With too many lines he means that your model has too many polygons and automatically too many lines (edges). The polygons are also called faces. You should make a low-poly (less edges and polys) model at first and then smooth it.

And with linear he means that your edges are not smooth. They must be adapted to the shape of the fish.
You can see that on the picture. (had to draw it with my mouse )

Just play a bit around with the vertices and you'll see how to make the lines rounder



ps: sorry if it's bad explained

OH; SORRY FOR THE DOUBLEPOST! PLEASE DELETE THE FIRST POST!