Patin Buah, Pangasius nasutus is one of the most promising native catfish species for aquaculture due to its high market value and popularity among locals. The popularity of this species has raised concern as the supply of this species is still dependent on wild catch, and the number of landing specimens has declined from 32.60 tonnes in 2018 to 16.49 tonnes in 2021. Gonadotropin-releasing hormone (GnRH) one of the important reproductive hormone in vertebrates, and is widely used in hormonal therapy due to its advantages in lower species-specificity and targeting at a high level in the hypothalamus-pituitary-gonad (HPG) axis, which play important roles in stimulating the release of the sex steroid hormones. This research was conducted to assess the effect of GnRH agonist (GnRHa ) implant to activate HPG axis of P. nasutus. P reparation of a slow-release delivery system loaded with GnRHa was conducted to evaluate the effect of hormonal induction through the slow-release implant using ethylene-vinyl acetate (EVAc). In this experiment, juvenile P. nasutus were allocated into four treatment groups (n=6, 2 replicates): Group 1 = empty EVAc (control), Group 2= GnRHa+domperidone (DOM)+EVAc, Group 3= GnRHa+EVAc, and Group 4= Ovaplant . Each treatment group received two administrations of the implant, one on Day 0 and another on Day 15. Data were collected at specific intervals (Day 0, 7, 17, and 22) after treatment, including blood sampling, and fish were sacrificed to collect pituitary and gonad. Histological observation of the gonad development of GnRHa-treated fish (GnRHa+DOM+EVAc, GnRHa+EVAc, Ovaplant) showed continuous development in the oocyte and spermatogenesis stages until day 22 compared to the control group. The plasma level for 17β-estradiol (E2) showed a gradual increase until day 22 post-implantion with GnRHa+DOM+EVAc, followed by GnRHa+EVAc and Ovaplant. The plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) marked a peak higher level at day 17 post-implantion in the GnRHa-treated group than in the control and decreased until day 22. The results showed that GnRHa treatment has a significant effect on the prolonged release of GnRH. The mRNA expression level of the α, FSHβ, and LHβ subunits showed the rapid burst of pituitary FSH was seen to have a greater fold change in the GnRHa-treated (GnRHa+DOM+EVAc, GnRHa+EVAc, and Ovaplant) fish compared to the control fish. This reveals the role of GnRH in stimulating the pituitary to produce FSH in response to the GnRH implant successfully activated endocrine axis in juvenile Pangasius nasutus . The use of GnRHa slow-release delivery systems has the potential to facilitate captive breeding, enhance reproductive efficiency, and promote sustainability in aquaculture practices for Pangasius nasutus and catfish species.