Deep-water Shark Research Articles

Food habits of the frilled shark Chlamydoselachus anguineus collected from Suruga Bay, central Japan.

In this paper, a stomach content analysis of frilled shark Chlamydoselachus anguineus is presented based on 139 specimens caught incidentally by sergestid shrimp midwater trawling or bottom gill-net fishing conducted in Suruga Bay from 1984 to 1988. The food items of this shark were mostly decapodan cephalopods and fishes, which were found at the frequencies of 60.5% and 10.5%, respectively among the stomachs containing food. Food items found in the stomach, except for two cases of common squid Todarodes pacificus were digested to such an extent that it was not possible to identify the original shape. Therefore, species identification of decapodan cephalopods was performed by their beaks. These included bathypelagic species as well as epipelagic species. The empty stomach rate of specimens examined was 73.4% showing an extremely high level as compared with other deep-water sharks.

THE CELLULAR STRUCTURE OF THE LEYDIG ORGAN IN THE SHARK,ETMOPTERUS SPINAX(L.)

In Etmopterus spinax, a small deep water shark, the predominating lymphomyeloid tissue is the so called Leydig organ. This consists of bone marrow-like tissue situated between the muscularis and the mucosa of the esophagus. Examination by light and electron microscopy shows that the Leydig organ produces large numbers of granulocytes and lymphocytes. Two main types of granulocytes occur, tentatively called heterophilic and eosinophilic. The heterophilic cells may be subdivided into three types which differ in the ultrastructure of the granules. Cells structurally resembling mammalian plasma cells are common. The presence of these cells indicates that the tissue is part of the shark immune system.