How Many Fish Can Be Kept

7/31/2019 How Many Fish Can Be Kept

1/7

How many fish can be kept?

There are guidelines about how many fish you can keep in an aquarium, but few experts would claim

they are scientifically exact. The two main rules of thumb on stocking an aquarium are based

respectively on the surface area of the tank (which influences oxygen levels) and the tank volume (this

takes pollution as well as oxygen into account).

Many other things can alter how many fish an aquarium can healthily support, including:

The shape of the aquarium The filtration system employed Surface agitation Water temperature Tank maintenance regime The kinds of fish being kept

Note: You cant stock to the maximum capacity on first setting up!If your tank can hold, say, 20 small tropical fish, you should build up to that over a period of 3-6 months,

to give the tank a chance to mature without a dangerous spike in pollutants.

With those caveats in place, lets consider the common guidelines.

Fish cm per liter / fish inches per gallon

This was the rule I was taught when I first started keeping fish, and its still the most common stocking

guide today.

1. Calculate the volume of your aquarium in liters or gallons2. Work out the length of your chosen fish from nose to base of the tail3. Consult the table below

Kind of fish Inches / gallon cm / liter

Coldwater 1" / gallon 2.5cm / 4.55 liters

Tropical 1" / 0.5 gallon 2.5cm / 2.25 liters

Marine (reef) 1" / 4 gallon 2.5cm / 18 liters

Marine (Fish-only) 1" / 2 gallons 5cm / 9 liters

For example, a 30-gallon aquarium could hold 30 of coldwater fish, 60 of tropical fish, or 15 of marine

fish.

Important: I am using Imperial (UK) gallons here. To work out US gallons, multiply UK gallons by 0.83 (or

just stick to liters!)

The advantages of the fish inches per gallon rule are that it is easy to understand, since most people

know their tanksvolume, and it takes into account the total volume of the tank. The solution to

pollution is dilution is an old fishkeeping phrase. Bigger volumes of water can obviously carry more fish

waste such as nitrate before theres a problem.


2/7

The disadvantage of the rule is it does not take into account the tank shape. A tall, thin tank of 40-

gallons will,

according to this rule, have the same carrying capacity as a shallower, longer tank. But in reality the

shallow tank will offer a much bigger surface area for gas exchange. In filter-less tanks particularly, it

makes a big difference.

Fish length per unit of surface area

This rule puts aquarium surface area to the fore:

1. Calculate the surface area of the tank in square inches or centimeters2. Work out the length of your chosen fish from nose to base of the tail3. Consult the table below

Kind of fish Inches / sq inches cm / sq cm

Coldwater 1" / 30 sq inches 2.5cm / 190 sq cmTropical 1" / 12 sq inches 2.5cm / 75 sq cm

Marine 1" / 48 sq inches 2.5cm / 300 sq cm

A 36-inch long by 12-inch wide tank will therefore hold 14 of coldwater fish, 36 of tropical fish or 9 of

marine fish.

The advantage of using the surface area guideline is that it takes oxygen exchange directly into

account. The per gallonrule also does (thats why coldwater fish need more gallons than tropicals) but

not so directly.

The disadvantageof the rule is that people arentso aware of their tanks surface area. Its easy to workout: just multiply the width of the tank by the length. But its harder to keep in mind when youre in the

aquarium store wondering if you can add a few more fish.

Other issues with stocking levels

This article could run forever, so Ill just add a few more caveats and pointers you should take into

account.

Water displacement because of decoration means your

tank wont hold as much as its theoretical volume. Take off at least 10% to account for gravel, rocks, lots

of bogwood and so on. With a very heavily furnished tank, take off 15%.

Different fish need a different amounts of space.

Active fish like tangs or danios require more swimming room then relatively static fish like clownfish or

neon tetras. Many fish require a certain-sized territory. For instance, Id only keep one pair of dwarf

cichlids in a two-foot freshwater aquarium. These measures have nothing to do with theoretical volume.

Big fish need more room than the equivalent number of little fish. Two six-inch long catfish will require

a much bigger

tank than 12 one-inch tetras. Their biological load is greater, and theyre messier eaters.


3/7

You can generally ignore shrimps, snails, plants and inverts

when making your calculations, as they have a small biological load and often contribute to the tanks

carrying capacity (such as plants which oxygenate by day or critters that clean up detritus). Two caveats:

In large numbers they will make a difference (such as a snail infestation in a tropical tank), and marine

inverts can be more sensitive to poorer water quality

(hence the lower stocking suggestion per gallon above).

Strong water circulation, big filters, airstones

and so on can increase the stocking level of your aquarium, but I wouldnt recommend it. Better to have

healthy fish with enough room to roam unmolested than to cram in another fish or two and risk disease

and infighting.

Remember, these are just rules of thumb. Erring on the side of caution is always the best policy with

aquariums, and an under-stocked tank is far easier to keep in good condition than even a slightly over-

stocked one.

Physical checks for a new fish

1. Look at the fishs eyes

Healthy fish have bright, clear eyes and an active look about them. You may think this is a ridiculous

thing to say about a fish, but with time youll agree. In particular, avoid fish with cloudy eyes.

2. Check its body for lumps or white spots

White spot disease is one of the easiest diseases to see on tropical freshwater fish. Look out for pin-

sized white spots raised away from the body of the fish. Dont buy any fish from that tank (or any othertanks its connected to ask somebody at the store).

3. Look for complete fins and tail

Damaged fins might be a sign of disease, or they could be a symptom of in-fighting between the fish in

the same tank. Fish are often packed in large numbers into shop tanks, so a bit of scrapping and minor

damage is always going to occur. But as a newbie its safer to avoid any damaged fish, especially as you

might be looking at fin rot and not realise it.

4. Avoid fish with missing scales

Same as torn fins, really. A few missing scales arent fatal, but its better to avoid damaged fish to be

sure youre not buying a fish with built-in problems, or worse looking at a disease. Fish with huge bite

marks should be avoided completely!

Fish behaviour and tank checks

5. Active fish should be active, docile fish docile

This is hard for newcomers, who dont know fish behaviour yet. Basically, fast-moving or active fish such

as barbs, danios, and platies should be busily moving about the tank a Zebra danio lurking around the

surface of the water is almost certainly sick. On the other hand, a Corydorus catfish will often sit

motionless on the substrate, while dwarf cichlids typically move with a start-stop motion. Until you get


4/7

more experience, the best bet is to compare your potential purchases behaviour with other similar fish

in nearby tanks.

6. Look out for loners

On a similar note, most freshwater community fish should be out and about, taking an interest in the

tank. Any fish lurking on its own should be viewed with suspicion; even non-shoaling species should

usually look like theyre aware of the tank and its inhabitants. This is only a general principle there are

many common tropical fish that will lurk under a piece of wood all day, or hide in the weeds but when

it comes to more common fish its a good rule-of-thumb.

7. Ask to see it feeding

Very few freshwater tropical fish that are suitable for beginners will respond when a few flakes or a

chunk of frozen food is placed in the aquarium. Not eating is definitely a bad sign, so ask to see your fish

being fed whatever its been eating since arriving at the store. Avoid fish that dont eat.

Bonus tip!

Always ask to inspect your fish in the bagA difficulty with some of these tips is that you may be choosing fish from a tank of 40 or 50 other near-

identical fish, and the store assistant could catch any one of them.

Its unrealistic to ask the assistant to capture a particular Neon tetra in a tank full of them for you, so in

such instances youll haveto accept you wont be able to handpick each fish.

Do ask to see the selection of fish that have been caught, however, before agreeing to buy them. Look

out for the physical warning signs above.

Behavioural warning signs are harder to judge, since all fish are traumatised by being caught and popped

in a bag.

As I wrote a couple of times above, its safer to avoid tanks withany suspect inhabitants in it altogether.

Plenty more fish in the sea!

BANGLADESH AQUARISTS (BA)

SAFETY TIPS FOR DIY PROJECT:

1. Do not carry out a task that is beyond your capability and do not over estimate your capabilities.

2. Do not use tools until you know how to operate them safely. If you buy a new tool read theinstructions fully and practice in a safe area first.

3. Wear protective clothing including safety goggles, gloves and dust mask when working with

potentially hazardous materials such as glass or spray paint. It is also advisable to wear a mask when

working in a dusty environment e.g. sawing wood.


5/7

4. When painting, or using any material that generates toxic fumes or dust, keep the room well

ventilated. Never smoke while painting or standing close to a freshly painted area.

5. Always use the correct tools for the job. It is worth investing in high quality equipment as this will be

safer and will probably do the job quicker.

6. Store tools in a safe place, out of the way of children and pets. Keep them in a box or a rack.

7. When using knives, always cut away from you. Use a baton as a guide and run a sharp knife along the

edge of it. Always store knives securely.

8. When fixing or checking electrical appliances or connections, always switch off the power and remove

the fuse or circuit breaker. If you're fixing an electrical appliance, switch off the appliance at the socket

and pull out the plug. Wear rubber-soled shoes when working on electrics.

9. Always keep a chemical fire extinguisher in the house. Never use water to put out a fire in an

electrical appliance. Gas and electrical work is best left to a registered professional.

10. When using a power drill, choose a model that has a plastic non-conducting body. Unplug the drill

before fitting parts and remove the chuck key before switching it on. Avoid wearing loose clothing or

jewellery, which could get caught in the drill.

11. Ladders are one of the main causes of DIY accidents. Erect the ladder according to the

manufacturer's instructions. Never lean to one side as you could lose balance.

12. Don't rush as you're more likely to have an accident. Carefully plan the job before you start work.

Know your limitations and consult a professional if you are unsure. It's also a good idea to ask someone

if they can help you.

Important: Perform DIY project at your own risk. In case of injury you cant blame any

members/admins of Bangladesh Aquarists. Bangladesh Aquarists cannot be held responsible for any

injury/accident caused by any DIY project.

Five ways to save money

Bad times in the economy neednt meanyou forsake your aquarium hobby. Sure, if youre worried

about your job

then this probably isnt the time to set up a huge saltwater reef tank. But there are ways you can save

money with more modest tropical freshwater aquariums.

If you have any more tips to add after reading, please drop us a line in the comments below!

1. Use plants instead of a filter

Setting up a new tank to grow plants? If youre already spending money on decent lighting and a good

quality substrate to help ensure your plants thrive, you may be able to save money by skipping the filter.


6/7

On her excellent natural aquariums website, Rhonda Wilson explains how she uses plants to keep her

tropical tanks naturally sweet:

There are several reasons why I enjoy natural aquariums as opposed to those that are mechanically

filtered. I find the equipment to often be distracting from the beauty of the tank. Im interested in the

interaction of different factors that make up a living system.

I know some people really like to play with all the aquarium equipment and thats OK if you like to

collect equipment. I prefer collecting different types of plants, fish and invertebrates to go in my tanks.

Heres one of her articles explaining how to set-up a natural aquarium.

2. Use rabbit or guinea pig droppings as plant fertiliser

Filled your tank with plants but worried about the cost of expensive German fertilizers? Some plant

enthusiasts swear by using rabbit or guinea pig droppings as targetted fertiliser tablets.

Dry them out in the sun, and then bury a couple in the substrate near big specimen plants like Amazon

Swords and Cryptocyrenes. Go slow at first, and dont overdo it.

Dont use any other animal waste as it wont be appropriately constituted and could pollute your tank.

3. Build your own DIY stand

Most aquarium stands are absurdly expensive for what they are four or five pieces of machine cut,

man-made wood, stuck together with screws

If youre at all handy, there are loads of guides on the Internet on how to build your own stand. Heres afew to get you started:

A DIY stand plan generator to suit any tank size A guide to making joints to support the weight of a fishtank Plans for a heavy-duty stand you can scale to your needs it looks like it could hold up a house! Heres a 4-foot aquarium cabinet step-by-step guide

4. Get your fish for free

Ever moved house and had to give your fish away for free? Ive done this more than once, and I know

others have as well.

Generally youre forced to push your homeless fish onto aquarium-owning friends, or even return them

to a shop who reluctantly takes them off your hands then sells them the next day. (A mans got to make

a profit, I suppose.)

This is the age of the Internet, however, and there are countless opportunities for you to advertise your

need for particular free fish in your local geographical area. Craigslistand Gumtree are two ad services,

or you could simply post your requirements in an aquarium forum.


7/7

If youre after livebearers you will be inundated with offers. I bought three supposedly female platies

last summer. I now have about 20 platies in one of my tanks, and theyre still breeding. I cant give them

away fast enough!

5. Turn down the temperature

Many tropical freshwater fish are quite happy at temperatures of 21C / 75 degrees Fahrenheit, yet are

kept at 26C or higher. A few do require higher temperatures, most notably discus and some South

American tetras, so be careful.

If you check the lower safe range of the fish you keep, you may find you can bring the temperature

down by a few degrees, which may stop the heater going on at all for most of the year in a centrally-

heated house.

A few fish kept as tropicals, such as White Cloud Mountain Minnows, actually prefer no heater at all

an indoor unheated tank will suit them fine, which will save you buying a filter. And coldwater fish likegoldfish certainly shouldnt be kept in heated tanks (but people do).

How Many Fish Can Be Kept

Documents

Transcript of How Many Fish Can Be Kept