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PostPosted: Jul 22nd, '13, 16:13 
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I have a 2,000 litre system and at the end of autumn it was stocked with 3 batches of approx 20 fish (1 batch of length 20-25 cm, a second of length approx 10 cm and a third of length approx 7 cm). There now seem to be less than 5 of each of the 2 smaller size range fish left in the tank, even through none have seemingly died (i.e. I haven't seen any floating on the surface) and sliver perch reportedly don't prey on one other. Any ideas about what might be going on here?

And a second question. Has anyone tried rotating pond water through a length of black poly pipe laid out in the garden during winter to elevate the water temperature and encourage more feeding and thus growth? Any experience re this or theoretical concerns would be gratefully accepted.

Thanks

Craig


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PostPosted: Jul 22nd, '13, 16:18 
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What is your system configuration? Could they have been sucked up the pump? Are they just hiding beind the pump? Is your tank covered? If not, could you have been visited by a cat or a bird?

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PostPosted: Jul 22nd, '13, 16:51 
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I am guessing that your larger silvers are very happy and growing nicely. Big silvers are vicious

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PostPosted: Jul 22nd, '13, 18:59 
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Yep, My big silvers have eaten many little perch in the past.

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PostPosted: Jul 22nd, '13, 19:15 
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Had fat goldfish just vanish and they didn't go up any pipes cause they wouldn't fit

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PostPosted: Jul 22nd, '13, 19:23 
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I doubt a Silver Perch of 25cm could eat a 10 or 7cm sized fish. I would expect that your fish are all hiding under the pump though I dont advise you go looking for them with a net and cause them unnecessary stress whilst your water is still so cold. Once things warm up a bit I expect you will see all your missing fish re-appear.

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PostPosted: Jul 22nd, '13, 19:55 
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That is possible as I have 40 7-10mm catfish hiding behind an airlift filter. If you open the lid you might see one or two fish

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PostPosted: Jul 22nd, '13, 22:22 
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Is your tank covered?

Image?

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PostPosted: Jul 23rd, '13, 08:12 
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Thanks for the replies. My tank isn't covered, but I do have floating plants in the system which provide a a fair bit of cover. My pump has a pretty fine mesh cover over the intake, so I doubt fish are being sucked up. So it seems that either I have lots of small ones hiding or some of the smaller ones have been eaten by the larger ones. I guess if the missing ones don't re-appear come spring time, I will have to assume that they have been taken by the older fish.

Any thoughts about how best to stage silver perch size-wise if they are prone to being taken by the larger ones?

And any thoughts about the black poly pipe heating idea in my original post?

Craig


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PostPosted: Jul 23rd, '13, 09:44 
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Yep, I'd guess a night herron... Come in at night time, very sneaky birds...

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PostPosted: Jul 23rd, '13, 09:59 
I have often wondered about the polypipe option myself.

I passed on it for several reason:

i) The black polypipe will certainly raise temps during the day, but then you would be losing heat through grow beds & tank surface at night quite rapidly which may stress the silvers a tad due to the increased fluctuations. I would think that 2000L isn't large enough to achieve any thermal stability. Is the tank insulated?? You could try turning off your pump during the night to reduce heat loss but then you need to ensure enough aeration & water movement to deal with dissolved CO2. Ammonia build up through out night would also be a concern to me, particularly with your reasonably heavy stocking density.

ii) I am generally not allowed in the garden, that is the domain of my lady, who is angered by past events like severed retic pipes, pulled out weeds (which turn out to be seedlings). Piping around the garden was a no go so the roof was the only other option, which requires bigger pumps to deal with greater pressure head. My attached to aquaponics was the minimal energy required to run the system. Although you aren't pumping up, every bend, change in diameter, extra length etc reduces the efficiency of the flow. You would be stepping away from the fountain type pumps to possible dirty water or bore/sump tank pumps with greater energy requirements.

iii) I believe in not trying to mess with nature where possible. Sounds daft when considering how far removed from the natural state we grow fish & plants in, but seasons & associated water temps have a purpose. Look at how trees use winter for their growth period. It may not be optimum for silvers growth rates, but the poor buggers might need some dormant time to be healthier & thus more nutritious once harvested??? Might be hippy crap....

I'd love to know how it actually works from those who've tried it.


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PostPosted: Jul 23rd, '13, 10:02 
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CraigSalt wrote:

Any thoughts about how best to stage silver perch size-wise if they are prone to being taken by the larger ones?

And any thoughts about the black poly pipe heating idea in my original post?

Craig


Silver Perch have very small mouths and I doubt a 7 - 10cm fish would even fit in the mouth of a 3kg Perch let alone your 25cm fish. I have plenty of customers who add fish of 80mm plus to a tank of fully grown Silvers and never have any issues. If you want to add the cheaper perch fry of around 40mm then it may be best to incorporate a IBC tank into your system to grow them on a bit before moving them across to the larger tank.

Running water thru black poly will increase your water temps in summer, autumn and spring but I found it pretty useless in the winter. You also need to be mindful that you dont get large fluctuations in water temp as this can be more stressful for the fish than just leaving the water temps to adjust naturally.

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PostPosted: Jul 23rd, '13, 10:38 
:headbang:

I've always staged/mixed my Silver Perch.... and never had any issues with cannibalisation....

Sorry but due to their mouth size, as Troutman says... I just don't believe it...


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PostPosted: Jul 23rd, '13, 13:35 
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Yea I read the numbers wrong. My big silvers have eaten perch fry before. I introduced some last year in a floating basket but some slipped through the gaps of the basket and were snatched up quite quickly. They were small though, about 20mm.

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PostPosted: Jul 23rd, '13, 14:01 
Charlie wrote:
. I introduced some last year in a floating basket but some slipped through the gaps of the basket and were snatched up quite quickly. They were small though, about 20mm.

Possible I suppose... I've never had fingerlings that small. .. :D


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