This function is only for determining if the loot window is related to fishing.

Returns

isTrue 

Boolean - is it true

Example

This will identify that the loot window should display the fish graphic, then play the sound and update the image.

if( IsFishingLoot() ) then
   PlaySound("FISHING REEL IN");
   LootFramePortraitOverlay:SetTexture("Interface\\LootFrame\\FishingLoot-Icon");
end