Preliminary observations on growth and survival of Oreochromis spilurus x GIFT Oreochromis niloticus F1 reciprocal hybrids in fresh and seawater

Tilapia has a significant potential for culture in saline environments. There is an increasing demand among tilapia producers to develop a tilapia hybrid that can survive well in marine water conditions. This study compared mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), survival, feed conversion ratio (FCR), condition factor (K), production rate (PR) and rate of skin lesions, and tail and fin rot as well as eye cataract in the Genetically Improved Farmed Tilapia strain (GIFT) of the Nile tilapia, Oreochromis niloticus (NN) and the salt‐tolerant Oreochromis spilurus (SS), and their F₁ reciprocal hybrids; O. niloticus ♀ x O. spilurus ♂ (NS) and O. spilurus ♀ x GIFT O. niloticus ♂ (SN) in freshwater (0 g L^?1) and seawater (40 g L^?1). Fish (3.5 g) were stocked at 150‐fish m^?3 and fed with sea bream pellets (47% protein) for 180 days. Results showed that in seawater, the SN hybrid had the highest values for MWT (165.9 g), DGR (0.9 g fish^?1 day^?1), SGR (2.14% day^?1), survival (96.3%), PR (23.9 kg m^?3) and best FCR (1.53) followed by the NS hybrid and the NN parent. Both hybrids had significantly lower rates of skin lesions and fin and tail rot than the NN genotype. In freshwater, the NN had the highest values for MWT (255.1 g), DGR (1.40 g fish^?1 day^?1), SGR (2.38% day^?1), K (2.13%) and PR (34.9 kg m^?3) followed by the NS and SN hybrids. High estimate of heterosis for MWT (41.3%), DGR (42.5%), SGR (10.7%) and survival (22.1%) was obtained in the hybrids reared in seawater, indicating that a hybrid vigor was produced and the fast growth trait from the GIFT parent was successfully combined with the salinity tolerance trait from the O. spilurus parent. The better growth performance and survival of the SN hybrid in seawater indicate that this hybrid is more suitable for culture in seawater than its reciprocal hybrid.     

Observations on the reproductive performance of three mouth-brooding tilapia species in low-salinity underground water

The reproductive performance and seed production of three mouth‐brooding tilapia species, Oreochromis spilurus (Günther), Oreochromis aureus (Steindachner) and Taiwanese red tilapia hybrid, were compared in low‐salinity underground water (3–5 g L^?1) to select species with the highest reproductive rate. Two‐year‐old males and females having average body weights of 454 and 259 g, respectively, were stocked in 2‐m³ fibreglass breeding tanks (two tanks per species) at 1:3 male to female sex ratio and at average density of three fish m^?2. Seeds (unhatched eggs; yolk‐sac fry and the swim‐up fry) were collected weekly for 112 days. The results showed O. spilurus to have significantly higher (P<0.05) mean spawning parameters expressed as total seed tank^?1 (84 154), seed kg female^?1 day^?1 (284), seed m^?2 day^?1 (190.3) and seed female^?1 day^?1 (76.3), than O. aureus and red tilapia. Monthly seed production in O. spilurus and red tilapia gradually increased from May, peaked in July and declined in August, while in O. aureus, it continued to decrease from May to August. In this study, the observed production levels of seed in O. spilurus were among the highest levels reported for tilapia; therefore, O. spilurus could be selected as a potential candidate for mass seed production in commercial tilapia hatcheries.     

Effect of light intensity and photoperiod on Nile tilapia Oreochromis niloticus L. seed production

The objective of this study was to compare the effect of six light intensity/photoperiod combinations (2500 lux/18 h, 2500 lux/15 h, 2500 lux/12 h, 500 lux/18 h, 500 lux/15 h and 500 lux/12 h) on seed production in the Nile tilapia Oreochromis niloticus L. Each combination represented a treatment and was triplicated in 0.4‐m³ fibreglass tanks within a recirculating water system. Water temperature was maintained at 29.0 ± 1.0 °C. Males and females with mean body weights of 116.8 and 91.6 g, respectively, were stocked at a rate of eight fish/tank with a male to female ratio of 1:3. Seeds (eggs, sac fry and swim‐up fry) were collected every 2 weeks. The experiment lasted for a total of 120 days. The results showed that the 2500 lux/18 h treatment produced significantly greater (P < 0.05) total seed/tank (4944), seed kg^?1 female day^?1 (50.9), seed m^?2 day^?1 (40.3) and seed/ female day^?1 (6.7) than treatments with medium or short photoperiods (15 and 12 h day^?1 respectively) or lower light intensity (500 lux). The degree of spawning synchrony and percentage of the sac and swim‐up fry stages were significantly higher in the 2500 lux/18 h treatment than in the other treatments. Under the conditions tested in this study, seed production and spawning synchrony in the Nile tilapia may be improved by subjecting breeders to a light intensity of 2500 lux and a photoperiod of 18 h day^?1.     

Studies on fish heterosis with DNA fingerprinting

One Tilapia hybridization, Oreochromis aureus, (Steindachner) ♂ × Oreochromis niloticus, (Linnaeus) ♀, and two common carp, Cyprinus carpio, (Linnaeus) ♂, hybridizations, Russian mirror carp ♂ × Xingguo red carp ♀, and German mirror carp ♂ × Xingguo red carp ♀ were used to study the feasibility of predicting heterosis using genetic distance from DNA fingerprinting. The results indicated that highly polymorphic DNA fingerprints could be obtained with human minisatellite 33.6 as a probe on the studied varieties. The within‐population similarity indices of O. aureus, O. niloticus, Russian mirror carp, German mirror carp and Xingguo red carp were 0.785, 0.577, 0.432, 0.348 and 0.339 respectively. The similarity indices between F1 and their parents of three hybridization combinations were not significantly different (P > 0.05). There were larger genetic distances between two hybridization combinations, O. aureus♂ × O. niloticus♀ and Russian mirror carp ♂ × Xingguo red carp ♀, which showed heterosis in production and were extensively used in Chinese aquaculture. The genetic distance between O. aureus♂ and O. niloticus♀ was 0.338, and that between Russian mirror carp and Xingguo red carp was 0.344. However, the genetic distance between German mirror carp and Xingguo red carp was 0.129; this corresponded with the fact that their F1 generation did not show heterosis in the Chinese fish hybridization experiment. The study suggested that genetic distance could be used to predict fish heterosis.     

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.     

Nursing duration and pond fertilization level affect polycultures of Indian major carp (rohu Labeo rohita and mrigal Cirrhina mrigala) with monosex Nile tilapia Oreochromis niloticus

This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90‐day trial based on 40 20‐m² pens fixed in four 400‐m² earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day^?1 compared with 1.1–1.6 g per fish day^?1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day^?1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=?1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r²=0.98, P<0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha^?1 day^?1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day^?1, P>0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day^?1 and 1.6 g per fish day^?1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha^?1 day^?1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P>0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha^?1 day^?1) was calculated at 4.06±0.08 g·m^?2 day^?1, which was significantly higher (P<0.001) than the yield (1.82±0.12 g·m^?2 day^?1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high.     

Comparative Growth and Survival of Reciprocal Hybrids Between Clarias gariepinus and Clarias anguillaris

Reciprocal, interspecific hybrids of Clarias gariepinus and Clarias anguillaris were produced via hypophysation and dry stripping. Two-week-old fry (0.06 ± 0.02 g) of the parental Clarias species and their interspecific hybrids were stocked in duplicated 1 m³ hapas suspended in outdoor earthen ponds (16 m²) for a rearing period of 56 days. Growth and survival of the hybrids was intermediate to the faster growing and better surviving C. gariepinus and the more slowly growing and more vulnerable C. anguillaris parental lines. The weight gain attained by C. gariepinus, C. anguillaris, C. gariepinus (♂)?×?C. anguillaris (♀), and C. anguillaris (♂)?×?C. gariepinus (♀) were 3.18 g, 2.99 g, 3.16 g and 3.05 g, respectively. Among hybrids, the growth of C. gariepinus (♂)?×?C. gariepinus (♀) was higher than the reciprocal C. anguillaris (♂)?×?C. gariepinus (♀). Heterosis for growth was a negligible 0.65% and for survival was negative (?5%). C. gariepinus appears to be the best species for aquaculture in terms of growth rate and survival.     

Protein requirements of Nile tilapia (Oreochromis niloticus) fry cultured at different salinities

Effect of isolipidic (62.7 ± 5.0 g kg^?1) diets with protein levels of 204.6 (T20), 302.3 (T30), 424.6 (T40) or 511.0 g kg^?1 (T50) on growth and survival in Nile tilapia (Oreochromis niloticus Linnaeus 1758) fry cultured for 70 days at one of four salinities (0, 15, 20 and 25 g L^?1) was evaluated. A bifactorial (4 × 4) design was used with 16 treatments run in triplicate and 20 fry (0.25 ± 0.04 g) per replicate under semi‐controlled conditions. Four independent, recirculating systems (one per salinity level) were used, each one with 12 circular tanks (70 L capacity), filters and constant aeration. The different salinities had no significant effect on growth. Weight gain improved significantly as dietary protein content increased, although organisms fed the T50 diet had a lower growth rate. Survival was highest (98.33%) in the T50/15 (protein/salinity levels) treatment and lowest (71.0%) in the T20/20 treatment, with no pattern caused by the variables. The T40/25, T40/20 and T50/0 treatments produced the most efficient growth and feed utilization values while the T20 treatments at all the salinities resulted with the lowest performance. With the exception of the T50 treatments, a non‐significant tendency to increased weight gain was observed as water salinity increased, suggesting that the salinity of the culture environment does not influence dietary protein requirements in Nile tilapia O. niloticus fry.     

Survival rates of tilapia, Oreochromis spilurus (Günther), fingerlings reared at high densities during winter using warm underground sea water

The study was conducted to determine the optimum stocking density for rearing tilapia. Oreochromis spilurus (Günther), fingerlings in tanks during winter using warm (21-26°C) underground sea water (37%o). Seawater-acclimated fingerlings with mean weight of 2 g were stocked in eighteen 400-1 fibreglass tanks at 750 and 1000 fish m^?3. Fish were fed at the rates of 2.5, 3.0 and 3.5% day^?1 of the fish biomass. After 83 days, the mean individual daily weight gain was significantly higher (P < 0.028) at stocking of 750 fish m^?3 than at 1000 fish m^?3. Feed conversion ratio was significantly higher at stocking of 1000 fish m^?3 than at 750 fish m^?3 and at feeding rate of 3.5% day¹ than at 2.5% day^?1. However, because no significant differences were observed on survival rates between the two stocking densities and among feeding rates, it is recommended that the stocking density of 1000 fish m^?3 and a feeding rate of 2.5% day^?1 be used for optimum production of tilapia fingerlings in tanks during winter using warm underground sea water.     

Effects of controlling temperature and light duration on seed production in tilapia, Oreochromis spilurus (Günther)

An experiment was conducted to compare the seed production of tilapia, Oreochromis spilurus (Günther), under ambient water temperature and photoperiod, and under controlled water temperature (29.0 ± 2.0 °C), and photoperiods of 13 and 14 h day^?1. Male and female breeders with average weights of 155.4 and 78.7 g, respectively, were stocked in nine 1.04 X 1.04 X 0.40 m (L X W X H) fibreglass tanks. Each tank was stocked with two males and six females. Seed collection was carried out biweekly for 300 days. The results showed that the seed kg^?1 female day^?1, seed m^?2day^?1, total seed production per tank and spawning rates of females were highest during the 14 h day^?1 photoperiod (112.4, 77.4, 24 724 and 42.1%, respectively), followed by ambient spawning conditions (104.0, 57.9, 18 356 and 36.6%, respectively), and lowest during the 13 h day^?1 photoperiod (49.5, 36.5, 12 021 and 25.7%, respectively). Under ambient spawning conditions, peak spawning occurred in May. Monthly seed production was affected by changes in temperature and light duration. In both controlled photoperiods, the peak of seed production was observed during the first month after stocking. In all treatments, spawning declined gradually after the peak, which can be attributed to exhaustion of the breeders. The findings of this study indicate that seed production of O. spilurus in Kuwait can be extended beyond the restricted spawning season of 6-7 months by maintaining water temperature at 29.0 ± 2.0 °C and photoperiod at 14 h day^?1.     

Effect of different broodstock densities on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.), in a recycling system

The present study was conducted to evaluate the effect of different stocking densities on the seed production of Nile tilapia, Oreochromis niloticus (L.), under intensive recycling hatchery system conditions. Males and females with mean body weights of 163.2 and 105.0 g, respectively, were stocked at three broodstock densities (4, 8 and 12 fish m^–2) at a male:female ratio of 1:3 in 1 × 1 × 0.43 m (W × L × H) fibreglass tanks. The tanks were illuminated at 2500 lux for 18 h day^–1 and the water temperature was maintained at 29 ± 1 °C. Effluent from spawning tanks was recycled through a biological filter with 10–15% replacement of new water per day. The experiment lasted for 126 days. The results showed that breeders stocked at 4 fish m^–2 had significantly higher (P < 0.05) mean values for total seed production, seed kg^–1 female day^–1, seed female^–1 day^–1, seed m^–2 day^–1 and spawning synchrony than at 8 and 12 fish m^–2 broodstock densities. The mean percentage of seeds in the yolk-sac and swim-up fry stages was highest at 4 fish m^–2 broodstock density. However, the recovery rate was not affected by broodstock density. It is recommended that further research should be conducted to determine whether weight m^–2 , number m^–2 or age of broodstock should be the basis for stocking broodstock.     

Effect of dietary protein levels and feeding rates on growth performance, production traits and body composition of Nile tilapia, Oreochromis niloticus (L.) cultured in concrete tanks

A 28‐week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 61.9±6.03 (g fish^?1) and 17.6±0.45 (cm fish^?1), respectively, to examine the effect of two protein levels and three feeding levels (% body weight (BW) day^?1) on growth performance, production traits and body composition. Twelve 4‐m³ concrete tanks (2 × 2 × 1.25 m, long, width and height) were each stocked with 100 fish and fed diets containing either 25% or 30% crude protein at rates of 1%, 2% and 3% BW daily (2 × 3 factorial experiment). The results revealed that there was no significant increase in growth rate with increasing dietary protein levels, whereas there was significant increase in growth rate with increasing feeding levels (P≤0.05). The same trend was also observed for mean BW (g), mean body length (cm), production rate (kg m^?3), specific growth rate (SGR % day^?1), feed conversion ratio (FCR), condition factor (K) and survival rate (%). The best final mean BW (g), final mean body length (cm), SGR (% day^?1), FCR, K, production rate (kg m^?3) and survival rate (%) were recorded in groups of fish fed with 25% dietary protein at the 2% feeding level. Whole fish fat and energy contents were not significantly influenced (P>0.05) by protein levels and feeding levels. Protein and ash contents were significantly (P≤0.05) influenced by feeding level, but not by dietary protein level. Economic evaluation indicated that dietary protein 25% (diet A) at the 2% BW day^?1 feeding level was the most cost‐effective and affordable feed strategy for farmers. We conclude that a 25% protein diet fed at 2% BW day^?1 is recommended for adult Nile tilapia reared in concrete tanks.     

The Effects of Dietary Yeast Culture or Short‐chain Fructo‐oligosaccharides on the Intestinal Autochthonous Bacterial Communities in Juvenile Hybrid Tilapia,Oreochromis niloticus♀×Oreochromis aureus♂

The effects of dietary yeast culture (YC) or short‐chain fructo‐oligosaccharides (FOS) on intestinal autochthonous bacterial communities in juvenile hybrid tilapia, Oreochromis niloticus♀×Oreochromis aureus♂ were studied by 16S rDNA denaturing gradient gel electrophoresis (DGGE). Ninety Tilapias in tanks (10 fish per tank) were randomly and equally divided into three groups. At the end of an 8‐wk feeding period of CK (the control treatment), YC (3 g/kg), or FOS (1 g/kg), autochthonous gut bacteria were analyzed in intestinal samples of all fish in each tank of a recirculating aquaculture system. The clear differences in the banding patterns indicated the obvious effects of dietary prebiotics on intestinal communities in hybrid tilapia. Higher variation was detected within the dietary YC group. This difference might be due to the effects of certain immune‐stimulating agents in YC on the immunity response of hybrid tilapia. It was concluded that dietary prebiotics, YC, and FOS obviously affected the intestinal bacterial community in hybrid tilapia with different patterns for different kinds.     

Efficacy of an experimentally inactivated Streptococcus agalactiae vaccine in Nile tilapia (Oreochromis niloticus) reared in Brazil

Tilapia aquaculture is one of the fastest‐growing segments of fish production in Brazil. Nile tilapia (Oreochromis niloticus) is largely cultivated in the state of Parana, where Streptococcus agalactiae is the cause of severe disease outbreaks. The objective of this paper was to evaluate an inactivated S. agalactiae vaccine in tilapia for the control of streptococcal disease outbreaks. Tilapia, weighing approximately 20 g each, were intraperitoneally (i.p.) inoculated with 0.1 mL of the vaccine at a dose of 2.0 × 10⁸ colony‐forming unit (CFU) mL^?1. One group of tilapia (treatment 1) received one vaccine dose, and the other group of tilapia (treatment 2) received two doses, with an interval of 21 days. The control group was i.p. inoculated with 0.1 mL tryptic soy broth fish^?1. Immunized and control tilapia were i.p. challenged with 0.1 mL of 3.0 × 10⁷ CFU mL^?1 at 30 days post vaccination. The fish were monitored daily for disease signs and for mortality for 16 days post challenge. A statistically significant difference (P=0.0045) was found between the mortality of treatments 1 and 2. The value of relative per cent of survival of 83.6% and 96.4%, respectively, indicate that this vaccine was efficient in Nile tilapia.     

Pond farming of Nile tilapia, Oreochromis niloticus (L.) in northern Cameroon. Comparing two different strategles for feeding cottonseed cake in tilapia male monosex culture

Two cottonseed cake feeding strategies were tested in pond culture of hand-sexed male Nile tilapia, Oreochromis niloticus (L.). (W₀ > 80 g), with the objective of making better use of the algal blooms which develop when cottonseed cake is applied to a pond. In the conventional ‘progressive feeding strategy’, the daily amount of cottonseed cake was adjusted monthly for the total tilapia bioweight estimated from sampling, assuming that cottonseed cake primarily acted as a tilapia feed. In the ‘linear feeding strategy’, ponds received a fixed daily amount of cottonseed cake throughout the trial, based on the hypothesis that tilapia would cover their nutritional requirements mostly by grazing the algae. Each feeding strategy was tested at two feeding levels. Mean daily feeding rate R in the progressive feeding strategy averaged 48.6 (low feeding level) and 102.5 kg ha^?1 day^?1 (high feeding level), and 49.8 and 82.9 kg ha^?1 day^?1 in the linear feeding strategy. Significantly better growth rates and feed conversion rates were obtained in the progressive feeding strategy. Average extrapolated net pond production was highest at R_pr=6% body weight day^?1 (10.61 ha^?1, year^?1). It was concluded that cottonseed cake contributed to tilapia growth mainly directly as a tilapia feed rather than indirectly as a pond fertilizer via algal production. Finally, the appropriateness of the metabolic feeding rate R_mb(BW^0.8 day^?1) was discussed, compared with the progressive feeding rate R_pr (%BW day^?1). (BW denotes body weight). A practical, two-step linear feeding method was proposed for cottonseed cake as a ‘rule of thumb’ that is workable in the field.     

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.     

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.     

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).     

Relationship Between Dietary Protein Source and Feeding Frequency During Feeding Nile Tilapia,Oreochromis niloticus (L.) Cultured in Concrete Tanks

ABSTRACT

A 24-week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 50.87 ± 6.03 g and 14.4 ± 0.45 cm, respectively, to examine the effect of two protein sources and two feeding frequencies on growth performance, production traits, and body composition. Twelve 4 m³ concrete tanks (2 × 2 × 1.25 m, long, width, and height) were each stocked with 100 fish and fed diets containing either fish meal protein or soybean meal protein at two feeding frequency of two times daily or four times daily (2 × 2 × 3 factorial experiment). The results revealed that there was no significant effect of dietary protein sources on growth rate, whereas there was a significant increase in growth rate with increasing feeding frequency (P < 0.05). The same trend was also observed for mean body weight (g), production rate (kg/m3), specific growth rate (SGR % day^?1). The best final mean body weight (g), specific growth rate (SGR % day^?1), and production rate (kg/m3) were recorded in groups of fish fed with feeding frequency four times daily. Whole fish moisture, protein, fat, and ash contents were significantly influenced (P ≤ 0.05) by protein sources and feeding frequency, except protein not influenced with feeding frequency. Energy was significantly (P < 0.05) influenced by feeding frequency, but not by dietary protein sources. Economic evaluation indicated that soybean meal (Diet B) at four times feeding daily was the most cost-effective and affordable feed strategy for farmers. We conclude that a soybean diet fed four times daily is recommended for adult Nile tilapia reared in concrete tanks.     

Faecal coliforms in pond water, sediments and hybrid tilapia Oreochromis niloticus×Oreochromis aureus in Saudi Arabia

Total bacterial load, total coliforms faecal coliforms in pond water, sediment, intestine of hybrid tilapia Oreochromis niloticus×Oreochromis aureus and pigeon Columba livia faeces were investigated monthly over a period of 1 year from July 1999 to June 2000. Fish were collected randomly by a cast net. Samples were analysed for coliforms using the multiple‐tube fermentation technique. Results showed total viable bacterial counts in the pond water, sediment, intestine of tilapia and pigeon faeces ranging from 1.8±0.9×10² to 6.0±1.2×10⁴ cfu mL^?1, 3.2±1.2×10⁵ to 2.8±1.5×10⁷ cfu g^?1, 8.2±1.6×10⁵ to 9.9±1.5×10⁷ cfu g^?11.0±0.4×10⁷to9.7±0.2×10⁹ cfu g^?1respectively. The most probable number (MPN) of coliforms and faecal coliforms ranged from 287±12 to ≥1600±0 100 mL^?1 in pond water; the MPN ranges for sediment, tilapia intestine and pigeon faeces were 257±29 to ≥1100±0 g^?1, 237±46 to ≥1100±0 g^?1 and 403±98 to ≥1100±0 g^?1 respectively. The abundance of normal bacteria coliforms was greater in the warm months than in the cold months. Ground water was free from any sort of coliform organisms, and there were no sources of human faecal matter in the pond. So, it is clear that faecal coliforms from pigeon faeces significantly contaminated (P<0.05) the ponds and tilapia intestines. Escherichia coli was the only coliform organism found in pond water, sediment, intestine of tilapia and pigeon faeces.