Final answer:
The toxin commonly linked to tuna, bonito, mackerel, and mahimahi is Histamine, which can cause scombroid poisoning if consumed at high levels.
Step-by-step explanation:
The toxin that is commonly linked to fish such as tuna, bonito, mackerel, and mahimahi is Histamine. This chemical can accumulate in these fish species, particularly when they are improperly stored at warm temperatures. Consumption of fish with high levels of histamine can lead to scombroid poisoning, characterized by symptoms such as rash, diarrhoea, cramping, and, in severe cases, hypotension and tachycardia.