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International Journal of Aquaculture, 2013, Vol.3, No.25, 147
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151
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148
effects of feeding rate on growth of pirarucu juveniles.
This preliminary study aimed to evaluate the effects of
feeding rate on the performance of pirarucu in cages
in a reservoir located in Ceará State, Brazil.
1 Results
The water characteristics did not present any
significant difference among fish densities or the two
points monitored in reservoir. Water temperature
averaged was 27.8
℃
in the morning and 28.6
℃
in
the afternoon during the culture period. Mean
dissolved oxygen concentration was 3.6 mg/L in the
morning and 5.8 mg/L in the afternoon. The pH
fluctuated between 7.6 and 7.8 throughout the culture
period. In all cages, transparency reading ranged
between 100 and 135 cm. Ammonia, nitrite and nitrate
ranged between 0.01 mg/L and 0.02 mg/L, 0.00 and
0.63 and 0.00 mg/L to 1.00 mg/L, respectively.
Survival was high and not significantly affected by
feeding rate. Mean survival rates ranged from
91.2±1.2% to 92.5% among fish fed at 2% and 3%
body weight/day, respectively (Table 1). Feeding rate
did not affect the weight and length of pirarucu
juveniles. Mean final weights were 6800.0±170.0 and
6680.0±420.0 g, while mean final lengths were
89.8±3.2 and 88.7±3.5 cm in the groups fed at 2% and
3% body weight/day, respectively (Figure 1). The
growth rates for pirarucu juveniles in cages submitted
to different treatments are given in Table 1. Mean
AGR and SGR at 2% body weight/day were 25.0±9.4
g/fish/day and 0.7±0.1%/day, respectively, compared
to 24.4±4.9 g/fish/day and 0.7±0.1%/day at 2%
body weight/day. Similarly, production was not
significantly affected by feeding rate and ranged
from 46.8±0.7 to 46.0±1.2 kg/m
3
in the cages fed at
2% and 3% body weight/day, respectively. However,
feeding rate did significantly affect FCR. FCE was
significantly lower in the group fed at 2% body
weight/day (2.8±0.1) than at 3% body weight/day
(4.3±0.1).
Table 1 Survival, initial and final weights, weight gain, absolute growth rate (AGR), specific growth rate (SGR), production and feed
conversion ratio (FCR) of pirarucu juveniles (initial mean weights, 1550.0±85.0 g) fed at rates of 2.0% or 3.0% body weight/day
in 4 m
3
cages and cultured for 210 days
Parameter
Feeding rate (% of body weight/day)
2
3
Survival (%)
91.2±1.2
92.5±2.5
Initial weight (g)
1550.0±85.0
1550.0±85.0
Final weight (g)
6800.0±170.0
6680.0±420.0
Weight gain (g)
5250.0±155.0
5130.0±350.0
AGR (g/day)
25.0±9.4
24.4±4.9
SGR (%/day)
0.7±0.1
0.7±0.1
Production (kg/m
3
)
46.8±0.7
46.0±1.2
FCR
2.8±0.1
a
4.3±0.1
b
Note: Data are means±S.D. of two replicate cages. For each row, means with different letters as superscripts are significantly
different (
P
<0.05)
2 Discussion
Throughout the experiment most physico-chemical
parameters of the water were maintained within the
appropriate range for cage aquaculture (Beveridge,
1996; Boyd and Tucker, 1998). Nevertheless, it is
important emphasize that the pirarucu accepts low
water dissolved oxygen levels, due to its obligatory
aerial breathing (Ono et al., 2004; Núñez, 2009). On
the other hand, there are not studies that indicate
critical oxygen levels and others physico-chemical
parameters in culture of pirarucu.
The feeding rates tested did not affect growth
parameters, except for FCR. Many studies have not
found any significant effects of feeding rate on
survival (Eroldogan et al., 2004; Silva et al., 2007;
Okorie et al., 2013). Various studies with pirarucu
report similar results according to the type of culture.
Pereira-Filho et al. (2003), Menezes et al. (2006) and
Oliveira et al. (2012) reported survival rates varying
from 90 to 100% in ponds and cages culture of
pirarucu. Fish appear to continuously increase in
weight with feeding rate up to satiation although this
increase may not correspond with the incremental feed
consumption (Okorie et al., 2013). In this study, the