Morphological structure and peripheral innervation of the lateral line system in the Siberian sturgeon (Acipenser baerii)

Light and scanning electron microscopy (SEM) were used to study the epidermal lateral line system of the Siberian sturgeon (Acipenser baerii Brandt, 1869). This system consists of mechanoreceptive neuromasts, ampullae and the electroreceptive organ. The neuromasts are located in 5 pairs of cephalic and 1 pair of trunk canals and superficially in the middle and posterior pit lines that lie dorsomedially along the top of the skull immediately adjacent to the otic ampullae field. Both canal neuromasts and pit organ superficial neuromasts have opposite polarized hair cells that are parallel along the axis of the canal and pit line, respectively. However, they differ in both size and shape and in the density and length of the hair bundles. The ampullae are confined on the head, adjacent to the neuromast lines. The morphological structure of the ampullae in the Siberian sturgeon is similar to the ampullae in elasmobranchs and other primitive fish. Nevertheless, it has a relatively large mucus-filled ampulla, and a shorter and narrower canal leading to a small opening to the outer epidermal surface. We also present new information concerning the peripheral innervation of lateral line receptors in sturgeons. The receptors of the lateral line system are innervated by 2 pairs of cranial nerves: anterior and posterior lateral line nerves. The peripheral processes of the anterior lateral line nerve form superficial ophthalmic, buccal, otic and anteroventral rami. The peripheral processes of the posterior lateral line nerve form middle, supratemporal and lateral rami.