Possible Clues:

• Burbot
• Viviparous blenny, small broad-headed fish found in cold seas
• Slender and mostly bottom-dwelling marine fish
• The burbot; the viviparous blenny
• Old PM, quietly diving to bottom, determined to get fish
• Initially postmaster general goes back and forth for fish
• Swimmer's toupee bobbing round end of pool
• In Bow a chap'll look sullen, we're told, given fish
• Small broad-headed cold water fish — up to lee (anag)
• Burbot made another fish look petulant