meal protein in tilapia diets.