MORPHOLOGIC FEATURES OF PEROSOMUS (“SHORT SPINE”) IN FARMED SALMON (SALMO SALAR)

Abstract

This study was done to characterize morphologically the spinal changes in stunted salmon, 1.5–2 years of age, spontaneously appearing in a Swedish fish farm. Radiographic examination and alizarin‐alcian blue preparations showed compressed areas of the spine, most often near the dorsal fin. Of the average 50–52 vertebrae, 20–30 were often compressed, resulting in an average shortening of the fish by 23%. The histopathologic character of the shortened spine was a replacement of the chorda (intervertebral pad or disc) with a poorly differentiated hyaline cartilage, in which proliferative and degenerative processes produced a very irregular pattern. The origin of this cartilage, which had severely impaired ossifying capacity, was perichordal and it often had direct connections with the growth centers of the vertebrae. The disappearance of the large strongly convex (spheric) chorda and the arrest of the vertebral endochondral ossification resulted in narrow disc‐like vertebrae in contrast to the normal X‐shaped ones. The pathologic changes resemble those observed in chondrodystrophic types of perosomus (“short spine”) in certain mammals, including humans, and in turkeys.

Platyspondyly and shortness of vertebral column in farmed Atlantic salmon Salmo salar in Norway-description and interpretation of pathologic changes

“…The presence of inflammatory cells is the fourth change to be described, and this is apparently the first description of these cells, as they are not mentioned in previous histologic examinations of short columns (Vavra 1906, Schaferna 1923, Henschke et al 1982, Hansen & Yalew 1988, Lom et al 1991 or columns with similar changes (Couch et al 1979). RubensDuval & Desse (1972), who also found protrusion of chordal tissue into the vertebral canal, state that no inflammatory lesions were found.…”

“…Fifthly, the mainly caudal localization of changes in the body, as also described by Hansen & Yalew (1988) and Beverfjord et al (1996), may possibly be related to the mode of swimming, with maximal side-to-side amplitude of the undulations in the caudal part of the body (Lindsey 1978), where the column is more flexible (Hubner 1961).…”

“…However, a condition with a mainly straight column where some or all of the centra are too short, i.e. platyspondyly (Wunder 1971), and in some cases ankylosed, has been described in shark (Hoenig & Walsh 1983) and wild and farmed teleost fish (Gemmill 1912, Schaferna 1923, Chabanaud 1939, Gill & Fisk 1966, Rubens-Duval & Desse 1972, Wunder 1975a, Henschke et al 1982, Wells & Cowan 1982, Hansen & Yalew 1988. Genetic factors (Schaferna 1923, Wunder 1949, Hansen & Yalew 1988) and exposure to toxicants (Wunder 1975a, Henschke et al 1982, Wells & Cowan 1982 have been proposed as causes of platyspondyly, but in most cases the etiology remains unknown.…”