Doesn't look skinny to me, actually looks reasonably thick. Fish don't need to be fat to be healthy and well fed; in fact, underfeeding a little can lengthen their lives. That's the science of it. As to preference, I feed fry and juvies reasonably well but not to the point of bulging bellies or changing their body profile. Adults I feed somewhat sparingly, but that's me. Not my intention to give a critique on fish feeding here.
Otherwise, a few of the basics regarding severums in general (which are among my perennially favorite fish)... They're SA, there are several varieties, including several wild varieties, plus some cultivated strains. You can expect 8 inches or more adult size (occasionally, much more). Other than clean, good quality water, they're not too fussy over exact conditions; I've kept mine over the years anywhere from 7-7.8 pH and 76-82 water temperature. In a tank they're generally omnivorous, do quite well on a quality pellet-- mine get NLS and/or Omega One. Some feed them veggie treats, peas, lettuce, zuchini, and the like, which a lot of them enjoy but it's hardly a requirement with a good diet otherwise. I had a wild rotkeil (red head) severum that finally died a few months ago, was minimum 13 years old, probably older (I got him as an adult and before I got him he was kept in too small a tank, cheap food, etc.) who over the years was fed probably 95% pellet (HBH soft krill and soft spirulina for a while and NLS and/or Omega One for about 80% of his time with me) and treats of freeze dried mysis, freeze dried brine shrimp, etc. On just a handful of occasions over the years I tried peeled, thawed frozen peas, which my rotkeils loved, but this was such a rarity it can't be said it contributed anything significant toward their overall health or nutrition.
Due to their size they need a decent sized tank. I've seen them get mean in too small a tank, like kill everything in the tank mean. They're not predators, but may (or may not) pick off small tetras, etc.
