First on the cory pictured in post #1, it is Corydoras trilineatus, without question. This species is almost always labelled "julii" in stores in North America. As JD mentioned the true C. julii is very rare in the hobby. It is actually fairly easy to tell them apart: C. trilineatus has a more reticulated pattern with respect to the black markings on the silver body, whereas C. julii has no reticulated markings and all "spots" are more like roundish spots, and this is especially evident on the head region. There is also a difference in the horizontal line, which extends closer to the head on C. trilineatus while on C. julii is less distinct and may even be absent.
Now to your link on angelfish. Fluttermoth provided the three natural species. All of the varieties in the hobby such as Marble, Blushing, Black Lace and many others were developed by humans from the wild species Pterophylum scalare. So far, there have been no variants that I am aware of from the other two wild species, and as fluttermoth said, these latter two species are very rare and thus very expensive. The commercially raised P. scalare varieties are better adapted to water parameters different from the natural habitat (to some degree, there is a limit), more "normal" aquarium temperatures (= high 70's; not necessary to have the temp is the 80's as it is with wild caught angelfish), and are less expensive. However, they are "community fish" only up to a certain point, but they do have specific requirements and issues that must be understood and planned for if you are to have success, and this involves the tankmates.
As for "predatory," it is natural for adult angelfish to attempt to eat smaller fish, especially linear shaped ones like many of the tetras (neons, glowlights, rummys, etc). In the reverse, as it notes in your linked article, tankmates must be very peaceful and sedate fish. It is rather surprising how many so-called "peaceful" tetras will become nasty fin nippers in the presence of angelfish.
Being a shoaling fish, angels should be in small groups, minimum five though sometimes four can work, but absolutely never three. And only two if they are a bonded mated pair. A single angelfish is often suggested, and while this may or may not cause issues (no one can predict fish behaviour when the fish is suddenly placed in a completely un-natural environment like being alone with other species), I personally am not a fan of treating fish like this. See the green citation in my signature. And as JD said, having a group will almost inevitably result in a pair forming, and then you may have real issues depending upon their inherent traits respecting aggression and territorial defence.
Byron.
/www.petsmart.com/live-pet/live-fish/angelfish-zid36-15215/cat-36-catid-700002?var_id=36-15215&_t=pfm%3Dcategory ( and these are predatory? )
