Some cytological observations on male sterility in the carp-funa hybrids

概要

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When kept under a confined condition, the carp (<I>Cyprinus carpio</I>) and the funa (<I>Carassius carassius</I>) mate and can produce hybrids. Reciprocal crosses are also possible with similar results. The hybrids grow regularly with no observed anomalies in their developmental course. They rank intermediate between the parent species in several characters. The hybrid males are completely sterile. Their testes generally lack spermatogenetic activity. The chromosomes as observed in spermatogonial division are 99 in number, being the total sum of the haploid numbers of the parents, 52 for carp and 47 for the funa. Meiosis in the hybrid testes is highly disturbed, being arrested at early stages of the meiotic prophase. Most of germ cells undergo pycnotic degeneration during the period from late leptotene to pachytene, and no spermatozoa are produced. In some hybrid specimens, the gonads show mosaic structures composed of testicular and ovarian elements, an evidence suggesting that sterility is associated with intersexuality, caused by the genetic unbalance between the parents.
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