Histological investigation of the muscle spindle of mediterranean horse mackerel (Trachurus mediterraneus (Linnaeus, 1758)) and whiting (Merlangius merlangus (Linnaeus, 1758))

The muscle spindle was observed in mandibular muscle (adductor mandibulae ІІ ), operculum muscle (levator opercula) and pectoral muscle (superficial adductor) of Mediterranean horse mackerel and whiting fishes. General histological techniques (paraffin and cryostat serial sections by Hematoxylin and Eosin) was applied to see muscle spindle structure, number, distribution and density, and silver impregnation technique to see muscle spindle morphology and innervation. This is the first time have been demonstrated its existence in the pectoral and operculum muscles as well as have been demonstrated its existence in the mandibular muscles that had previously been confirmed by Maeda and his colleagues. Whiting mandibular muscles have more number and density than Mediterranean horse mackerel. Mediterranean horse mackerel operculum muscles have more number and density than whiting. whiting pectoral muscles have more density and an equal number to Mediterranean horse mackerel. The sensory and motor innervations of muscle spindles in both species were studied from teased preparations stained. Most muscle spindles have one sensory innervation and only one muscle spindle with two sensory innervations was observed and receives its motor supply to the polar region from axon that supplying the extrafusal muscle fibers. A complex pair spindles were observed in adductor mandibular ІІ of whiting in which two spindles combined together and their intrafusal muscle fibers remain separately encapsulated and a blood vessel was observed linked to the outer capsule of one of the spindles which forming the complex pair spindles. Key Words: Muscle spindle, Intrafusal muscle fiber, Extrafusal muscle fiber, Mediterranean horse mackerel, Whiting, Kastamonu, Blacksea