Q. Was this wa­ter con­tam­i­nated?

Practical Fishkeeping (UK) - - Fishkeeping Answers - PAUL HAGGIE, EMAIL BOB MEHEN

I re­cently bought some Otocin­clus cat­fish from a well known pet store. I added them to the tank but also added the wa­ter they were bagged in. Fool­ish, I know but I did it — and ever since I have had a wave of fish deaths. I’ve tried to rem­edy this with wa­ter changes and my pa­ram­e­ters seem OK. What is the best way to in­tro­duce new fish? Is it pos­si­ble that a pet shop’s wa­ter was con­tam­i­nated?

AAd­ding new fish to an es­tab­lished tank al­ways brings with it the pos­si­bil­ity of in­tro­duc­ing dis­ease and par­a­sites at the same time. The best shops fully quar­an­tine their live­stock be­fore putting them up for sale but even this can’t guar­an­tee that they aren’t har­bour­ing prob­lems. Wher­ever pos­si­ble it is best for the hob­by­ist to quar­an­tine new fish at home for sev­eral weeks where they can set­tle and any signs of dis­ease or par­a­sites can be spot­ted and dealt with.

How­ever, many of us don’t have the fa­cil­i­ties or space to do this, so we have to take the gam­ble of ad­ding fish di­rect to the dis­play tank. You don’t men­tion any symp­toms that the sick fish showed be­fore death so it’s very hard to work out what the prob­lem is.

Not ad­ding the wa­ter from the tran­sit bag is usu­ally a good idea, but dis­eases and par­a­sites are more likely to be ac­tu­ally on or in the fish than in the wa­ter it­self. Some shops keep con­stant lev­els of med­i­ca­tion in their dis­play tanks, es­pe­cially ma­rine fish where cop­per is of­ten used to keep par­a­sites at bay, and ad­ding this wa­ter to a tank with in­verts in it can cause real prob­lems.

If your Otos were not vis­i­bly ill when you bought them, then there isn’t much more you could have done with­out quar­an­tine fa­cil­i­ties. Fish deaths around the in­tro­duc­tion of new fish to a tank usu­ally go two ways in my ex­pe­ri­ence.

The first is that the new fish die soon after in­tro­duc­tion, of­ten due to a sud­den change of chem­istry from their stock tank to the home dis­play, where the fish have of­ten got used to a steady drop in wa­ter qual­ity or chem­istry with­out show­ing any ob­vi­ous signs, mean­ing that the owner doesn’t test the tank, think­ing that the wa­ter qual­ity must be fine.

The sec­ond sce­nario is that the new fish are OK, but the ex­ist­ing stock drops like flies. This is usu­ally due to dis­ease, and hap­pens in much the same way as some­thing as ap­par­ently mun­dane as a com­mon cold can wipe out an iso­lated com­mu­nity in the Ama­zon. The fish in your stock tank have lived in iso­la­tion for so long that they haven’t been ex­posed to any pathogens. The new fish are hardy sur­vivors of all the nas­ties thrown at them dur­ing the process of cap­ture, ex­port and so on, and they bring with them dis­eases that they are largely im­mune to. Once added to the dis­play the ex­ist­ing fish are rapidly wiped out while the new­com­ers carry on as if noth­ing is wrong in the tank.

My ad­vice is to quar­an­tine, but if this isn’t pos­si­ble, then get a read­ing of the shop’s tank wa­ter (not the wa­ter in the bag which can change dur­ing tran­sit) and com­pare this with your own aquar­ium wa­ter. Make sure they match as closely as pos­si­ble.

Only buy healthy fish that are not shar­ing their sales tank with any ob­vi­ously sick in­di­vid­u­als.

When ac­cli­ma­tis­ing the new­com­ers, do so in the usual way (see the step by step process on the right) and then net the fish out of the bag and dis­pose of the wa­ter in the bag af­ter­wards.

Could Paul’s new Otos have brought some­thing nasty into the tank with them?

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