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Five different tilapia pond management strategies were evaluated for economic potential in 0.1-ha earthen ponds at the Central Laboratory for Aquaculture Research, Abbassa, Egypt. Pond management strategies were based on use of chemical fertilizer only, feed only, combination of organic fertilizer and feed, and combination of organic and chemical fertilizers and feed. Ponds were stocked with either mixed-sex or all-male populations of Nile tilapia. Yield and input data from 145-day pond trials were used to develop full-cost budgets for each management system. Net returns, values for production for major inputs, break-even prices and yields, and average rates of return to capital were estimated for each system based on a 2.1-ha production pond.
Net returns ranged from Egyptian pounds (L.E.) 19,102/2.1 ha for ponds stocked
with all-male tilapia and receiving organic fertilizer and feed to L.E. 985/2.1
ha for ponds stocked with all-male tilapia and receiving chemical
fertilizer only. The rates of return to capital for these two systems were
29.97% and 2.42%, respectively. Net returns to land and management for
management systems that combined fertilization and feeding were, on average,
16.1 times the net returns for the extensive system. Management systems that
combined fertilization and feeding also had the highest margins between average
prices and break-even prices to cover total costs, which indicated reduced
risks to farmers in the event of a decline in market prices. Sensitivity
analyses indicated that combined fertilization-feeding systems maintained
positive net returns if fish yield decreased by two standard errors and price
decreased by 20%. Nile tilapia are generally stocked at 20,000 fish/ha in semi-intensively
managed production ponds. Nutrient inputs into these ponds include fertilizers
and supplemental feeds; both natural pond productivity and supplemental feed
contribute to fish growth. Often, pond carrying capacity and critical standing
crop are not attained during the 5-month grow-out period, which indicates
under-utilization of available pond nutrient resources. Knowledge of pond
carrying capacity and density-dependent fish growth for a particular management
system provides the ability to manipulate production management to improve
efficiency and economic returns. The objective of this experiment was to
quantify the growth and yield of Nile tilapia stocked at 30,000 and
40,000 fish/ha in production ponds.
This study was conducted at the Central Laboratory for Aquaculture Research
(CLAR), Abbassa, Egypt. Three replications of each treatment (stocking rates of
30,000 or 40,000 Nile tilapia/ha) were randomly assigned to 0.1-ha earthen
ponds. Sex reversed Nile (Oreochromis niloticus) tilapia fry (mean weight:
0.5 g/fish) were stocked into ponds on 20 and 24 July 1994. Chicken
litter was applied weekly at 1,000 kg dry matter/ha for the first eight
weeks of the production cycle followed by feed (25% protein commercial fish
feed) only. Average mean individual fish weights based on seine samples were
69.9 and 79.4 g/fish for the 30,000 and 40,000 fish/ha stocking rates,
respectively. Estimated respective mean fish biomasses, assuming 100% survival
at the effective stocking rates, were 2,098 and 3,178 kg/ha. Ponds are
scheduled to be harvested after 150 days of grow-out.
A consistent, reliable supply of fingerlings of the desired
species, sex, and size is critical to the success of any aquacultural
enterprise. Of the four tilapia species endemic to Egypt, Nile and blue tilapia
are considered better species for pond culture than Sarotherodon galilae
and Tilapia zilli. Hormonal sex reversal is the most efficient means of
mass production of monosex tilapia fingerlings at present. Newly hatched fry of
9- to 11-mm total length are given an androgen-treated feed during a 28-day
period. Fry for sex reversal can be mass produced in earthen ponds, but water
temperature can affect productivity. The objective of this research is to
quantify production of Nile and blue tilapia fry in relation to water
temperature in Egypt.
A total of 68 reproduction pond harvests have been completed since trials were
initiated on 17 April 94. To date, 858,300 fry have been harvested; of
these 659,000, or 79%, were suitable for sex reversal. The contributions of
Nile and blue tilapia to these totals was approximately equal. The reproductive
performance of Nile and blue tilapia appeared similar. Grading fry through a
3.2-mm square plastic mesh consistently yielded fry of uniform size and
weight; fry passing the grader were within the size range (9- to 11-mm TL)
desired for sex reversal.
Forty-nine sex reversal trials have been completed and 16 were in progress
at the time of this report. The mean stocking rate of fry in 2-m2 treatment
hapas was 4,200 fry/m2. Two hundred sixty-nine thousand Nile tilapia
fry and 275,600 blue tilapia fry have been stocked into treatment hapas to
date. After the 28-day androgen treatment period, fry averaged 23.8 mm
total length. Overall mean survival has been 51% to date. Water quality
deterioration, primarily due to high concentrations of ammonia caused by high
feeding rates, was probably responsible for much of the fry mortality. Tank
management was modified and survival improved. However, limited availability of
water, because of equipment malfunction, continued to restrict the ability to
manage water quality in tanks, even at moderate feed loading rates.
(Printed as submitted)
Masculinization of sexually undifferentiated tilapia fry is achieved by oral
administration of the androgen 17a methyltestosterone (MT). An
anabolic response to androgen treatment of tilapia has been reported. Growth of
control and MT-treated tilapia was evaluated during consecutive treatment,
nursery and grow-out phases under conditions approximating commercial,
semi-intensive tilapia farms in Central America. Oreochromis niloticus
(L.) fry were fed a 0 or 60 mg/kg MT diet for 28 days. Growth curves
for control and MT-treated fish did not have significantly different slopes.
Mean harvest fry weights were similar, averaging 0.1 g/fry for both
treatments. Fry were subsequently stocked into 0.2-ha nursery ponds for
94 days of growth. Slopes of control and MT-treated fish growth curves
were significantly different. Mean final individual weights did not differ
significantly between treatments. Control fish did not deviate from the 1.1
male:female ratio, but MT-treated fish were 97% males. Control-male and
MT-treated male fingerlings were stocked for grow-out into 0.1-ha organically
fertilized earthen ponds. No significant difference in growth was observed
between control and MT-treated fish. Mean gross yields after 150 days and
mean final individual weights were similar for both treatments.
Published in Aquaculture and Fisheries Management 25:613-621.
(Printed as submitted)
Recently hatched tilapia 9 to 11 mm total length (TL) are
preferred for hormonal sex reversal because they are most likely to be sexually
undifferentiated. Thirty-three trials were conducted in Honduras between
September 1998 (sic) and March 1990 to quantify the effect of water temperature
on Oreochromis niloticus fry production in earthen ponds for hormonal
sex reversal. Two 0.1-ha ponds were simultaneously stocked with brood fish in
each trial; generally, one pond was harvested after 17 days, the other
after 20 days (range 16 to 21 days). Fry production was evaluated in
relation to degree-days from the threshold temperature of 15deg.C. Harvests
averaged 86,000 fry/0.05 ha. A total of 4,897,000 fry were produced, of which
4,363,000 fry were of appropriate size for hormone treatment. No fry production
occurred at less than 140 degree-days; fry production increased significantly
with increased degree-days above this level. Above 195 degree-days percent of
the population retained by a 3.2-mm vexar-mesh grader (too large for androgen
treatment) increased significantly with increased degree-days. Fry retained by
the grader averaged 14.2 mm TL, while fry not retained by the grader
averaged 9.5 mm TL. No significant linear relationship between degree-days
and number of fry not retained by the grader was observed between 140 and 280
degree-days. However, production appeared to peak at about 210 degree-days.
Published in Journal of Applied Ichthyology 9:230-236.
(Printed as submitted)
Two experiments were conducted to determine effective phosphorus (P)
fertilization strategy in fish ponds in relation to sediment P saturation
level. Experiment 1 was conducted in cement tanks with five levels of P
saturated sediments (5%, 24%, 44%, 60% and 79%) and with three P-fertilization
rates (0.2, 0.1 and 0.05 g/m3/day, N:P ratio of 2:1, 4:1 and 8:1,
respectively. Nile tilapia (Oreochromis niloticus) were cultured in
those cement tanks for 57 days. Results showed that the mean concentration
of soluble reactive phosphorus (SRP) in water column increased with increasing
sediment P saturation and P fertilization rate. The maximum net fish yield
(NFY), 4.2+/-0.3 g/m3/day, was obtained at SRP concentration of
0.3 mg/L and higher concentrations did not increase fish yield. This level
of SRP and NFY were attainable with P fertilization rate of 0.2, 0.1 and
0.05 g/m3/day and N:P ratio of 2:1, 4:1 and 8:1 in ponds were
the level of sediment P saturation was below 10%, above 45% and above 60%,
respectively. Experiment 2 was conducted in earthen ponds to test and
verify the P fertilization rate based on cement tank experimental results.
Three new and three old ponds with 8+/-1.7% and 88+/-7.3% sediment P saturated
in top 5-cm mud were fertilized at a rate of 0.2 and
0.05 g/m2/day and N:P ratio of 2:1 and 8:1, respectively. Nile
tilapia were cultured at 2/m2 for 85 days. The mean NFY obtained
in new and old ponds were 1.73+/-0.08 and 2.24+/-0.32 g/m2/day,
respectively, which were not significantly different (P > 0.05).
Results conclude that P fertilization rate should be based on P saturation
level in mud to overcome the problem of under supply or over supply of P in
fish pond.
Accepted for publication by Aquaculture.
(Printed as submitted)
An experiment was conducted to determine the amount of phosphorus (P) needed to
saturate simulated fish pond sediments which were made up to contain six levels
of clay at 0%, 30%, 41%, 64%, 73% and 81% by weight. A series of cylindrical
cement tanks were filled to 20 cm depth with six sediment types and triple
superphosphate (TSP) solution was added to reach P saturation in sediment.
Results showed that all sediment types reached constant inorganic-P
concentration in upper 5-cm after 12 weeks of TSP application, and P adsorption
capacity of sediment increased with increasing clay content. Sediment P
adsorption was slower and not significant (P > 0.05) below the 5-cm
depth except that contained 0% clay. Regression analysis showed that rate and
adsorption capacity of P in sediment are primarily governed by clay content and
its dominant minerals. While organic-P and loosely bound-P are commonly
deposited in sediment most inorganic P is absorbed by cations to form cation-P
complex. The linear relationship between cation-P saturation level and percent
clay in sediment is highly significant (r2 0.34, P < 0.001)
and therefore, the maximum adsorption capacity of cation-P in pond sediment can
be calculated by Y = 0.019 X (Y = 100% saturation level
mg-P/g soil: X = % clay in sediment). In practice the level of P
saturation (%) in sediment can be calculated by the initial cation-P and clay
content (%) in top 5-cm of pond mud using the equation: P saturation
(%) = initial cation-P (mg/g soil) X 100/P adsorption capacity (mg/g
soil).
Accepted for publication by Journal of Aquaculture Engineering.
The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
Effect of Stocking Rate on Growth and Yield of Nile Tilapia
Abstract
Mass Production of Nile (Oreochromis niloticus) and Blue
(O. aureus) Tilapia Fry
Abstract
Growth of Control and Androgen-Treated Nile Tilapia, Oreochromis
niloticus (L.), during Treatment, Nursery and Grow-Out Phases in
Tropical Fish Ponds
Abstract
Production of Oreochromis niloticus Fry for Hormonal Sex
Reversal in Relation to Water Temperature
Abstract
Phosphorus Fertilization Strategy in Fish Pond Based on
Sediment Phosphorus Saturation Level
Abstract
Determination of Phosphorus Saturation Level in Relation to Clay Content in
Pond Mud
Abstract
Disclaimers
