Abstract
The African catfish (Clarias gariepinus) has increasingly become an economically important food source especially in Africa, Asia and Europe, with exports extending to countries throughout the world. In the last 25 years, aquaculture of this species has been particularly effective with large increases in production and this is in part due to the catfish being highly resistant to disease. In order to further understand the immune system of the catfish, the spleen was investigated using a number of staining, immunohistochemical, light and transmission electron microscope techniques in order to verify the histological features of this organ. The gross histological features of the spleen confirmed the presence of a capsule containing numerous collagen fibers surrounded the spleen of the African catfish. Melanomacrophage centers, lymphocytes and surrounding arterial vessels were the main components of the white pulp whilst the red pulp contained sinusoids, capillaries and splenic cords of erythrocytes, macrophages and lymphocytes. Transmission electron microscopy identified Langerhans-like cells which were irregular to ovoid in shape with an electron lucent cytoplasm. The cells were characterized by the presence of numerous Birbeck-like granules, varying in shape from oval, round, rod to racket shaped granules. In total, three types of Birbeck-like granules were identified. The first type had heterogenic content, the second type were cored granules and the third type were racket shaped granules. Some of the racket shaped granules were enlarged and contained granular content. The Langerhans-like cells were further identified and characterised by showing a positive reaction with antibodies to S100 and CD1a. The existence of Langerhans-like cells within the spleen helps to identify the components of the immune system within the African catfish.
Highlights
The African catfish is an important freshwater fish in terms of commercial gains with global capture and aquaculture production standing at 55,417 and 237,124 tonnes respectively in 2014, a rise from 15,000 tonnes in 1950 and 5,013 tonnes in 1992[1]
Langerhans-like cells were observed by transmission electron microscope among the cells of spleen of catfish (Clarias gariepinus), they were irregular to ovoid in shape and no cytoplasmic processes could be observed
The present study aimed to identify whether Langerhans-like cells were present in the African catfish spleen in order to further understand why these fish are especially resistant to disease[4]
Summary
The African catfish is an important freshwater fish in terms of commercial gains with global capture and aquaculture production standing at 55,417 and 237,124 tonnes respectively in 2014, a rise from 15,000 tonnes in 1950 and 5,013 tonnes in 1992[1]. There has been increasing interest in farming catfish as a source of nutrition as they withstand difficult environmental conditions, have a relatively high growth rate, and the consumer holds it as an attractive food source[3]. The spleen is responsible for antigen trapping as fish have no lymph nodes[6]. Langerhans cells are a type of dendritic cell which identified as containing unique Birbeck granules[10][11]. Cells similar to Langerhans cells have been detected and their classification was based upon the presence of Birbeck-like granules[13]. Langerhans cells were originally thought to be specific to epidermal tissues, they have been found in healthy spleen and kidney and diseased gills in salmonids[13][14]. The specific immunophenotypic profile is helpful distinguishing Langerhans cells, in addition the detection of Birbeck granules, seen in both pathological and resting Langerhans cell is a prominent feature[18]
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