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and found them to be alive until the 10th week after introduction (see
Pandian, 2003). Apparently, Leydig cells in this sterile fi sh may have been
active providing nutrients to the transplanted sperm. Attempts have
been made to induce sterility in commercially important fi shes under the
impression that these 'broilers' may grow faster. As indicated elsewhere,
sterile gonads have not yet attracted electron-microscopic studies (cf Fig.
41,54) to provide details on the presence of PGCs, OSCs SSCs and germ
cells supporting somatic cells. Dorsch et al. (2004) have identifi ed 20 male
sterile mutants in zebrafi sh shooting banks ( shb p12idc ) and are known to cause
a defect in sperm motility. Transmission and scanning electronmicroscopic
investigations of the spermatozoa of Cyprinus carpio have shown 9.5, 5.3 and
2.4% of bifl agellar, trifl agellar and double-headed abnormal spermatozoa.
These sperms also show differences in ultrastructure, motility and relative
DNA content, compared to normal sperms (Psenicka et al. 2009). Reports on
the natural occurrence of steriles are indeed very rare. But they are artifi cially
produced following hybridization, and ploidy and hormonal inductions.
For details on ploidy and hormonal induction of steriles, Pandian and
Koteeswaran (1998), Pandian and Sheela (1995) may be consulted. Artifi cial
hybridizations have been induced in more than 300 species (see Argue
and Dunham, 1999; Bartley et al., 2001; Pandian, 2011); however, viable
and fertile progenies are generated only in very few instances. It is now
established that hybridization results in male sterility but triploidization
in female sterility. Triploid males are hormonally fertile but cytologically
sterile, while female triploids are both hormonally and cytologically sterile.
Corresponding information is needed for hybrid male sterility.
4.3 Mutants
Mutants provide a crucial tool to investigate the role of genes in a biological
process. Collection of mutants in a process can be the key to elucidate
molecular mechanisms or pathways controlling the process. The growing
number of sequenced genomes and overall genome resources available
for fi shes have made them an important tool for investigations of human
genetics, development and diseases. For instance, experimental studies
of spinal deformities in fi shes remain an unexplored resource, capable
of answering questions of vertebrate development, basic stability and
deformity (Gorman and Breden, 2007). Among the vertebrate species, in
which the mechanisms of embryogenesis are currently investigated, the
zebrafi sh offers several advantages. Generation time of three months,
and regular weekly spawning of about 100 eggs undergoing synchronous
development outside the mother are some advantages (Solnica-Krezel et al.,
1994). Besides the almost transparent embryos allow monitoring the early
development of the brain, eye, trunk musculature, gut, heart and nervous
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