Re: [Killietalk] Sex

[Dick Powell <oldcarbuff at earthlink_net>]

I suspect that each family of fish are different, but I know how sex determination in bettas occurs.  The sex organ in bettas is linear and all fry start out as female.  If development continues along the linear organ it becomes a male, but in addition to any environmental factors that may affect sex determination, development of males is hindered if the fry that have already developed into males are not removed from the rearing tank.  Removal of males somehow permits the development of additional males within the group remaining in the rearing tank.  This accounts for those occasional reports of a "female" betta changing sex, but a male cannot, since that would require development along the linear organ to reverse itself, rather than continue.  Temperature is seldom a factor in betta rearing, however, since most people follow a fairly standard procedure of breeding at 80 degrees and only start dropping the temperature after development has occurred, generally.  Temperature !
 plays a more important role in killies because there is no standard breeding or rearing "formula" that everyone follows.  I doubt that sex determination in fish is the same across all families or groups, however.

Dick
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