Effect of water temperature on energy budget of Nile tilapia,Oreochromis niloticus

A 21‐day growth trial was undertaken to investigate the effect of water temperature (25, 28, 31, 34, 37 °C) on growth, feed utilization and energy budget of juvenile Nile tilapia (Oreochromis niloticus) (initial body weight around 12 g) with four replicates at each temperature. Feed intake energy (IE), recovered energy (RE), faecal energy (FE), excretory energy (UE + ZE) and heat energy (HE) were calculated to obtain the energy budget. The results showed that feeding rate and ammonia excretion were not significantly affected by water temperature. Specific growth rate in wet weight (SGRw) and FE was significantly lower in the fish reared at 37 °C while no significant difference was observed between the fish reared at 25–34 °C. Protein retention efficiency was highest at 28 °C and lowest at 37 °C. The proportion of IE channelled into RE and UE + ZE was lower while those lost in HE was higher in the fish reared at 37 °C. The optimal growth temperature was estimated as 30.1 °C based on the regression of SGR and water temperature. Energy budget at maximum growth (34 °C) was: 100 IE = 27.0 RE + 1.1 (ZE + UE) + 10.6 FE + 59.2 HE. HE accounted for 69.3% and RE for 30.7% of metabolizable energy.     

Effects of exogenous enzyme supplementation in diets on growth and feed utilization in tilapia, Oreochromis niloticus x O. aureus

A 12‐week feeding trial was conducted to investigate the effects of supplemental exogenous enzyme on growth performance in juvenile hybrid tilapia Oreochromis niloticus×O. aureus (18 g, average initial weight). A commercial enzyme complex (neutral protease, β‐glucanase and xylanase) was included at the level of 0.0 (control group), 1.0 and 1.5 g kg⁻¹ diet in three test diets. Each diet was fed to triplicate tanks of the juvenile three times a day at 4–6% of wet body weight, and each tank was stocked with 50 fish. The results showed that specific growth rate and feed efficiency ratio significantly increased (P<0.05) with increasing dietary enzyme levels. The highest feed intake was recorded in the group fed the control diet (P<0.05). The highest apparent protein retention was observed in fish fed the diet containing the 1.5 g kg⁻¹diet (P<0.05). No significant differences were observed in the apparent digestibilities (ADC) of protein, lipid and gross energy among dietary treatments (P>0.05). However, the ADC of dry matter in fish fed high supplementation (1.5 g kg⁻¹) was significantly higher than the control and low supplementation (P<0.05). There were no significant differences in condition factor, whole body moisture, protein, lipid and ash among dietary treatments. Viscera ratio, hepatosomatic index and the liver lipid decreased significantly with increasing enzyme (P<0.05). Both protease and amylase activities in the intestine and the hepatopancreas of juvenile hybrid tilapia significantly increased (P<0.05) with increasing dietary enzyme levels. The results suggested that enzyme supplementation can significantly improve growth performance and feed utilization in juvenile hybrid tilapia.     

Effect of Nile tilapia, Oreochromis niloticus (L.), size on phytoplankton filtration rate

Four different‐sized (390±3, 140±2, 40±2, 16±1 g) Nile tilapia, Oreochromis niloticus (L.), stocked at the same biomass in timed pulse feeding chambers were provided 27–29°C water dominated by Microcystis (82%) and Scenedesmus (18%) to determine the effect of fish size on filtration rates. The number of Microcystis and Scenedesmus units filtered from the water decreased significantly with increasing tilapia size. The shaping constants and maximum filtration rates for Ivlev's feeding model used to describe the relation between filtration rates and the suspended particulate organic carbon (POC) concentrations were significantly different among the four sizes. Filtration rates of 763, 671, 512 and 300 mg C kg^?1 h^?1, which correspond to 70%, 82%, 86% and 90% saturation levels, were achieved at POC levels of 30, 32, 32 and 33 mg C L^?1 for 16, 40, 140 and 390 g Nile tilapia respectively. Smaller tilapia achieved these rates at lower POC concentrations than larger tilapia.     

Low-temperature tolerance of Nile tilapia, Oreochromis niloticus: effects of environmental and dietary factors

This study was conducted (1) to evaluate the effects of photoperiod (fixed vs. decreasing light), fish size (136 vs. 220 mm), dissolved ions (hardness and salinity) and diet (menhaden oil vs. coconut oil‐based) on the tolerance (survival) of Nile tilapia, Oreochromis niloticus, to low temperatures (decreased by approximately 0.5 °C per day) and (2) to evaluate the effect of dietary fatty acid composition on selected physiological characteristics of Nile tilapia exposed to decreasing temperatures. Size significantly affected mortality, with smaller fish being less tolerant to low temperatures than larger fish. Results were equivocal in the photoperiod, dissolved ion and dietary lipid experiments, and were dependent on the method of data analysis employed. Diet significantly affected plasma osmolarity, with higher values in fish fed the menhaden‐based diet. Haematocrit, serum glucose, sodium and cortisol concentrations, serum and splenic lysozyme activities, lymphocyte count and hepatosomatic index were not affected by diet. Haematocrit, white cell count and serum glucose and sodium concentrations were significantly affected by temperature, but serum and splenic lysozyme content, hepatosomatic index, and serum cortisol concentrations were not. The results of this series of experiments indicate that altering the environment or diet has little effect on the ability of Nile tilapia to survive low temperatures.     

A farmer-oriented Nile tilapia, Oreochromis niloticus L., breed improvement in the Philippines

Opportunities for developing small‐scale tilapia industry in the Philippines is hampered by the shortage of good‐quality seeds and broodstock. Most small‐scale farmers are dependent on distribution centres for improved tilapia seeds that are expensive and not sufficient to meet market demands. An option would be for farmers to develop their own tilapia breeds using simple procedures within their technical and financial resources. This option will also help sustain the diversity of locally adapted domestic stocks of tilapia. The Philippine tilapia production of ～122 316 MT can be increased by ensuring a stable supply of quality seeds and transferring suitable technology to fish farmers. The study was carried out in a tilapia hatchery/nursery pond in the Philippines to explore the potential for a farmer‐based research on tilapia breed improvement using relatively simple artificial selection procedures. One generation of size‐specific mass selection based on the early culling of large fry (collimation procedure) was applied on a Nile tilapia strain, Oreochromis niloticus L., in net cages set in a small earthen pond. Two episodes of directional selection were performed after initial removal of large fry at 21 days. Selection of parents and progeny testing were conducted in hapa and B‐net cages set in earthen ponds. The selection resulted in a significant response of 8% for standard length and 29% for weight relative to the control. The crude estimates of realized heritability is ～16% for standard length and ～26% for weight comparable with similar studies conducted by other workers.     

Evaluating fungi‐degraded date pits as a feed ingredient for Nile tilapia Oreochromis niloticus L.

Five isocaloric‐isonitrogenous diets containing 0, 150, 300, 450 and 600 g kg^?1 of fungi Trichoderma reesei‐degraded date pits (DDP), as a replacement for dietary corn, were fed to triplicate groups of Nile tilapia Oreochromis niloticus L. fingerlings (1.88 g initial weight), for 9 weeks, in 70 L fibreglass tanks. Each tank was considered as an experimental unit and was part of a water recirculating system utilizing filtered and aerated ground well water (24 ± 3 °C). Tilapia growth performance, namely, weight gain, feed conversion, specific growth rate and protein efficiency ratio were similar and superior in fish fed diets containing 150 and 300 g kg^?1 DDP, when compared with those fish fed the other diets. Fish fed the control diet with 450 g kg^?1 DDP had better growth efficiency performance than those fed diets containing 0 and 600 g kg^?1. Fish fed the diet with 600 g kg^?1 DDP were inferior to all other groups. Tilapia body composition was affected by increasing DDP level in the diets as body fat was decreased, while body moisture was increased. In conclusion, DDP could replace 300 g kg^?1 of dietary corn with better growth results. Further increase of date pits replacements to 450 g kg^?1 will affect growth performance, when compared with the control.     

Effect of salinity on carrying capacity of adult Nile tilapia Oreochromis niloticus L. in recirculating systems

Effect of salinity on carrying capacity of a recirculation system for Nile tilapia, Oreochromis niloticus L.; production was assessed. Survival, growth and feed conversion ratio of adult Nile tilapia fed 30% crude protein diet for 88 days were measured at three different salinity levels (8, 15 and 25 g L^?1) and two stocking densities (20 and 40 m^?3) in three independent recirculating systems. Highest survival (98%) and a linear growth in net biomass (P<0.01) was observed in both densities at 8 g L^?1 and in 20 m^?3 treatment at 15 g L^?1. Highest net biomass growth was observed in the 40 m^?3 stocking density treatment at 8 g L^?1 salinity level (P<0.05). Overall biomass growth was significantly affected by salinity indicating a decrease in Nile tilapia carrying capacity with increased salinity. About 11 000 kg ha^?1 crop^?1 of Nile tilapia can be obtained in recirculating systems at 8 g L^?1 salinity, significantly higher than the net production at 15 g L^?1 (5200 kg ha^?1 crop^?1) and 22 g L^?1 (4425 kg ha^?1 crop^?1).     

Effects of pretreatment with microbial phytase on phosphorous utilization and growth performance of Nile tilapia (Oreochromis niloticus)

This study was to assess effects of the pretreatment in all‐plant based diets with microbial phytase on phosphorous utilization and growth performance of Nile tilapia (Oreochromis niloticus). Pretreatment trials were conducted using phytase at graded doses to determine the optimal dose of phytase. Available phosphorus (P) levels increased significantly with the increased doses of phytase and the dose of 1000 U kg^?1 was most efficient. Based on the pretreatment trials, plant based diets for Nile tilapia were formulated by pretreating with phytase at 1000 U kg^?1. Experimental diets were supplemented with graded levels of mono calcium phosphate (MCP) at 25, 18.75, 12.5, 6.25 and 0 g kg ^?1 diet. In addition, there were three controls: one phytase control, one inorganic P control and one pretreatment control. The results showed that diets pretreated with phytase gave better growth performance, feed conversion ratio and protein efficiency ratio of Nile tilapia compared with the phytase control diet and pretreatment control diet (P < 0.05). There were no significant differences in growth performance of Nile tilapia between the inorganic control diet and phytase pretreated diets supplemented with MCP at 25, 18.75 and 12.5 g kg^?1 (P > 0.05), which resulted in significantly better performance than those at 6.25 and 0 g kg^?1 (P < 0.05). Dietary interaction effects of phytase were observed for phosphorus retention efficiency and phosphorus load. Apparent digestibility coefficient of P (ADCp) was improved significantly by phytase pretreatment (P < 0.05). No significant difference was detected on ADC of crude protein among all experimental diets (P > 0.05).     

Effect of temperature and phytoplankton concentration on Nile tilapia Oreochromis niloticus (L.) filtration rate

Nile tilapia Oreochromis niloticus (L.) held in timed‐pulse feeding chambers, were provided with algal‐rich water dominated by either green algae (Scenedesmus, Ankistrodesmus, Chlorella and Tetraedron) or cyanobacteria (Microcystis) to determine the effect of temperature and phytoplankton concentration on filtration rates. Green algae and cyanobacteria filtration rates were measured as suspended particulate organic carbon (POC) kg^?1 wet fish weight h^?1. Ivlev's filter‐feeding model described the relationships between filtration rates and suspended POC concentration of green algae and cyanobacteria. Filtration rates of both green algae and cyanobacteria increased linearly as water temperature increased from 17 °C to 32 °C and were significantly higher in the warm‐water regime (26–32 °C) than in the cool‐water regime (17–23 °C). Filtration rates at 95% saturation POC (FR₉₅) in green algal and cyanobacterial waters were 700 mg C kg^?1 h^?1 and 851 mg C kg^?1 h^?1 in the warm‐water regime and 369 mg C kg^?1 h^?1 and 439 mg C kg^?1 h^?1 in the cool‐water regime respectively. The FR₉₅ in warm water were achieved at lower POC concentrations than in cool water.     

A comparative study of growth and feed utilization efficiency of sex-reversed diploid and triploid Nile tilapia, Oreochromis niloticus L.

Growth performance, survival and feed utilization of diploid (2n) and triploid (3n) sex‐reversed male and female Nile tilapia were evaluated at maintenance feeding (1% body weight (BW) day^?1), fixed feeding (3% BW day^?1) and apparent satiation feeding levels in a freshwater recirculation system comprised of thirty‐six 1‐m³ concrete tanks at the Asian Institute of Technology, Bangkok, Thailand. Triploid Nile tilapia (3n) was produced by subjecting fertilized diploid (2n) tilapia eggs to heat shock. After hatching, fish were sex‐reversed to all‐male and all‐female populations by oral administration of 17 α‐methyltestosterone (60 mg kg^?1 feed) and ethynylestradiol (100 mg kg^?1 feed) respectively. There was significantly higher growth with increased ration levels in both male and female groups. There were no significant differences in final BW, specific growth rate, survival rate, feed conversion ratio and protein efficiency ratio between diploid and triploid fish. Triploids had lower gonad weights than diploids, and this was particularly evident at the satiation feeding level. Triploid fish had a significantly higher apparent net protein utilization and percentage of gutted weight than diploids at all feeding levels. Higher protein utilization efficiency of triploids might be an advantage for commercial tilapia culture but further research is necessary to make such a conclusion.     

Spontaneous diploidization of the maternal chromosome set in Nile tilapia (Oreochromis niloticus L.) eggs

Spontaneous diploidization of the maternal chromosome set (SDM) in Oreochromis niloticus is described here for the first time. The SDM phenomenon was observed in progeny of only one XY neofemale out of 11 such neofemales from which eggs had been fertilized with UV‐irradiated sperm: this treatment produced only the expected haploid embryos from the other females. SDM progeny were produced from three different batches of eggs from this female. No significant differences in survival at different stages of embryonic development were observed between the SDM and the diploid control group. The maternal inheritance of SDM progeny was verified using multilocus DNA fingerprinting. Only diploid karyotypes were observed in these fish and diploid control groups. In both the SDM and control groups, sex ratios were significantly skewed towards males (93.3% and 65.0% males respectively). The actual mechanism of SDM in eggs from this particular female remains unknown.     

Effect of mixed protein schedules combined with choline and betaine on the growth performance of Nile tilapia (Oreochromis niloticus)

Reducing feed cost has been a major issue in fish nutrition. Mixed protein schedules have been proposed as one of the methods successfully tested in many fish species to reduce feed cost. Meanwhile, the effect of dietary choline and betaine supplementation on fish performance was assessed. The aim of the present study was to investigate the effect of mixed protein schedules, combined with choline and betaine, on Nile tilapia performance. This experiment was conducted in a (4 × 3) factorial arrangement of treatments. Four mixed protein schedules were examined, in the presence of choline 0.3% and/or betaine 0.5%. The four mixed protein schedules were achieved by alternating diet (A; 31%CP) and diet (B; 24%CP) as follows: (6 days‐A), (5 days‐A/1 day‐B), (4 days‐A/2 days‐B) and (3 days‐A/3 days‐B). The results indicated that in the presence of betaine 0.5% and choline 0.3%, the optimal mixed protein schedule for tilapia was (3A/3B). Fish fed on the 4A/2B or 3A/3B schedules utilized protein more efficiently than fish fed on the (6A) schedule. Fish fed diets supplemented with betaine (b) only showed the highest energy retention. The lowest feed cost was recorded for fish fed on (3A/3B) in the presence of betaine 0.5% and choline 0.3% in fish diet.     

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.     

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 dietary protein-energy levels and fish initial sizes on growth rate, development and production of Nile tilapia, Oreochromis niloticus L.

The effects of dietary protein‐energy levels on the growth rate, proximate composition and production were examined in Nile tilapia, Oreochromis niloticus, at two starting weights (22.9 and 39.8 g) reared in concrete ponds for 180 days. The highest weight gain (183.1 g) was obtained with fish fed a 30% protein and 10.5 kJ g^?1 diet for the small initial size and 180.2 g for a diet containing 25% protein and 12.6 kJ g^?1 for the large initial size. Dressed yields (edible mass) and fillets increased to 56.9% and 52.5% in fish fed diet with 25% protein and 10.5 kJ g^?1 at the initial size of 22.9 g, while fish started at 39.8 g exhibited the best values (56.5% and 52.1%) when fed the 30% protein and 10.5 kJ g^?1 diet. Proximate composition of soft tissue (wet weight basis) in small fish was significantly influenced by dietary protein‐energy levels. Protein was 26.1±0.3% in fish fed the high protein (30%) and low energy (10.5 kJ g^?1 diet), while lipid content was 6.4±0.3% at diet containing 20% protein and 14.7 kJ g^?1 diet. Large initial size fish fed the diet with 25% protein and 14.7 kJ g^?1 had the highest body protein (32.0±0.4%) and lowest lipid content (2.2±0.3%). Feed conversion ratio (FCR) and protein efficiency ratio varied with different dietary protein‐energy levels and initial fish sizes. Feed conversion ratio increased with increasing protein and decreasing energy level in the diet, and values in small fish were higher than values in large fish. Protein efficiency ratio decreased with increasing dietary protein level and decreasing energy level. The maximum total production (7.6 tons feddan^?1) was with dietary high protein (30%) and low energy (10.5 kJ g^?1) for small‐sized fish, while large initial fish had the highest production (3.7 tons feddan^?1) when fed the 25% protein and 12.6 kJ g^?1 diet energy. Starting with 22.9 g fish was more advantageous than the initial size of 39.8 g for rearing Nile tilapia. Small fish required a high‐protein and low‐energy diet, whereas large fish required a low‐protein and high‐energy diet to achieve highest production.     

Effect of different schedules for broodstock exchange on the seed production of Nile tilapia Oreochromis niloticus (L.) in freshwater

This study compares the effect of three broodstock exchange treatments (exchange every month, two months and three months) versus no-exchange control treatment on year-round seed production and spawning synchrony of Nile tilapia Oreochromis niloticus stocked in 0.4 m³ fiberglass tanks within a recirculating water system. Adult males and females with mean body weights of 161.7 g and 127.6 g, respectively, were stocked at a rate of 4 fish/tank with a male to female sex ratio of 1:3. Water temperature at 29 ± 1.0 °C and photoperiod of 18 h/day were maintained throughout the experiment. The results showed that broodstock in the exchange treatments had higher seed production and spawning synchrony compared with those in the no-exchange treatment. The exchange treatments resulted in 70.5 to 97% increase in seeds kg female^–1 day^–1. The different spawning parameters of broodstock in the two- and three-month exchange treatments were higher than the one-month exchange treatment. Results suggest that broodstock exchange strategy has a long-term improvement effect on seed production and spawning synchrony, and exchanging all breeders every three months is more profitable in terms of better utilization of breeders and in reducing both the holding/conditioning facilities for broodstock and the labor cost.     

Relative bioavailability of zinc in supplemental inorganic and organic sources for Nile tilapia Oreochromis niloticus fingerlings

A 90‐day feeding experiment was conducted with sex reversed Nile tilapia (Oreochromis niloticus) fingerlings fed purified or practical diets supplemented with different zinc sources to evaluate fish growth performance and zinc and iron retention in fish bones, fillets, liver, skin and eyes. The relative bioavailability value (RBV) of zinc in the supplemental sources tested was also calculated. Fish were fed with isonitrogenous and isoenergetic purified or practical diets supplemented with 150 mg Zn kg^?1, as zinc sulphate monohydrate (ZnSO₄), zinc oxide (ZnO) or zinc amino acid complex (Zn‐AA). The feeding trial was conducted in 30, 50 L aquaria where four 0.66 ± 0.01 g (mean ± SD) fingerlings were initially stocked. No significant differences were observed for any growth performance variables (P > 0.05). In practical diets, only ZnSO₄ and ZnO presented bone zinc retention similar to that for the standard zinc source. Zinc concentration in the bone of fish fed practical diet supplemented with Zn‐AA (171 ± 3.62 μg g^?1) was significantly lower than that verified for the practical diets supplemented with the standard zinc source (200 ± 17.7 μg g^?1) or with ZnSO₄ (204 ± 19.9 μg g^?1). Assuming the concentration of zinc in bones as the response criterion, the supplemental zinc RBV from ZnSO₄ (105%) was higher than the RBV for Zn‐AA (95.1%) or ZnO (94.9%). Iron concentration in the bones of animals fed the non‐zinc‐supplemented purified diet was significantly higher than that observed for purified diet supplemented with Zn‐AA (P < 0,05). The results of the present work allowed us to conclude that ZnSO₄ in relation to ZnO or Zn‐AA was the supplemental zinc source with higher zinc bioavailability to Nile tilapia.     

Effects of experimental hypo- and hyperthyroidism on iodothyronine deiodinases in Nile tilapia, Oreochromis niloticus

In the present study, we examined the effects of experimentally-induced increases or decreases in plasma concentrations of thyroid hormones on iodothyronine deiodinases in tilapia, Oreochromis niloticus. To obtain hyperthyroid tilapia, fish were injected with porcine follicle stimulating hormone (pFSH) 36 hours before sampling or fed on demand for 11 days with tilapia pellets containing 12 ppm T3. Tilapias were made hypothyroid by providing them food containing 0.2% methimazole for 11 days. Plasma T4 and T3 and the in vitro deiodinase activity in liver, kidney, brain and gill were measured at the end of the treatment period. Injection with pFSH caused an increase in plasma T4 but had no influence on plasma T3 levels. A small increase in plasma T3 was observed in T3-fed fish. Plasma levels of both T4 and T3 were decreased by methimazole treatment. We observed no changes in kidney type I deiodinase (D1), whereas liver type II deiodinase (D2) was increased during hypothyroidism and decreased during hyperthyroidism. Hypothyroidism resulted in a significant decrease in brain, gill and liver type III deiodinase (D3). An pFSH-induced increase in T4 stimulated brain and gill D3 but not liver D3, whereas the opposite was true in T3-fed fish. We conclude that the regulation of D1 and D3 in tilapia is probably different compared to mammals.     

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.     

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.