Hey Senshine! Lovely little froggies you have there, great shots!
The first one is certainly a male, but the only way to reliably sex these frogs (that I know of) is by the presence of the postauxiliary subdermal gland (big words for little pimples!) on their side. They don't appear until maturity, but if one has it, I'd think the other would too - they look to be about the same age.
Typically, females will be chubbier than males, and in my experience are more prone to being intentionally aggressive while feeding (though any frog can fight for their share of the meal if they feel it's necessary). Typically, frogs don't cause any harm with their chomping - especially since they don't have any teeth! Oftentimes it's seems to be accidental - they lunge and happen to nom on each other when they try for a mouthful of dinner. Since ADF don't see very well, they hunt by tracking movement. Unfortunately for them, we feed 'dead' foods, so they get a little bit confused at times and pounce on each-other. I have a couple of fairly aggressive (lol, aggressive for ADF isn't typically very aggressive! ^.^) frogs in my community tank, and one little male who would just starve to death if I didn't keep a close eye on his intake - none of them seem bothered by being chomped on by their buddies, I've never seen any damage done. Good job with target feeding - it can be so important.
You can tell a full frog by looking at their underbelly. Their stomach is located in the center and slightly to the left of the spine - you should be able to see a gentle rounding there when they're full. . . as long as you know your skinny frog is eating well, don't worry too much about that part. Just like people, they can come in different shapes and sizes (all cute!) One of my adult males is fairly thin compared to his buddies, but with a great appetite, and I've had him for over a year and a half - he's healthy as can be!
The frog in the bottom picture doesn't *seem* overly thin to me, though I do see the hunched back that has you concerned, he looks healthy enough, otherwise! Has he always been this way, or is it something that has come about recently? As long as he's swimming and eating well, I would try not to worry too much about it. . . I'm not sure why this would happen, but I've known frogs to live a good long life with similar issues. . . possibly just a genetic defect? :/
Hopefully one of the others will have something more to offer you on these concerns - wish I could be more help! Welcome to frogville just the same!!!
Last edited by Chesh; 08-26-2013 at 08:58 AM.