[Peter Finke]

1. Crossbreeding in Parosphromenus is generally possible since the genetic interrelations between the “species” are widely unknown.
2. Many forms are probably related on a subspecies- or semispecies-level, and here crossbreeding is highly probable. In nature, this is mainly prevented by exclusive ocurrence.
3. In aquaria, it is generally recommended to keep different “species” apart, especially since the distinction of females is often nearly impossible (at least for the aquarist).
4. The differentiation between the “species” is often executed rather carelessly, especially in the international trade and additionally in cases of hitherto undescribed forms. It is highly probable that there are some (or even many) crossbred fish existing in our aquarium stock.
5. But: There are clear cases of species differentiation, especially when structural properties are clearly to be identified in both sexes, one is between the two you mentioned: anjunganensis and deissneri. Both are easily to be identified.
6. The problem is with the latter. I doubt that the fish you are offered as to be “deissneri” really is deissneri. (Look for the description of this species in our species accounts to know why). Most fish offered in the trade under this name are misidentified. Therefore, the fish offerd to you is probably equally a round-tailed form of the harveyi-bintan-group. If it were real deissnerithat is endemic from Bangka, it would be clearly discernible by man (and fish) from anjunganensis at the first sight. But since it is probably a different form, it may be not.
7. Since anjunganensis is not belongig to the narrower harveyi-bintan-group, crossbreeding is not as probable as in other cases. But think of the unnatural closeness of the aquarium-situation; I would give no guarantee.
8.Conclusion: If the fish you are offered would be really anjunganensis and really deissneri, in a tank big enough would be hardly a risk of crossbreeding. But since the latter is probably a different form, there is. I should not keep them together.
9. It is generally very important to take this problem seriously. As long as we have no clear genetic data, we should be very careful with mixing different forms, even the same form from differnet locations.