The Nile Tilapia (Oreochromis niloticus) and the African catfish (Clarias gariepinus) are the two most cultured fish species in Africa. Genetic improvement in these fish species, specifically the Nile tilapia has resulted in significant gains in the past few decades. This is particularly true for the Genetically Improved Abbassa Nile Tilapia (GIANT) developed in Egypt and the Genetically Improved Farmed Tilapia (GIFT) developed by the WorldFish, which reported up to 20% gain in growth rate per generation (Yáñez et al., 2020; Hamzah et al., 2014). The GIFT strain has been distributed to several countries such as Bangladesh, China and recently, Nigeria. Genetic improvement in the African catfish has shown an accumulated gain in growth rate of up to 50% in over three generations in Indonesia (Imron et al., 2020). There is yet a successful genetic improvement programme for C. gariepinus in Africa, however, the Dutch-domesticated strain of the African catfish has been reintroduced to Africa, particularly Nigeria and some other countries such as Kenya, Uganda, South Africa.
The distribution of the GIFT tilapia and the Dutch Clarias to other countries is often met with concerns over the ecological impact upon native populations (Ansah et al., 2014; Eknath & Hulata, 2009). Of even more concern is the fate of such stocks post-reintroduction. In the case of the African catfish in Nigeria, the dert in knowledge on genetic management of broodstock in various hatcheries, the mating designs, sex ratios, the use of shooters as broodstock and reliance on very few initial populations has led to very low levels of genetic variation within and between farms. Results from a survey on hatchery practices show that no hatchery operator tagged his/her broodstock and broodstock from different sources are often mixed together without any means of identification. Only 3% of the respondents used sex ratios of 1:1 as 97% used skewed sex ratios (between 1:2 – 1:5). A total of 76% of the respondents used shooters as broodstock and 68% also reuse their broodstock at least three times in a year. Using DArTSeq, a next generation sequencing technology, the observed heterozygosity recorded from a study conducted by the author, to assess levels of inbreeding in 33 farmed and 2 wild populations of Clarias gariepinus in Nigeria involving 276 individuals and 6797 loci was 0.0802, while the expected heterozygosity was 0.09. Many farmers now report poor survival, poor and uneven growth and increased skeletal deformities, most of which they attribute to inbreeding depression.
Today, inadequate supply of good quality fish seeds is one of the major problems of the Nigerian catfish aquaculture industry. While the tilapia industry in Nigeria is still young, the possibility of trailing the part of the African catfish is not completely uncertain. There is therefore the need for the evaluation of different strains of tilapia and C. gariepinus for suitability in aquaculture in Nigeria, and assess their genetic relatedness to ensure biodiversity.