Hello! I have a tank that currently does not contain shrimp, but does contain neon tetras which I am currently treating for Ich, as well as some bladder snails. Shrimp will be a later addition, likely cherry shrimp but I'm still doing research just to be sure.

Initially I'd intended to buy some sort of Ich-fighting product that contains malachite green after doing a decent bit of research on it, most of which indicated that it should be shrimp-safe so I'd be good if I ever needed to use it again once shrimp were actually introduced (though I should note I'm aware shrimp can't get Ich, I'm more wondering in case the tetras could get Ich again, or something else that responds to similar medication). I ended up not being able to find any MG-containing products without either having to travel quite far or wait multiple days for delivery (which I was worried could lead the Ich to be fatal), and ended up picking up 'Top Fin Ick Remedy', a product that contains gentian violet which is a triarylmethane dye like malachite green. The bottle has two slightly differently worded warnings about its use with invertebrates ("not recommended for" and "not safe for" respectively), but when I'd been researching malachite green, I'd also heard of products that contain MG but not any other ingredients that would be harmful to inverts still being branded with warnings that they could be harmful, just as a "just-in-case" since the manufacturer didn't test it on any inverts, and I'm wondering if maybe it could be a similar situation here. I'm having a very very hard time finding information about gentian violet's use in fishkeeping at all though, it seems currently extremely uncommon. What I will say though is that I'm on day 2 of treating my tetras with it, and the bladder snails seem just fine -- in fact today I noticed what looked to be a bladder snail that appeared to be newly hatched (because of its size) that I hadn't seen before that was zipping around the tank without issue. But obviously, shrimp are not snails, and bladder snails are also notoriously hardy little guys, so what I'm seeing right now could easily be totally inapplicable to cherry shrimp. It might even be inapplicable to other species of snails, for all I know.

Has anyone else here ever used anything that contains gentian violet in a tank that actually does contain shrimp? Were they okay, or should I make sure to not use it once shrimp are added?

Edited April 29, 20242 yr by ngoomie

Can't help you with Gentian Violet, sorry. It is banned in Australia violet for potential toxicity, and even possible cancer risks. I thought it was banned in Canada as well.

At least, you now know why there isn't much info on gentian violet medication and it's use.

But keep an eye on the snails after a week. If it affects the snails, it might not kill them immediately. So keep checking for up to a week.

Much safer options out there. No point risking your own life over unsafe products.

Yeah, cancer risk was a thing I'd seen mentioned a lot when looking into gentian violet briefly. I kinda just figured it might only be as bad as the cancer risk of malachite green as well, but maybe I should look into it more. I've been doing a pretty good job of not getting it on my skin and also avoiding dunking my unprotected hands into the tank water while treating my fish at least, though. Maybe I'll just not use it once I'm done this course of medication anyways, because I know a store I can sometimes get to that's pretty distant carries both malachite green and methylene blue, and in pretty large quantities.

Edited April 29, 20242 yr by ngoomie

Alright, I've done a bit more research on gentian violet's cancer-causing potential but I haven't yet done research on malachite green's to compare. But from reading the California propositon 65 document about GV (North Americans incl. some Canadians will recognize this as the law that causes some products they buy to be labelled with "known to the state of California to cause cancer", including the exact product I bought) it seems that the risk of cancer is related to internal use, either injection or ingestion.

Speaking of ingestion, I think GV bans mainly relate to its use in treating fish/shrimp/etc. which are intended for human consumption, because of the above. And in countries where GV isn't banned for this purpose, it does seem to get used on various species of shrimp without causing any issue for the shrimp themselves (at least enough so for shrimp farming purposes). See the following:

• In February, the FDA Began Rejecting Imported Shrimp for Gentian Violet and Chloramphenicol (2022 article by Southern Shrimp Alliance)
• FDA Starts New Calendar Year by Refusing Antibiotic-Contaminated Shrimp from Three BAP-Certified Indian Processors and Adding a BAP-Certified Vietnamese Processor to Import Alert (2024 article by Southern Shrimp Alliance)

Southern Shrimp Alliance and some other organizations have tons of other articles in this vein, but I'd be here for a while and would end up writing an absolutely massive post if I were to link every instance I found of articles mentioning shrimp shipments with gentian violet and/or leucogentian violet registering as contaminants.

That being said, I know shrimp farmed for consumption and dwarf shrimp are often somewhat distantly related (in fact, the one time a shrimp's species name is listed that I can see, it's the prawn sp. Macrobrachium rosenbergii, who at best occupies the same infraorder as Neocaridina davidi but nothing nearer), but this at least gives a slightly better way of guessing whether it will be safe for aquarium dwarf shrimp or not than my bladder snail anecdote from the OP.

I’ve never personally used gentian violet in a tank that already contained shrimp, and honestly I wouldn’t risk it.

 

While it’s in the same dye family as malachite green, gentian violet is much less commonly used in aquariums, which is why you’re struggling to find info on it. That alone is a bit of a warning sign for shrimp. Malachite green at very low, controlled doses has at least been used by shrimp keepers for years; gentian violet just doesn’t have that track record.

 

Bladder snails being fine doesn’t really tell us much unfortunately — they’re incredibly hardy compared to Neocaridina. Shrimp tend to be far more sensitive to dyes and medications, especially ones that affect cellular processes like these do.

 

If you’re treating now with no shrimp present, I’d just make sure to do several large water changes afterward and run fresh carbon before adding any. Once shrimp are in the tank, I’d strongly recommend treating fish in a separate hospital tank if ich ever shows up again.