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International Journal of Aquaculture, 2013, Vol.3, No.25, 147
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151
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150
and tilapia aquaculture are the main uses of the
reservoir.
Pirarucu were randomly selected, counted and stocked
into 4 m
3
cages,
each measuring 2.0×2.0×1.0 m deep
,
at density of 10 fish/m
3
with two replicate cages for
each treatment. Prior to the start of the experiment,
fish were fed the commercial diet to apparent satiation
for a week to acclimate them to the experimental
conditions. Cage frames were made of steel pipes
covered with a 30-mm galvanized wire mesh coated
with UV resistant PVC. Plastic bottles, attached along
the four sides of each cage, were used as floats. Cages
were installed at a distance of 70 m from the reservoir
margin, where water depth ranged from 4.5 to 7 m
according to water level. The distance between cages
was 2 m and cages were docked with anchoring poles
fixed inshore.
Pirarucu juveniles were reared for 210 days and fed
four times a day with a commercial pelleted feed with
40% crude protein and 14.2 MJ/kg of feed (TC 40;
Purina®, São Paulo, Brazil). Feed of 6.0–8.0 mm
diameter was used for the first 168 days and 12-14 mm
diameter from the 169
th
day until termination. Fish
were fed at rates of 2.0% or 3.0% body weight/day
until termination. The low number of treatments and
replicates occurred due to low supply of fingerlings in
Ceará State. This occurs due to the absence of specific
studies on plankton or other available food sources for
larvae feeding, resulting in low survival in larval and
fingerling stages (Carreiro et al., 2011; Núñez et al.,
2011; Oliveira et al., 2012). Fish were sampled every
21 days to evaluate growth in weight and total length.
For this 100% of fish in each cage were captured,
anesthetized with 100 mg/L of benzocaine, weighed
and measured. After each sampling period the amount
of feed given was adjusted to the mean weight and
biomass in each cage.
Temperature and dissolved oxygen (DO) were
monitored twice daily at 08:00 h and 17:00 h with an
oximeter (YSI model 55). The pH and transparency
were measured daily at 12:00 h with a digital pH
meter and Secchi disc, respectively. Water samples
were collected from inside of all the cages and from
two different points in the reservoir at a distance of
20 m from the cages. Total ammoniacal nitrogen
(TAN), ammonia, nitrite and nitrate were analyzed in
the water samples according to the APHA (1995).
Fish were harvested after 210 days and survival (%),
finals weight and length, absolute growth rate
(AGR, g/fish/day), specific growth rate (SGR = ln
final weight–ln initial weight/days×100, %/day),
production rate (kg/m
3
) and feed conversion ratio
(FCR, weight of feed/gain in wet weight of fish) for
each cage and treatment were calculated.
Differences among the treatment groups were
analyzed using Student’s
t-
test. A probability level of
p
<0.05 was considered statistically significant. The
values were expressed as the mean±SD.
Acknowledgements
We are indebted to The National Brazilian Council for the Scientific and
Technological Development (CNPq), Ministry of Science and Technology,
for the financial support of this work, which was made available through the
CT-HIDRO Sectorial Fund of federal assistance (grant no. 504367/2003-0).
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