I have a fully cycled 10 gal heated tank with 2 african dwarf frogs, male betta, and (now) 2 endler’s livebearers. Just a few weeks ago I had about 6 livebearers in that tank. They have slowly been disappearing. I haven’t found some of the bodies still but those that I did find, were missing their stomachs like something took a big bite out of them. It was just the belly missing, and the bite was always the same shape. Just the stomach, nothing else. Could it be the frogs having a late night snack while the fish are sleeping? I feed them sinking frog pellets and hand feed bloodworms a couple times a week. I do 40% water changes once a week. My parameters are all stable. Ammonia - 0, nitrite - 0, nitrate - 10-15, pH - 7.0, temperature - 78.