Tropical Fish Forum

Tropical Fish Keeping Help and Advice => General Fishkeeping advice => Topic started by: Matt on April 02, 2019, 08:01:10 PM

Title: Opinions: Fish size and tank size
Post by: Matt on April 02, 2019, 08:01:10 PM
I found myself thinking today about fish tank size recommendations... if we assume that 60cm is the 'norm' for a 3cm fish, then does it not stand to reason that for say a 7cm fish, that a tank of 140cm would be considered appropriate? That said, I look at my 100cm tank and I don't for a minute believe that the 3cm fish look lost in there, 2cm fish look perhaps more "at home" and less "caged in" to me personally. I appreciate that different fish have different requirements eg. schooling fish vs otocinclus vs gourami. In my tank I would say that the cories, gobies, gourami, ember tetra seem to be ok space wise, but I always feel like the rummynose, goldeneyes, pencilfish would probably benefit from more space for territories, or simply swimming space in the case of the rummynoses.

But random rant over... I just wanted to ask the overall question as to if anyone knows how the minimum tank sizes are formulated? Is there any science behind them?
Title: Re: Opinions: Fish size and tank size
Post by: Sue on April 02, 2019, 08:18:33 PM
I don't think there is any rule for working out tank size. A lot of the recommendations come from personal experience of keeping the fish - but recommendations from people who study fish, not just keep them. Anyone can set up a website saying "I keep these fish in this tank and they are fine" when anyone who really knows about fish can say those fish are "surviving not thriving"

There is more to consider besides size.
Shoaling species need a bigger tank than the same sized solitary fish simply because you have to keep more of them. A single male betta can be kept in a tank as small as 20 litres, but a shoal of Boraras needs a bigger tank.
Fast swimming fish need a longer tank that sedate fish. For example, on size alone zebra danios are fine in 60 cm but because of their swimming type they need at least 100 cm with some experts recommending 120 cm.

The most reputable site, Seriously Fish, gives a minimum tank size, but someone who writes fish profiles for the site has made the comment that their sizes refer to species-only tanks, something I had not realised before. As soon as you add other species, the tank requirements are bigger than those given on SF.
Title: Re: Opinions: Fish size and tank size
Post by: fcmf on April 04, 2019, 03:23:57 PM
The minimum size fishtank does seem to increase as time goes on, as more information and experience becomes more readily known, and I can understand why. Observing my own fishes' behaviour, I wouldn't feel comfortable with anything larger occupying my tank - cherry barbs and lemon tetras would have been considered ok for a 54-litre/60cm-long tank until recently but my own feeling is that they would be too large when fully grown, and particularly when younger and much more active (albeit smaller in size). Interestingly, fishkeeper.co.uk's databank seems to be a bit more realistic/pragmatic in terms of both appropriate numbers of fish and size of tank to have.
Title: Re: Opinions: Fish size and tank size
Post by: Matt on April 04, 2019, 08:22:45 PM
I can't find the tank sizes on their site... could you post a link @fcmf ?
Title: Re: Opinions: Fish size and tank size
Post by: fcmf on April 04, 2019, 09:42:15 PM
Hmmm - it doesn't seem to be a universal feature on their species profiles. My recollection was that in the prose section / Care for some of the species' profiles I'd looked at on the bottom left. Now you have me doubting myself as I've just put in a few species and am struggling to find the info - I wonder if they've revamped the profiles and have removed that info...  ???   
Title: Re: Opinions: Fish size and tank size
Post by: Littlefish on April 06, 2019, 12:32:11 PM
They updated their site in the past year or so. I just checked on the black ghost knifefish profile, as it was a fish I considered keeping a couple of years back, and in the prose that still has the information (at least 6ft long and 2.5ft wide) in the further information/care section. A lot of other fish don't seem to have tank size information.
Title: Re: Opinions: Fish size and tank size
Post by: adenann on June 27, 2019, 11:01:32 AM
 :wave:
I've always worked to the recommendations from the Community Creator here on the Think Fish site. :fishy1:
I think though, there was some discussion a while ago about the accuracy of the CC and how up-to-date the database is.
Anyway, it seems to have worked out OK for me.
 :cheers:
Title: Re: Opinions: Fish size and tank size
Post by: Robert on June 27, 2019, 11:28:11 AM
:wave:
I've always worked to the recommendations from the Community Creator here on the Think Fish site. :fishy1:
I think though, there was some discussion a while ago about the accuracy of the CC and how up-to-date the database is.
Anyway, it seems to have worked out OK for me.
 :cheers:


We did run a number of updates to the CC recently, some profiles were amended as were some of the minimum recommendations around tank size and groups too.


Good to hear it's worked well for you  :cheers:
Title: Re: Opinions: Fish size and tank size
Post by: Hampalong on June 27, 2019, 05:52:16 PM
In my opinion it’s not so much about what the fish need or want, but what we can make them put up with. There’s a lot of selfishness(?) going on with minimum tank sizes.
It’s easy to say a 3cm fish needs a 60cm tank, as we can all then afford to keep them. But apply the same rules to a 6” fish and you have a 10ft x 5ft tank. And a foot long Oscar in a 20ft tank.
Nobody would recommend a 1” fish in a 4” tank, but apparently a 12” fish in a 4ft tank is fine.
The bigger the fish, the smaller the minimum tank size...
Title: Re: Opinions: Fish size and tank size
Post by: Matt on June 27, 2019, 06:31:48 PM
Couldn't agree more with this... I much prefer the smaller species, it make me feel l like less of a zoo keeper with animals in a cage! I have 2cm 3cm and a couple of 4cm fish in my 220 litre. Only exception is the Goldeneye Chichlid male which is my centrepiece fish and reaches 7cm.  I doubt I will ever own anything bigger than this.
Title: Re: Opinions: Fish size and tank size
Post by: Sue on June 27, 2019, 07:10:18 PM
The only actual rule that I can see is that a tank must be long enough to allow a fish to swim according to its nature, and be wide (front to back) enough to allow a fish to turn round. For example, small sedate fish can be kept in small tanks, and by small I mean minimum 60 cm for all but the few so-called nano species. But small fast swimming fish need a longer tank than the same sized sedate fish.


There is a very old fashioned rule which states 1 inch of fish per American gallon, where the fish are pencil shaped and less than 3 inches long, adult size. Besides being very out-dated it is usually mis-quoted, omitting the pencil shaped and less than 3 inches parts. So the rule never applied to fish like oscars and angelfish. But you still see this "rule" on-line, and with the omissions.
Title: Re: Opinions: Fish size and tank size
Post by: Hampalong on June 28, 2019, 11:56:59 AM
I’m pretty sure the rule of 1” per (UK)gallon started as a British thing. It was in all the old books, and was still well ‘in force’ when I started in the early 70s. For most 1” non-territorial fish it works quite well, for a standard shaped tank. The mistake is applying it to anything bigger. A 2” fish is 8x a 1” fish so the rule breaks down very quickly.

There was also a “rule” of 1” per 12 square inches of surface area (=12x 1” fish per square foot).
Title: Re: Opinions: Fish size and tank size
Post by: Sue on June 28, 2019, 04:29:28 PM
I've only ever seen the "1 inch per gallon" refer to American gallons, which are smaller than Imperial gallons. When we talk about gallons nowadays it is usually US rather than Imperial gallons, so I guess that's why it's now quoted as being US gallons.
As a side point, this is why I use litres when working out the tank volume, and things to add to a tank - there's only one kind of litre  :)


I have also seen the 1 inch per 12 square inches of surface rule. One book I read when I first started keeping fish stated that this is because is the surface area that can dissolve enough oxygen for 1 inch of fish if the water is motionless - eg if the filter stops working. Was the book correct?
Title: Re: Opinions: Fish size and tank size
Post by: fcmf on June 29, 2019, 12:30:59 PM
Here are a couple of articles which look at various alternatives: http://injaf.org/articles-guides/general-guides/understanding-fish-stocking-guides/ and https://www.practicalfishkeeping.co.uk/features/frequently-asked-questions-on-stocking-densities/
Title: Re: Opinions: Fish size and tank size
Post by: Hampalong on June 29, 2019, 04:08:12 PM
@Sue

12 square inches of stagnant surface area providing enough gaseous exchange for a 1” fish. I’ve no idea. I can see many many variables.
Exchange occurs at the rate it’s required, since equilibrium is always maintained (the same ratio of gases in the water as in the air). But the different gases have different levels of solubility, which are also temperature dependent, pressure dependant (although air pressure doesn’t change a lot), also there’s the issue of dust/film on the surface which will have a big effect on stagnant water and can totally prevent gas exchange.

I think the best way to view these rules is to use them as a starting point for your own research. Unfortunately it seems to be something that has to be learned from experience, and the ‘rules’ are ‘general advice’ at best.
Also most people don’t realise that a 2” fish needs as much oxygen as 8x 1” fish (and produces 8x the ammonia, etc). A 4” fish is equivalent to 64x 1” fish. Ballpark figures but mathematically accurate. So when they work out that their tank can hold x” of fish, they don’t know that they have to be 1” fish.

I think the most important rule is, whatever rule you use, stock less than the potential, the more less, the better, if that makes since.

I seem to have engaged ramble mode...
Title: Re: Opinions: Fish size and tank size
Post by: Littlefish on June 30, 2019, 09:55:20 AM
It's such a complex issue, and so much of the information available seems to be quite dated.
It is also part of human nature to lean towards the information that backs up what they think, e.g. @Sue  example of "forgetting" that particular information relates to pencil-shaped fish.

Looking at the links that @fcmf posted, my favourite bit from the PFK article was

"So stocking densities are an oversimplification of something more complex?

Yes. Exactly. The actual amount of fish a tank can support is determined by its carrying capacity, but calculating this is complicated and beyond the average fishkeeper."


There is so much to take into account when considering the welfare of fish, and so much of the information available can be contradictory. As @Hampalong  has noted, use the rules as a starting point for research.

My knowledge and experience is what I would describe as "limited", and so far I think I've been quite lucky to have the experience and information available here to make sense of information I find elsewhere. It has always been encouraged to stock based on adult fish size, and not to stock to full capacity, whilst also taking into account the nature of the fish.

It could be my imagination, but now there also seems to be more of a leaning towards what I think of as "creating environments" for fish. In general, people have become more aware of animals and their suffering, in all aspects of life. Limiting any suffering and/or harm, caring for the environment, and trying to do the right thing is encouraged. With regards to fish, magazines and online articles show biotopes, and the creation of environments that mimic those found in the wild. On top of that local fish shops provide quite a selection of plants, decor, etc. and on-line shopping can pretty much get you anything. With a bit of artistic licence (can a fish tell the difference between a natural cave, or half a coconut shell covered in moss? and does it care?) we can provide our fishy friends with what they need, within the confines of a tank. Fingers crossed we are keeping them happy, healthy, and entertained.

Title: Re: Opinions: Fish size and tank size
Post by: Hampalong on July 05, 2019, 04:21:51 PM
Interesting new piece here by Nathan Hill. In it he proposes a 12x rule for the more active species.

https://www.practicalfishkeeping.co.uk/features/will-my-fish-grow-to-the-size-of-its-tank/?fbclid=IwAR2z78Qf4GjaeW09LMaI0sX1zFSYnC-FPIU48ZlwkeL_7-kS3u2sl8PNMi4
Title: Re: Opinions: Fish size and tank size
Post by: Sue on July 05, 2019, 05:10:40 PM
There is a great difference between "what bioload (how many fish) can this tank hold" and "what size tank does this fish species need"

Most newcomers to the hobby think just in terms of the first. But a properly stocked tank also takes into consideration the needs of every species planned for the tank. Hampalong's link explains this well.
Title: Re: Opinions: Fish size and tank size
Post by: Littlefish on July 05, 2019, 07:32:58 PM
Great article, I like his style of writing.  :cheers:

Since moving my temperate fish into the river tank (larger tank, FX6 filter, stronger water flow) they do seem to have a new lease of life. Even my final remaining zebra danio, one of my very first fish purchased from Pets@Home towards the end of 2015, who seemed comfortable swimming with the leopard danios & WCMM in the temperate tank, she's like a new fish. All the danios & WCMM seem to have more energy and be even more active, and appear to be loving the space, the water flow, and swimming with the rainbow shiners in the river tank. It's a pleasure to watch them.  :)
Title: Re: Opinions: Fish size and tank size
Post by: Hampalong on July 05, 2019, 10:17:02 PM
A lot of people (not just newcomers) stock right up to ‘the limit’ aswell. Some even ask “am I fully stocked yet”, like they believe you’re supposed to fill the tanks with fish. It’ll hold 36” so let’s go and get 36” of fish. Some of these, some of these, one of these... will they all live together? Yes. Boom. Fish soup. Every one of them feeling crowded, intimidated, intruded, stressed, no quiet place to rest... then the diseases start...

Like @Littlefish has done with her little fish, give any fish it’s ideal environment and you see a very different fish. This includes space and fewer tankmates. Which means stocking less is a good thing, rather than a limitation, as some would see it.



Title: Re: Opinions: Fish size and tank size
Post by: Matt on July 06, 2019, 07:15:29 AM
Another good point... I am slowly trying to get to a position with all fish from South America and fewer different species in my 220 litre but tripped up the other week with the addition of the rocket panchax.  It's similar to the old debate about there being two kind if fishkeepers, those who have large numbers of a few species and those with low numbers of a large number of species. I know where I want to be, but temptation of a new fish got the better of me. (plus Mrs Matt wanted them... that's a whole other angle to the debate).

I do agree that beginners would get on far better with lightly stocked tanks. I've seen the impact of high stocking densities and whilst definately doable for experience dedicated fishkeepers, beginners should I feel stick to 75% stocked as a maximum to help ensure success. Im on 65% ish in mine currently. They look full of fish too... I drew to think what nearly doubling the number of fish would look like!

The article does suggest we may need to revise the maximum size of fish for your tank size measure on the community creator. In a 60cm tank it suggest a maximum fish size of 10cm.  Perhaps we should drop this to say 6cm?
Title: Re: Opinions: Fish size and tank size
Post by: Littlefish on July 06, 2019, 09:34:36 AM
I have noticed that on this forum it is certainly encouraged to stock a tank to around 85% (on average).
I lean in the same direction as @Matt  and will often be drawn to the temptation of new fish when I see one I like.

Sometimes, with a tank that's more lightly stocked, you get to know the individual fish because you can actually see them. With active fish the tank always looks full with stock levels well below 100%, and the chance to watch some more natural behaviour is priceless.

It's always worth leaving quite a bit of stock space in a tank, what if your fish decide to breed?

And finally, I think that tanks with less stock are easier to keep clean. Always a good thing.  :)