The male tetra produces spermatozoa, whereas the female produces ova. It may be thereotically possible to visually differentiate the genders, from the latter's gravidity, but the practice of gluttony imposed by like-minded caretakers could render equally elephantine proportions to both members. Some authorities with an anal fixaion have reported to observing a marked distintion in the said fin of the two genders. You are advised to search the worldwide web (i.e., to google) for more detailed data on inducing these characins to propagate (however, typing "anal" in the search parameter is not recommended).
Paracheirodon axelrodi commands a premium from the now debased P. innesi, as the latter is, like many other forms of merchandise, mass-produced in the sub-tropical southern provinces of China. The quality thereof may be said to be questionable as well, due to the dearth of fresh genetic material in the captive breeding pool. This is what results when brothers and sisters (and cousins and 13th aunts) have no choice but to "do" each other.
P. axelrodi, on the other hand, is a noble savage, scoured from the pristine paradise of the Rio Negro in seasons of dryness. Airfare from Brazil is by no means a song, even for miniscule Amazonians. Moreover, interim captive periods impose a high casualty rate upon the lil' darls, so their minders must surely seek greater compensation from us who love the darls to their death.
I have little idea what a high grade cardinal is. You may be thinking of a fish larger than average, fatter than average, or with a fatty protuberance on its forehead. Common sense does tell me that a more mature and robust creature would be more valued than a scrawny, underfed weeny.
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