Induction of Monosex Fish Production and its Potentials for Catfish Aquaculture in Nigeria

The application of genomic and biotechnologies has contributed significantly to genetic and reproduction developments in fisheries and aquaculture. Though, the technologies are still far to be fully optimized but genetic manipulation techniques have been really employed in developed economies to increase fish production. In this study, monosex larvae of African giant catfish (Clarias gariepinus) were produced using simple and safe techniques such as androgenesis and gynogenesis where catfish gametes were treated with UV irradiation at 30000 µWcm^-2 for 15 min and subjected to cold shock treatment after fertilization at 2^oC for 20 min. Eggs numbering 100 ± 10 each in quadruplicates were used for each technique. Induced gynogenesis was carried out through activation of normal eggs with irradiated sperm and then cold shock, while for androgenesis irradiated eggs were fertilized with normal sperm. For the control experiments, 100 ± 10 normal eggs in quadruplicates were fertilized with irradiated sperm to produce haploid embryos and normal milt to produce normal diploid embryos. Fertility, hatchability, and survival were monitored and recorded. Androgeneic, gynogeneic, haploid and normal diploid treatments gave fertility of 80%, 72.5%, 100% and 100% with standard error of mean (SEM) of 2.65 respectively. Hatchability was 5.5%, 22%, 15% and 93% with SEM of 7.93 for androgeneic, gynogeneic, haploid and normal diploid embryos. No fry that survived was recorded at yolk absorption for the haploid group while survival after one week for androgeneic, gynogeneic and normal diploid embryos gave 5%, 13.25% and 91% (SEM = 8.46) respectively. Ploidy levels of the embryos were determined in 1-day old posthatched embryos immersed in 0.02% colchicine for 4 h, later treated for 5 min in distilled water and then in diluted catfish serum 1:3 in distilled water for 25 min, then stained with 20% Giemsa (Scharlau) obtaining chromosome number of 28 for haploid, 56 for normal diploid, androgeneic and gynogeneic larvae. Expected outcomes from sex specific DNA analysis by comparative RAPD will further confirm their sex determination. Hence its potential applications in enhancing breeding strategies for research and commercial catfish aquaculture in Nigeria are discussed.

Keywords: Clarias gariepinus, androgenesis, gynogenesis, chromosome, RAPD-Randomly Amplified Polymorphic DNA