The cost of fish food can represent 30 to 90 percent of the total cost of raising fish! In some situations (like indoor culture), feed must provide 100 percent of the complex nutritional requirements fish need. A less-than-complete diet will show up as poor feeding response, slow growth and/or disease problems. Poor water quality can also be caused by bad feed. All feed should be used within the normal 6-month shelf life. Do not overfeed. In general, give fish a little less than they will eat (stop feeding them before they stop feeding).