Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 49

Lymphomyeloid tissues of cartilaginous fish are the epigonal organ, Leydig organ, thymus, meninges of the brain, eye orbit, spleen, and gut‐associated lymphoid tissue (GALT) (Rumfelt 2014).

The epigonal organ is physically associated with the gonads. In some species, the gonads are enclosed within the epigonal organs, e.g. common guitarfish (Rhinobatos rhinobatos) and dogfish (Squalus spp.), and in others the two are attached, e.g. stingrays (Hypanus and Aetobatus spp.). Generally, where there is a prominent epigonal organ, the Leydig organ is unapparent or absent.

The Leydig organ is a lymphomyeloid organ found in some species; it differs from the Leydig gland which is involved in sperm maturation. It is sometimes identifiable as a lighter‐colored area within the dorsal (and occasionally ventral) submucosa of the esophagus. The area may be raised. Species with recognizable Leydig organs include skates, some rays, guitarfish, and some shark species, e.g. velvet belly lanternshark (Etmopterus spinax) (Rumfelt 2014).

All elasmobranchs have a bilateral thymus located dorsally near the gills (Luer et al. 1995; Rumfelt 2014). In some species, like the catsharks (Scyliorhinus spp.) and nurse sharks (Ginglymostoma cirratum), involution occurs with age and it cannot be found in adulthood. In others, it remains visible albeit small through life, e.g. bullhead sharks (Heterodontus spp.) and some rays (Rumfelt 2014).

The spleen is dark red and strap‐like to oval in shape. Unlike mammals, it lacks marginal zones and germinal centers, likely because there is no true lymphatic system. There are melanomacrophages in the spleen and liver, but they do not aggregate as they do in teleosts (Rumfelt 2014).