Those discarded parts should be frozen then when you plant your tomatoes put them underneath. Divers suffer from nitrogen exposure but fish do not. All parts of the fish are rich in nitrogen Nitrogen Narcosis In Diving - StatPearls - NCBI Bookshelf
What makes you healthy from eating fish is its packed with vitamins and protein making it a near perfect food
The food you eat is at least 16% amino nitrogen
This is why animal urine and feces is so high in nitrogen. Since poultry dont have urine their feces it is super fertilizer.
Years ago i raised tropical fish for pet stores and cleaned their tanks regularly. The water on the bottom was sucked up by siphon which contained fish feces. That water applied to vegetables was gold for a garden. Many people realized this and the aquaponics movement started as a result.