Abstract
Background:
Disease prevention in cultivating ranchu goldfish (Carassius auratus) can be prevented by giving immunostimulants in the food. One immunostimulant can come from herbs such as calabash fruit (Crescentia cujete L.).

Aim:
This study aims to analyze the potential of calabash fruit extract (BFE) on the hematological profile of ranchu goldfish.

Methods:
This study used 30 ranchu goldfish, which were divided into six treatments, as follows: P1 = standard food; P2 = food + 0.5% CMC Na; P3 = food + 0.1% POWER C®; P4 = food + 0.5% BFE; P5 = food + 0.3% BFE; and P6 = food + 0.6% BFE. The treatment was performed for 28 days with a feeding frequency of 2 times a day. On the 28th day, fish performance was measured. The blood was collected for hematology and immunohistochemistry against antibody anti-COX-2 and CD4+. The data were statistically analyzed using SPSS with confidence level at 95%.

Results:
The group P6 indicated the highest growth performance compared to the other groups (p<0.05). This group also showed a significant elevation of heterophils compared to the others (p<0.05). In contrast, the levels of Hb, PCV, MCV, MCH, MCHC, WBC, lymphocytes, monocytes, and thrombocytes did not differ from each other (p>0.05). Interestingly, there is a decrease in CRP and immunoreactivity of COX-2 and an elevation of CD4+ following the increase in BFE concentration (p<0.05).

Conclusion:
It can be concluded that BFE affects the performance and hematological profile of ranchu goldfish and has the potential as an immunostimulant.

Key words: Calabash fruit extract, CD4+, COX-2, Hematology, Ranchu goldfish