Related Clues:

• Air-gulping swimmer
• One in a dangerous school
• Alligator ___ (underwater menace)
• Fierce small fish of the Amazon
• Small voracious carnivorous fish
• That's a fishy way to have a bit of a material turn
• Is it up to a bit of stuff to be so fishy?
• Up here there's a scrap of fish
• The scrap turns up for the start of 21 across (3)
• Fish the bit of stuff up
• So fishy to have a scrap up like this
• The fish might get to a blooming den
• Spearlike fish
• Skinny swimmer
• Maybe Sam Spade managed a half-laugh for one in a dangerous school