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Live food culture - Crangonyx pseudogracilis

dw1305

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Hi all,
I've found a potentially useful alternative crustacean to Asellus aquaticus and Hyalella azteca as "tank janitor" and live food source.

It's called "Crangonyx pseudogracilis" and it has the advantages of being quite small (less than 10mm) and very tolerant of warm water and low oxygen levels etc.

They look like a small, translucent green coloured Gammarus ("Freshwater Shrimp"), and they both swim like a Gammarus (on one side), walk around like an Asellus ("Water Louse").

I've found them for a while now in some of the filter sponges in the aquariums, and wondered about what they were, and why they seemed happy in the tank (Gammarus struggle with the low dissolved oxygen levels found at warm temperatures).

After the students fished some out of the ponds at work I had a proper go at ID (I knew by then that they weren't a native species, and was a bit worried they were a Dikerogammarus "Killer shrimp").

Once I'd got a name I found that Crangonyx are used as a live culture fish food and as a bioassay organism, partially due to their "ease of culture".

If any-one wants some I can have a go at posting them in damp moss.

cheers Darrel
 

zozo

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Very intresting find Darrel.. So you say our indigenious Gammarus pulex doesn't like the tropical temps in our tanks? I read they also don't like acidity only found in near nutral invironment and stop to excist at ph5.5.. Any thoughts on Crangonyx pseudogracilis how they cope with higher acidity like what much of us have in high tech.. How they do in for expample ph6 to 6.5?
 

dw1305

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Hi all,
Yes please Darrel, I've got a new tank set up with a built in refugium
PM me your address.
So you say our indigenious Gammarus pulex doesn't like the tropical temps in our tanks?
They don't last long in the tanks, even at high dissolved oxygen levels. Asellus are fine, and can maintain their population through the summer.
Crangonyx pseudogracilis how they cope with higher acidity like what much of us have in high tech.. How they do in for example ph6 to 6.5
I don't think high tech., as such would be a problem. The pH changes due to the CO2 ~ HCO3- equilibrium don't effect alkalinity. Snails struggle in high tech. because their shell whorls are biogenic CaCO3 that can't be repaired by the snail. The carapace of a shrimp etc is slightly different.

The pond the Crangonyx came from is alkaline, but the tanks are soft water. I couldn't find anything that specifically states their pH tolerances, other than they have <"much wider environmental tolerances"> than Gammarus spp.

cheers Darrel
 

zozo

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Thanks Darrel great info.. Makes me think twice before i dive into the swamp again with my net and introduce self caught critters to the tank without proper research. Incidently introduce some baby dikero's?

Came across this one, people with nets and buckets like we are might like it.. Straight foreward identification..
https://www.fba.org.uk/sites/default/files/DVillosusID_Web_0.pdf

By the way, do you propagate them first in a seperate tank? Since fish feed on them, i guess they might be eaten before getting a chance to reproduce in sufficient numbers?
 

dw1305

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Hi all,
Thanks Darrel great info.. Makes me think twice before i dive into the swamp again with my net and introduce self caught critters to the tank without proper research. Incidently introduce some baby dikero's?

Came across this one, people with nets and buckets like we are might like it.. Straight foreward identification..
https://www.fba.org.uk/sites/default/files/DVillosusID_Web_0.pdf

By the way, do you propagate them first in a seperate tank? Since fish feed on them, i guess they might be eaten before getting a chance to reproduce in sufficient numbers?
It was only after I'd found them in the tank that I started to worry.

I think they may have come in with some Baetid Mayfly nymphs and Glassworms (Chaoborus sp. midge larvae) that I fed the fish in the winter.

The FBA link is really useful, as soon as I had the picture of the urosome (below) I knew that they were Crangonyx pseudogracilis
Crangonyx_pseudogracilis.jpg


I'm assuming that I'll be able to culture them just like Asellus, they persist in the tanks, but I have spares in the buckets that I culture the Daphnia in. I just have some dried leaves (and pond snails) in the buckets and that works pretty well for both Daphnia and Asellus. I got the idea from the link on Caudata.org <"http://www.caudata.org/forum/f1173-...ation-daphnia-cultures-alternate-feeding.html">.

A suggestion is that <"green filamentous algae"> forms a major part of Crangonyx's diet, so they may be a more resilient Cherry Shrimp alternative.

cheers Darrel
 

dw1305

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Hi all,
Yes please Darrel, I've got a new tank set up with a built in refugium and my Hyalella seem to have all vanished.

Sent from my HUAWEI GRA-L09 using Tapatalk
Tom I'll post some Monday.

cheers Darrel
 

zozo

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Very intresting all.. :) I bred some daphnia last summer in the garden in a small tank.. It's indeed difficult to keep the population healthy for long term in a controled invironment.. For me i guess it was the temperatur finaly being fatal with a glass tank at a sunny spot.. Leaving a bucket of water with leaves in it at a filtered light spot outside to it's own divices did a better job than trying to control it.

Those shrimps and asselus never realy crossed my mind before.. I have a few fishless natural ditches of water near my home, i walk by this week and see what i can find after a scoop there must be something in there. Tho those dikero's kinda spook me a bit too.
 

DTL

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Darrel,
If you have any more to spare, I'd love to give culturing these a go in a spare tank I have set up.
Cheers
 

dw1305

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Hi all,
If you have any more to spare, I'd love to give culturing these a go in a spare tank I have set up.
I'l see how many I can find on Monday, but I should be able to collect a reasonable amount.

cheers Darrel
 
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