lol...geez man...don't call me an expert....gonna make peeps expect too much of me!! I'm still learning too! Goober...lol....
Aight, I'll try to answer ur question to the best of my ability. There are several factors that will determine the growth rate. Obviously, powerfeeding, larger tank space, and frequent water changes are gonna give yaz the fastest, most optimal growth rate. How big is ur xingu? when they are younger they seem to grow a little slower...at about 1/2" a month or so.....but around 4 to 5" they seem to explode, growing at almost an 1" a month. Its crazy. Mine went from 3" to 13" in 8 months.....I was powerfeeding them a wide variety of foods, and they were in a much larger tank, 125, with two water changes a week. I would suggest feeding it chopped up earth worms. you can get them from a bait shop or any fishing store. even walmart carries them in the sporting goods. Cut them into smaller pieces until the pikes are large enough to take it whole. Definately accelerate the growth rate. Also, cocktail shrimp is a great booster. Be careful with the beefheart though, as its not really a natural food, most fish don't ever get this in the wild....lol...and it is kinda fatty and high in protein. Pikes are able to handle it though cuz they are predators. Just feed it in moderation cuz it can really cloud the water and cause problems. Another food that i really like is I think Hikari Sinkin Carnivore Pellets. They are designed for predatory catfish...so they promote rapid growth. Great stuff. Soak them first though, so that they are fully expanded. It took me about two weeks to get my pikes on to it...but now they take it with gusto! Hope that helped man! BTW...u know ur xingu I isn't gonna look like the pretty, orange juv. when its an adult right? Females are gorgeous burgandy wine red to cherry red, while the males are a drab olive green...still attractive though! Just a heads up. And once they reach sub-adult...about 6 to 8" they are gonna seriously start gettin an attitude...be prepaired!