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American Journal of Animal and Veterinary Sciences
Year: 2009  |  Volume: 4  |  Issue: 2  |  Page No.: 32 - 36

Comparative Hematological Values, Morphometric and Morphological Observation of the Blood Cell in Capture and Culture Asian Eel, Monopterus albus (Zuiew)

Siripan Ponsen, Nual-Anong Narkkong, Supaporn Pamok and Worapol Aengwanich    

Abstract: Problem statement: Monopterus albus (Zuiew), Asian Eel, is one of the common fish found mainly in Asia. At present, the habitats of Asian Eels have been on the decrease. Contrarily, consumption of Asian Eel has increased. Whereas, data regarding blood cell characteristics, blood cell sizes and hematological values of Asian Eel are limited. As such, the objective of this study was to establish the blood cell characteristics, blood cell dimension and hematological values of capture and culture Asian Eel. Basic knowledge from this study is important for hematological research, conservation, clinical diagnosis and in-depth study of this Eel. Approach: Blood samples of capture (n = 13) and culture (n = 19) Asian Eel, Monopterus albus (Zuiew) were collected in northeastern Thailand. Hematological values, morphometric and morphology of the blood cells were determined using standard techniques. Hematological values and morphometric between captive and cultural Eel were compared. Results: Hematological values and morphometrics of the capture and cultural Eel were not significantly different (p>0.05), but the hemoglobin and neutrophil of the capture eel were significantly higher than those of the culture eel (p<0.05). Neutrophil, monocyte, eosinophil and thrombocyte characteristics of Asian Eel were not different from other Eels. Nucleus characteristics, cytoplasmic shape and nucleus: Cytoplasm ratio of small cell I and small cell II were different. Lymphocyte of Asian Eel was different form the previous report. Conclusion: This study indicated that sources of eel influenced to some hematological values.

Table 1. Some hematological values of Asian eel in this study, i.e., PCV, total red blood cell, MCV, MCH, MCHC and total white blood cells were different from the report of Siang et al.[5] that studied the effect of pesticides on some hematological values of Asian eel in Malaysia. Sahan et al.[3] studied the effect of different stations in the Ceyhan river (Adana, Turkey) on hematological values of European eel (Anguilla anguilla L., 1758) and found that water quality, i.e., temperature, NO3-N, NO2-N, NH3-N, SRP and COD had an effect on the total white blood cell and neutrophil. Moreover, the packed cell volume of the Asian eel in this study, both capture and cultural, were higher than the packed cell volume of the European eel Anguilla anguilla L., 1758, as reported by Yavuzcan et al.[6] and Van Ginneken et al.[7].

Table 1: Comparison of hematological values and cell sizes (Mean ± SD) between capture and culture Asian eel, Monopterus albus (Zuiew)
PCV: Packed cell volume: HB: Hemoglobin concentration: RBC: Red blood cell: WBC: White blood cell: MCV: Mean corpuscular volume: MCH: Mean corpuscular hemoglobin: MCHC: Mean corpuscular hemoglobin concentration, *: p<0.05

These documents indicated that the environment and species of eel had an effect on hematological values. Besides, the neutrophil’s percentage of capture Asian eel was higher than culture eel. This result was in accordance with the report of Sahan et al.[3]. They found that different environments had an effect on the neutrophil of eel and that an increase of neutrophil meant environmental stress. Generally, fish show a large variation in the number of hemoglobin components which relates to their ability to adapt to widely different environmental condition[8,9]. In this study, the hemoglobin of the capture was higher than culture eel. Therefore, all above documents showed that the different sources effect to neutrophil and hemoglobin of Asian eel.

Cell morphology and morphometric: Leucocytes were identified on basis of number, their cell size, shape, structure and ultrastructure. These were: Small cell I, Small cell II, monocyte, neutrophil, eosinophil and thrombocytes. Summaries of the blood cell morphology of capture and cultural Asian eel were as follow:

Small cell I was found about 50-60% in blood film. Small cell I of capture and cultural Asian eel were 6.430±0.890 and 6.500±0.846 µm in diameter. Small cell I had a dark purple, segmented nuclei, clumped chromatin with clear cytoplasm. Frequently, small cell I had cytoplasmic pseudopods. Small cell II was found about 6-9% in blood film. Small cell II of capture and cultural Asian eel were 5.338±0.972 and 5.400±0.853 µm in diameter. Small cells II were characterized by a large nucleus which usually spherical. Nucleus of Small cell II was round and dark purple in color. Nucleus: cytoplasm ratio was higher than small cell I. Monocytes were the largest and most variably shaped of the peripheral blood leucocytes. Monocyte of Asian eel was found about 6-10% in blood film. Monocyte of capture and cultural Asian eel were 10.960±2.255 and 10.080±1.580 µm in diameter. The large spherical or indented nucleus of this rarely encountered leucocyte type occupied about half the cell, occasionally exhibiting the classical ‘horse shoe’ shape. The relatively abundant basophilic cytoplasm was often vacuolated. Neutrophil was found about 20-30% in blood film. Neutrophil of capture and cultural Asian eel were 11.690±1.690 and 11.850±10.254 µm in diameter. Neutrophil cytoplasm was striped, gray to slightly basophilic and had occasional vacuoles and basophilic, intracytoplasmic inclusion bodies. Cytoplasmic borders were irregular. Eosinophil was found about 0-1% in blood film. Eosinophil of capture and cultural Asian eel were 10.357±1.598 and 10.411±2.265 µm in diameter. Eosinophil of Asian eel had round, light purple, often eccentric nuclei with open chromatin. Eosinophil cytoplasm was lightly basophilic and contained numerous eosinophilic granules. The eosinophil granules occasionally obscured the nucleus. Thrombocyte of capture and cultural Asian eel were 9.790±1.710 and 9.060±2.281 µm in diameter. Thrombocyte had clear cytoplasm, purple nuclei and occasionally vacuolated. The thrombocyte showed some similarities to the lymphocyte, but the thrombocyte was larger and able to radiate cytoplasmic pseudopodia.

Kusuda and Ikeda[10] studied characteristics of leucocyte of eel, Anguilla japonica and found that eel composed of four leucocytes, i.e., lymphocyte, thrombocyte, neutrophil and monocyte. They reported the principal characteristic of the leucocytes isolated from the eel was as follows: Lymphocyte-like cells were round and ranged from 5-10 µm in diameter, with round nuclei. Cytoplasmic volume was relatively small and cytoplasm was stained dark gray. Neutrophil-like cells were round or oval and ranged from10-15 µm in diameter and with eccentrically located, oval or bilobed nuclei. Cytoplasm was stained whitish or whitish-gray. Monocyte-like cells were round and ranged from 10-15 µm in diameter; round or oval nuclei occupied more than half of the cytoplasm. Cytoplasm was stained light to dark gray. Thrombocyte-like cells were oval to spindle shape and ranged from 8-10 µm in length, 3-5 µm in width, with an oval to spindle nuclei. The cytoplasm was stained light pink. Moreover, McArthur[11] reported the morphology of erythrocytes, neutrophils, lymphocytes, thrombocytes of the New Zealand freshwater eels, Anguilla australis Schmidtii (Phillips) and A. dieffenbachii (Gray). Neutrophil of the New Zealand freshwater eels was oval to round fine granules comparable to the mammalian neutrophil and this leucocyte found rarest in blood smear. The largest mature cell, neutrophils vary tremendously in size among eels (diameter 7-13 µm, mean 10 µm). The nucleus of mature neutrophil is usually eccentric and moderately clumped and stains deep purple. The cytoplasm of neutrophil of the New Zealand freshwater eels stain light grey and has varying number of colorless or basophilic threadlike inclusions which give it a reticulate or web-like appearance. Lymphocytes of the New Zealand freshwater eels are divided into small (4-6 µm in diameter, mean 5.3 µm) and large (7 µm) lymphocytes. Mature large lymphocytes have a bean-shaped nucleus less dense than that of mature small lymphocytes. The small lymphocyte was round to oval with a large, densely chromatic nucleus. Thrombocyte of the New Zealand freshwater eels was 8.5x4.7 µm in diameter.

Fig. 1: A-H micrograph of Asian eel blood cells with Geimsa-Wright stained. I-Q SEM micrograph of Asian eel blood cells. (a): 5 Erythrocytes; (b): 3 small cell І (arrows); (c): A small cell ІІ (arrow) compared to small cell І (*); (d): A monocyte (arrows); (e): Neutrophil with round nucleus (arrow), (f): Neutrophil with bilobe nucleus (arrow); (g): Eosinophil (arrow); (h): Thrombocytes; (I) 4 erythrocytes with a small cell І (*); (j): Abnormal erythrocyte; (k): Small cell І (arrow); (l): Small cell ІІ; (m): Monocyte (arrows); (N-O): Neutrophil (arrows); (p): Eosinophil (arrows); (q): Thrombocyte (arrows) (from A-H, bar = 10 µm I, bar = 2 µm J-Q, bar = 1 µm)

The blood cell characteristics of the eel, Anguilla japonica that was reported by Kusuda and Ikeda[10] was different than some findings of this study. In this study, we found 2 types of cell-like lymphocyte, small cell I was different from the lymphocyte of Anguilla japonica. However, small cell II was similar to the lymphocyte of eel, Anguilla japonica. The differences between leucocytes were the nuclei shape and diameter. Furthermore, the differences between the Asian eel and the New Zealand freshwater eels were classification of lymphocyte: The New Zealand freshwater eels are divided into small and large lymphocytes, but the Asian eel’s 2 types of lymphocytes were Small cell I and small cell II. The results from this study showed that leucocytes of eels were different in classification, especially the characteristics of lymphocyte.

Under SEM examination, the mature erythrocytes of the Asian eels were flat with a smooth surface. The small cell I was round and irregular membrane surface. The small II was round with smooth or fine irregular membrane surface. Monocytes were larger than lymphocytes. They were round cells with a rough membrane. The neutrophil were round with irregular membrane surface. Eosinophils were round cells with many spherical spines protruded from their membrane surface. The thrombocyte was round and presence of a spread monolayer. SEM micrograph of blood cells in Asian eels that reported in this study was the first report (Fig. 1).


Environment and location have influenced some hematological values of Asian eels. Lymphocyte characteristics of Asian eel was divided into two types’, i.e., small cell I and small cell II and lymphocytes of Asian eel were different from the previous report on the Japanese and the New Zealand eel.


This research was founded by Mahasarakham University. We would like to thank to Faculty of Veterinary Medicine and Animal Science, Mahasarakham University for laboratory support.

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