Development of Pectoral Apparatus in Ictalurid Catfish

Abstract

Catfish have a complex pectoral spine that can be bound, locked or rubbed to produce stridulatory sounds and which functions in swimming and as an antipredator adaptation. There are 8 pectoral muscles including four for the first spine and four for the remaining rays. Pectoral muscles in the Blue Catfish Ictalurus furcatus, an invasive species in Chesapeake estuaries, are known to grow continuously. In this study I categorized growth of six pectoral muscles in young of the year to young mature adults of 5-6 years of age including muscle weight, fiber diameter and fiber number. The abductor muscles for the spine and ray are larger and have more fibers than the arrector ventralis and arrector dorsalis that mediate specialized spine functions (locking and stridulation). In this size range muscle weight and fiber diameter increase linearly, but fiber number exhibits a complex nonlinear increase. Fiber number barely increases in small fish and then jumps dramatically over two fold in fish of about 30 cm TL before stabilizing in larger fish. The fiber increase correlates with dietary shifts to piscivory.