Basic HTML Version
International Journal of Aquaculture, 2014, Vol.4, No.16 96
-
101
http://ija.biopublisher.ca
98
β
j
= the effect of feed on
O. tanganicae
(j=1,2)
(τβ)
ij
=
interaction between two species
ε=
experimental error
Statistical Package for Social Scientists (SPSS)
version 16.0 was used to analyze the data on body
weight, length, first maturity and Gonadosomatic
index. A two-way analysis of variance (ANOVA) was
used to determine whether there was any significant
difference in the variables measured among the
experimental groups.
2 Results and Discussion
Figure 1 shows the changes in mean weight of fish
over 12 weeks experimental period. The initial mean
weights of fish were 30g for both species while final
body weights were 73.65g for
O. niloticus
and 66.30g
for
O. tanganicae
.
Figure 1 Mean body weights of
O. niloticus
and
O. tanganicae
reared in hapas for 12 weeks
Slow growth was observed in both species in the first
four weeks of trial. However, the species showed
faster growth in the sixth week. Based on the results
of growth it was clear that
O. niloticus
performed
better than
O. tanganicae
. Higher growth could partly
be influenced by effective feed utilization and gonadal
development (Figure 1). However, final weight
showed no significant difference (p>0.05) between the
two species.
The smallest
O. niloticus
matured at the weight and
standard length of 34g and 73mm while that of
O.
tanganicae
, it was at the weight and standard length of
42g and 111mm respectively, an indication that some
fish matured earlier than others. The present study
showed that
O. niloticus
reaches sexual maturity at a
smaller size and younger age than
O. tanganicae
. This
present study was in agreement with that conducted
by Al Hafedh et al (1999), which revealed that fish
that grew fast matured earlier. According to the Popma
and Lovshin (2005),
O. mossambicus
reached sexual
maturity at a smaller size and younger age than
O.
niloticus
and
O. aureus
. Morales (1991) also reported
that the tilapias attained their sexual maturity at three
months old with a total length of 8 to 16 cm. The
results of the present study were also in agreement
with de Graff et al. (1999) who reported that the first
maturation size for reared Nile tilapia was between 30
and 50 g.
However, at the end of the experimental period, the
length at first maturity at which 50% of the fish
population reaches sexual maturity (L
50
) was observed
to be 136mm for
O. niloticus
and 129mm for
O.
tanganicae
(Figure 2).
Figure 2 Length at first maturity of
O. niloticus
and
O.
tanganicae
The results of the present study therefore disagree
with the results obtained by Popma and Lovshin
(2005). The differences in length at first sexual
maturity could be attributed to the differences in
genetical and environmental conditions such as food
supply and changes in water quality parameters such
as temperature, pH and dissolved oxygen.
The gonadal development for
O. niloticus
showed that
12 % were in immature (I) stage, 15 % were in
maturing (II) stage and 73 % were in mature (III)
stage (Figure 3).
In a similar manner,
the gonadal development for
O.
tanganicae
showed that, 17 % of the fish were in
immature (I) stage, 25 % were in maturing (II) stage
and 58 % were in mature (III) stage (Figure 4).
The maturity stages of these tilapia species were
classified macroscopically and three stages were observed,