Possible Clues:

• Zoo heavyweight, for short
• Old doctor drops boxes — one's very heavy!
• 12 23 down's fruit to order
• Metropolitan Museum mascot William is a blue one
• 22 aquatic animal
• Beastly cheerleader on the river?
• Animal doctor refusing cases
• Ballerina in 'Fantasia'
• One form of the Egyptian god Set
• Wallowing mammal