Formaldehyde is dangerous to health because it is a carcinogen that can cause cancer. Jakarta Province has an integrated food control program, namely fish supervision, free from formaldehyde. The test results during the management there were several fish containing formaldehyde, namely moonfish (Lampris guttatus), hardtail scad (Megalaspis cordyla), rank goby (Saurida tumbill), and mackerel scad (Decapterus spp). There is no information regarding the detected formaldehyde in these fish, so this study aims to analyze the natural formaldehyde formation process of the four types of marine fish to ensure that the detected formaldehyde results from addition or naturally occurring. This study also describes how fishers in Jakarta consider environmental factors in the fish handling process. This study used a completely randomized design and ANOVA in determining levels of formaldehyde. The qualitative approach carried out using interviews and observations. The parameters studied were formaldehyde levels, Total Volatile Base (TVB), and Trimethyl Amin (TMA). The results showed that moonfish, hardtail scad, rank goby, and mackerel scad increased natural formaldehyde content during storage, namely 0 mg/kg on day 0 to 6.51 mg/kg on day 18. The formation of natural formaldehyde in the four types of samples during storage in freezing temperature correlates with the degradation process based on the TVB and TMA parameters. Although the fishermen understand that environmental factors determine natural formaldehyde formation in fish, they are not worried because it does not directly impact consumers’ health. Therefore, it is necessary to increase environmental awareness for anglers to maintain consumer health.