Frequently asked questions on freshwater shrimps

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Matt Clarke answers some of the most frequently asked questions on keeping freshwater shrimps in the aquarium.

Aren't shrimps marine?

Not all of them. Freshwater shrimps are found virtually all over the world, but they are much less diverse than marine species. A small but growing range is becoming available in the aquatic shops now.

Can they be kept safely with fish?

Yes, providing the fish are small and non-predatory. Many fish look upon small crustaceans as food, but they are usually ignored by similar sized fishes. Be careful when adding the very small species, like Neocaridina. Even seemingly non-predatory tetras could have a go at swallowing these, so unless you've got really tiny fish, keep them in a special tank of their own.

How many shrimps should I add?

Many shrimps live in groups so add a large 'shoal' if you can afford to. You could haggle for a discount if you're buying a big group all at once.

What conditions do they need?

This really depends on the type of shrimp. Like fish, freshwater shrimps are found over a wide area so their requirements differ depending on the habitat they come from.

Most prefer slightly hard or neutral water, but there are some species from softer, more acidic waters. The majority seem quite adaptable. However, they are very sensitive to heavy metals, such as copper, and to pollutants including ammonia and nitrite.

What do they need to be fed on?

Most are omnivorous or detritivorous feeders and generally prefer vegetable matter when it's available.

Caridina and Neocaridina feed predominantly on algae, but will also nibble at algae wafers for catfishes and may get extra nutrients from things like flakes or soft-leaved plants.

Larger shrimps, like Macrobrachium, also eat vegetable matter, but may take meatier foods, including frozen brineshrimp and mysis. Fan shrimps are filter feeders and extract fine particles from the water. These probably won't get all of the nutrients they need in this way, so drop in some algae wafers, finely crumbled flakes, frozen brineshrimp nauplii or cyclops to the tank to ensure they get plenty of food.

How do you sex them?

It depends on the species, but you can normally tell by looking at the pleopods, or swimmerets. These are leg-like appendages behind the walking legs.

The first two pleopods on males are modified for transferring sperm and appear longer while those of females are used for carrying eggs. The easiest way to sex them is to look for eggs on the underside of the female.

Are they easy to breed?

No, they are rather difficult. Although females may be seen carrying eggs on their bellies and they often spawn when conditions are right. The larval offspring are extremely small, so they are tricky to feed. PFK's fish breeding guru, John Rundle, managed to spawn the Long-arm Macrobrachium shrimps and Caridina japonica and gave a fascinating account of his experiences in the June to August issues 2000.

I keep finding dead shrimps, but oddly when I do a head-count, I still seem to have the same number. What's going on?

The 'dead shrimps' you're finding are actually their empty cases (or exoskeletons), not corpses. Shrimps are encased in a hard exoskeleton to protect their soft parts from predators. The exoskeleton is quite inflexible, so the shrimp needs to shed it every so often in order to grow - a process known as ecdysis, or moulting. Ecdysis is a hormonal process.

Y-organs in the maxillae of the shrimp inhibit moulting, while X-organs and sinus glands in the eye stalks promote it. During the moulting process, the shrimp is soft-bodied and vulnerable to predation. Moulting usually occurs at night and the soft shrimp will usually hide for a short while after. It can take from a couple of days to a couple of weeks for the exoskeleton to harden.

What species are available?

A handful of species are commonly sold in the UK, but there are many more unusual species available from specialists. There are lots of new ones turning up at the moment. Unfortunately, these shrimps are rather tricky to identify.

Rock shrimp, Atyopsis spp.

Rock, or Mountain, shrimps are mainly imported from Singapore, and are often large (up to 8cm/3") and quite colourful. They are normally browny-red with a pale stripe running along the back. However, more than one species appears to be imported under this name, including Atyopsis moluccensis.

These shrimps are filter-feeders and have special fan-like appendages for extracting micro-organisms from the water. They are interesting to watch and quite active in the tank. Unlike Caridina japonica, the Rock shrimps are found in warmer water.

Cameroon-armoured shrimp, Atyopsis gabonensis

The Cameroon-armoured shrimp has started to become more readily available in the UK over the past year. It's a big (up to 15cm/ 6"), bulky, and quite ugly-looking species, and is rather shy in the aquarium. Like the Rock shrimp, it is equipped with fans for catching food particles from the water. However, it will also eat larger particles.

Amano shrimp, Caridina japonica

The Yamato, Algae or Amano shrimp has been made popular by aquascape expert Takashi Amano. It's a small species, fully grown at around 5cm/2", which is found in Taiwan and Japan in cooler mountain streams. Therefore it does best at lower temperatures (under 25C/77F).

How much are they?

Commonly imported shrimps such as Caridina japonica sell for 1-2.50. Larger species, such as the Rock shrimp, Atyopsis mollucensis, usually sell

for about 7.50, with bigger or more unusual ones like the Cameroon shrimp changing hands for 10-14. Some of the tiny Neocaridina species are less than a pound. each, but you don't get much for your money.

Are they sensitive to pollution or chemicals in the water?

Shrimps are sensitive to the same sorts of pollutants as fish. Ammonia, nitrite and raised levels of nitrate can be dangerous to them, as can chlorine and chloramine, so always ensure that new water has been properly treated.

Are disease treatments harmful to shrimps?

Some fish disease treatments, algicides and snail eradication chemicals can contain copper in levels high enough to kill shrimps, so be ultra cautious when adding anything to the tank. You can use the Treatment Finder program on this PFK website to locate medications that are safe to use in an tank containing invertebrates, such as shrimps. If you are in any doubt about the safety of the treatment, call the manufacturer for more details.

Breeding shrimps

For details on breeding freshwater shrimps, including Macrobrachium and Caridina, see the July and August 2000 issues of PFK. If you missed these articles, photocopies are available from PFK for 1 each. Call Hannah Travers on 01733 282764 during office hours.