Description and scaling of pectoral muscles in ictalurid catfishes

Abstract

The pectoral spine of catfishes is an antipredator adaptation that can be bound, locked, and rubbed against the cleithrum to produce stridulation sounds. We describe muscle morphology of the pectoral spines and rays in six species in four genera of North American ictalurid catfishes. Since homologies of catfish pectoral muscles have not been universally accepted, we designate them functionally as the spine abductor and adductor and the arrector dorsalis and ventralis. The four muscles of the remaining pectoral rays are the superficial and deep (profundal) abductors and adductors. The large spine abductor and spine adductor are responsible for large amplitude movements, and the smaller arrector dorsalis and arrector ventralis have more specialized functions, that is, spine elevation and depression, respectively, although they also contribute to spine abduction. Three of the four spine muscles were pennate (the abductor and two arrectors), the spine adductor can be pennate or parallel, and ray muscles have parallel fibers. Insertions of pectoral muscles are similar across species, but there is a shift of origins in some muscles, particularly of the superficial abductor of the pectoral rays, which assumes a midline position in Ictalurus and increasingly more lateral placement in Ameiurus (one quarter way out from the midline), and Pylodictis and Noturus (half way out). Coincident with this lateral shift, the attachments of the hypaxial muscle to the ventral girdle become more robust. Comparison with its sister group supports the midline position as basal and lateral migration as derived. The muscles of the pectoral spine are heavier than muscles of the remaining rays in all species but the flathead, supporting the importance of specialized spine functions above typical movement. Further, spine muscles were larger than ray muscles in all species but the flathead catfish, which lives in water with the fastest currents.

Mechanisms of Fish Sound Production

“…Many ostariophysine fishes have two or even three chambers, and we suggest that all chambers contribute to buoyancy but divisions likely indicate acoustic specializations. Note differences in the channel catfish Ictalurus punctatus and the blue catfish Ictalurus furcatus, which have, respectively, one and two chambers despite being in the same genus (Miano et al 2013). Piranhas and other characids (Ladich and Bass 2005) have a large anterior and a smaller posterior chamber.…”

Developmental variation in sound production in water and air in the blue catfish Ictalurus furcatus

“…Larger fish produce louder calls at lower frequencies owing to a more massive pectoral girdle (Duvall, 2007) that would have a lower natural frequency. Both sweep duration and pulse duration increase with fish TL, and high-speed camera data indicate that time to abduct the spine increases in larger individuals, whose muscles are longer and should take longer to contract (Connaughton et al, 1997;Connaughton et al, 2000;Wainwright and Richard, 1995;Miano et al, 2013). The number of jerks and pulses per sweep as well as pulse rate decrease with fish size.…”

Sound Communication in Fishes

“…The swimbladder in the oyster toadfish has a thin septum containing a sphincter that separates anterior and posterior parts of the organ (Fänge and Wittenberg 1958), and Tracy indicated that this partitioning separated gas secreting and reabsorbing parts of the bladder (Tracy 1911). Note differences in the channel catfish Ictalurus punctatus and the blue catfish Ictalurus furcatus, which have, respectively, one and two chambers despite being in the same genus (Miano et al 2013). Many ostariophysine fishes have two or even three chambers, and we suggest that all chambers contribute to buoyancy but divisions likely indicate acoustic specializations.…”