When a house smells like fish it is usually a sign of overheating electrical wires or overheating electric outlets.
If you're not cooking fish or fishy foods and smell fish smell in your house then you should check all the outlets and breakers or shut the power off and call an electrician.
Go around and smell the outlets and feel the outlets and see if they are warm or hot and if so shut the power off to them.
Electrical fires when they are about to start usually smell fishy.
When a circuit develops a fault and overheats, the plastics and heat-resistant chemicals used in sockets, circuit breakers or wiring insulation often emit a fishy or urine-like smell.
This fishy odor can be carried throughout the house by things like heating, ventilation, and air conditioning systems.
When an electrical fire begins, the smell is often described as “fishy,” but as it progresses, the components of the wiring can give off a burning plastic smell.
If you are able to recognize the smell early, you can intervene to address the underlying cause before it becomes dangerous.
If your outlets or circuits etc are not overheating and you still smell fish then it could be a phantom smell but always have the outlets and circuits checked out.