The hot water denatures the protein. This takes about an hour of having your foot immersed in as hot water that keeps getting refreshed as you can take to get the toxin out. Depends on the size and depth. I had this happen in Wyatt Miller and Tyson Poor's place La Ventana, Baja MX last year. I was just coming ashore after a awesome foiling session. Forgot to stomp/slide feet. The hot water was accompanied by several beers as oral medication (optional).

After an hour the pain was gone.
If part of the barb breaks off then medical treatment is required.