I did set the C++ and Objective-C Interoperability build setting to C++ / Objective-C++. I was able to fix it by adding #ifdef __cplusplus and #endif around my code, but that isn't an ideal solution, so any further pointers on how to solve this would be greatly appreciated.

I did set it to C++ / Objective-C++. I was able to solve this bug by inserting #ifdef __cplusplus to before class Fish and #endif after };, but I don't think that is ideal.