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How important is flow?


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Ok so I get that flow rate is important for oxygenation/gaseous exchange, plus plays a role in filtration. 

But hypothetically speaking, if oxygen level and filtration was taken care of by other means unaffected by flow - is flow still important?

Do fish that 'prefer high flow' actually just prefer higher oxygen levels or is there more to it?

Do any fish require the flow for breeding? Or feeding even? Get stressed without it?

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Excellent question! I’ve found a few US Native fish that come from small, or fast-flowing streams appreciate flow, and use water flow in breeding processes. Many “River-theme” tank setups feature sone sort of a powerhead to direct current.

Hydrophlox shiners, Dace, and Darters along with Chubs appreciate it.

I have not found flow essential with most tropical fish, except that  circulation prevents dead spots where certain algae or Cyanobacteria may grow more easily.

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On 3/11/2022 at 7:46 PM, Fish Folk said:

Excellent question! I’ve found a few US Native fish that come from small, or fast-flowing streams appreciate flow, and use water flow in breeding processes. Many “River-theme” tank setups feature sone sort of a powerhead to direct current.

Hydrophlox shiners, Dace, and Darters along with Chubs appreciate it.

I have not found flow essential with most tropical fish, except that  circulation prevents dead spots where certain algae or Cyanobacteria may grow more easily.

Thanks for the reply! Actually it was rainbow shiners (amongst one or two others, e.g white cloud minnows) that I had in mind - much of the literature I've seen say they 'appreciate it' just as you said.

I suppose was trying to understand why? What is meant by 'appreciate' it? I assume there must be some specific reason for it so I was just wondering if we knew why? If it is to do with breeding processes could this be achieved another way without the flow? Or is it one of those things we don't really know why we've just observed it to be so? 

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My Harlequin Rasboras like to play in the out flow of my powerheads. They will swim into it fighting the current until they swim past it, then swim around and do it over and over again. It is like kids playing on the playground.

Does your child require a swingset in the back yard, or just appreciate it?

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I’ve been keeping and breeding Notropis Chrosomus for a year now. I set up a HOB filter that dumps water in on one side / back of tank, and affix a mini pond pump to push water across the lower third.

 

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I’m not sure for this fish but in some tanks I have especially with plecos that like quicker moving water I have a wave maker to push some flow across. In most tanks with tropical fish I don’t think it’s needed unless you are worried about dead spots. Fish that I have seen( I have not kept many fish from streams but I do great to watch a lot of you tube they tend to have more movement for the fish. For my neons I addded a power head to the undergravel and it was just to much I though I had the size right for the flow( I still think I did) but it was to much for the fish

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Flow will change the behaviors of fish for good and bad. 

The examples of shiners and plecos is excellent - their native habitats are fast moving rivers and streams, their bodies are made for the current - streamlined and long shiners and squat/low rounded and long plecos. 

I have found rainbows to like flow, they play in the flow and at times it has induced spawning behaviors. Some tetras love the flow - I have found red eyes and diamonds to like a bit of flow - without it I would say they were shoaling not schooling but with the spray bars as they are now they school and surf the flow as a group. MD Fishtanks has a great group of Congos who seem to like the flow. 

However, smaller tetras like green neons or other species that congregate in blackwater creeks and areas that flood then recede in the Amazon do not like flow. Neons in flow tend to congregate in what I call huddles and they move as a group but only for the purposes of getting out of the flow or feeding.

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I think Cory has a video on one of his streams talking about hillstream loaches specifically. It’s a preference is all it is for viewer and fish. If you want to see natural behavior and natural coloration it helps. But for the most part fast fish just need good dissolved oxygen levels. Which can be achieved with a simple airstone and lowering temperature. 
 

interestingly when I worked at petstore, I moved the white clouds into their own tank with the dojo loaches and cut the tank off from the sump and gave it its own 40 gallon internal filter no heater and those fish went from being drab and boring to the most talked about tank. Constantly got comments like “I didn’t know white clouds were so beautiful” as the males would flex their fins and show off bright reds and that beautiful neon pink stripe across their lateral line.

 

Of course now they get the praise they deserve along with some of the more striking danios.

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Many moons ago I had some glass catfish. They congregated in the highest flow area in the tank and rarely left that spot. There was enough flow there that it looked like they were constantly swimming upstream but they seemed to love it and lived a long time. There are some fish that need a certain amount of flow or stillness, and other fish that are adaptable to a certain point. I have had fish that didn't do well in this tank because the flow was too high. Hillstream loaches were another one that loved the higher water flow.

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On 3/11/2022 at 1:07 PM, Biotope Biologist said:

think Cory has a video on one of his streams talking about hillstream loaches specifically. It’s a preference is all it is for viewer and fish. If you want to see natural behavior and natural coloration it helps. But for the most part fast fish just need good dissolved oxygen levels. Which can be achieved with a simple airstone and lowering temperature. 

I agree. For instance, trout that live in moving water need the current for oxygen and food delivery, but in most cases, they will be found near but not in the current. It takes a lot of calories to stay in an area of strong current. As temps rise and dissolved oxygen levels fall they'll be found in current in shallow rocky areas, but that just reinforces the point that it's the oxygen they need and not the flow. 

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Thanks for all the replies/input.

Ill briefly explain why I was pondering it in the first place - I'm setting up some zero tech small garden patio ponds soon to keep Medaka rice fish in - in Japan it is common to keep Medaka all year round in this way without any filter except for plants (and algae and the bacteria etc). 

I was basically just wondering if this style would work for anything else year round, now I can find a few species that are hardy and cold tolerant and small enough not to need a huge amount of space like say goldfish would but most of them apparently 'appreciate' some flow. 

If it's just an oxygen issue then with enough plants or maybe something like a sochting oxydator (i.e. no power supply required) could possibly provide the necessary oxygen but if it's literally the flow itself they need it isn't possible without some sort of filter or pump or whatever. 

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I don't want to generalize too much from a N of 1, but I have done one anecdotal experiment along these lines.  I have a Rhinogobius species which are known to come from streams.  Assuming it was DO that was going to be critical, I added a microbubbler behind the matten filter.  I didn't really want to see it or impede their behavior.  That saturated the DO.  They were listless and not super enthused about food.  They ate and survived, but seemed pretty lethargic.  Not what I had expected.

So, I decided to try something else.  I cranked up the air on the JetLifter tube and pulled the microbubbler out.  This created a serious flow in the tank.  Really it seemed like too much!  I'd decided to watch them closely because I didn't want them to suffer from exhaustion.  However, and much to my surprise, the next day they were energetic!  They ate like pigs, and the males started excavating for breeding sites.  It was night and day.  And the DO was lower in the second instance.

Again, this is one example, from one species, in one tank.  But I did at least want to toss this example out there as part of the conversation.  My suspicion is that it's probably challenging to know a priori whether it is O2 or actually the flow a species is really after in moving water.  Or whether some species from flowing water need it at all.  I would guess there are species that are all of these, or some combination of them.  All I know is that I now keep that JetLifter tube really clean to get maximum air for my Rhinogobius.  

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On 3/11/2022 at 10:58 AM, KentFishFanUK said:

Ok so I get that flow rate is important for oxygenation/gaseous exchange, plus plays a role in filtration. 

But hypothetically speaking, if oxygen level and filtration was taken care of by other means unaffected by flow - is flow still important?

Do fish that 'prefer high flow' actually just prefer higher oxygen levels or is there more to it?

Do any fish require the flow for breeding? Or feeding even? Get stressed without it?

Hmmmm..lol

Hard to say right? How/why would anyone test this? (assuming nothing to do with air or food like you say)

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On 3/12/2022 at 12:18 AM, Wrencher_Scott said:

Hmmmm..lol

Hard to say right? How/why would anyone test this? (assuming nothing to do with air or food like you say)

I test each type of new fish with increased flow rates using different filters and now powerheads to see what they seem to be happiest in.  They make dissolved oxygen test kits. I use the salifert but sera also makes one.  Though I do not test for the purpose of this it could be done. 
surprisingly many fish that I read don’t like current, my guppies and celestial pearl danios for examples actually love it and seem to do even better.  

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On 3/12/2022 at 5:54 AM, Guppysnail said:

many fish that I read don’t like current, my guppies

After I put a f107 on a 20L the guppies were like all right we can go surfing very active and if they need quiet time they hang out by the intake. (They seem to want food all day long, I guess the flow works up an appetite) 

I see the same thing with a small hob on a 20T. (I`ve only got guppies so far, so no idea how other fish would react.)

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On 3/12/2022 at 9:20 AM, BuzzDaddy21 said:

After I put a f107 on a 20L the guppies were like all right we can go surfing very active and if they need quiet time they hang out by the intake. (They seem to want food all day long, I guess the flow works up an appetite) 

I see the same thing with a small hob on a 20T. (I`ve only got guppies so far, so no idea how other fish would react.)

The flow does burn calories but also the added more strenuous activity builds stringers muscles to hold the spine. I see much less bending nowadays in girls after multiple births their tail does not droop as they did when I tried soft flow. I still have a few with droopy tails and feel bad I didn’t give them what they need. 

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On 3/12/2022 at 8:02 AM, Guppysnail said:

The flow does burn calories but also the added more strenuous activity builds stringers muscles to hold the spine. I see much less bending nowadays in girls after multiple births their tail does not droop as they did when I tried soft flow. I still have a few with droopy tails and feel bad I didn’t give them what they need. 

Yeah, Whale is all endler... but has the thickest cauduncle muscle I have ever seen on a livebearer. And in 68 degree water, I expect these fish to live quite some time. I have to trim plants regularly, or the plants will choke the flow from the waterfall.

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