Do you have a pic, there are over 100 mormyrids and about 12 are often sold as baby whales. in general they are all peaceful, shy, and mainly nocturnal. they range as adults, depending on species, from 3"- around 15", all are mildiy "electric". all are fond of small worms and lots of plant matter like spirolina, boiled spinach, and hair algae. Even your guppies should be safe with these. The most commonly sold few types all top out around 8"s. Except for a few uncommon ones they like ph and hardness level suitable for a standard community tank but like the temp. a little warmer, between 78-90 degrees F., they are susceptable to ich and if wounded, fungus at lower temps.