## 4 Discussion
### Biochemical Components in Vitreous Humor of CE  
The human eye contains vitreous humor, which is 80% of the eyeball's volume and comprises 99% water. The residual 1% consists of proteins, inorganic salts, carbohydrates, lactic acid, urea, vitamin C, amino acids, and lipids, among other substances. The structural macromolecules of the vitreous include hyaluronic acid, proteoglycan, collagen, and non-collagen proteins [47]. Vitreous cells are sparse and predominantly located at the vitreous base and cortex [47]. In our study, the vitreous humor was extracted from the central region of CE's vitreous body, which is typically devoid of cells.  
[PERSON]. [48] indicated that while the vitreous humor might contain most serum components, their concentrations were usually lower than those in the serum. Our findings confirmed this, showing that the concentrations of 11 indices in the vitreous humor of CE were lower than those in the serum, in agreement with the research by [PERSON]. [48]. However, there was no significant difference in the levels of ALP, TBA, urea, Cl\({}^{-}\), Ca\({}^{2+}\), Cre, and CHE between the vitreous humor and the serum. Notably, the serum levels of ALT and GGT were considerably lower than in the vitreous humor. The synthesis of alanine is linked to ALT activity [49], while GGT was associated with the transmembrane transport of amino acids and the regulation of glutathione (GSH) levels [50]. These disparities might be indicative of abnormal metabolism in the vitreous humor of CE.  
A trace amount of ALB present in the vitreous humor might serve as an indicator of the integrity of the blood-ocular barrier [51]. Research by [PERSON] [51] suggested that in celestial goldfish, ALB levels in the vitreous humor rose in correlation with ocular enlargement in larger fish. The largest group of telescope goldfish demonstrated an ALB concentration of 2.41 g/L in the vitreous humor, only slightly lower than that found in our CE, which was 2.50 g/L.  
Both celestial and telescope goldfish had suffered from visual function deficit, but the eye diseases were different between them. CE, along with telescope goldfish, exhibitedeye abnormalities; however, CE development was often accompanied by varying degrees of retinal degeneration [6], leading to impaired vision and sensitivity to light. In contrast, despite the protruding eyes of telescope goldfish, they predominantly suffered from severe myopia without retinal degeneration [52]. Through comparative analysis, we noted that the ALB concentration in the vitreous humor of our CE was higher than that in [PERSON]'s telescope goldfish [51]. This could imply that CE might experience more pronounced alterations in the blood-retinal barrier compared to telescope goldfish.  
In CE, levels of GLU, Cre, and UREA were found to be lower in the vitreous humor compared to those in deceased humans [51]. This difference might stem from increased membrane permeability of the blood-eye barrier postmortem, allowing blood constituents to permeate into the vitreous humor. Notably, the vitreous humor samples from the CE in this study were collected in vivo. Furthermore, no significant variations were observed in the concentrations of Cre and UREA between the vitreous humor and blood of CE. This contrasted with findings in cattle [53] and humans [51], where Cre and UREA levels in vitreous humor were lower than in blood, suggesting a unique permeability of the blood-retinal barrier in CE eyes regarding these substances.  
Regarding Ca\({}^{2+}\) content, CE's vitreous humor exhibited levels similar to those in humans (2.45 mmol/L) [54]. However, the concentrations of Ca\({}^{2+}\) and Cl\({}^{-}\) in the vitreous humor and blood of CE did not display noticeable differences, unlike the disparity observed in humans [51]. This implies that the mechanisms of ion transport and metabolism in the vitreous humor of CE might diverge from those in the human vitreous body.