Hmm. No expert on plecs myself either but someone else will know. Maybe post on the catfish sub-section.
Easy one this: you need to look at fin shapes. Females have a triangular anal fin, males have a long pointy fin: see diagram.
Always better to keep at least two females to 1 male, or single sex groups. So once you know what you have, you can add another or leave it as it as accordingly.
As so often happens you've picked some of the most attractive fish, which often prove to be the most unsuitable!
- red tail sharks - Not recommended. They are very active and can be very aggressive over territory as they mature. Wouldn't add it to a tank with a potentially large plec. Also not sure your tank is large enough.
- angel fish - Tricky to get the balance right with these. One may be miserable alone, two should only be kept together if they are an established breeding pair (not just a male or female), or they should be kept in a group of 5 or 6, but your tank isn't big enough for that - they can get quite big, and tall. I don't think these are a good idea. Others will inevitably disagree though.
- siamese fighters - not recommended as community fish as they can be picked on by tetras andd other nippy fish, and conversely can take objection to other fish.
- ruby barb - again, very lively active fish that need to be in groups and need large tanks, but they are fairly peaceful.
- guppies - all males maybe, say around 5. Males and females = even more babies, and with platys and mollies in the tank already I don't think that's a good idea!
Any others?
