<p>The fungus <i>Cunninghamella echinulata</i> PA3S12MM exhibited remarkable chitinolytic capacity for direct valorization of fishery residues.Tilapia scales induced the highest extracellular chitinase activity (5.20 U mL⁻¹), followed by colloidal chitin + glucose (3.62 U mL⁻¹) and shrimp shells + glucose (2.62 U mL⁻¹). The crude enzyme (1.8 U mL⁻¹) released 16.32 ± 0.81&#xa0;µmol&#xa0;mL⁻¹ of reducing sugars from tilapia scales and 9.34 ± 0.42&#xa0;µmol&#xa0;mL⁻¹ from shrimp shells after 24&#xa0;h (p ≤ 0.01), confirming effective hydrolysis of native substrates without chemical pretreatment. Optimal catalytic conditions (pH 4.5, 55&#xa0;°C) yielded 22.76 U mL⁻¹, indicating a thermoacidic endochitinase with structural stability and catalytic adaptability under proton-rich and moderately heated environments. The enzyme’s activity under these conditions likely results from enhanced protonation of catalytic residues and increased molecular flexibility, promoting substrate accessibility and resistance to thermal denaturation. SDS-PAGE and zymogram analyses revealed an active ~ 70&#xa0;kDa band consistent with GH18 chitinases, while TLC confirmed chitooligosaccharide formation. SEM imaging demonstrated surface erosion of biowaste materials. Collectively, <i>C. echinulata</i> PA3S12MM provides a robust, low-cost enzymatic system for sustainable biodegradation of chitin-rich fishery residues, coupling thermoacidic stability with efficient sugar release, supporting eco-friendly bioremediation and circular bioeconomy strategies for producing bioactive oligosaccharides.</p> Graphical Abstract <p></p>