I do not know culinary terminology; so I use 'piscine' to mean 'with a positive flavour of fish' (because 'fishy' connotes negativity).
My friend drank some flavorous fish soup with a milky white colour at his favourite Cantonese restaurant, one of whose chefs recommended using a fish called 黄鮨斑, which a laborious Google search revealed as yellowfin grouper (abbreviated as YFG).
My friend could not find live YFG to purchase; so he bought some frozen heads. He pan-fried/seared one head which turned a golden brown, then simmered it (over low heat and an electric oven) in around 4 litres of water for around 2 hours. The final product tasted like water (lacked any piscine flavour) and resembled water (lacked the desired milky white colour). The fish itself tenderised and still retained flavour though. How can my friend correct the problems?