Comparative study of hatching rates of African catfish (Clarias gariepinus Burchell 1822) eggs on different substrates

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because, unlike the artificial substrates,
most of the natural substrates used were
able to float thus ensuring better aeration
of the eggs. During incubation, the eggs
should be well oxygenated for maximum
hatching to occur (de Graaf and Jansen
1996; Hogedoorn 1980; Viveen et al. 1985).
This experiment demonstrated high
hatching rates of the eggs incubated on
the roots of free-floating substrates such
as water hyacinth (Eichhornia crassipes),
Nile cabbage (Pistia stratiotes) and the
green grass leaves (Commelina sp.). The
best performing were the Pistia roots,
probably due to their numerous thin
fibrous roots that allowed greater
aeration of the eggs during incubation.
However, the hatching rates from the C.
dermasum substrate were quite low;
this could have been due to their
characteristic of decaying and gradually
sinking to the bottom. A decaying
substrate usually hosts pathogenic
microorganisms that cause bacterial,
fungal (Saprolegnia sp.) and protozoan
(Vorticella sp., Epistylis sp.) infections of
eggs and larvae, resulting in low egg
hatchability and high larval mortality. The
hatching rates in the artificial substrates
were low because of the relatively low
dissolved oxygen levels at the bottom of
the concrete hatching tanks where the
artificial substrates were placed. In Kenya,
it is common practice in hatcheries to
spread the eggs on mud, sand or concrete
surfaces, with manual separation of dead
eggs, shells and hatchlings. The hatching
rates usually average about 25% (Obuya
et al. 1995), which is well below the 50-
70% recorded in well-managed hatcheries
in other countries (de Graaf et al. 1995).
Moreover, the poor survival of eggs and
larvae is mainly the result of inadequate
nutrition during the nursing phase and
careless nursery management practices.
Successful hatching of fish eggs and careful
feeding of larvae during the early stages of
their development is essential for better
survival of larvae.

The main limitation on the expansion of
catfish culture in Kenya is the inadequate
supply of high-quality seed, especially
at the right time and place, for stocking
purposes. It is totally dependant on the
government to produce and supply the
fish seed. One way to overcome this
constraint is to develop and promote
low-input systems for producing the
fish seed by the farmers themselves. The
technology for such hatching and nursing
systems should be quite simple, use local
materials and be easily transferable to
rural fish farmers (Charo and Oireri 2000;

Dugan 2003; Jamu and Ayinla 2003). In
this experiment the hatching rates of eggs
on natural substrates, especially those of
the Pistia, were high as compared to the
hatching rates recorded in government
fry production centers in Western Kenya
where artificial substrates are commonly
used (Obuya et al.1995). The C. gariepinus
hatching protocols described in this study
are easy for small-scale fish farmers to
follow, and they are particularly suitable
for rural areas with no electricity and
where most of the small-scale farmers
are based.

Acknowledgement

The authors gratefully acknowledge the
Lake Victoria Environment Management
Project (LVEMP-Kenya) for sponsoring
the research work and the Government
of Kenya-Fisheries Department, Moi
University and the Lake Basin Develop-
ment Authority (LBDA) for providing
research facilities.

References

Charo, H. and W. Oireri. 2000. River-based
artificial propagation of the African
catfish Clarias gariepinus: an option for
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Clay, D. 1979a. Biology of the tropical
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emphasis on its suitability for culture.
Fish & Marine Ser. Manu. Rep. 11-58
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de Graaf, G.J., F. Galemoni and B. Banzoussi.
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catfish, Clarias gariepinus (Burchell 1822)
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Aquaculture Research 26: 233-42.

de Graaf, G. and H. Janssen. 1996.
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Nesfisco Foundation, Amsterdam, the
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Dugan, P. 2003. Investing in Africa: the
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NAGA, WorldFish Center Quarterly Vol. 28 No. 3 & 4 Jul-Dec 2005 25

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