International Journal of Aquaculture, 2013, Vol.3, No.22, 126
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sources of EPA and DHA.
3
Conclusions
The dominance of SFAs 16:0 and 18:0; MUFAs
18:1
n9 and 18:1n7 and PUFAs LA, LNA, AA, EPA
and DHA in catfish larval tissue across all diets is an
indication of a dietary requirement of these fatty acids
in the diet of Catfish larvae. The consequential higher
composition of the essential fatty acids and improved
growth performance of catfish larvae fed on Cyclopoid
copepods as compared to the case where
Artemia
is
used indicates higher nutritional suitability of the
former to the latter as a starter live feed for catfish
larvae. Nevertheless, further investigation are required
to assess the feasibility of mass culture of Cyclopoid
copepods and associated cost effectiveness before
more definite decisions are made on the partial or total
replacement of
Artemia
with Cyclopoid copepods.
4
Methods and Materials
4.1
Culture of Cyclopoid Copepods
Zooplankton samples were collected using 45 μm
mesh size plankton nets from grow-out fish ponds.
Samples were coarse-screened through a 100 μm
mesh followed by a 200 μm mesh for purposes of
isolating a size fraction containing predominantly
adult Cyclopoids and later-stage copepodites that were
needed to initiate the culture. A subsample was taken
and viewed under a microscope to ascertain presence
of Cyclopoid copepods. On confirmation of presence
of Cyclopoid copepods, Flubendazole was applied to
the screened stock culture at a concentration of 0.5 mg/L
for elimination of any remaining rotifers (Steenfeldt
and Nielsen, 2010). Once a clean (95%) Cyclopoid
copepod stock was achieved; cultures were initiated
by hand picking and introducing at least 10 Cyclopoid
copepods in each of 20 L plastic culture units using a
micropipette. Twenty culture units were set up for the
experiment and green micro algae (
Chlorella
species)
that had been grown in parallel tanks used as a source
of food. Cultures were maintained indoor at a room
temperature range of 25
℃
-27
℃
,
and illuminated daily
for 12 hours using 40 watt electric lighting. pH
remained at 6.5~9.0. Every 4~5 days, the cultures
were renewed by descanting off 10 L of water through
a 45 m screen from each 20 L culture unit and topping
up with 10 L of green algae water. In order to avoid
overcrowding that would lead to a culture crash,
culture density of 10 L
-1
Cyclopoid copepods was
maintained by up scaling the culture whenever the set
density was attained. Up scaling was achieved by
dividing up the culture unit into two and topping up to
20
L using algae green water.
4.2
Feeding Experiments Using Cyclopoids Copepods
and
Artemia
as Starter Food for African Catfish
Larvae
A commercial fish hatchery unit located in Ssenya fish
farm, Masaka district, Uganda was utilized for the
feeding experiment following the protocol outlined
below:
(1)
All water supplied to the hatchery was sieved
through a 50 μm mesh to eliminate zooplankton
contamination from the water supply ponds.
(2)
Experimental plastic basins (30 L) were placed in
triplicate in the hatchery unit for each of the three feed
experimental set ups under investigation, modified to
fit in the flow- through system of the hatchery unit.
(3)
Catfish larvae were obtained by through artificial
dissemination of catfish brood. Approximately 500
larvae were stocked in each of the 30 L experimental
basins (16.6 larvae/L) and maintained under ambient
hatchery conditions. Water temperature, dissolved
oxygen levels, pH and ammonia levels were monitored
and where required, necessary remedies were made.
(4)
African catfish larvae were fed for three days on
starter feed following commencement of exogenous
feeding (day three) as is the practice of fish farmers in
Uganda.
(5)
The starter diets constituted three test diets namely:
Decapsulated
Artemia
;
Cyclopoids copepods; 50%
decapsulated
Artemia
with 50% Cyclopoid copepods
(
nauplii and early copepoditie stages).
(6)
Desired Cyclopoid copepods stages were obtained
by coarse screening through 100 μm and 200 μm
plankton nets. Decapsulation of
Artemia
cysts followed
standard decapsulation procedures (Sorgeloos et al., 1977).
Estimated of the required daily ratios (0.5 mL
-1
-5.0
mL
-1
Cyclopoid copepods and 1 mL
-1
-10
mL
-1
Artemia
cysts) was adopted, with slight modifications from
Molejo and Alvarez-Lajonch
è
re (2003). Fish larvae
were fed five times a day in intervals of two hours and
feed provided slightly above required estimates to
allow feeding to satiation.