Effect of fertilization of nile tilapia reared in earthen ponds

    The present study was carried out in a 24 earthen pond system (one feddan each, three replicates for each treatment) to investigate the effect of feed, feed plus fertilization (organic± inorganic fertilizer), improved (fertilized with organic± inorganic± supplementary feeding with rice bran) and poor nutrient inputs (fertilized with poultry manure, PM) on the performance of mixed-sex and mono-sex Nile tilapia. Treatment 1 (T1) fed a diet containing 25% protein only, Treatment 2 (T2) feed plus fertilization with (poultry manure only 50 kg dry matter feddan^-1 week^-1± urea and Triple super phosphate, TSP), Treatment 3 (T3)  fertilized with poultry manure only (50 kg dry matter feddan^-1 week^-1) ± urea± TSP± supplementary feeding with rice bran, Treatment 4 (fertilized with poultry manure only 50 kg dry matter feddan^-1 week^-1))  for Mono-sex; T5, T6, T7, and T8 the same as T1, T2, T3 and T4 but for mixed sex Nile tilapia. Artificially incubated first feeding hatchlings were nursed under similar conditions to produce mixed-sex and mono-sex fry before stocking in one feddan ponds at 14000 fingerlings/ feddan. Growth and net yields after 6 months were affected by nutrient levels and sex (mono- or mixed-sex). Average final body weight, weight gain, SGR and average daily gain were significantly higher in T2 than T1, T3, T6, T5, T4, T6 and T8 respectively. Total yield, total gain, daily net yield, percent of net yield/ kg feed and survival rate followed the same pattern of growth performance data. Based on results obtained in this study and on the economical evaluation it could be concluded that mono-sex Nile tilapia can be cultured in ponds by using diet containing 25% crude protein plus fertilization (50 kg/ week/ feddan dry poultry manure plus 3.75 kg urea plus 30 kg triple super-phosphate/ feddan/ week.  The importance of nutrient levels and the use of mono-sex fish were demonstrated. The study has implications for promoting small holder tilapia production; both the nature of demand for fish and the resource base need to be understood before developing tilapia hatchery strategies.

Keywords: Nile tilapia, Fertilization, Feeding regime, Growth performance, Feed utilization, Economic evaluation. 

Egypt is facing a sharp shortage in animal protein production. The need for increasing fish production is necessary in view of the high demand for fish to cover the shortage in animal proteins. The decline of fish availability from the natural sources during the past few years, and the high fish price has supported the development of the fish culture. Tilapia is one of the most important species for the 21^st century aquaculture and is produced in more than 100 countries (Fitzsimmons, 2000 and López and Bjørndal, 2009). Nile tilapia Oreochromis niloticus is cultured worldwide mostly in semi-intensive culture systems using fertilization. Addition of artificial feeds plays an important role especially under conditions of heavy stocking, when natural feed supply has declined or completely disappeared. The added feeds should be rich in protein, carbohydrate and fats, and should also contain vitamins, minerals and growth-promoting substances to be physiologically balanced (Magouz, 1990; NRC, 1993; Tahoun, 2002 and 2007). However, in the last few years the price of artificial feeds increased dramatically.  A number of studies have been done on feed and fertilizer combinations. Such combinations may be very effective because fertilization rates can be reduced due to enrichment gained from excreta and exhibited rapid growth rate of tilapia, larger size could be attained in shorter time than fertilizer alone (Milstein et al., 1991; Mostafa, 2005) and also may be reduce the production cost. The importance of mono-sex tilapias has been established in many commercial contexts but their role in resource-poor environments where small fish are marketable has often been assumed. The importance of the genetic quality of the mono-sex stock, and the quantity and quality of pond-based nutrition available to such fish, have also often been ignored. Elsewhere, mixed-sex fish may be valued for their ability to produce seed for restocking and reach a preferred size on the resources available (AIT/ DOF, 2000, Dan and Little, 2000 a and Little and Edwards, 2004). De Graff et al. (1999) found that early maturation of fish and breeding was not a major bottleneck to production of Nile tilapia for fish raised on supplementary feed and marketable at a size of under 200 g. Brummett (2000) reported that most fish consumed in rural Africa are less than 200 g and that huge demand among poorer people exists. The present study, therefore, compares performance of Nile tilapia (O. niloticus) in which age and system of productivity is known. Mono- and mixed-sex tilapia fry performance was compared under poor nutrient inputs typical of smallholder aquaculture (fertilized only with poultry manure) and an 'improved' nutrient input system (urea and TSP supplemented poultry manure and rice bran as a supplementary feed) and poultry manure ± urea and TSP ± formulated diet. Both input regimes are within the resource base and range of current practice found in some farms in Egypt under semi-intensive management systems.

Fingerlings Nile tilapia (Oreochromis niloticus) weighing 2.0± 0.19 g were stocked in 24 earthen ponds each of one feddan at densities of 14000 fish/ feddan. Each treatment was replicated in three ponds supplied water from Ismailia channel.

A 2×4 factorial design was used to compare the performance of mixed-sex and mono-sex tilapia in ponds receiving four levels of nutrient input (Table 1). Treatment 1 (T1) fed diet containing 25% protein only (Table 2), Treatment 2 (T2) feed plus fertilization with (poultry manure 50 kg dry matter feddan^-1 week^-1± urea and TSP) at a rate 3.75 Kg and 30.0 Kg/ pond biweekly, respectively. Treatment 3 (T3) fertilized with poultry manure only (50 kg dry matter feddan^-1 week^-1) ± urea ± TSP at a rate 3.75 Kg and 30.0 Kg/ pond biweekly ± supplementary feeding with Rice bran at rate 2% fish body wt. day^-1, Treatment 4 (fertilized with poultry manure only 50 kg dry matter feddan^-1 week^-1)) for mono-sex; T5, T6, T7, and T8 the same as T1, T2, T3 and T4 but for mixed-sex Nile tilapia. The daily amount of diet was given 3 times daily at a feeding rate 3% of body weight. Feed input was adjusted after sampling of standing stock that assumed 75% survival of stocked fish. A random sample of 1000 fish was taken from each treatment once a month. Individual body weight was recorded. The amount of diet was adjusted every month based upon the latest weight measurement. Poultry manure (total nitrogen 2.61; total phosphorus 2.01% and organic matter 21.07%) was spread over the pond surface weekly at a rate of 50 Kg/ pond.  Urea and TSP were spread over the water surface after soaking to give total N and P loading rates of 3 and 0.3 kg feddan^-1 day^-1, respectively. Ponds were fertilized for 1 week before stocking fish to allow natural food to develop and thereafter biweekly; respectively as recommended by (Green et al., 1989) and daily additions of rice bran as a supplementary feed and the third input was formulated diet containing 25% protein. Treatments were replicated three times and randomly allocated to ponds within the same series. The experiment was conducted in a private fish farm located in El-Qantra, Ismalia Governorate. The experiment started from 1^st of April to 30^th of September 2006.

Table1. The eight experimental treatments.

              Water quality parameters (temperature and dissolved oxygen) were measured daily by oxygen temperature meter (YS1 model L 57); pH by pH meter (mod 56. NR 87 BB 203) daily, ammonia and nitrite nitrogen) weekly by ammonia test kit Hanna instruments; and (alkalinity, hardness, C02, phosphate and turbidity) biweekly by total suspended solids (APHA, 1989); phytoplankton and zooplankton biomass were determined according to the methods of (APHA, 1989). The average water quality parameters of the ponds during the experimental period are presented in Table (3). Growth was monitored through sampling of a minimum of 10% of fish in each pond every month with a seine net. A stick sampler with attached 300-ml bottle was used to collect water samples from a depth of 50 cm for all other parameters. Water quality parameters throughout the whole experimental period are shown in Table (3).

At the end of growing season (7 months) ponds were drained from the water and the fish were harvested by seining. The total fish production for each treatment was recorded. A column sampler constructed from a PVC pipe (5-cm diameter, 1.5 m long) was used to collect water samples for all suspended materials

Table (2). Composition and proximate analysis of experimental diet.

Ingredient         (%)

Fish meal (70%)           3.0

Soybean meal (44%)     45.0

Yellow Corn                  45.0

Vegetable oil                 5.0

Vitamin Mix.¹                 1.0

Mineral Mix.²                 1.0

Total                          100.0

Proximate Analysis (%).

Moister                         7.10

Crude protein                25.50

Ether extract                 6.20

Ash                              7.14

Crude fiber                   2.80

NFE³                             51.26

GE⁴ (Kcal/ 100g)            412.83

P/ E⁵                             61.76

Price of Kg (L.E)                          2.20

(1) Vitamins mixture contained (as g/ kg premix): Thiamine 2.5; Riboflavin 2.5, pyridxine 2.0 Inositol 100.0 ;Biotin 0.3; pantothenic acid 100.0 ; folic acid 0.75; Para-amino-benzioic  2.5 Choline 200.0 Nicotinic acid 10. Cyanocobalmine 0.005; tocopherol acetate, 20.1; Ascorbic acid 50.0; Menadione 2.0. ; Retinol palmitate 100.000IU; Cholecalciferol 500.000 IU.

(2) Minerals premix (as g/ kg of premix) ChaHpo4.2H20 727.7775; Mg So4; H20 127.5 ; Kcal 50.0; Na Cl 60.; FeSo4. 7H20 25; Zn  So4. 7 H20 5.5; Mn So4. 4 H20 2.53; Cu So4.5 H₂o, 0.785; CoSo4. 7 H20 0.4775; Calo3.6H2 0.295; CrC13.6H20 0.1275

 (3) NFE (Nitrogen Free Extract) = 100 - (protein ± lipid ± fiber± ash).

(4) Gross energy were calculated, the energy value (Kcal/ g) for protein 5.65; for lipid 9.45 and carbohydrate 4.1, according to NRC (1993).

Average weight gain (AWG), Average daily gain (ADG), (g/ day); specific growth rate (SGR, %/ day); survival rate were calculated according the following equations:

WG (g) = mean final fish wt (g) - mean initial fish wt (g).

AGR (g/ day) = Final fish wt (g) - Initial fish wt. (g)/ time (days).

SGR = Ln final wt- Ln initial wt. X 100

Time (days)

Survival rate % = Nt x 100 / NI

Where: Nt = Number of fish at t days NI = Number of fish initially stocked.

At final harvest the ponds were drained, fish including recruits counted and the total weight of fish in each length class was determined using a spring balance (±1 g). Survival rates of stocked fish were estimated from counts of fish harvested of more than 10 cm total length. The statistical analysis of data was carried out by applying the computer program, SAS (2002). Means were tested for significant differences using Duncan's multiple range test (1955).

 

RESULTS & DISCUSSIONS

As shown in Table (3), the concentration of dissolved oxygen (DO) treated ponds were significantly influenced by the experimental treatments. Oxygen levels in all treatment ranged between (5.3-5.6mg/ L) throughout the experiment, and were within the optimum range and higher than 5 mg/ L which reported by Boyd (1979) as the minimum desirable DO level in fish ponds. In this connection, it can be say that, tilapia routinely survive at dawn DO concentrations less than 0.5 mg/ L (Egna and Boyd, 1997). Diurnal DO levels varied more in ponds with improved nutrition than in ponds receiving poultry manure alone. Pre-sun rise DO declined with time in the experiment but probably did not cause fish mortality as it remained above zero for most of the time. The pre-sunrise DO levels in the present study were higher than the level of DO (0.3 mg/L) which reported by Lawson (1995) as a lethal level.

Table (3). Average water quality parameters throughout the experiment.

Mean ± SE for treatment values and ranges observed through the experimental period.

                 Means in the same column having the same letter were not significantly different (P≤0.05).

The Use of inorganic fertilizer improved water quality through stimulation of natural food, mainly phytoplankton and zooplankton, suitable for the filter feeding Nile tilapia. Both phytoplankton and zooplankton biomass were significantly higher in ponds with improved fertilization compared to ponds with poor nutrition (Table 3). Total ammonia nitrogen fluctuated throughout experiment but remained below 1 mg/ L and at the pH levels observed; unionized ammonia probably did not adversely affect fish performance. Major water quality parameters measured during the study remained in the favorable range for tilapia (Boyd, 1990), suggesting that tilapia growth performance was not limited by any of the water quality parameters. Comparable results were obtained by Meade (1989) and Lawson (1995).

The dissolved oxygen varied between 5.3-5.6 ppm (Table 3). This range was beneficial to fish culture and agreed with Elgendy (1998). They reported water dissolved oxygen increased with using poultry and duck manure).  In contrast, Batterson et al. (1998) reported that increasing poultry manure from 12.5 to 100 g/ m²/ week, in tilapia ponds decrease DO. The pH ranged between 7.5 and 8 and significantly influenced by the experimental treatments and this is in disagreement with Boyd (1998) and Wurts (2004). The ammonia concentrations were significantly influenced by the experimental treatments and they ranged between 0.25-0.37 ppt. These results show a slight increase in ammonia concentration with the increase of the pH, which is in agreement with Diana et al. (1996). They reported an ammonia concentration of (0.37-0.41 mg/ L) in ponds fertilized with chicken manure and inorganic fertilizers. These low concentrations of ammonia may be attributed to ammonia utilization by phytoplankton (Boyd, 1998) or oxidation of ammonia nitrite especially in high dissolved oxygen level conditions (Boyd, 2000).

 Number of phytoplankton per liter in water of different treated ponds and Performance of mono-sex and mixed-sex Nile tilapia cultured for 6 months in earthen ponds using feed, feed plus fertilizer, improved and poor inputs are presented in Table (3).

 The data on the growth performance of Nile tilapia fingerlings as affected by the experimental treatments (the sex of fingerlings and feeding regime) are presented in Table (4). It can be noticed that, the mono-sex group of fish on T2 had a significantly (P≤0.05) highest body weight gain, SGR and daily gain followed by T1, T3, T5, T6, T7 and T8 respectively. The lowest values of body weight gain, SGR and daily gain was found in T8 (mixed sex group which received poor input, poultry manure only). Some researches have shown that, supplemental feeding in fertilized ponds resulted in significantly higher growth rates and greater yield than fertilization alone (Green, 1992; Diana et al., 1994). Diana et al. (1996) emphasized that, from a pond management perspective, pond fertilizing early in the grow-out phase, then adding supplemental feed once Nile tilapia reach 100- 150 g, is an efficient way to grow large tilapia. However, excessive increase in variable cost due to the high price of formulated feed is a growing concern among tilapia growers as this could lead to a negative net return and thus, an economically unviable practice. Certainly, it is more economic procedure of aquaculture practice, more than any other factor, which influences its long-term adoptability and, therefore, proper assessment of economic performance of culture system is essential.

The data on the effect of feeding regime regardless of the sex of Nile tilapia fingerlings, cultured for 6 months in earthen ponds are presented in Table (5). The average final weight (AFW), average weights gain (AWG), average daily gain (ADG) and specific growth rate (SGR) were significantly affected by the feeding regime regardless of the sex. Treatment 2 (feed plus fertilization with (poultry manure only 50 kg dry matter feddan-1 week-1± urea and Triple super phosphate, TSP) recorded the best AFW, AWG, ADG, and SGR values as compared to other fish groups. They were 150.20±13.426; 148.10±13.426; 822.778 and 2.321±0.065 respectively. While the fish groups in ponds received the poultry manure only exhibited the lowest values of the above growth parameters. They were 80.175± 4.337; 78.025± 4.360; 433.472± 24.220 and 2.127± 0.048 respectively for AFW, AWG, ADG, and SGR.

 

Table (4). Performance of mono-sex and mixed-sex Nile tilapia cultured for 6 months in earthen ponds using feed, poor and improved inputs (Mean ±SE).

                 Means in the same column having the same letter were not significantly different (P≤0.05).

 

Table (5). Effect of feeding regime of cultured Nile tilapia regardless to sex throughout the experiment (Mean ±SE).

                               Means in the same column having the same letter were not significantly different (P≤0.05).

The data on the effect of the sex regardless of feeding regime of Nile tilapia cultured for 6 months in earthen ponds are presented in Table (6). It is observable that, the mono-sex group recorded the better growth performance as compared to mix-sex groups. These results are in parallel line with those of Sule (2004) who experimented on Nile tilapia Oreochromis niloticus fingerlings with initial mean weight of 25.7±1.3 g and found an increase in weight for the all-male was significantly higher than the values for the all-female and mixed-sex Tilapia.

Table (6) Effect of the sex of Nile tilapia cultured for 6 months in earthen ponds regardless of feeding regime (Mean ±SE).

 

                               Means in the same column having the same letter were not significantly different (P≤0.05).

The increased fish production in ponds received fertilization with feeding may be mainly due to the abundance of natural food which resulted from the available nutritive elements required for increasing the concentration of phytoplankton in ponds. Moreover the suitable environmental conditions may be also participating in these results (Table 3). Some researches have shown that supplemental feeding in fertilized ponds resulted in significant higher growth rates and greater yield than fertilization alone (Green, 1992; Diana et al., 1994). However, excessive increase in variable cost due to the high price of formulated feed is a growing concern among tilapia growers as this could lead to a negative net return and thus, an economically unviable practice.

The highest values total yield (2017.33± 4.667 Kg/ feddan), net yield gain 12987.0±4.650 Kg/ feddan, net daily gain (11.044 Kg/ feddan/ day) was found in T2 treatment (Table 7). The lowest survival rates were noticed in the poor input T4 and T8 in the mono and mixed-sex ponds (Table7).

Table (7). Harvest results of mono-sex and mixed-sex Nile tilapia raised for 6 months in earthen ponds using feed, poor and improved inputs (Mean ±SE).

                 Means in the same column having the same letter were not significantly different (P<0.05).

 

In this connection, Sule (2004) compared the growth and survival rates of all-male, all-female and mixed-sex Nile tilapia fingerlings and found that, the percentage survival of all-male O. niloticus was 94 % and that of all-female was 88 %, while that of the mixed population was 74 %. All-male O. niloticus grew better than the all-female under the same experimental conditions. The author added that, the culture of all-male tilapia species by fish farmers should be encouraged for increased fish production. Inversely, Little et al. (2003) indicated that, survival, daily weight gain, specific growth rate and net fish yield were not significantly different (P>0.05) between mono-sex and mixed-sex tilapia. Survival rates of mono-sex and mixed-sex tilapia during advanced nursing were comparable (>70%).

The results on total yield, net yield and daily gain of Nile tilapia fingerlings cultured fed for 6 months as affected by feeding regime regardless of the sex are shown in Table (8). They were significant differences among different feeding regimes regardless of the sex of fingerlings. The 2^nd feeding regime (Feed+ fertilizer) had the highest Total yield, total gain, daily net yield and survival rate followed in descending order by the 1^st (Feed), 3^rd  (poultry manure+ urea+ TSP) and finally 4 ^th (poultry manure only).

Table (8). Harvest results of mono-sex and mixed-sex Nile tilapia raised for 6 months in earthen ponds using feed, poor and improved inputs regardless of the sex of fingerlings (Mean ±SE).

                 Means in the same column having the same letter were not significantly different (P<0.05).

The data of total yield, net yield and daily gain as affected by the sex of Nile tilapia cultured for 6 months regardless of feeding regime are shown in Table (9). The mono-sex Nile tilapia had the higher total yield, total gain, daily net yield and survival rate as compared to mixed-sex tilapia. The results of the present work may be confirmed by those of Little et al. (2003) who found that, overall, mono-sex fishes reached a larger final individual size (128.8± 6.8 g) than mixed-sex (112.7±14.6, P<0.05). This effect was most pronounced for the 6-month-old seed of which mixed-sex reproduced early in the production cycle.

Table (9). Harvest results of mono-sex and mixed-sex Nile tilapia cultured for 6 months in earthen ponds regardless of feeding regime.

                               Means in the same column having the same letter were not significantly different (P≤0.05).

The optimal level of poultry manure had been estimated from a response curve determined from a previous experiment (Mostafa, 2005) and was typical of the level of sustained fertilization managed by resource-poor farmers. The loading levels of dry poultry manure alone used in the current study produced low and erratic production, unlikely to satisfy needs of farmers for subsistence or cash. The carrying capacity of the system was quickly exceeded at the stocking density used, resulting in minimal individual growth. Edwards et al., 1994 demonstrated that poultry manure was a relatively ineffective fertilizer, which (Mostafa, 2005) subsequently related to it being a poor source of both particulate and soluble nutrients, and through its negative impact on water quality. Significantly higher mortality (P<0.05) in the poor input could be explained by the greater competition for food in the low input ponds receiving poultry manure alone, resulting in weak fish. In a previous experiment in which a higher stocking density was used (3 fish/ m²), a higher level of production was predicted (Edwards et al., 1994). There was little evidence that lack of food stimulated breeding of fish even at the lowest level of nutrient input. The implication for fish culture is that the age of fry is crucial. If hatcheries supply farmers with young fry, then breeding in ponds is not likely to be a problem even with mixed-sexed fry. However, if hatcheries hold such fry for any period of time before selling them which results in the fry being 'old and small' (De Graff et al., 1999), the fish are likely to breed shortly after being stocked in the pond. This is common hatchery practice, however, especially where they serve highly seasonal markets of smallholders dependent on rain-fed systems or in areas with low seasonal temperatures (Dan and Little, 2000a). Over-wintered mixed-sex fish can still be raised to a larger individual size if the effects of breeding are controlled through frequent removal by seining (Dan and Little, 2000b) and/ or use of an efficient police fish (De Graff et al., 1996). Sustained adoption of mono-sex tilapia has occurred mainly among resource-rich, usually commercial, producers with ready access to hatcheries. The role of mono-sex tilapia for resource-poor farmers with limited access to nutrients for pond fertilization and for who harvested yield may be more important than individual size, has been challenged by this study. The problem of poor performance of mixed-sex tilapia in farmers' ponds receiving little input was clearly demonstrated in the current trial with low-nutrient ponds. A stocking density of 3 fish m-2 quickly exceeded the critical standing crop (Hepher, 1988). The fish showed very little growth as the natural food barely supported maintenance requirements. Overstocking of mixed-sex fish in infertile ponds is common practice and leads to dissatisfaction among farmers. The poor survival under such conditions also suggests how tilapia "disappears" according to farmers' perceptions (Little et al., 1991 and Edwards et al., 1996).

The economical analyses for all treatment are presented in Table 10. Results revealed that the total cost were highest in T1 followed by T3, T6, T2, T7, T4 and T8 respectively. These results indicate that use feed alone tend to increase the cost of production and reduce the net revenue. The highest total incomes were obtained in T2 followed by T1, T3, T6, T5, T4, T8, T7 and T5 respectively. Fish growth and net yield were significantly affected by nutrient level and sex (mono-sex or mixed-sex). Significant differences in individual weight of fish raised on different levels of nutrient input were observed from month 2 onwards. Fish harvest data for the experiment (Table 7) indicated that recruitment was minimal in both mono- and mixed-sex ponds for the improved input systems but could make up an important component of the low yields observed for poor nutritional conditions. Appearance of fry was noted from June (3^rd month) in all of the mixed-sex ponds and 25% of mono-sex ponds but relatively few fry and fish of less than 10 cm were found at final harvest. Survival was highly variable ranging from less than 60% to 72% in low-input systems and 83-90% in improved systems and high survival 85 to 90% in the group of fish received feed for both sex (mono and mixed-sex). The relative importance of sex control and level of nutrient inputs to performance of pond-cultured tilapias is often disputed. Much research has focused on the 'problem' of stunted cultured stocks without clear description of the environment in which the fish have been raised, both during seed and food fish production. This study clearly indicates the primary importance of the level of nutrients used during food fish production, and under the conditions compared, the relatively importance of using mono-sex fish. Growth of sex-reversed all-male Nile tilapia was only 5% faster than mixed-sex Overall; Mono-sex fish grew significantly faster than mixed-sex fish (Nguyen and Little, 2000). Sex control has been developed primarily to produce larger, uniform fish that are more valuable than typical harvests of mixed-sex fish (Green et al., 1997). Poor performance of mixed-sex Nile tilapia (Oreochromis niloticus) in semi-intensive systems has been a major constraint to the commercial development of the species (Hepher and Pruginin, 1982 and Teichert-Coddington et al., 1997). Use of mono-sex male juveniles has been identified as the answer to the problem and has been widely, if inconsistently, promoted and adopted (Green et al., 1997). The issue is more complex, however, as much of the rapid growth in global tilapia production in recent decades has been based on mixed-sex fish (Little and Hulata, 2000). In contrast the demand for sex control has been mainly associated with the needs of urban and export markets, rather than the demand by rural people. Several studies from both Asia (AIT/ DOF, 2000 and Barman et al., 2002) and Africa (e.g. Brummett, 2000) suggest that small-sized individual fish are not only acceptable in many rural areas but that small size reduces risks to producers and, as prices are lower, increases their attraction for consumers.

In the current trial, the levels of recruitment in mono-sex and mixed-sex fish raised from fingerlings for a period of 6 months were different, as was the harvested individual mean size and yield of fish. Two main reasons may explain this result. Firstly, the effect of fertilization which increase the phytoplankton and zooplankton which utilized by tilapia and feeding which help for growth performance. Nile tilapia fed on planktonic algae, detrial/fungal flocs, or zooplankton which feed on algae and detritus (Knud-Hansen et al., 1993). Supplemental feeds are used in pond culture to increase fish growth and yields (Li and Yakupitiyage, 2003 and Mostafa, 2005).

The results of the study showed a significant increase in net income in culturing tilapia under fertilization plus feeding as compared to culturing tilapia under feeding only. In the present study, negative net return obtained in the treatment with fertilization followed by feeding was due to the low production caused by poor growth performance of tilapia in the treatment. This study demonstrated that fertilization plus formulated diet produced higher yield than formulated diet only, and, hence, the practice of fertilization plus feeding is more cost-effective than using fertilization followed by feeding for Nile tilapia culture.

 

Table (10). Economic efficiency of mono-sex and mixed-sex Nile tilapia cultured for 6 months in earthen ponds using feed, poor and improved inputs (Mean ±SE)

Net Revenue: Net Return (LE)/ Total costs.

The results of the study confirms the view of Engle et al. (2002) that the yield of tilapia in the high-input monoculture system was a determining factor in its selection in the profit-maximizing production activities. Further to this accounting of the cost to produce 1 kg tilapia revealed that unit production cost was lower in the treatment with fertilization plus feeding (3.33 LE/ kg fish) than that in the treatment with fertilization only (2.03 LE kg/ fish), suggesting that production costs can be significantly reduced in a tilapia farming system where an efficient fertilization program is applied. As costs of fertilizer is much less than feed, better feed conversion ratio in fertilization plus feeding treatments were reflected in feed costs saving and thus, an increased net return.

In conclusion, Mono-sex Nile tilapia growth was better in the treatment with fertilization plus feeding than feeding alone or fertilization plus supplementary feeding or fertilization alone for both mono and mixed sex Nile tilapia in terms of economic efficiency and net revenue (Table 10), The study suggested that maximizing production efficiency would require the combination of the two nutrient input sources (feed and fertilizers). The study throw the lights on the importance of the need to increase yields of tilapia to meet the needs of smallholder farmers raising fish for household consumption.

REFERENCE

AIT/ DOF, (2000). Fish seed quality in Northeast Thailand. State of the System report. Aquaculture Outreach Programme, AIT, Bangkok. 31 pp.

APHA, (1989). Standard Methods for the Examination of Water and Wastewater (17^th edn.), American Public Health Association, American Water Works Association and Water Pollution Control Federation, Washington, DC 146 pp.

Barman, B., Little, D. C. and Edwards, P. (2002). Small-scale fish culture in Northwest Bangladesh: a participatory appraisal focusing on the role of tilapia. In: Edwards, P., Little, D. C and Demaine, H., Editors, 2002. Rural Aquaculture, CABI Publishing, Wallingford, pp. 227-244.

Batterson, T. R, Mc nabb, C. D and Hansen, C. K. (1998). Effect of chicken manure additions on fish production in ponds in west Java, Indonesia. Research Reports, Pond Dynamics Aquaculture Collaborative Research Support Program, 54-67.

Boyd, C. E. (1990). Water Quality in Ponds for Aquaculture. Alabama Agriculture Experiment Station, Auburn University, Alabama, USA.

Boyd, C. E. (1998). Water quality for pond aquaculture. Research and development series No 43. pp37. International Center for Aquaculture and Aquatic Environments. Alabama Agriculture Experiment Station. Auburn Univ.

Boyd, C. E. (2000). Water quality- an introduction. Kluwer Academic published Bosto, Massachusetts.

Boyd, C.E. (1979). Water quality in warmwater fish ponds. Auburn Univ. Agric. Exp. Sta., Auburn, Alabama.

Brummett, R. E., (2000). Factors influencing fish prices in Southern Malawi. Aquaculture 186: 243-251.

Dan, N. C. and Little D. C. (2000a). The culture performance of monosex and mixed-sex new-season and overwintered fry in three strains of Nile tilapia (Oreochromis niloticus) in northern Vietnam.  Aquaculture, 184:221-231.

Dan, N. C. and Little, D. C., (2000b). Over-wintering performance of Nile tilapia Oreochromis niloticus (L.) broodfish and seed at ambient temperatures in northern Vietnam. Aquaculture Research 31 (6):485-493.

De Graff, G., Galemoni, F. and Huisman, E. A. (1999). Reproductive biology of pond reared Nile tilapia, Oreochromis niloticus L. Aquaculture Research 30 1, pp. 25-33.

De Graff, G., Galemonie, F. and Banzoussi, B. (1996). Recruitment control of Nile tilapia, Oreochromis niloticus, by the African catfish, Clarias gariepinus (Burchell, 1822), and the African snakehead, Ophiocephalus obscuris: I. A biological analysis. Aquaculture 146, pp. 85-100.

Diana, J. S., Lin, C. K. and Jaiyen, K. (1994). Supplemental feeding of tilapia in fertilized ponds. J. World Aquaculture. Soc., 25(4): 497-506.

Diana, J. S., Lin, C. K. and Yi, Y. (1996). Timing of supplemental feeding for tilapia production. J. World Aquacult. Soc., 27(4): 410-419.

Duncan, D. B. (1955). Multiple range and multiple F-test. Biometrics, 11: 1-42.

Edwards, P., Demaine, H., InnesTaylor, N. and Turongruang, D., (1996). Sustainable aquaculture for small scale farmers: need for a balanced model. Outlook on Agriculture, 1: 19-26.

Edwards, P., Kaewpaitoon, K., Little, D. C and Siripandh, N. (1994). An assessment of the role of buffalo manure for pond culture of tilapia: II. Field trial. Aquaculture, 126: 97-106.

Egna, H. S. and Boyd. C. E. (1997). Dynamics of pond aquaculture. CRC Press LLC, Boca Raton, Florida. USA.

Elgendy, M. A. (1998). Effect of fish culture systems on pond productivity and their economic evaluation. M.Sc. Theses Fac. of  Agric. E-lAzhar Univ.

Fitzsimmons, K., (2000). Tilapia: the most important aquaculture species of the 21^st century. In: Fitzsimmons, K., Filho, J. C. (Eds.), Proceedings from the Fifth International Symposium on Tilapia Aquaculture, Rio de Janeiro, Brazil, vol. 1, pp. 3 -8.

Green, B. W. (1992). Substitution of for organic manure for pelleted feed in tilapia production. Aquaculture, 101: 213-222.

Green, B. W., Veverica, K. L. and Fitzpatrick, M. S., (1997). Fry and Fingerling production. In: Egna, H. S. and Boyd, C. E., Editors, (1997). Dynamics of Pond Aquaculture, CRC Press, Boca Raton, USA, pp. 215-243.

Green, B. W; Phelps, R. P and Alvarenga, H. A. (1989). The effect of manures and chemical fertilizers on the production of Oreochromis niloticus in earthen ponds. Aquaculture, 76:37-42.

Hepher, B. and Pruginin, Y., (1982). Tilapia culture in ponds under controlled conditions. In: Pullin, R.S.V. and Lowe McConnell, R.H., Editors, 1982. The Biology and Culture of the Tilapias, ICLARM Conference Proceedings vol. 7, International Centre for Living Aquatic Resources Management, Manila, Philippines, pp. 185-203 432 pp. .

Hepher, B., (1988). Nutrition of pond fishes. , Cambridge Univ. Press, Cambridge.

Knud-Hansen, C. F; Batterson.T. R. and Mc Nabb.C. D. (1993). The role of chicken manure in production of Nile Tilapia (O. niloticus). Aquaculture and Fisheries Management, 24:483-493.

Lawson, T. B. (1995). Fundamentals of aquaculture engineering. Chapman & Hall. An International Thomson Publishing Company. New York. USA.

Li, L. and Yakupitiyage. A. (2003). A model for food nutrient dynamics of semi-intensive pond fish culture. Aquaculture Engineering 27:9-35

Little, D. C. and Edwards, P. (2004). Impact of nutrition and season on pond culture performance of mono-sex and mixed-sex Nile tilapia (Oreochromis niloticus). Aquaculture 232, 279-292.

Little, D. C. and Hulata, G., (2000). Strategies for tilapia seed production. In: Beveridge, M. C. M. and Mc Andrew, B. J. Editors, (2000). Tilapias: Biology and Exploitation Fish and Fisheries Series vol. 25, Kluwer Academic Publishing, Dordrecht, pp. 267-326.

Little, D. C., Innes-Taylor, N. L., Turongruang, D. and Komolmarl, S., (1991). Large fish seed for small-scale aquaculture. Aquabyte 4 2, pp. 2-3.

Little, D. C.; Bhujel, R. C. and Pham, T. A. (2003).Advanced nursing of mixed-sex and mono-sex tilapia (Oreochromis niloticus) fry, and its impact on subsequent growth in fertilized ponds. Aquaculture, 221 (1-4): 265-276.

López, A. N. and Bjørndal, T. (2009). Is Tilapia the same product worldwide or are market segmented? Aquaculture Economics & Management, 13(2): 138 - 154.

Magouz, F. I. (1990). Studies on optimal protein and energy supply for tilapia (Oreochromis niloticus) in intensive culture. Ph. D. Dissertation. George-August-Univ. Göttingen.

Meade, J. W. (1989). Aquaculture management New York: Van Norstrand Reinhold. (Cited after) Lawson, T. B. (1995). Fundamentals of aquaculture engineering. Chapman and Hall. An International Thomson Publishing Company, New York, USA.

Milstein. A., Alkon. A., Avnimelech. Y. Kochba. M, Hulata. G. and Schroeder. G. (1991). Effect of manuring rate on ecology and fish performance in poly-culture ponds. Aquaculture, 96:25-43.

Mostafa,Y. T. (2005). Effect of fertilization on fish production in earthen ponds. Ph. D. Thesis fac. Of Agric. Saba Basha. Univ. of Alexandria.

Nguyen C. D, and Little. C. D. (2000).The culture performance of Mono-sex and mixed-sex new-season and overwintered fry in three strains of Nile tilapia (Oreochromis niloticus) in northern Vietnam. Aquaculture, 184: 221-231.         

NRC, (National Research Council). (1993). Nutrient requirements of fish. National Academy Press. Washington, D. C.

SAS Institute (2002). SAS. Software Version 8. SAS Institute Inc, Cary, North Carolina. United States of America.

Sule, O. D. (2004). Growth performance of mono-sex and mixed sex population of Oreochromis niloticus fed similar diet. Animal Research International, 1 (2): 106-109.

Tahoun, A. M. A. (2002). Effects of some environmental factors on growth performance and feed utilization of some warm water fishes in earthen ponds and glass aquaria. M. Sc. Thesis, University of Tanta.

Tahoun, A. M. A. (2007). Studies on some factors affecting the production and reproduction of Nile tilapia. Ph. D. Thesis, University of Kafr El-sheikh, Egypt.

Teichert-Coddington, D. R., Popma, T. J and Lovshin, L. L., (1997). Attributes of tropical pond cultured fish. In: Egna, H.S and Boyd, C. E, Editors, 1997. Dynamics of Pond Aquaculture, CRC Press, Boca Raton, USA, pp. 183-198.

Wurts, W. A. 2004. Organic fertilization in culture ponds. World Aquaculture magazine 35(2):64-65.

Engle, C. R., Demaine, H. and Dasgupta, S. (2002). Economics and social returns to technology and investment in Thailand. In: McElwee, K. Lewis, K. Nidiffer, M. and Buitrago, P. (Eds.), Nineteenth Annual Technical Report. Pond Dynamics/Aquaculture CRSP, Oregon State University, Corvallis, Oregon, pp. 141-147.