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International Journal of Aquaculture, 2014, Vol.4, No.02,
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4
al., 2006; Olivotto et al., 2010). The occasional poor
performance (growth and survival) of rotifers in the
rearing of marine fish larvae (when compared to other
live feeds like copepods) normally is attributed to its
imbalances in fatty acids composition rather than its
size (Olivotto et al., 2010). So far, there no records
that have confirmed the suitability of rotifers in the
rearing of either
C. gariepinus
larvae or any other
fresh water fish larvae. This is because most fresh
water fish larvae are appreciated as are of large size at
the time of their first feeding, thus requiring big sized
food particles such as cladocerans and copepods
(Yilmaz et al., 2006). According to Yilmaz et al.
(2006), African catfish larvae normally have mouth
size big enough to even ingest some big sized
zooplankton such as copepods and cladocerans at the
time of their first feeding.
Generally, as regards to this study, both diets indicated
poor growth and the lowest survival % during the
weaning period, especially rotifers. This fact could be
implicated with immaturity of the digestive system of
African catfish larvae in that period. According to
Rønnestad et al. (1999) and Lubzen et al. (2001), live
feeding fish larvae is important for the supply of
nutrients and exogenous enzymes important for the
digestion of other feeds and enhancement of the
development of larvae’s pancreas. And, according to
Olivotto et al. (2010), the length of metamorphosis
time during the larval phase also depends on the type
of administered feed to larvae and has implications on
survival and growth. Therefore, the indicated poor
survival percentages and poor growth of the larvae
from the three treatments is because of the indicated
poor nutritional quality of the diets and thus failed to
supply the necessary nutrients and enzymes for larvae
growth and digestive system development. Thus, egg
yolk and rotifer cannot be recommended as first
choice for the profitable rearing of catfish larvae,
unless for assuring survival in risks of mass mortality.
As compared to other feeds, the performance (growth
and survival) of chicken egg yolk was good. The
finding implies that the feed contains simple
absorbable compounds important for the larvae in a
certain reasonable ration (Krawczyk, 2009). In the
regards of the objectives of sponsors of this study, for
example, promotion of simple technologies to lead
into availability and affordability of quality fish seed
to poor farmers, the finding is appreciated as of quite
important. Of the major problems when using egg
yolk as a feed for the fish is that, water quality get
degraded very fast thus raising the risk of increased
larval mortality due to quick development of ammonia.
This is because the likeliness to oversupply the feed is
high, thus resulting into high food remains in the
rearing media. The mixture of rotifer and egg yolk
feed performed the second after egg yolk. This study
expected this feed treatment to perform better than
using egg yolk alone due to broad spectrum of
nutrients provided, and so far we are not in position to
account for the observed situation.
Generally, DO values as monitored during our
experiments were in a range acceptable (5.31±0.61 to
6.30 ± 0.14 mgO
2
L
−1
) for a farmed fish. According to
Beveridge et al. (1993), a minimum of 3 ppm of DO at
temperature between 25
℃
-3
0℃
is suggested as ideal
for fish farming in fresh waters. However, the
recorded temperature values, a range of 21.53±0.11 to
24.30±0.42
℃
were less than the suggested range of
25 to 30
℃
(Britz and Hecht, 1987; Beveridge et al.,
1993). It is quite probable that the generally bad
results (in terms of growth in size and survival) we got
during this time experiments (as compared to the past
ones) are contributed by the observed low temperature
conditions in the hatchery. Higher temperature in
hatchery (i.e. 30
℃
) is highly recommended for
improved hatching rate, growth, and survival (Britz
and Hecht, 1987). Temperature is positively associated
to egg developmental processes and metabolic
activities of the larvae after hatch (Ouellet et al., 2001;
Hamoutene et al., 1999; Hamre, 2006; Suzer et al.,
2006).
3 Materials and methods
3.1 Preparation for African Catfish larvae
Nine African catfish (three females of 450g, 500g, and
600g and six males of the size range of 1300g-1500g)
were collected from wetland areas in the upper
catchments of Lake Victoria in Misungwi district and
used in the artificial propagation processes to lead to
larvae. After arrival at Tanzania Fisheries Research
Institute (TAFIRI)-Mwanza station, the fish regardless
of their sex were stored for some time in an outdoor
concrete pond of 10m x 10m size to stabilize them
physiologically and acclimatization for reproduction.
The female fish were then taken into TAFIRI hatchery