Is whitebait safe at 42c?
what am i doing wrong since safe seems to be overcooked and cooked seems to be unsafe 


You are doing nothing wrong, this is as it should be. It is the cooking which scrambles the proteins of both the fish and the bacteria living in it, making the food safe in the process. The fish is not safe at 42 C. I don't have charts here, but if you looked it up and saw it is safe at 63 C, then that's the temperature needed for safety. 

You just have to decide what you want - safety or a given state of cooking - and cook your fish to the respective temperature.