Band: Defensive Seismitoad and Gastrodon seem to be the best bets for right now. Toad has Water Absorb and Gastro has Storm Drain to shut down Fishious Rend, and Dracovish doesn't have anything more dangerous than a non-STAB (but still Strong Jaw-boosted) Psychic Fangs to hit them with. Both can Earthquake for damage or (in Toad's case) set up rocks. Defensive Jellicent is also a good option for an immunity, as it can switch in on a Rend and threaten to burn with Wisp, though it has to watch out for Crunch (it takes about 70%). Defensive Appletun has a x4 resist to Water and good bulk (though it still takes like 40% from Rend in rain jesus christ), but it also has to watch out for coverage, as Ice Fang is almost a guaranteed 2HKO. Additonally, without the speed boost from Scarf, Dracovish is also pretty slow, so you can simply just bring in a faster Pokemon after a sack and threaten it out.
Scarf: A little more manageable, as without the boost from Choice Band, Defensive Ferrothorn and Toxapex are pulled out of the 2HKO range from Fishious Rend in rain (though it still does a huge chunk of damage to both) and can threaten it out with status or (in Ferro's case) a Power Whip. Faster Scarfers can outspeed it, and uber-fast 'mons such as Dragapult can even outspeed without a Scarf (Adamant/Modest Pult outspeeds Adamant Vish, and Jolly/Timid Pult always outspeeds).