Fish allergy is the important food allergies in childhood, often persisting into adulthood. It can cause severe hypersensitivity reactions, including fatal anaphylaxis; furthermore, avoiding-fish diet has negative nutritional and psychological effects. Recent research studies focus on epitope structures and aim to develop sensitive and specific diagnostic tools, which have a better correlation with clinical reactions. Protocols with hypoallergenic parvalbumin or other recombinant antigens are also under study and will likely lead to new immunotherapy protocols. IgE-mediated fish allergy differs substantially from other forms of immunological adverse reactions to fish, such as Food Protein-Induced Enterocolitis Syndrome and eosinophilic esophagitis. In addition, fish ingestion can cause non-immunological adverse reactions, such as in the case of scombroid poisoning, anisakiasis and toxic poisoning. This review aims to summarize the characteristics of the main immunological and non-immunological fish reactions, analyzing the epidemiology, clinical manifestations, diagnosis and therapy, with a particular focus on clinical management.