Should I give my kittens a salmon oil supplement in their food?

They are eating Innova turkey/chicken wet food, a bit of Nature's Variety Instinct rabbit dry food, and Stella and Chewy's lamb. They are both males, about nine weeks old. They were abandoned and malnourished when I found them, so their coats are a bit dull and they have some weight to gain. I thought salmon oil might be a healthy way to deliver more calories into their diet and improve their fur, but I don't know if it's good for young kittens.