Spoon the tilapia filling evenly down the center of the
salmon. Lifting the plastic from one of the long edges, gently roll the
salmon around the tilapia into a
sausage shape. Tighten the plastic as much as possible without squeezing the
salmon out the ends. Twist the ends of the plastic and secure with string. Wrap the
salmon roll in another layer of plastic wrap and secure the ends with more string.