Monosex Fish Production in Fisheries Management and Its Potentials for Catfish Aquaculture in Nigeria

Abstract

Sustainable fisheries and aquaculture production serve as means of achieving nutritional security and sources of employment for large number of people in the world. Fisheries play an important role in enhancing foreign earnings and solving malnutrition problems. However the state of global food fish insecurity due to continuous decline in capture fisheries needs serious attention. This is as a result of variability in climate, anthropogenic pressures, ecosystem degradation and increasing demand for fish and its products by increasing human population. Developments of biotechnology strategy such as genetic manipulations in fisheries management have been recently employed in developed economies to increase fish production. In this study, monosex larvae of African catfish (Clarias gariepinus) were produced using biotechnology techniques such as androgenesis and gynogenesis where catfish gametes were treated with UV irradiation at 30,000 μWcm⁻² for 15 min. The fertilized treatment were then subjected to cold shock at 2 °C for 20 min. Eggs numbering 100 ± 10 each quadruplicates were induced for gynogenesis through activation with UV irradiated sperm and then cold shock. For androgenesis, irradiated eggs were fertilized with normal sperm followed by cold shock. 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 3.19 respectively. Hatchability (number of hatched embryos) was 5.5 %, 22 %, 15 % and 93 % with SEM of 9.05 for androgeneic, gynogeneic, haploid and normal diploid embryos. No survived larvae was recorded at yolk absorption for the haploid group while survival after 1 week for androgeneic, gynogeneic and normal diploid embryos gave 5 %, 13.25 % and 91 % (SEM = 9.65) respectively. Ploidy levels of the embryos were determined in 1-day old post-hatched embryos following modified protocol of Don J, Avtalion RR (Theor Appl Genet 72:186–192, 1986). The mean chromosome number (n) of 28 was obtained for haploid and 56 for normal diploid, androgeneic and gynogeneic larvae. However, sex specific DNA analysis is necessary to further confirm their sex determination, hence its potential applications in enhancing breeding strategies for research and commercial catfish aquaculture in Nigeria are discussed.