Spawn egg are meant to be sorted alphabetically, thus:

• Spawn Cod must be placed after Spawn Chicken and before Spawn Cow
• Spawn Puffer Fish must be placed after Spawn Polar Bear and after Spawn Rabbit
• Spawn Salmon must be placed after Spawn Rabbit and before Spawn Sheep
• Spawn Tropical Fish must be placed after Spawn Stray and before Spawn Turtle

(Correct me if I am wrong)