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International Journal of Aquaculture, 2014, Vol.4, No.02,
http://ija.sophiapublisher.com
5
and injected with an Ovaprim hormone (a synthetic
hormone used as a substitute of catfish’s male
pituitary hormone) at a concentration of 0.5ml/kg fish
to induce an ovulation process (Adebayo et al., 2008;
Olumuji and Mustafa, 2012).
Thereafter, each hormone induced female fish was
kept in a white plastic tank of 900 litres capacity and
left for 13hours (from 18.30hrs to 7.30hrs-latency
period) at a room temperature of 25.1±0.4
℃
before
was striped. Catfish females were considered ripe if
had distended abdomen and eggs oozed freely when
the abdomen was gently pressed anterior posteriorly
while ripe males had genital papilla reddish in colour
(Olumuji and Mustafa, 2012). Before striping the
female fish to obtain the eggs, it was important that a
sperm solution (milt) was prepared first. One to two
male catfish were sacrificed to fertilize the eggs of one
female.
The milt was obtained by dissecting the male catfish
and the respective tips of the ripe tests cut and sperms
squeezed into 10ml saline water (Saline water: NaCl
dissolved in distilled water) (Olumuji and Mustafa,
2012). The time interval since making the milt and
stripping of eggs to allow fertilization averaged 5
minutes. The female fish was weighed using a 10kg
capacity weighing balance before stripping and its
eggs were weighed too (using a 1000g capacity
weighing balance with a sensitivity of 0.01g) and their
total number calculated. For fertilization to effectively
take place, the mixture of milt and eggs was carefully
and gently stirred for approximate one minute.
Thereafter, the fertilized eggs of each female were
evenly spread with assistance of a chicken feather in
45cm x 45cm potassium permanganate pre-treated
trays (made using a net of 30µ mesh size) and
incubated at mean room temperature of 25.1±0.4
℃
in
tanks of 900 litres capacity and maintained at a flow
through system of water to allow dissolved oxygen of
5.83±0.45mgO
2
L
−1
.
Soon after hatching (averagely
26 to 27 hours since incubation), the incubation trays
were washed with water, soaked with potassium
permanganate and dried in the sun ready for the next
re-use.
The hatched larvae were left for four days before the
commencement of exogenous feeding (mouth opening
period). In the fifth day, the larvae from the three
fish were mixed together in one separate tank and then
randomly reallocated into nine experimental tanks
(white plastics of 900 litres capacity) for the test of
performance of rotifer
B. plicatilis,
chicken egg yolk,
and mixture of egg yolk and
B. plicatilis
feeds.
Each
tank averagely contained a total of 600 larvae.
Before the start of the experiments, some
representative larvae were randomly chosen, and then
measured their weight and total length to obtain their
initial average weight (g) and length (mm). The used
nine tanks (each feed treatment at replicate of three)
were maintained at flow through system from water
directly pumped from Lake Victoria, then filtered,
aerated, and allowed to flow under gravity to the tanks
in hatchery. The larvae in both tanks were fed three
times a day, at 9.00hrs, 13.00hrs, and 16.00hrs.
Concurrently with feeding, also physical and chemical
parameters like pH and temperature were monitored
three times a day using a portable pH-Temperature
meter (HI 991300 pH/EC/TDS/Temperature meter)
while dissolved oxygen (mgO
2
L
−1
) was measured
using a portable Oxygen meter (HI 9143
Microprocessor Oxygen meter HANNA instruments)
in the duration of the experiment.
3.2 Preparation and application of the feeds
To mass culture
B. plicatilis,
tape water was filled in
three black plastic tanks of 900 litres capacity and
then left for two days to allow de- chlorination. In the
third day, each tank was fertilized with 3kg of local
chicken manure wrapped in a perforated plastic bag.
After two days since fertilization, the tanks were
inoculated with 5 litres of water containing
phytoplankton and 1 litres of solution of
B. plicatilis
.
Thereafter, the tanks were left for 10 days to allow
growth of phytoplankton and the rotifer. After this
period, the rotifers in the tanks had already multiplied
to a density of > 2000 individuals in a litre of water.
Rotifers were concentrated using a zooplankton net of
60µm to make a feed of the day. During feeding, the
larvae of
C. gariepinus
aimed at testing the
performance of
B. plicatilis
were supplied with 500ml
of its solution at each feeding interval as specified
above. In each day, one chicken egg was boiled and
the yolk measured its weight. At each feeding interval,
10g of the yolk was used to make a solution of 1.4
litres used as feed of the day. Each tank with the