isn't it so unhealthy for pokemon to be fat?
I'm going to answer this one in way more detail than you wanted!
Firstly, the simple facts. At 2 or more kilograms underweight, a magikarp will fail to thrive and then die unless rapid intervention occurs. At 2 to a little under 4 kilograms overweight, a magikarp might want to lose some weight, but can usually continue to perform most magikarp activity. While a healthy weight is ideal, if you're going to be trending in one direction or the other, chubby is safer than skinny. Secondly, a female magikarp that has a male magikarp's lean build is usually underweight. That's part of their sexual dimorphism. This tendency is exaggerated during the breeding season- male magikarp look extremely lean because they're more active in the spring, while female magikarp need to put on fat to develop eggs and protect themselves during breeding and are thus eating as much as possible and moving as little as possible. Older magikarp also tend to have more fat than younger ones, as an older magikarp is typically a more successful magikarp and thus is better at finding food and eating as much of it as possible. Thirdly, all magikarp need to have some fat, because of all the jumping and swimming they do. Fat stores energy, and helps protect their organs.
If you look at a picture of an obese magikarp, you'll notice a few things. Obese magikarp have protruding eyes, slightly exaggerated prominence of the scales (NOT pineconing, which is a different thing), fat deposits in inappropriate places such as the face, and little to no taper between the body and the tail. Obese magikarp also have difficulties swimming, jumping, or otherwise participating in typical magikarp activities. Sharkie exhibits none of these traits, although she does have a lessened taper between body and tail than that which would be present in a magikarp of ideal weight. She is chubby, but she is still within the healthy range. Sharkie in particular leads a very active lifestyle, and some of that extra weight is actually pure muscle mass from being older and stronger than other magikarp in the ponds.
In short, Sharkie's a little fatter than she would be in a perfect world, but given her age, sex, and lifestyle, she's no more than on the high end the range where we want her to be.
