What are you preparing? are you using the whole "marine organism"? using just the fish scales? the muscle? the sperm? are you interested in looking at protein changes? the lipid profile?
Regardless of what your aim is, it is mandatory to remove any salts and other potential contaminants introduced during sample preparation. So even if "marine organisms" sample preparation requires the use of phosphate buffers or detergents (SDS or Triton) you need to get rid of these before injecting your sample into the LC-MS. You can discard these unpleasant salts by introducing extra desalting steps in your experimental protocol. In case you're analysing lipids contaminants often introduced come from the use of organic solvents in contact with plasticware. For this reason minimise the use of plastic ware in your protocol or better use high quality plastic (organic resistant).
I am guessing that you might be wanting to look at environmental pollutants. There is a lot of literature on using QuEChERS to extract pollutants and clean up the extracts.
I have added a link to an overview of the method (UCT/Achrom).
I agree with both Tim and Ana. It really depends on what you want to analyze from your crude sample. That being said, desalting and removing detergents are very important steps to maintain your LCMS system in good order.