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The head-kidney (HK) is a unique immune, hemopoietic, and endocrine organ in fish. Twenty fish were used to study the structure, ultrastructure, and immunohistochemistry of the HK of Grass carp. The HK of grass carp was consisted mainly of a network of hematopoietic cells with a few kidney tubules. The HK contained all the developmental stages of erythrocytes and leucocytes, in addition to the presence of rodlet cells, dendritic cells, and epithelial reticular cells. Two populations of lymphocytes could be identified in HK; B-lymphocytes expressed CD20 and T cells expressed CD3. The cytotoxic T lymphocytes (CTLs) expressed CD8, while polymorphic granulocytes expressed iNOS2. Neutrophils showed myeloperoxidase immunoreactivity, as well as eosinophils expressed CCR3. Furthermore, macrophages were the most frequent cells found in the anterior kidney, which aggregated into structures called melanomacrophage centers (MMCs). Macrophages and monocytes showed immunoreactivity for CD68, CD163, and CD64. On the other hand, the interrenal cells (ICs) and chromaffin cells were mixed and arranged in large anastomosing cords intermingled with numerous capillary vessels that that lined the posterior cardinal veins of the head kidney. The cytoplasm of the interrenal cells showed the characteristic features of steroid-producing tissues. Three types of chromaffin cells; noradrenaline, adrenaline, and small granule containing cells could be distinguished in HK of grass carp. GFAP-positive sustentacular cells were identified for the first time among the chromaffin cells. The present study showed the presence of hemopoietic cells, MMCs, rodlet cells, immune cells, as well as one type of interrenal cells and three types of chromaffin cells in the HK of grass carp.

The present study aimed to isolate and characterize bacteriophages (phages) specific for Edwardsiella ictaluri to be used as a biological control of the infection in fish as a final goal. Twenty-six phages (PEi1 ~ PEi26), lytic to E. ictaluri were isolated from ayu Plecoglossus altivelis and its surrounding environment (water and mud) using enrichment and double agar layer methods. All phages formed clear plaques ranging in size from 0.3 to 8 mm in diameter. Transmission electron microscopy revealed that all the isolated bacteriophages belonged to the family Myoviridae. According to phage morphology, plaques size and DNA restriction patterns with EcoRI, the phages were classified into four groups (I ~ IV). E. ictaluri strains isolated from ayu (n=57) were sensitive to these phages with various degrees, resulting in twenty-five phage types of the bacterium. E. ictaluri strains isolated from catfish in the USA (type strain; JCM1680), Indonesia (n=4) or Vietnam (n=2) exhibited no or very limited susceptibility to the present phages. In addition, E. tarda, the most closely related species to E. ictaluri, as well as other fish pathogens were not susceptible to any of the phages examined.

Fifteen adult Soay rams were employed in this study to investigate the effect of melatonin on the scrotal skin using histological, histochemical, and morphometrical analysis. The results revealed that the melatonin treated group showed a significant increase in the thickness of the epidermis, the cross-sectional area of blood capillaries and nerve fibers compared with the control one. In addition, obvious hypertrophy and hyperplasia were detected in the sebaceous glands in association with a significant increase in the number and diameter of apocrine sweat glands with well-developed secretory activity. S100 protein and cytokeratin-19 strongly stained the basal cells of sebaceous glands in the melatonin treated group incomparable to the control group. Moreover, the nerve fibers were intensively immunoreacted for S100 and cytokeratin proteins in the melatonin treated group in contrast to the control one. A high number of telocytes (TCs) could be identified in the treated group around the nerve fibers and blood vessels in the dermis. The number of Langerhans cells showed a significant increase in the melatonin groups that were identified by MHC II and PGP 9.5 within the epidermal layer. Furthermore, a significant increase in the number of dendritic cells was identified in the melatonin group, which were distributed within the dermis, around hair follicles, sebaceous glands, and sweat glands and were strongly expressed PGP-9.5, MHC-II, VAMP, SNAP, keratin-5, and cytokeratin-19 immunoreactivity. Notably, Merkel cells showed a significant increase in the number in the melatonin group that could be stained against nestin, SNAP, and VAMP. On the other hand, the secretory granules in sweat glands were exhibited a strong positive reactivity for synaptophysin in melatonin group. The current study showed that the administration of melatonin induced a stimulatory effect on keratinocytes, non-keratinocytes, sebaceous and sweat glands, hair follicles, as well as the vascular, neuronal, and cellular constituents of the dermis.