Skin histopathological responses of Oreochromis niloticus (Nile tilapia) to transportation in water with and without salt

Abstract Oreochromis niloticus (Nile tilapia) is a well-known economic fish species that can thrive under the right environmental circumstances. The transport of live fish, either for food or as companion animals, presents a big issue for animal welfare at the same time it is considered one of stressful conditions. Hence, the present study investigated the skin histopathological responses of O. niloticus that were attributed to stress and salt addition during transportation. Three experimental groups of O. niloticus the 1st is the control non-transported group (CG), the 2nd is transport in water without salt (PT-S) and the 3rd is transport in water containing 5gL− 1salt (PT + S), the last 2 groups were transported in 5 h transport model. Results indicate that the skin of PT-S fish showed a marked decrease in epidermal thickness, decreased number of goblet cells, and an increase in the sub-epidermal and dermal pigments with the presence of large edematous vacuoles. Fish skin from PT + S demonstrated mild hydropic swelling in epidermal cells with normal goblet (mucous) cells density, and more or less normal melanin pigment distribution in sub epidermis and on the dermis layers, however, dermis showed mild edematous spaces. Scanning microscopy of PT-S skin tissue showed few scratched white patches among normal regions that may represent a thickened surface with the decreased number of goblets cell opening, while the PT + S group showed moderate preservation of surface skin architectures with the presence of goblet (mucous) cells opening in spite of presence of slight thickened white patches. The estimated total lesion changes present in PT-S group showed a significant increase (P < 0.001) compared with the control (CG) group. On the other hand, PT + S showed significant (P < 0.001) improvement in the overall previously recorded changes compared with the PT-S group, and a non- significant change in the histological architectures compared with the control group. Our findings underlined the importance of skin and its mucous cover health during transportation. The use 5 gL− 1salt during O. niloticus transportation appears to preserve the surface skin features, and keep the goblet (mucous) cells open to the external surface, and may act as a deterrent for the release of mucus from goblet (mucous) cells in response to stress and lessen the stress of transportation.