Possible Clues:

• Small fish, set to catch whales
• 'Fish, like small herrings (6)'
• Use them to catch mackerel
• Nursery-rhyme fussy eaters
• Small fishes used to catch larger ones
• Small fish like sardines
• Picky eaters of rhyme
• Jack and the missus of verse
• Nursery rhyme couple with restricted 23-Downs
• Canvas hoisted on board to get fish