Amano shrimp: Spineless heroes


Amano shrimp: Spineless heroes

Nathan Hill explores the origins, benefits and breeding of one of the hobby's biggest game changers, the Amano shrimp.

I’m not sure aquascaper Takashi Amano realised just how much he’d change the face of fishkeeping when he asked a local collector to round up a few thousand bland, colourless shrimp for him. Now, three decades on, there are few tanks that haven’t felt the presence of these hard-working, tenacious invertebrates.

My own experiences with these fastidious grazers have been positive through and through. They’ve saved aquascapes as well as my large retail displays (in my aquatic store manager days) and I’ve even had them breed, which is something I didn’t know was remarkable at the time and something that many Amano shrimp adherents will vehemently deny; more on that later.

The true Amano shrimp is Caridina multidentata, but you might see them bandied about under their synonym of Caridina japonica. Certainly when Takashi stumbled across and popularised them in the 1980s, that was the name they were recognised by. It was only in 2006 that revision took place and gave them their current identity of C. multidentata.

If 'japonica' sounds a little Far Eastern to you, then you’re on the right track. This name refers to their Japanese heritage, where Takashi came across them and where many come from today. The original specimens were recorded from the Ogasawara (or Bonin) Islands, though they’re just as happy on mainland Japan too.

Some folks have the impression that Amano shrimp only come from Japan and its immediate vicinity, but this is far from true. In reality, Amano shrimp are also found in Taiwan, the Ryukyu Islands (between the Philippine and East China seas), Fiji and maybe even Madagascar, though this is unlikely. There was contention over the validity of the Madagascan shrimp. As far back as 1965 taxonomists (namely Dr Holthuis) have been marking them out as different and have cited features such as moving rostral teeth as adequate features that have granted them their own species status.


There’s even the strong chance that some of the Amano shrimp on offer in the trade are not true C. multidentata. Caridina make up a huge genus of approximately 280 different species spanning across Asia, Oceania and Africa — there’s even a Caridina species in Lake Victoria. With such an abundance of species, many physically very similar, it’s easy for imposters to slip under the net and enter aquaria. One shaky train of thought is that many 'Amano' shrimp on sale are not true, Japanese specimens but a Taiwanese variant.

These 'Taimanos' are identified by two features: the first being their shorter, compact rostrum, and the second being their inherent laziness. Supposedly, these false shrimp also breed entirely in freshwater, which is something that C. multidentata do not do. But aside from that they have the same, nondescript colours and similar markings.

There are even hints of an Indonesian variant doing the rounds, but these are also contested on a species level; they have a straight rostrum and not a crested one. Buyers beware, and be diligent. True Amano shrimp should be relentless workers, and that’s exactly what fuels their popularity. Tirelessly padding away with their tiny maxillipeds, they will graze on almost all forms of algae with just the dreaded Black beard algae and some cyanobacteria types being sometimes averse to their palates.

Lacking cutting or biting mouthparts, at best they can softly rasp away at surfaces taking away the topmost film. This inability to cause harm makes them ideal workers in tanks where there are small fish and even fry, which they will largely ignore. My own experiences have seen the occasional, bold Amano tootling off with a prize in the form of a fish egg, but their impacts on breeding populations are negligible at best.

Some aquascapers have griped and bickered that their Amanos have damaged planting, but this is unfair condemnation. Amano shrimp will indeed rasp away at plants but are only able to take away material that is already dead or dying. It’s not unusual to find perfectly cut holes in leaves, where plants have degraded through nutrient deficiencies and the shrimp have cleaned the site up. Much like maggots in a wound, they’ll only eat the bad and leave the healthy.

Second to none

The benefit to the aquarist in keeping these shrimp is huge. Their eating efficiency and digestive capacity is second to none, and, in part, a reaction to what can be an oligotrophic lifestyle.

In the aquarium they will pick up on almost any waste, be it uneaten food, fish faeces, decaying plants, or whatever, and convert it into tiny packages of shrimp waste, almost like large grains of jet black sand. These can then be easily siphoned from the tank during a water change.

Regardless of how good a cleaner they are, remember that Amano shrimp do not impact on nitrate levels at all. It does not matter if you have ten or two hundred of them, you’ll still need to water-change just as frequently!

There’s little reason to consider a biotope for these creatures, but if the idea appeals then simply go in for a large tank with big rocks and boulders inside it. Alternatively, Amano shrimp can be found in swamps with a handful of mossy plants and organic litter.

Don’t be scared of a little turbulence either. In their natural range, Amano shrimp are often subject to middling to strong flows and have a better grip on surfaces than you might expect.

Tolerant creatures (Picture above by George Farmer)

Amano shrimp tolerate a range of water conditions with the exception of the usual suspects that are ammonia and nitrite. Some sources cite Caridina as being indifferent to nitrite, but this isn’t always the case. Although nitrite reacts in different ways to shrimp blood as it does to fish blood (contact with the latter forms the lethal methaemoglobin), at high doses it can still cause a degree of mortality and difficulty.

As well as ammonia and nitrite, heavy metals should be avoided so remove any rocks with striated lines of metal through them and avoid lead weights for plants. Although these become issues in mainly softer, acidic water, even in hard systems they can form dangerous levels.

Aquascapers are occasionally worried about the heavy metals found in plant nutrients, but to my knowledge there is no credible evidence that even a major overdose of ferts causes health issues or fatalities in Amano shrimp.

Avoid salt, too. Though this chemical is essential for the rearing of larval shrimp, the adults have no tolerance of it and even background levels used as tonics (3g per litre) can be lethal to them. Hardness needn’t be high, but GH should not be below 6° for successful moulting. Temperatures are tolerated between 18 and 27°C/64.4°F and 80.6°F, and fluctuations between day and night largely ignored.

Health issues

One area of caution is the use of CO2, especially where Amanos are in planted tanks. Excess CO2 will drive the pH down, and below 6.0pH they will struggle.

They will go up much higher and all the way to 7.5pH without problems. Above this they don’t fare as well and their lifespans will be shortened. Caridina multidentata are pretty resilient when it comes to diseases and aren’t affected by the gamut of usual fish ailments.

White spot and fin rot is not something they’ll experience. In fact, aside the problems of Planarian flatworms that sometimes fight to get under the carapaces of shrimp there are few health issues. Some commercial shrimp suffer fungal issues and many fancy types carry a small flatworm on top of their heads called Scutariella japonica, a miniature symbiont that does little except eat particles of shrimp food and lay eggs in the gills. Amano shrimp, however, seem rarely afflicted by this.

The biggest danger to your shrimp is poisoning, especially from airborne insecticides and more so from imported aquarium plants that haven’t been properly rinsed. Subjected to these chemicals, shrimp will rapidly turn from transparent to white and/or pink and lose all composure and momentum. Shortly afterwards they will be immobile on the base of the tank with only their tiny pleopods twitching, and then they will die. There is no cure for poisoning once it takes hold, so avoidance is the only sure course.

Keep them correctly and you can expect a lifespan of up to four years from your shrimp, over which time they can reach up to 5cm/2" in length.

Choosing the best filter for the job

Filtration for Amano shrimp needs to be unable to suck them in, but they also benefit from having access to sponge filter media where they will nibble at the biofilm and waste contained within. Foam, air-powered filters are a good choice, but better still is the Hamburg mat. This involves placing an entire sheet of foam within two guide rails to create a filter 'wall'. An uplift is then placed behind the mat, just like the uplift of an undergravel filter, and water pulled through the foam and back over the top into the tank.

Hamburgs provide a huge filtration surface, as well as an ongoing source of food for shrimp, and cost pennies to put together. Your local aquatic store can likely give you more advice and the parts required to put one together if you choose.

How well do your Amanos grow?

All crustaceans need to shed their shell in order to grow, and this stage is called moulting.Shrimp moult more when they are younger and, subsequently, growing faster, though adults may moult on around a monthly basis. This also helps to keep the shell healthy and free of pathogens.

With insufficient GH in the water, moulting is impaired. Some keepers rattle sabres over whether or not to leave the shell in the tank once the shrimp has shed.

In theory, the shrimp will ingest some of their own shells and regain some of the valuable chitin within. But in reality if diet is appropriate and GH levels adequate, then this will be surplus to requirements.

That said, there’s no harm in leaving the shell in the tank for grazing purposes.

Differences between prawn and shrimp

People often ask what the difference is between a prawn and a shrimp, and everyone likes to hold a pet theory about what constitutes each.

In reality there is no difference between the two words, and they are arbitrarily assigned to whatever takes the whim of the user. Scientifically the two names carry no meaning, so you should feel free to call your own tank inhabitants a troupe of Amano prawns if that’s what you prefer. So there you have it. Prawn and shrimp are common names, which vary considerably depending on where you are.

If you’re in America you might be sold prawn as shrimp, and in the UK you’ll get the reverse but it’s nothing deeper than that.

How many legs do shrimp have?

Shrimp belong to the order Decapoda, like crabs and lobsters. The common feature between them is that their ancestral progenitor had, at some stage, ten pairs of legs.

Looking at a shrimp it might appear obvious that nowadays they have anything but ten pairs, but the point still holds. They have just adapted and changed the forms and roles of their legs, so that the ten pairs are now divided up between the pereopods, or walking legs, and maxillipeds, or mouthpart legs. The swimming legs, the pleopods, at the rear end are a different matter altogether and are not classed as legs in the same sense.

Copper and crustaceans don’t mix!

Most medications come with clear warnings that they shouldn’t be used with shrimp and for good reason. Anything containing copper compounds is lethal to crustaceans and needs to be avoided.

The reason it is so dangerous is down to the blood of the shrimp. We humans use haemoglobin, which is basically iron that makes up our blood cells, to carry our oxygen around. Crustaceans, however, have blood cells made up of haemocyanin, which uses copper instead of iron to carry oxygen. When using copper-based medications this blood is affected, ruining the crustacean’s ability to ventilate.

Some keepers are reluctant to use water that has been stored in a hot water tank or run through copper piping for fear of contamination, though this only tends to be reported as an issue in new plumbing systems that have not had the chance to calcify inside. An offshoot of having copper-based blood is that unlike our own, which is red, in shrimp and other crustaceans it is blue.

Breeding antics (Picture above by ふうけ, Creative Commons)

Caridina multidentata is incredibly difficult to breed. Though the leaner males will frequently engage with the plumper, larger females, raising the larvae (sometimes called the Zoea) requires a marine and brackish stage.

Wild shrimp live coastally, where they release their young downstream into the sea. After some four to five weeks, during which the Zoea frequently moult and fatten up on plankton, they become parva, which move back upstream to restart their lives in freshwater mode. This explains their distribution over so many sea bound islands. As the females become increasingly pregnant (or berried) they will show a telltale darkening in the first segment of their abdomens.

My own Amano shrimp bred more by extreme coincidence than skill of any kind. Kept in a 120cm/47.2" cube tank with diabolically slow flow, the tank and adjoining system would be periodically treated with salt to help new arrival fish.

Also in the tank were large, adult Piranha who frequently bred. With ample surface cover in the form of dense duckweed, I would periodically tap the surface growth while holding a net underneath to frighten the Piranha fry into the net. Each and every time I did that, I would yield around 50 to 100 shrimplets for every juvenile Piranha. My only explanation is that with such slow flow and large volume my tank may have developed a slightly saline 'layer' within it, in which the young shrimp had enough salt to survive. Either that, or I had a species that wasn’t the true Caridina multidentata all along.

Other diligent breeders have had stabs at breeding Amanos, usually involving a separate larval system rigged up with seawater, with mixed success. It’s certainly possible to do, but unless you’ve got something close to lab-grade facilities, including plankton sources, then I wouldn’t hold out too much hope for you!

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