The valorization of fish-processing by-products as sources of high-value biomaterials has gained increasing attention in support of sustainable bioresource utilization. In this study, collagen was extracted from the skin of Napoleon wrasse (Cheilinus undulatus) using ultrasound-assisted extraction (UAE), with the aim of evaluating an efficient and environmentally friendly alternative to conventional extraction methods. Proximate analysis of the fish skin showed a protein content of 20.23 ± 0.40%, indicating its potential as a collagen-rich raw material. Collagen extraction was performed using three organic acids (acetic, lactic, and citric acids) under different ultrasound treatment durations (0, 10, 20, and 30 min). The effects of acid type and extraction time on collagen yield were assessed. The results demonstrated that UAE significantly enhanced collagen recovery, and both extraction duration and acid type significantly influenced the extraction yield. Among the acids tested, citric acid produced the highest collagen yield (9.56 ± 1.41%), followed by lactic acid (5.99 ± 1.79%) and acetic acid (4.10 ± 0.35%). UV absorption analysis confirmed the characteristic collagen profile, with all extracted samples exhibiting a maximum absorption peak at 230 nm, indicating collagen purity and structural consistency. These findings highlight the potential of Napoleon wrasse skin as an alternative marine collagen source and demonstrate that UAE, particularly in combination with citric acid, is an effective and sustainable approach for collagen extraction from fish-processing by-products.