## 4 Discussion
### Analysis of the Number and Composition of White Blood Cells andPlatelets in CE  
White blood cells serve as a crucial component of the immune defense system in fish, and their variation in peripheral blood is often used to assess the immune system [31]. CE had a higher white blood cell count than that of goldfish [14] and carp [25], though all three species shared a similar order of magnitude (\(10^{9}/\)L). In contrast, koi carp [28] and Furong crucian carp [26] showed a significantly higher range, both in the \(10^{11}/\)L range. These discrepancies may arise from factors such as varying fish species, different environmental conditions, and measurement methodologies [16].  
The primary types of white blood cells in fish include neutrophils, monocytes, lymphocytes, eosinophils, and basophils [16]. Neutroph, crucial for non-specific immune responses and inflammation [32], were found in CE, comparable to goldfish [14]. Monocytes, also involved in non-specific immunity through phagocytosis of senescent cells and foreign materials [33], were measured at \(2.05\times 10^{9}/\)L in CE. Lymphocytes, the most prevalent white blood cell type [16], showed in CE, higher than in goldfish [14]. Eosinophils and basophils, less commonly found in fish peripheral blood, were only observed in certain species, with some fish lacking both [34]. In the study, conducted by [PERSON]. [14], eosinophils and basophils in goldfish were identified at 0.499 \(\times\) 10\({}^{9}/\)L and 0.04 \(\times\) 10\({}^{9}/\)L, respectively. However, our investigation did not detect eosinophils and basophils in the peripheral blood of CE. Similar findings were reported in various studies. For example, [PERSON] [35] observed the absence of these cells in the blood of various ploidy crucial carps (_Carassius auratus_). [PERSON] [36] also did not detect basophils in crucian carp (_Carassius auratus_), and [PERSON] [37] found no eosinophils or basophils in three Pu'an crucian carp varieties (_Carassius auratus_). Furthermore, [PERSON] [16] observed the absence of these cells in several economically significant fish species in the middle and upper reaches of the Yangtze River. Eosinophils and basophils in fish are primarily located in tissues such as the head, kidney, spleen, and liver, rather than in the peripheral blood [16]. This could explain why these cells were not detected in the peripheral blood of CE in our study, possibly due to their low presence or near absence in this blood type.  
Platelets, in addition to participating in defense through phagocytosis, areas required for hemostatic plug or fibrin clot formation [16]. PLT measured in this study for CE was (6.00 \(\pm\) 0.94) \(\times\) 10\({}^{9}/\)L, which was significantly lower than the (51.55 \(\pm\) 3.32) \(\times\) 10\({}^{9}/\)L reported by [PERSON] et al. [14]. This discrepancy might be due to differences in the sampling and counting methods. [PERSON] et al. [14] used tail amputation for blood collection and manual counting under a microscope, while we employed tail artery blood collection and automated counting with a blood analyzer using a transmission microscope. The tail amputation might have caused higher stress in the goldfish, leading to elevated PLT levels. Additionally, under a light microscope, PLT and small lymphocytes appeared similar and were difficult to distinguish, potentially resulting in an overestimation of PLT. In contrast, with a transmission electron microscope, PLT could be distinguished by their boundary, vascular bundles, and vacuoles--structures absent in small lymphocytes [16]--thus reducing the error.