The safety of oral antidiabetic drugs as the first-line therapy for Diabetes Mellitus (DM) has been a prevailing issue. Meanwhile, these drugs are used for long-term treatment and they often require combination therapy. Natural medicine is an alternative to address the safety issue of drugs because of its minimal side effects and abundant availability. One of the alternatives is snakehead (Channa striata), which has been reported to have antidiabetic activity derived from the regeneration of the damaged pancreatic islets of Langerhans. In addition, snakehead fish is a source of amino acids that lower the accumulation of blood glucose. This study aimed to examine the protein profiles and antidiabetic activity of catfish (Pangasius hypopthalmus) and mackerel (Rastrelliger spp) and to determine their capacities as alternatives to snakehead. The albumin measurements showed that the albumin levels of snakehead, catfish, and mackerel were 4.84 ± 0.54%, 2.57 ± 0.29%, and 2.39 ± 0.29%, respectively. The proximate analysis showed a protein content of 11.8%, 13.58%, and 16.93%, respectively. The screening of α-glucosidase inhibitory activity obtained that the inhibitory activities of the samples were lower than that of acarbose as the control (p < 0.05). Interestingly, all the samples indicated a similar pattern in α-glucosidase inhibitory activity, of which the hydrolysate had a higher potency than the albumin, and the albumin was higher than the powder content (p < 0.05). Briefly, catfish and mackerel can be the alternatives to snakehead to support the management of DM therapy.