You usually get it on the foot, walking on the shore. Initially produces an intense pain and may radiate toward the limb later. The skin reddens. In severe cases it can cause heart diseases and a general malaise caused by the toxin injected by the spider fish.
What to do. One of the most efficient ways to reduce pain is to deep one’s limb or foot into salted water, even sea water, at about 45/50°C, for one hour. In this way injected toxins stop circulating.
What not to do. Do not apply cold water, ice, rub with alcohol or scratching the affected part: doing so you only encourage the spread of the toxin.