I'm not sure I understand the question, so my answer might not be what you are looking for. First, the umber of chromosomes in one species will not make it more or less amenable to improvement via selection. You could use selective breeding programs that have been done in other species of fish as examples of how to conduct a selective breeding program in your species. Selective breeding for improved growth in tilapia has two major problems: femaleas and age of reproduction. Females grow half as fast as males and when you cultuer mixed-sex tilapia, you end up with uinwanted reproduction. That's why so much effort has gone into the production of all-male tilapia. If you want to see a good example of selective breeding for improved growth in tilapi, look up the GIFT tilapia breeding program. There are many published papers about creating all-male tilapia.