This sounds like an allergic contact dermatitis. If you have observed direct associations between exposure to the fish and the skin condition then it is likely that handling the fish may be the trigger. Other triggers should also be identified. You may apply 0.05% Fluocinonide cream over the affected areas. Also, if you have no other disease conditions, you may take oral antihistamines for this.
Does the skin condition revert spontaneously or do you take any medications for its resolution?