1. CARRYING CAPACITY OF TROPICAL RESERVOIRS FOR TILAPIA CAGE
CULTURE: CASE STUDIES AT UPPER PARANÁ RIVER BASIN,
SOUTHEASTERN BRAZIL.
David, G. S.*, Carvalho, Vivanco,A, Gerardo D., Dallaglio- Sobrinho, M., Silveira, A. N.
GIANMARCO SILVA DAVID
GERARDO VIVANCO A.
Proc. no. 07/58246-4 and 08/52139-4

2. Carrying capacity: concepts (Beveridge, 2004)
Cage aquaculture production needs to be sustained by surrounding
environment, considering:
• What determines the productivity of the environment – in this case, total
Phosphorus in water.
• What the farmed fish consume/produce, in terms of wastes – here, we consider
P loads.
• How the environment responds to waste loadings – such a good question!
• How much charge is permissible – in this case, Brazilian environmental
regulation states the limit for water total P of 30mg/m 3 in reservoirs to farm
aquatic animals (this is the limit of total P for a lake be classified as eutrophic
(Vollenweider, 1975).
 Environmental carrying capacity for cage aquaculture for freshwater lakes
can be defined as the maximum amount of P that can be loaded keeping total P
below the levels assumed to indicate eutrophication

3. upper Paraná river basin
Brazil
Sites considered in this study
Cage culture of tilapia in large reservoirs is an emergent aquaculture
practice in Brazil. Due to the availability of large amounts of suitable
quality waters in hydroelectric dams at Grande, Paranapanema and
Tietê rivers, there is a large but still undetermined potential for cage
aquaculture in the upper Paraná river basin.

4. South American
major river basins
Parana river basin

5. In this work, are presented
evaluations of two among 18
suitable sites at Ilha Solteira
reservoir, one of the biggest at
Brazil (1200 km2) and one
among at least 12 at Xavantes
reservoir.
Only 1% of the reservoirs area is
allowed to be occupied by
aquaculture.
Brazilian government will assign
part of the Ilha Solteira studied
sites to receive small scale,
familiar aquaculturists.
Distribution of hydroelectric
power plants in Brazil

6. Multiple uses for reservoirs
Eletric
Power
generation
Aquaculture
Tourism
Irrigation
Artisanal
fisheries

7. Today, fisheries are scarce, resulting on
low incomes for fishers.
Former fisheries collapsed after
installation of hydroelectric
dams, due to ecological
constrains for fish production.

8. After many attempts of stock enhancement,
tilapia cage culture have became the first
ecologically and economically feasible option
for fish production in southeastern Brazil
hydroelectric dams, since impoundment of
rivers in the 60’s.

9. Model used for tilapia cage aquaculture at upper Paraná river basin.

10. • Nile tilapia (Oreochromis niloticus) is reared in intensive system
• 8-16 m3 cages made of synthetic materials
• up to100 kg fish/m3 at the end of cycle
• fish weights 500-800 g at the end of cycle
• one or two cycles of 4-8 months per year, depending on water temperature.

11. Ipaussu

16. METHODS
Hydrodynamics - in reservoirs with linear morphology, water exchange rate can
be obtained from flow measurements of power plants and bathymetry.

17. Ilha Solteira reservoir
Rio Grandinho
Sao Jose dos Dourados

18. For dentritic reservoirs, water flow must be obtained for each portion by means from
current measurements and hydro dynamic modeling for the site named Can Can
Numerical solution
grid
Bathymetry
Winds
ADCP current profile

19. Bathymetry
Land use
Waves modeling
Water circulation pattern

20. Carrying capacity was estimated based on the Dillon
& Rigler (1975) mass balance model, considering
limnological data to evaluate area-specific
Phosphorus loads from tilapia cage culture that can
be assimilated in each selected site.

21. Limit for environmental carrying capacity for P
assimilation (L, in grams of Phosphorus/m2/year)
L = (∆P*Z*θ) / (1-R),
∆P - is the allowable phosphorus increase, in mg/m 3; is the difference of
total P from analysis of water samples collected with van Dorn bottles, and
the limit stated by environmental agencies (30 mg/m3) and by Vollenweider
(1975) as an indicator of eutrophication
Z - is the mean depth obtained from acoustic bathymetry, in meters;
θ - is the rate of water exchange, i.e., how many times the water is totally
exchanged in a year. (this is calculated as 1/residence time); and
R - is the sedimentation coefficient, obtained from direct measurements
with sediment traps (desirable), or from numerical modeling based on
hydro dynamics data.

22. Estimation of P loads per ton of tilapia produced
Pe= (Pf x FCR) – Pa
Pe= Phosphorus loads, in kg P/ton tilapia produced
Pf= mean feed Phosphorus content (%), obtained from chemical analysis of
samples (N=15) of fish feed used in farms in the study area. (= 27 kg ton-1)
FCR= Food Conversion Rate, obtained from average field farming data for
the upper Paraná river basin (= 1,6 ± 1)
Pa= whole fish Phosphorus content (%), specific for Nile tilapia (Dantas &
Athayde, 2007) (= 9 kg ton-1)
Pe= 37 kg P ton-1

23. Parameters used for the estimation of carrying capacity for tilapia cage culture in
selected sites on tropical hydroelectric reservoirs at southeastern Brazil.
Rio S.J.
Grandinho
Parameter unit Dourados Ipaussu
Water renovation rate years -1 31,52 9,38 7,80
Area km² 9,62 69,49 25,49
Mean depth m 8,00 11,11 28,89
P water concentration mg m-3 5,34 12,36 16,6
Limit P concentration mg m-3 30,0 30,0 30,0
Sedimentation
coefficient - 0,230 0,352 0,373
Area loading rate g m-2 year -1 8,080 2,835 4,814
Total allowable
production for the site ton year -1 2106 5340 3326
Area specific production ton km-²year -1 219 77 131

24. Tilapia Control
farm area
25 450
400
20 350
Total P (mg/m 3)
Total N (mg/m3)
300
15
250
200
10
150
5 100
50
Ipaussu: 0
Apr Jun Aug Oct Dec Feb
0
Apr Jun Aug Oct Dec Feb
comparative control cages control cages
limnological 5,0
4,5
70
60
data 4,0
conductivity (µS cm-1)
3,5 50
a clorophill (µg/L)
3,0 40
2,5
2,0 30
1,5 20
1,0
10
0,5
0,0 0
Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec Feb
control cages control cages

26. • Modeling provided evidence for the importance of
feed phosphorus content and availability for
determination of total allowable production
• Proper inputs of limnological field data are
expansive and demands sophisticated hydrographic
studies.
•The availability of sites with similar features for
cage culture in southeastern Brazil reservoirs
indicates a significant potential for tilapia production
at global scale.