Spermatozoa in triploids of the rosy bitterling Rhodeus ocellatus ocellatus

Artificially induced triploid male Rhodeus ocellatus ocellatus showed typic al nuptial colorations, irrespective of spermiation. In milt from triploids , abnormal spermatozoa (malformation of the head and mitochondrion, excessi ve formation of the head, mitochondrion and flagellum, and no flagellum) oc curred at 78.4% frequency. Spermatozoa with multiflagella were most common, often with a saccate-like organ. Many triploid spermatozoa moved actively as long as those of diploids (10.92 +/- 0.91 min = mean +/- S.D., P>0.05), but did not advance like diploids, spinning around until movement ceased. T he sperm density in triploids was <2% of that from diploids. In triploid te stes, deformed and variously sized spermatids were often observed, and norm al spermatids and spermatozoa were seldom recognized. The DNA content of tr iploid spermatozoa varied greatly, compared with that of diploids. Peak of sperm DNA content differed slightly between two triploid samples with two p eaks at 1.5 n and 1.9 n (P<0.0001 in both), respectively. Triploids had the greatest average sperm head diameter of 2.25 +/- 0.67 mu m (mean +/- S.D.) , while that of diploids was 1.83 +/- 0.15 mu m (P = 0.002). In the fertili zation test using the eggs of diploids (n = 1500, 30 trials), only one egg developed. The embryo chromosome number was 60 (2.5 n) and the ploidy of sp ermatozoa contributing to fertilization appears to be 1.5 n. The extremely low fertility of triploid R. o. ocellatus spermatozoa seems to be caused by the reduced motility and large head size of spermatozoa, and the low sperm density of the milt. The ploidy of spermatozoa that are successful in fert ilization is likely to be related to the distribution pattern in the DNA co ntent of cells. (C) 1999 The Fisheries Society of the British Isles.