Swimming and defense - competing needs across ontogeny in armored fishes (Agonidae)

Biological armors are potent model systems for understanding the complex series of competing demands on protective exoskeletons; after all, armored organisms are the product of millions of years of refined engineering under the harshest conditions. Fishes are no strangers to armor, with various types of armor plating common to the 400 million years of evolution in both jawed and jawless fishes. Here we focus on the poachers (Agonidae), a family of armored fishes native to temperate waters of the Pacific rim. We examined armor morphology, body stiffness, and swimming performance in the Northern Spearnose Poacher (Agonopsis vulsa) over ontogeny.  As juveniles, these fishes make frequent nocturnal forays into the water column in search of food, while heavily armored adults are bound to the benthos. Most armor dimensions and density increase with body length, as does body stiffness. Juvenile poachers have enlarged spines on their armor whereas adults invest more mineral in armor plate bases...