I think you are reaching the limit of push and pull extruding on the same body. As you put more details and features you will start getting more errors. You are basically creating by mathematic algorithms and when it reaches a limit you get errors.
The fishing lure, instead of manipulating the same body, create features separately, like the gills, eye, etc… Add them or boolean them off the body.
Also consider other softwares that is more push-pull friendly like a sculpt tool, like nomad or blender.
Might be a more fun experience, also there are lot more tutorials out for what you want to create for these other softwares.
