Juvenile Oreochromis Niloticus Research Articles

Interacting effects of water temperature and dietary protein level on hematological parameters in Nile tilapia juveniles, Oreochromis niloticus (L.) and mortality under Streptococcus iniae infection

Based on central composite rotatable experimental design and response surface method, the interacting effects of temperature (20 °C–34 °C) and dietary protein level (25%–50%) on hematological parameters including red blood cell (RBC), white blood cell (WBC) and hemoglobin (Hb) of juvenile Oreochromis niloticus were studied under laboratory conditions. The experiment lasted for 7 weeks. After the feeding trial, fish were challenged with Streptococcus iniae and mortality was recorded for within 8 days. Results showed that the linear and quadratic effects of temperature on RBC, WBC and Hb were highly significant (P < 0.01). When the dietary protein level was 25%–50%, the RBC, WBC and Hb were increased firstly and then decreased, but the linear and quadratic effects of protein level were insignificant (P > 0.05). The interacting effects of temperature and protein level on RBC and Hb were significant (P < 0.05). The regression equations of RBC, WBC and Hb toward the two factors of interest were established, with the coefficients of determination being 0.870, 0.836 and 0.881, respectively (P < 0.01). These equations could be used for prediction in practice. After the challenge, the mortalities for the combinations of 22.1 °C/28.7% and 20.0 °C/37.5% were significantly higher than 27.0 °C/37.5% (P < 0.05). The optimal temperature/dietary protein level combination was obtained at 27.9 °C/38.1% at which the lowest mortality (13.76%) was attained. This value was close to the optimal temperature/dietary protein level combination (29.4 °C/41.9%) for the greatest levels of RBC (2.560 × 106 μL−1), WBC (270.648 × 103 μL−1) and Hb (92.851 g L−1). The results of this study indicated that preferred temperature/dietary protein level combination might strengthen the non-specific immunity and reduce susceptibility to S. iniae.

In vivo acetylcholinesterase inhibition in the tissues of spinosad exposed Oreochromis niloticus

This study was conducted to evaluate the effects of an organic insecticide, spinosad on acetylcholinesterase (AChE, EC 3.1.1.7) specific activities in the brain and the liver tissues of juvenile Oreochromis niloticus, and also identify the indicator tissues in the fish. The fish were exposed to three sublethal spinosad concentrations (25, 50, 75mg/L) for 24–48–72h. Acetylcholinesterase activities were determined by spectrophotometrical methods. Acetylcholinesterase was significantly inhibited in both tissues tested. The inhibition percentages of AChE ranged for liver and brain tissues between 32–63% and 21–35%, respectively. The present study demonstrated that in vivo spinosad exposure caused AChE inhibition in the brain and the liver. The liver tissue might be suggested as an indicator tissue for spinosad exposure in the fish. Additional studies are needed to understand inhibition mechanisms of AChE by spinosad.

Oxidative and apoptotic effects of lambda-cyhalothrin modulated by piperonyl butoxide in the liver of Oreochromis niloticus

The aim of this study was to investigate the toxic effects of pyrethroid pesticide lambda-cyhalothrin in the presence of piperonyl butoxide as a modulator in the liver of juvenile Oreochromis niloticus. LC50 (96h) value of lambda-cyhalothrin was determined as 2.901μg/L for O. niloticus. The fish were exposed to 0.48μg/L (1/6 of the 96-h LC50) lambda-cyhalothrin and 10μg/L piperonyl butoxide for 96-h and 15-d. tGSH, GSH, GSSG, Hsp70 and TBARS contents, GPx, GR, GST and caspase-3 enzymes activities were determined. Lambda-cyhalothrin caused increases in tGSH, GSH, TBARS contents, and GST activity. Piperonyl butoxide treatment with lambda-cyhalothrin caused significant increases in tGSH GSH, Hsp70, TBARS contents, and GPx and GST activities while caspase-3 activity was decreased. The results of the present study revealed that lambda-cyhalothrin caused oxidative stress which upregulated GSH and GSH-related enzymes. Piperonyl butoxide increased the oxidative stress potential and apoptotic effects of lambda-cyhalothrin.

Comparative Studies on the Growth Performance of Four Juvenile &lt;i&gt;Oreochromis niloticus&lt;/i&gt; L., (1758) Strains in Pond Culture, Ethiopia

This study was conducted to investigate and compare the growth performance of four juvenile Oreochromis niloticus strains in pond culture. The fish having an average body length of 9.18 cm and weight of 12.48 g were collected from Hawassa, Ziway, Koka, and Hora lakes. They were stocked in triplicate in 5.0 m × 5.0 m × 1.5 m concrete earthen ponds in 1 m water depth. The stocking density was 2 fish/m 2 . The fish were fed 3% of their body weight per day manually, twice a day with locally available feed having 23% crude protein. The results showed that the Koka strain had the best strain and had significantly (p < 0.05) higher final mean body weight (FMBW), mean body weight gain (MBWG), specific growth rate (SGR) and gross fish yield (GFY) than the Ziway and the Hora strains, but not from the Hawassa strain. The Koka stain had the best feed conversion ratio (FCR) with slightly higher Fulton’s condition factors (FCF). However, statistical analysis showed that there was no significant difference in FCF and FCR among the four strains. Except for the Ziway strain, all the strains revealed an isomeric growth pattern. The overall conclusion is that growth performance between the four strains of Oreochromis niloticus was significantly different and thus, it is crucial to select the right strain for aquaculture purpose. However, further research may still be needed to compare more strains from different Ethiopian lakes to evaluate the genetic potential for Oreochromis niloticus breeding program.

Evaluation of Growth Performance, Feed Utilization Efficiency and Survival Rate of Juvenile Nile tilapia, &lt;i&gt;Oreochromis niloticus&lt;/i&gt; (Linnaeus, 1758) Reared at Different Water Temperature

This study was conducted to investigate the growth performance, feed utilization efficiency and survival rate of juvenile Oreochromis niloticus reared in aquaria at different water temperature. The fish with average body weight of 4.19 g were reared at 24, 26, 28, 30, 32 and 34℃water temperature for 90 days. The stocking density was 10 fish per 50 L of water. Diet of 27% crude protein was offered three times a day at the rate of 10% of their body weight. 100% of water volume was changed once in two days intervals. Growth and feed utilization efficiency of the fish were recorded at two weeks intervals. The results revealed that the growth of juvenile Oreochromis niloticus was found to be higher (57.24 g) with better BWG (53.14 g), SGR (2.93%/day), FCR (2.43), MGR (3.89 gkg 0.8 /day) and PER (1.97) on the fish reared at 32℃ water temperature followed by 30℃ (51.15 g), while the lowest growth was observed at 24℃ water temperature (29.32 g). The results also revealed that the fish reared at 34℃ water temperature had reddish colour around the fines and the operculum which were not occur on the other fish reared at other rearing water temperature. Moreover, the size at first sexual maturation was small for the fish reared at higher water temperature as compared with lower water temperature, but shorter rearing period. Survival rate of the fish was the same at all rearing water temperature. It is conclude that the water temperature ranging from 28℃ to 32℃ is optimum for rearing of Oreochromis niloticus . This study is also demonstrated that Oreochromis niloticus can be cultured in the rift valley region of the country where the average atmospheric temperature is above 26℃.

Efficacy of clove oil as anesthetic in handling and transportation of Nile tilapia, Oreochromis niloticus (Actinopterygii: Cichlidae) juveniles

This work evaluated the efficiency of clove oil as anaesthetic in handling and transportation of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). In the first experiment, safety concentrations of clove oil were assessed by measuring induction times to anaesthesia. The second experiment evaluated exposure times to anaesthetic. Clove oil efficiency during transportation was evaluated in a 24 h experiment using three concentrations of the anaesthetic (0, 9, and 18 mg.L-1). The most appropriate clove oil concentration to induce surgical anaesthesia was 90 mg.L-1. To biometry or other brief handling, the recommended concentration is 50-60 mg.L-1 as it provides fast recovery. Maximum anaesthesia time should be 10 min. The mortality rate of fish transported using 18 mg.L-1 of anaesthetic was significantly higher than that of the control group at 24 h of transportation and at 96 h after transportation. The fish transported using clove oil as anaesthetic presented more significant Na+ and K+ disorders as compared to the control group. As an anaesthetic, clove oil is efficient in the handling of Nile tilapia in routine fish hatchery procedures, although it should be avoided in the transportation.

Effect of Dietary Protein Level, Stocking Density, and Dietary Pantothenic Acid Supplementation Rate on Performance and Blood Components of Nile Tilapia Oreochromis niloticus

Protein in the diet (25 Vs 31%), stocking rate (100 Vs 200 fish per m3), and inclusion rate of pantothenic acid, vitamin B5, (10 Vs 20 mg/kg diet) were compared for their effects on blood plasma protein, albumin, urea-N, creatinine, plasma transaminase enzymes (AST and ALT), thyroxin (T3), and growth in Oreochromis niloticus juveniles. Blood total protein, albumin, ALT, T3, and growth were significantly (P < 0.001) higher in fish groups fed the high protein diet, while urea-N concentration in blood was significantly (P < 0.001) lower. Final body weight and daily weight gain were lower and food conversion rate was higher at the higher stocking density. Blood total protein, albumin, ALT, and T3 were lower in fish groups reared at high stocking density. Body weight and daily gain was significantly higher at the higher pantothenic acid inclusion level, while feed conversion ratio was lower. Blood total protein, albumin, ALT, and T3 were also elevated. The highest income to the system was from the group fed high protein, reared at low stocking density and fed diets supplemented with 10 mg vitamin B5.

Feeding behavior and stress response explain individual differences in feed efficiency in juveniles of Nile tilapia Oreochromis niloticus

Feed efficiency is a trait of enormous importance in any animal production sector including aquaculture. Individuals that are more feed efficient need to use less feed to achieve similar growth rates as compared to less efficient individuals. Considering that feed represents the largest cost of production and one of the main causes for the ecological footprint of a farm, more knowledge on the extent of individual differences in feed efficiency and underlying physiological processes are needed. This study is the first to investigate individual differences in feed efficiency, measured as residual feed intake and its relationship with feeding behaviour and stress response in one of the most important farmed fish, the Nile tilapia. The individual feed intake of twenty-four juvenile of Nile tilapia was followed during 57 days. Fish were fed until apparent satiation with a commercial feed twice per day. Individual feed behavior was registered once per week and consisted on measuring the latency to start feeding (LAT, min), total feeding time (TFT, min) and the number of feeding acts (NFA, min). Blood samples for plasma cortisol was taken at the end of the experiment (control, indicative of undisturbed levels) and after a stress test (netting), 15 days after the previous sampling. Individual growth rates and residual feed intake were determined at the end of the experiment. Results show pronounced individual differences in residual feed intake as well as a significant correlation with both feeding behavior (feeding latency, total feeding time and number of feeding acts) and stress (cortisol) response. Cortisol levels obtained after the stress test and feeding behavior could explain differences in residual feed intake by 4%. These results show that individuals with higher feeding activity and higher cortisol response are less efficient fish. This suggests that individual differences in feeding activity and stress response explain part of the differences in feed efficiency by explaining variance in maintenance energy expenditure.

Estratégia alimentar com ciclos de restrição e realimentação no desempenho produtivo de juvenis de tilápia do Nilo da linhagem GIFT

O objetivo deste estudo foi avaliar a ocorrência de resposta compensatória no desempenho produtivo de juvenis de tilápia do Nilo Oreochromis niloticus, linhagem GIFT, submetidos a diferentes estratégias alimentares. Foram utilizados 135 juvenis de tilápia, distribuídos em nove tanques de polietileno de 100L cada. As estratégias testadas foram: grupo controle (alimentado todo dia), grupo alimentado por cinco dias seguidos de dois dias de restrição de alimento (5A/2R) e grupo alimentado por quatro dias seguidos de três dias de restrição de alimento (4A/3R). Foram avaliados parâmetros físico-químicos da água e de desempenho produtivo. Os resultados foram submetidos à análise de variância, e as médias foram comparadas pelo teste Tukey, a 5% de probabilidade. A qualidade de água, o fator de condição e a conversão alimentar não foram influenciados pela estratégia alimentar. O grupo alimentado com a estratégia 5A/2R apresentou peso final, ganho de peso e taxa de crescimento específico semelhantes ao grupo continuamente alimentado (7,8 e 9,2g; 6,4 e 7,8g e 2,7 e 3,0% dia-1, para peso final, ganho de peso e taxa de crescimento especifico, respectivamente). A estratégia 4A/3R apresentou os piores resultados de desempenho produtivo, e a estratégia 5A/2R pode ser usada na alimentação de juvenis de tilápia do Nilo sem prejuízo ao desempenho produtivo, possibilitando inclusive redução de até 22,5% na quantidade de alimento ofertada.

Tissue‐specific in vivo inhibition of cholinesterases by the organophosphate fenthion in Oreochromis niloticus

This study was designed to elucidate the effect of the organophosphate fenthion exposure on cholinesterase-specific activities in brain, liver, and kidney tissues of juvenile Oreochromis niloticus, and to define the best indicator tissue to fenthion exposure. The 96-h LC(50) value was determined as 2.27 mg/L and fish were exposed to 20% of this concentration for 24-, 48-, and 96-h. Recovery periods in similar durations were provided to evaluate the ChE activities. AChE and BChE activities were determined spectrophotometrically. The activities of these enzymes were significantly inhibited in all the tissues tested, liver was the most and kidney was the least affected tissues. The inhibition percentages of AChE and BChE were at similar levels in the liver while BChE was more affected in kidney. BChE was not detected in the brain. A significant positive correlation in ChE inhibitions was found among tissues, and the effect of fenthion on ChE activities was tissue specific. In general enzymes activities were not significantly recovered in 96-h recovery period; however, an elevation in AChE inhibition was observed in brain. Based on the data of this study, the liver may be suggested as the best indicator tissue especially for phosphorothioate exposure.

Feeding Dietary Mannan Oligosaccharides to Juvenile Nile Tilapia, Oreochromis niloticus, Has No Effect on Hematological Parameters and Showed Decreased Feed Consumption

Abstract Impaired immune system by environmental stressors can lead fishes to be more susceptible to diseases that limit the economic development of aquaculture systems. This study was set out to determine the effect of six levels of mannan oligosaccharides (MOS; ActiveMOS®; Biorigin, Lençois Paulista, São Paulo , Brazil) on the performance index and hematology of Nile tilapia, Oreochromis niloticus juveniles. Fish (13.62 g) were randomly distributed into 18 plastic aquaria (300 L; 20 fishes per aquarium) and fed during 45 d with a commercial diet supplemented with 0, 0.2, 0.4, 0.6, 0.8, and 1% dietary MOS, in a totally randomized design trial (n = 3); biometrical and hematological data were collected and analyzed. There were no significant differences in hematological parameters between fish fed control and MOS supplementation diets, and daily feed consumption (FC) decreased (P &lt; 0.05) with increasing levels of dietary MOS. Dietary MOS did not increase leukocyte count and presented negative effects on FC of Nile tilapia. At 0.4% MOS supplementation, the individual weight gain was higher in absolute values but not different (P &gt; 0.05) compared to control diet.

Haematological Responses Of Oreochromis Niloticus (Trewavas) Exposed To Various Concentrations Of Poisonous Extract From Two Local Plants

Haematological studies were carried out on the blood Oreochromis niloticus juveniles exposed to various concentrations of poisonous extracts from two itcheotoxic plants, Parkia biglobosa (clappertoniana) and Tephrosia vogelii in separate bioassays. Haematological parameters invested include Hb, RBC, WBC, Platelet, Lymphocyte and Neutrophil counts, PCV/Haematocrit, MCV, MCHC and MCH values. Various physico-chemical parameters of the test water were also examined. These increased in value with increase in concentration of extract in water except for dissolved oxygen which had an inverse proportion to temperature and pH which reduced slightly with increase in concentration of extract in test water. Haematological analysis of the blood of the fish examined showed that Hb, RBC, PCV, MCH and Platelet count reduced in value with increase in concentration of extract in water of both bioassays, while WBC, Lymphocyte and Neutrophil counts increased with increase in concentration of extract in water of both bioassays. It was concluded that both plant extracts were poisonous and had significant depressive effect on the blood forming system as well as on the immune system of the fish and also affected the physico-chemical nature of the test water, which adversely affected the health of the fish. Keywords: Haematological, Oreochromis niloticus, poisonous extracts, local plants.Nigerian Journal of Fisheries Vol. 5 (1) 2008: pp. 23-30

Invasive tilapia juveniles are associated with degraded river habitats

Abstract Invasions are a main concern for conservationists. Identification of causes that raise or promote an invader's success is one of the first steps for preventing and/or fighting against invasions. In the Brazilian River Paraiba do Sul, juveniles of invasive tilapia Oreochromis niloticus were detected associated with degraded habitats (mainly pollution from various sources). The relative abundance of juveniles of the competitor native species pearl cichlid Geophagus brasiliensis, morphologically and ecologically very similar, was negatively associated with habitat degradation. A species‐specific molecular marker was employed to permit unambiguous identification of these small juveniles (2–3 cm long), which represent the most vulnerable life stage of both species. It is suggested that adaptation to degraded habitats is one of the characteristics of invasive species, and consequently habitat conservation and restoration may help to prevent fish invasions. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Influence of Dietary Palm Oil on Growth Response, Carcass Composition, Haematology and Organoleptic Properties of Juvenile Nile Tilapia, Oreochromis niloticus

An 8-week feeding experiment was conducted to determine the effect of replacing fish (codliver) oil with palm oil at 0, 33.33, 66.67, 100 % for diets 1, 2, 3, 4 respectively, of Nile Tilapia, Oreochromis niloticus. Each diet was formulated to contain 28% crude protein and fed to triplicate groups of 10 juvenile Oreochromis niloticus (mean wt., 9.09g). Fish mortality decreased with increasing palm oil substitution level. There was a significant difference (P< 0.05) in the survival of fish fed Diet 4 compared with other treatments. The result showed that carcass quality of experimental fish was not compromised as a result of the use of palm oil in diets. Blood parameters of fish fed experimental diets showed a common trend, namely the higher the palm oil substitution level, the higher the blood parameters. Organoleptic properties of experimental fish showed that palm oil replacement for fish oil had no negative effect on their sensory evaluation and eating quality. The present study provides evidence that palm oil can effectively replace cod liver oil in diets for Nile Tilapia, O. niloticus.

Prediction of cannibalism in juvenile Oreochromis niloticus based on predator to prey weight ratio, and effects of age and stocking density

Factors influencing size-dependent cannibalism in Nile tilapia, Oreochromis niloticus, were investigated in controlled conditions. First, individual-based trials were conducted to develop a linear regression model to predict the occurrence of cannibalism based on body measurements. Oral gape ( G, mm), body depth ( D, mm) and weight ( W, g) of 140 fish were measured and we estimated maximum prey weight ( W prey) for a given predator weight ( W predator): Log 10 W prey = 1.03Log 10 W predator − 1.13. This model was verified by conducting 76 single pair trials. The revised model based on observed cannibalism is: Log 10 W prey = Log 10 W predator − 1.17. Several experiments involving a group of prey and predators were conducted to elucidate the relative importance of factors that influence cannibalism. Cannibalism was significantly affected by stocking density, age of fish and predator/prey weight ratio. Logit models of mortality data of both the individual-based and observations based on a group of predators and prey estimated R 50 (the predator/prey weight ratio at which an encounter of a predator and prey resulted in a predation success of 50%) to be 14.6 and 14.8, respectively. The results of these experiments can be used to reduce fry losses due to cannibalism.

Acute toxicity of the insecticide, Dimethoate on juveniles of &lt;i&gt;Oreochromis niloticus&lt;/i&gt; (Trewavas) and &lt;i&gt;Clarias gariepinus&lt;/i&gt; (Teugels)

Juveniles of Oreochromis niloticus and Clarias gariepinus were exposed in glass aquaria to acute concentration of dimethoate for 96 hours. The various concentrations used for O. niloticus were in the following order; 15.00, 17.50, 20.00, 22.50 and 25.00 mg.1-1 while 32.00, 35.20, 38.40, 41.60 and 44.80 mg.1-1. Behavioral reactions in order to their appearance were agitated swimming, loss of equilibrium, air gulping, periods of quiescence and death. Copious accumulation of mucus was observed in the gill filaments and body surfaces of dead fish in both species. However, the intensity of mucus production was more pronounced in C. gariepinus than in O. niloticus. Possible reasons for the differences are suggested. Also, blood was observed around the gill coverings of the dead fishes. These reactions were more pronounced in the tanks containing higher levels of toxicants. Mortalities and 96h-LC50 values for O. niloticus (20.70 mg.1-1) were lower than that of C. gariepinus (39.40 mg.l-1). This infers that O. niloticus is more sensitive to dimethoate than C. gariepinus. Possible reasons for the differences in susceptibility of these two species to dimethoate are suggested. Acute exposure of the toxicant showed altered behaviors and mortalities in both fishes. Key Words: Acute toxicity, dimethoate; Oreochromis niloticus; Clarias gariepinus Journal of Aquatic Sciences Vol.19(1) 2004: 5-8

Apparent nutrient digestibility, growth performance and feed utilization of juvenile Nile tilapia, Oreochromis niloticus L., as influenced by stocking density and feeding frequency

Experiments were carried out to study the effects of stocking density and feeding frequency on apparent nutrient digestibility, growth performance and feed utilization efficiency of tilapia, Oreochromis niloticus juveniles. Significantly higher (P < 0.05) weight gain (%), specific growth rate (SGR %/day), feed conversion ratio (FCR), protein efficiency ratio (PER), apparent nitrogen utilization (ANU %) and carcass nitrogen deposition (CND mg/day) were achieved by the fish stocked at 0.5/L and receiving either 3 or 4 meals/day. Significantly lower growth performance was observed in all groups of fish fed twice/day. At all stocking densities tested, apparent digestibility coefficients (ADC) for protein were significantly better when the fish were fed 3 meals/day. In general the ADC values obtained in this experiment were low for all nutrients which may be attributed to the excreta collection method applied in this study

Effect Of Feeding Frequency On Consumption, Growth, And Efficiency In Juvenile Tilapia (Oreochromis Niloticus)

Triplicate groups of juvenile Oreochromis niloticus (34.4 g) were fed a commercial diet once, twice, three, or five times a day for 29 days. Consumption, growth, and feed utilization were eval- uated. No significant differences in growth, feed efficiency, or protein utilization were detected among the fish fed two, three, or five times daily, but all were significantly better than in fish fed only once. Fish fed three meals had significantly higher gross energy and lipid and lower crude protein contents than fish in the other treatments (p&lt;0.05). Energy retention in fish fed three times daily (84.7%) was significantly higher than in fish fed five times (49.4%). Feeding juvenile tilapia nutrient dense pelleted feeds obviates the need for frequent feedings.

THE EFFECTS OF STOCKING DENSITY, WATER EXCHANGE RATE, FEEDING FREQUENCY AND GRADING ON SIZE HIERARCHY DEVELOPMENT IN JUVENILE NILE TILAPIA, OREOCHROMIS NILOTICUS L.

The effects of stocking density and water exchange rate on size variation of juvenileOreochromis niloticus were studied. The fish subjected to the lowest stocking (0.5/L) and highest water exchange rate (20 times/hr) achieved the best (p < 0.05) final body weight. Exposure of fish to the highest stocking density (2/L) and lowest water exchange rate (5 times/hr) resulted in the poorest (p < 0.05) final body weight. The coefficient of variation of body weights of individuals subjected to the lowest and intermediate water exchange rates (5 and 10 times/hr, respectively) increased withincreasing stocking density (from 0.5 to 2 fish/L). Fish subjected to the highest water exchange rate (20/Times/hr) did not show a similar consistent trend. Water-borne stresses compounded by those resulting from crowding and/or competition for food was suggested as the primary causes of size variation within treatments. Manipulation of water exchange rates to improve water quality and hence minimize the adverse effects of crowding was suggested. The influences of stocking density,feeding frequency and grading on size hierarchy development were also investigated. Stocking density and feeding frequency had an effect on size hierarchy development. The coefficient of variation of body weights of fish fed least frequently (2 times/day) increased with increasing stocking density (from 0.5 to 2 fish/L). The two groups fed 3 and 4 times/day showed an inverse relationship. Size hierarchy in the homogeneous size distributions was observed to reestablish within two weeks and increased steadily thereafter, whilst in the non-graded group (mixed group), a steadyreduction in size variation was noted with time.

A partial economic analysis for Nile tilapia Oreochromis niloticus L. and sharptoothed catfish Clarias gariepinus (Burchell 1822) polyculture in central Kenya

Aquaculture development in Kenya has been hampered by lack of targeted feeds. Chemical fertilizers can enhance natural food production and thus indirectly provide protein to complement energy-rich cereal brans used as feed. Consequently, an experiment was conducted at Sagana Fish Farm in central Kenya to realize least-cost combinations of rice bran and fertilizer. Twelve 800 m2 (0.08 ha) ponds were stocked with juvenile (32 g) Oreochromis niloticus L. at 2 m−2 and Clarias gariepinus (Burchell 1822) (fingerlings of 4.6 g) at 0.2 m−2. Four treatments, calculated to approximate isonitrogenous conditions, were applied in triplicate as follows: (1) urea and diammonium phosphate (DAP) to provide 16 kg of N ha−1 week−1 and 4 kg of P ha−1 week−1; (2) urea and DAP applied to give 8 kg of N ha−1 week−1 and 2 kg of P ha−1 week−1, plus rice bran fed at 60 kg ha−1 day−1; (3) rice bran fed at 120 kg ha−1 day−1; (4) rice bran as in treatment 3 and fertilizer as in treatment 2. Ponds were sampled monthly to measure fish growth, and drained completely after 20 weeks. A partial economic analysis indicated minimal net profits of K.Sh. 18 851 (US$ 251), K.Sh. 9895 (US$ 132), K.Sh. 3299 (US$ 44) and K.Sh. 7015 (US$ 94) for treatments 1–4, respectively, because of high feed and seed costs.