Mystery Of The Disappearing Fish

hermit23

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Hi there,
I'm relatively new to tropical fish keeping, although kept cold water for a few years. Acquired 2ftx1ftx18inch tank, which came complete with substrate, mature filter etc, in March.
Began the slow process of adding fish gradually, with advice from local aquatics shop. Everything was fine until we bought the male betta (so beautiful!) to add as the crowning glory of our community tank. The other occupants were as follows; 2x male Gouramis, 5x male red platys, 5x male phantom tetras, 4x male guppies, 1x freshwater crab (practically invisible, lives in ornament).
Straight away the betta was very aggressive toward the other fish, constantly displaying, chasing and, as it turns out, nipping. Guppies fins were in shreds and one by one, our fish started dying, quickly disposed of by the crab.
We were advised to provide betta with floating plant cover, etc, but nothing worked and eventually we returned him to the shop. However, now our fish are still disappearing! They seem to be in good health, no white spot or anything, they are happy and active, no listless floating, but they keep vanishing, no doubt removed by the crab. We had our water tested at the shop, results came back as almost perfect (!), although PH was 7.5. We were told this was nothing to worry about. Plus the woman said that the returned betta had died 2 days after it had been taken back.

Any ideas what could be wrong? Woman at shop says its fine to add more fish, but we're reluctant to until this is cleared up. Thanks, Hermit23
 
Well, crabs are natural meat eaters and will catch live fish and eat them so are usually not compatible with fish. What species is yours?

One of the gouramis will probably eventually kill the other as they are very territorial, especially the males. What species are they?

The male guppies are perfect targets for the gouramis too as they have bright tails, which can impede swimming if they are long.

If you do not know what species the gouramis and crab are, try posting photos here for someone to ID them and Googling for images to use as a basis.

I would strongly advise you to stop all stocking until you can sort out the problems! But once they are sorted, you can continue stocking if your tank allows for it.

pH 7.5 is perfectly normal for a community tank :) I hope I am not putting you off here! But it is important to get your problem sorted as quickly as possible. Also, how do you know your phantom tetras are male? It is quite difficult to tell the sex of most tetras even for experienced keepers, but this is irrelevant in your case anyway as it is not a problem.
 
Hi, my Gouramis were both dwarf gouramis, although that doesn't matter now as they number among the deceased! In fact they were among the first to die. Our crab is a Red Clawed Crab, although having just googled it, I've found out that it needs access to air! (Why were we not told this?)

Were told it was fine to keep a freshwater crab in the tank. However, my boyfriend and I both leave for work early and so only get to see the tank in the evening, by which time another fish has usually gone.

Would it be possible the crab is catching them overnight? If so, why has it not done this before the betta was introduced to the tank? I've been racking my brains trying to establish if it's a mistake I'm making with feeding, or too much light? Also, before the gouramis died they looked dirty, sort of a darker shading to some of their scales.
 
It sounds to me like your betta got a bum rap. I have no doubt that he flared at the gouramis and even gave a half hearted chase of some other fish but the torn fins and missing or dead fish will have been the crab, not the betta.
 
Why were we not told this?
Rule #1 of fishkeeping: never trust everything anyone tells you and never trust anyone to tell you everything. Our mantra: research, research, research! It works :)

I have no doubt that he flared at the gouramis and even gave a half hearted chase of some other fish but the torn fins and missing or dead fish will have been the crab, not the betta.
I agree.

The gouramis would also have been fighting as they are quite aggressive fish. It is always better to keep females only or a male and a female as opposed to two males.
 

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