Hey so do they have any blue under the eyes? If so other than venting this is said to be reliable as well.
-Joe Mcelheron
Several authors have suggested that the sexes are distinguishable by the pattern of laterally-orientated, iridescent blue markings which extend from beneath the anterior portion of the eye to the tip of the snout.
In males these markings have been said to form unbroken stripes whereas in females they’re supposed to form a series of variable blotches, and it’s been suggested that the reason for this is that females inhabit deeper water while males prefer the shallows and are thus more easily accessible to collectors, but this seems questionable given that large batches of unsexable juvenile specimens are often exported.
A more plausible hypothesis may be that Biotodoma species require some time to become mature and are thus not immediately sexable, and this may also explain the apparent ‘difficulty’ in breeding them in aquaria (see ‘Reproduction’).
Based on observations from breeders both males and females can possess stripes on the head but males tend to grow a little larger, are deeper-bodied and develop longer filamentous extensions on the dorsal and caudal fins than females.
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