The Cobitis hankugensis-Iksookimia longicorpa (formerly C. sinensis-C. longicorpus) complex in South Korea includes diploid and triploid forms of hybrid origin that are most often females. However, there are a few males that show no differences from the hybrid females in their general morphology except the presence of a lamina circularis on the pectoral fin. An examination of 354 adult hybrid specimens revealed that 3 % of the complex are male specimens. The testes of the rare males are normal in shape and external morphology. The gonadosomatic index of hybrid males is similar to that observed in males of the parental species and changes during the year in a similar pattern. However, the testicular cells differ from those of the parental species in their morphology. Especially sperm cells are very rare and show abnormalities in their morphology, therefore we conclude that the rare males are sterile. This result suggests that although males are present with a low frequency in the complex, this complex functionally is unisexual and depends on the males of the parental species for perpetuation.
The epidermis of the amphibious mudskipper fish, Boleophthalmus pectinirostris, consists of three layers: the outermost layer, middle layer and stratum germinativum. The outermost layer consists of polygonal cells or rather flattened cells arranged in one to eight layers. In between these cells, round small cells and mucous cells are present. The round small cells are ovoid to round with an inclusion of fine granules, which are weakly positive to acid chemical reaction. The mucous cells are predominantly acid mucopolysaccharide in nature. The middle layer consists of 1 to 50 layers of small or voluminous cells swollen by epidermal cells. Owing to various sizes and layers of the swollen cell, the middle layer shows a web-like structure. The stratum germinativum consists of a single layer of cuboidal cells, or more or less columnar cells. A dermal bulge is located at each apical area of the epidermis of the body regions, but does not exist in all the fins or in the sucking disc. In the epidermis of the body regions, the dermal bulges are sparsely occupied by dermal tissue and have dermal capillaries just beneath the stratum germinativum. The value of the diffusion distance is the lowest in the top of the head (mean 5.5 μm) and the highest in the ventral region (mean 44.3 μm).
The epidermis of the Korean spined loach Iksookimia koreensis was divided into three layers: an outermost layer, middle layer and stratum germinativum. And the dermis was composed of two layers: stratum laxum and compactum. The outermost layer consisted of polygonal cells or flattened cells, small amount mucous cells, and the middle layer consisted of two types of skin glands, a small mucous cell and a large club cell. The mucous cell was acid sulfomucins (some sialomucins), but the club cell did not show any histochemical reaction to mucosubstances. The stratum germinativum was composed of a cuboidal epithelial cell and a well-defined lymphatic space containing small lymphocytes. There was a large number of blood vessels just below the basement membrane. The stratum laxum of dermis has small scales and a definite area that was AB positive and PAS positive.