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.     

Controlled hatchery production of Clarias gariepinus (Burchell 1822): growth and survival of fry at high stocking density

Abstract. The growth and survival of Clarias gariepinus (Burchell) fry was investigated at high stocking density. Significant increases in mean fry weight, and concomitant significant decreases in specific growth rate, were recorded over successive 5-day periods. Fry growth was negatively density dependent. Fry survival was in excess of 90% in all treatments. Increasing stocking density between 50 and 150 fish/l altered the pattern of mortality; non-cannibalistic deaths decreased significantly with increasing stocking density though cannibalism did not significantly increase. Periods of weaning fish onto larger feed particles were associated with temporarily increased rates of cannibalism.     

Bioenergetic modelling of effects of fertilization, stocking density, and spawning on growth of the Nile tilapia, Oreochromis niloticus (L.)

Abstract. A bioenergetic growth model was developed to examine the integrated effects of fertilization, stocking density, and spawning on the growth of tilapia, Oreochromis niloticus (L.), in pond aquaculture. The analyses showed that growth rates increase with higher levels of organic fertilization up to 500kg/ha/week. Growth rates increased with added food rations in ponds, reaching a maximum growth of 2-07g/day at about 44–48 days after stocking. Fish growth rates decreased with increased levels of stocking density. The stocking density for optimal growth is 1fish/m²; the optimal density for total harvesting weight and fish size is 2 fish/m². Model sensitivity analysis indicated that tilapia growth is most sensitive to catabolism (metabolism) and anabolism (synthesis) coefficients, both of which are geometrically related to the fish body weight. Food assimilation efficiency (b) and the food consumption coefficient (h) have a modest effect on fish growth. Spawning in grow-out ponds can have a major effect on fish growth.     

Small-scale fry production systems for Nile tilapia, Oreochromis niloticus (L.)

Abstract Experiments were conducted to evaluate and compare the production, quality and survival of eggs and the subsequent growth and survival of fry in two small-scale production systems: natural incubation and egg collection followed by artificial incubation. Artificial incubation produced a significantly greater number and biomass of fry per unit weight of female broodstock (P < 0·05). This was due to the significantly decreased spawning interval in females from which eggs were collected (mean = 23· days) compared to naturally incubating females (mean = 36·8 days). It is also hypothesized that survival during artificial incubation (85%) is greater than in natural incubation. Cost-benefit analysis demonstrated a threefold increase in total net returns for artificial incubation.     

Increased spawning activity of female Nile tilapia (Oreochromis niloticus) (L.) after stocking density and photoperiod manipulation

This study was conducted to evaluate the effects of stocking density and photoperiod in increasing the reproductive performance of Oreochromis niloticus. In experiment 1, a change in stocking density (from 47.7 to 6.8 kg m^?3) was performed, with groups of 48 females moved to single compartments. In experiment 2, 36 females experienced a 6L:18D photoperiod for 21 or 28 days (stocking density: 31.3 kg m^?3) before being placed in individual compartments (stocking density of 6.9 kg m^?3, 12L:12D photoperiod). The spawning rates in experiment 1 (32.2%) and in experiment 2 (21 days: 65.2%, 28 days: 36.1%) were significantly higher than those in the control (17.7%). On the other hand, hatching and swim‐up fry rates were significantly lower in experiment 2 – 21 days (41.3%, 40.4%) but not in experiment 1 (64.0%, 56.3%) compared with the control (67.0%, 62.3%). The spawning rate in experiment 2 – 21‐day treatment group was the highest, while the number of eggs collected per female was significantly lower than that in the control. In experiments 1 (20.8%) and 2 (21 days: 44.4%, 28 days: 19.4%), the daily spawning rates were the highest 3 days after maintaining females in single compartments. The current experiment demonstrates how specific stocking density changes can be used to induce higher spawning rates in Nile tilapia.     

Performance of Oreochromis niloticus (L.) fry maintained on mixed feeding schedules of differing protein content

Abstract. Oreochromis niloticus (L.) young of two size groups, 170-213 mg (±7) and 1-017-1-072 g (±0-04), were reared under seven different dietary schedules for 70 days. The two control diets had 18% and 30% protein content; the other five schedules were randomly determined, where the feeding of the low-protein diet alternated with the high-protein diet, for differing periods. On the basis of the observed rate of growth, food conversion ratio, protein efficiency ratio and percentage protein retained in both size groups of young O. nitoticus, those reared on a dietary schedule of 2A/3B performed best followed by those reared on schedule 1A/3B; where the numerical value refers to the number of days a particular diet was offered continuously. The feed cost-saving factor, by adopting alternate feeding schedules as compared to presenting a high-protein diet continuously, is shown to be significant.     

Influence of feeding rate and diet form on growth and survival of Nile tilapia (Oreochromis niloticus) fry

Young Nile tilapia (12 mg mean body weight and 11 mm total length) were stocked at a density of 5 fish/l in twelve 50-l aquaria filled with 30 l of tap water. They were fed pellet crumbles containing 35% crude protein at various daily feeding rates expressed as percentages of fish biomass. Mean increases in body weight after 5 weeks were 63, 198, 232 and 228 mg for the 15, 30, 45 and 60% feeding rates, respectively, when ambient temperature ranged from 19 to 21°C. Corresponding survival rates were 53, 85, 87 and 84%. Growth and survival rates were enhanced significantly (P < 0.01) at the 30, 45 and 60% feeding rates.Two feeding trials were conducted to compare the growth and survival of fry fed pellet crumbles and an unpelleted form of the same diet. Results showed that growth and feed conversion were similar for both forms of diet. However, the survival rate of fry fed pellet crumbles was significantly higher (P < 0.01) than the survival rate of fry fed the unpelleted diet. Prior pelleting of the formulated diet for the tilapia fry given at 30% to 45% of fish biomass daily ensured high survival, fast growth and efficient feed conversion.     

Effect of fluoxymesterone on sex ratio and growth of Nile tilapia, Oreochromis niloticus (L.)

The androgenic and anabolic potential of fluoxymesterone (FM) was evaluated by incorporating the hormone into the feed of Nile tilapia, Oreochromis niloticus(L.) fry. Phenotypic all-male populations were produced when FM was given at 1, 5 and 25mg/kg of feed. Fry fed methyltestosterone (MT) at 60 mg/kg of feed and 0-2 mg of FM per kg of feed had a sex ratio of 97-7% and 87-3% phenotypic males. No positive anabolic effect was evident in response to adding FM or MT to the feed at the end of the 28-day treatment period or after an additional 6 weeks of growth without hormone. Growth was less for fry which received 25 mg/kg of FM compared to those receiving lesser rates of FM, 60 mg/kg MT, and controls.     

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.     

Effect of density on survival and growth of cyprinid fish fry

One of the bottlenecks in Israel's cold water ornamental fish industry is the large loss of fish during the post-larval stage. As a first step towards increasing survival rates, the optimal stocking density in earthen ponds for fry of each species should be determined. The results of five consecutive experiments with fry of goldfish (Carassius auratus), common carp and koi (respectively, edible and ornamental morphotypes of Cyprinus carpio) are presented here. The experiments were run in 18 cages of 1 m³ and 0.8 mm mesh size placed in a 0.02 ha earthen pond, stocked at 50,100 and 200 fry per cage. The variables analyzed were growth rate, harvesting weight, biomass and survival. Equations to estimate growth rates under different conditions are given. The three fish types present different growth rates and survival patterns in relation to stocking density and season, which lead to different management implications. Koi can be stocked up to 2 million fry per ha without showing negative density effects. Goldfish should be stocked at low density (500,000–1 million fry per ha) in spring and at higher rate (2 million fry per ha) in summer. Common carp stocking density should be adjusted to obtain the required fish size at harvest.     

Effect of potential probiotic bacteria on growth and survival of tilapia Oreochromis niloticus L., cultured in the laboratory under high density and suboptimum temperature

This study examined the effect of potential probiotic bacteria on growth and survival of the tilapia Oreochromis niloticus , under high density and suboptimum temperature. Presumptive Bacillus and lactic acid bacteria (LAB) were isolated from tilapia and from their culture system and were characterized for haemolytic and enzymatic activity, and antagonism against Vibrio . Selected strains were included in the diet of juvenile tilapia and evaluated during a 134-day assay. The experiment was conducted with four treatments: (1) fish fed with commercial feed plus Dry Oil^®; (2) fish fed with commercial feed plus LAB; (3) fish with bacilli in water; (4) fish with a mixture of treatments 2 and 3. Tilapias in all treatments, including bacteria, grew significantly better than fish fed with commercial feed plus Dry Oil^® (control group). Survival was similar in all treatments. The physicochemical parameters of the culture system were maintained within the optimal ranges for the species, with the exception of temperature (19.9–24.82 °C). Animals fed diet supplemented with bacilli and LAB had good survival and the best growth performance, suggesting that bacteria are appropriate growth-stimulating additives in tilapia cultivation.     

Effect of feed colour on growth and feed utilization of Nile tilapia (Oreochromis niloticus L.) larvae and fingerlings

Two experiments were conducted to investigate the effects of feed colour on the performance of Nile tilapia (Oreochromis niloticus) larvae and fingerlings. In the first experiment, triplicate groups of newly hatched larvae (0.01 g fish⁻¹) were stocked in 40 L glass aquaria at a density of 2 fish L⁻¹. The fish were fed a test diet (400 g kg⁻¹ crude protein) with six different colours (dark blue, dark green, red, dark brown, yellow and light brown) for 60 days. The best performance and survival were achieved in fish fed on dark‐coloured diets, while light‐coloured diets (yellow and light brown) resulted in inferior performance. Dark diets also produced higher body protein than light diets. Body water, lipids and ash showed irregular trends. In the second experiment, triplicate groups of Nile tilapia fingerlings (5.30 g fish⁻¹) were stocked in 140‐L aquaria, in a recirculating indoor system. The fish were fed a test diet (350 g kg⁻¹ crude protein) with the same colours used in the larval trial, for 60 days. Growth rates, feed efficiency, survival and body composition were not significantly affected by feed colours. These results suggest that Nile tilapia larvae are visual feeders, and they prefer dark‐coloured diets to light‐coloured diets, while fingerling fish showed no preference to diet colours.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.     

Effects of stocking density on survival, growth, size variation, and production of Tilapia fry

In aquaculture, controls of size (length and weight) and production of fish are two important tasks to meet the market demands, and increasing the stocking density is a way of dealing with the problem of land shortage. In this study, tilapia fry were stocked at the densities of 0.1, 0.2, 0.4, 0.8, 1.6 and 3.2 fry I^?1 for an experimental period of 10 weeks. The size, size variation, percentage survival and production were found to be significantly affected by stocking density, but not for condition factor. The simple linear regression model, after the logarithmic transformation, was appropriate for the relationship between size and experimental period. The percentage survivals at all stocking densities were high (> 95%), especially at the stocking density of 0.4 fry I^?1 and less (100%). At the higher densities, percentage survival and experimental periods were anti-logistically related. At the end of the experiment, there was a negative relationship between the logarithms of size and the logarithms of stocking density, but a positive relationship between the logarithms of production and the logarithms of stocking density.     

Effect of feeding different grain sources on the growth performance and body composition of tilapia, Oreochromis niloticus (L.)

Growth performance and body composition of tilapia Oreochromis niloticus (L.), fed isonitrogenous and isoenergetic diets containing different grain sources (maize, wheat, barley, sorghum and rice) at a level of 25% were studied for a period of 62 days. Fish fed a diet containing sorghum showed the maximum weight grain, highest specific growth rate (SGR, 2.23), the best feed conversion (FCR, 1.07) and protein efficiency ratio (PER, 2.42) in comparison with all other diets. The diets containing maize, wheat and rice did not show any significant (P < 0.05) differences between each other. The barley diet showed the poorest values (SGR, 2.05; FCR. 1.34; PER, 1.98: and NPR, 30.65) in comparison with others. Although the diet containing sorghum showed the best net protein retention (NPR, 36.21) values, the results did not differ (P > 0.05) among maize, wheat and sorghum diets. The sorghum diet produced fish with lower moisture but higher body fat contents as compared to others. The fish fed diets containing maize, wheat, barley and rice did not show any significant difference (P > 0.05) in their body moisture and fat contents. The source of grain in the diet did not affect the crude protein and ash contents of fish (P > 0.05). It is suggested that cereal grains at the 25% level can efficiently be utilized in tilapia diets, sorghum being the best.     

Modelling growth in cultures of Oreochromis niloticus (L.) and Cyprinus carpio L. in Pernambuco, Brazil

Different growth models in cultures of Oreochromis niloticus (L.) and Cyprinus carpio L. were compared in Pernambuco, Brazil. The Chapman–Richards growth model was shown to be the most appropriate for Oreochromis niloticus, while Silva's model best expressed growth for Cyprinus carpio.     

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.     

Effect of probiotics on the survival, growth and challenge infection in Tilapia nilotica (Oreochromis niloticus)

This study was conducted in order to evaluate the potential benefit of Bacillus pumilus and a commercial product (‘Organic Green'^?) as a probiotic in the culture of the tilapia nilotica. Two doses of B. pumilus (10⁶ and 10¹² g^?1 diet fed) and Organic Green^? (1 and 2 g kg^?1 diet fed) were used as feed additives and administered for periods of 1 (groups 2, 3, 4 and 5 respectively) and 2 (groups 6, 7, 8 and 9 respectively) months; group 1 served as a control. Each group consisted of 4 equal replicates of 320 fish. Body weight, nitroblue tetrazolium (NBT) activity, haematocrit values and total and differential leucocytic counts (TLC and DLC) were recorded in each group after 1 and 2 months. At the end of the experiment (8 months), survival and individual body weights were recorded. Challenge infections were performed after 1, 2 and 8 months using 0.5 mL culture suspension of a pathogenic reference strain of Aeromonas hydrophila (10⁸ bacteria mL^?1). The NBT values were increased significantly in all treated groups, except those administered B. pumillus (groups 3 and 6). There were significant changes in haematocrit values and TLC and DLCs in the treated groups, except group 3, which showed a significant increase in TLC, lymphocytes and monocytes. There was a statistically significant increase in the individual body weight in groups 5, 6, 8 and 9. The survival rates of all treatment groups were higher than the control group, the differences being statistically significant in groups 3 and 9. The challenge infection showed a variable response with the type and dose of treatment and the period of application. The highest relative levels of protection were an average increase of 62.5% after 1 month (groups 3 and 5), 55.6% after 2 months (group 7) and 15.8% after 8 months (groups 8 and 9). Overall, both types of probiotics induced a similar effect. The results show the potential of using probiotics to enhance immune and health status and improve disease resistance in Oreochromis niloticus, thereby improving growth performance. However, further extensive testing, including a full commercial cost–benefit analysis, is necessary before recommending their application in aquaculture.     

Controlled hatchery production of Clarias gariepinus (Burchell): growth and survival of larvae at high stocking density

Abstract. The mean increase in African catfish, Clarias gariepinus (Burchell), weight with time over the entire larval period can be approximated by a cubic or exponential growth model. However, the growth rate indices specific growth rate ( k ) and the regression coefficient of a cube root transformation of the weight data ( b ), both vary significantly when measured over successive short intervals from first feeding. In particular, the onset of air breathing is associated with a significant depression in growth rate. The variation in specific growth rate ( k ) with larval age closely approximates the relationship between mean % increase in body weight per day and larval age; however, the cube root regression coefficient does not share this property. In addition to the effect of larval age the growth rate of African catfish larvae is significantly affected by the initial density at which they are stocked (between 25 and 250 larvae/1) and interactions between age and stocking density. Survival over the larval period, of 80% or more, is apparently unaffected by initial stocking density (between 50 and 250larvae/I); however, the onset of air breathing in particular is associated with an increase in fish deaths.