Journal of fish biology vol:53 issue:2 pages:402-413
The optimal ratio of spermatozoa : egg (15 000 : 1) for artificial insemination of African catfish Clarias gariepinus gave fertilization and hatching rates of 80 and 67%, respectively. Below a sperm:ova of 3000 : l fertilization success decreased significantly. Excessive sperm (>15 000 : l) partly inhibited fertilization success. Sperm motility was decreased significantly by 0.001 mg l(-1) Hg2+ as HgCl2, but its effect on fertilization was dependent on the sperm : ova ratio, since excess sperm masked the effect of the pollutant. The most sensitive sperm:ova ratio for monitoring pollutant effects on fertilization success was 1500 : l, which corresponds to half the minimal amount that yields a high fertilization rate in artificial insemination. There was a good correlation between fertilization and hatching rates (r = 0.83; P < 0.05). Although both fertilization and hatching rates provide equally good indicators of fertilization success, the more rapid fertilization rate test is recommended since it requires only 12 h. (C) 1998 The Fisheries Society or the British Isles.