Oh, if it's that infrequent then it's probably not as big a deal. In your original post it kind of sounded like you were feeding them that stuff as part of their main diet. That would be bad, too much fat and salt.
As for turtles, the feeder fish you get at the pet store are usually raised in minimal conditions meaning that they are not always in the healthiest conditions and may not be as nutritious as a wild fish would be (but wild fish also harbor parasites so it's a "catch-22"). Also shrimps are high in protein and cholesterol. Used as treats maybe once every week or two is good and provides variety as well as enjoyment to the turtles diet.
Turtles who are fed too much protein will develop pyramiding in their shells which can also be an indicator of other problems. Also, you need to make sure that the turtles overall diet provides him with a proper ratio of calcium to phosphates for proper bone and shell growth. You can find a lot more really good information in the Nutrition and Health sections of this website. Use the links at the top of the page to find them.
