International Journal of Aquaculture, 2016, Vol.6, No.7, 1
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In contrast, the African catfish has received recognition as the most robust species for Aquaculture in Africa (de
Graaf and Jensen, 1996; Nagoli and Balasubramaniam, 2008). The African catfish is an excellent species for
aquaculture as it is omnivorous, grows fast; able to reach 800 g in seven months, tolerates relatively poor water
quality and can successfully be stocked at very high densities (Borade et al., 2001; Rad et al., 2003; Hecht, 2013).
In addition, the yields of African catfish from ponds can be as much as 2.5 times higher than those of tilapia
(Abdelhamid et al., 2010).
The species occurs naturally throughout the country, inhabiting calm waters of lakes, rivers, swamps and flood
plains, and thus is ecologically safe to farm (Nagoli and Balasubramaniam, 2008). The widespread culture of the
species would not only prove more profitable among local fish farmers but also ease the need to lift the ban on the
introduction of exotic species that have better aquaculture output than
Oreochromis shiranus
and
Tilapia rendalli
,
such Nile tilapia (
Oreochromis niloticus
). Thus, the African catfish is both a profitable and sustainable alternative
to the three tilapia species commonly cultured in the country.
There are some challenges facing widespread Africa catfish culture that help in explaining the country’s marginal
production of the species despite its superiority to the tilapia species. Inability of African catfish (
Clarias
gariepinus
) to breed naturally in captivity and high mortality rates during larvae and fry stages have long been
recognized as the major hindrances to wide spread production of the species (Goos and Richter, 1995). The
introduction of synthetic hormones for induced propagation, albeit expensive, has tremendously improved seed
production. However, achieving satisfactory survival rates remains an ever present challenge. To put this into
perspective, Iita (2013) reported that survival rates of less than 10% are very common among private hatchery
owners and fish farmers in Malawi and cited poor feeding, among other management practices, as the cause of the
poor survival rates recorded. This represents the biggest challenge to small scale farmers, a category to which
most of the local farmers belong.
Matching the type of feed to the ontogeny of the alimentary tract of the fish is crucial to fish survival (Hecht,
2013). Exogenous feeding in fry starts immediately after the exhaustion of yolk reserves. However, it has been
noted that at this stage, the gastro-intestinal tract of African catfish fry is not fully developed to effectively utilize
dry feeds as is the case in tilapine fry (Viveen, 1984; Hecht, 2013). Only after the stomach becomes functional and
pepsin activity contributes significantly to protein digestion can the larvae be weaned from live food to a dry feed
such as Soybean meal (Verreth and van Tongeren, 1989; Verreth et al., 1993). Notably, these (the dry feeds) are
the common feeds for fry in Malawi. Consequently, this explains why feeding fry on such feeds results in high
mortality unlike in systems where fingering production is based on the use of
Artemia salina nauplii
diets
(Hogendoorn and Visman, 1980; Olurin et al., 2012). The local economic conditions imply
Artemia nauplii
is
largely unavailable and/or unaffordable for small scale farmers and thus the potential of milk sources of protein in
improving survival in the species needs to be looked into.
Soymilk and cow milk are the most common milk protein sources in Malawi. Soymilk has a comparable crude
protein content and amino acid profile to cow milk (Akinnuli and Olabanji, 2013), is easier to access and is far
cheaper. In addition, the use of cow milk in catfish fry nursing would be inconsiderate and unjustifiable in a
country where consumption of milk products remains very low, estimated to be 4-6 kg/capita/year (Tebug et al.,
2012). This is lower than the African average of 15 kg/capita/year, and far lower than the WHO recommended
intake of 200 kg/capita/year (Banda, 2008; Akaichi and Revoredo-Giha, 2014). Therefore, the use of Soybean
milk to improve survival rates in African catfish fry would represent a cheaper, socially acceptable and readily
available alternative to Artemia for small scale farmers. In addition, De Silva and Phuong (2011) reported the
successful use of soymilk among a great majority of striped catfish (
Pangasianodon hypophthalmus
) nursery
farms in Mekong delta, Vietnam. That being said, a common challenge in the use of Soybean meal and other
Soybean products in fish feeding is the presence of trypsin inhibitors (Serine Protease inhibitors) in untreated
beans which hinder growth. It is also important to determine if such problems exist in Soymilk. Further, the
authors are of the view that efforts to improve survival of fry of the species should not hinder growth. Thus, the
