Breeding Yamato (Amano) shrimp

Breeding amano shrimp (Caridina multidentata)

This is the shortened version of my overly long three-hour epic “Breeding Amano Shrimp”, originally published in 2005.

MATING

Obviously, you must have both males and females to breed Amano-shrimp. While there is a definite difference in size (males are much smaller) and body shape (females have broader tails), there is a much easier way of telling the sexes apart: you look at the second row of spots along the side of the shrimp. Females have elongate spots, more a broken line than individual spots really, while males have round spots.

Once you have determined you have males and females, you just have to make sure the animals are well-fed, and wait. Soon the females gonads will start swelling, looking like a yellowish-greenish ‘filling’ dorsally in the females – up to one third of the females volume will eventually be occupied by developing eggs!

As the female is getting ready to breed, she releases pheromones into the water, and the males become frantic; aquarists have named this phase the “shrimp race”. Prior to mating the males “swarm” around, much like moths around a lamp, trying to copulate with everything which moves, including each other and fish!

Copulation normally takes place late in the evening, with the male first swimming around, then landing on top of, the female. If she does not fight him off, he then climb in under her, belly to belly, to deposit the sperm. The whole procedure is over in a matter of seconds. If the female is not ready, or if there are many males trying to mate with her, fights may break out. With many males present, one may even get “communal” spawnings, with one female surrounded by numerous of males.

A couple of days after copulation, the female lays the eggs, gluing them onto her abdominal swimmerets. Literature suggests the female may lay as many as 2000 eggs. When freshly laid, the eggs are a dark moss-green color, but become progressively lighter and more khaki in color as they mature. The female carries the eggs for about 5 weeks before they hatch. The color of the eggs can be used as a rough guide to when they’re going to hatch, but a better estimate can be obtained by looking closely at the eggs (e.g. with a hand lens, or, as I do, via a macro photo): if you can see the eyes of the developing embryos through the eggshell, then the eggs will hatch within a few days.

When the eggs are close to hatching, the eyes of the embryos are visible through the eggshell.

I’d recommend you remove the female when hatching draws close and place her in a jar or small breeding tank, where the eggs may hatch in safety. The larvae are positively phototactic (swim towards light) and can be collected by shining a flashlight into the aquarium at night, and you can siphon out the larvae as they are drawn to the light.

The eggs do not all hatch at once. In my experience, most hatch during the night, and the remainder throughout the next day.

You should return the female, who does not eat her young, to the main aquarium as soon as the eggs have hatched. Within days of releasing the larvae, the female will have mated, moulted, and be carrying a new batch of eggs. Mature females are always producing eggs, and nearly always carrying some as well.

Note: do NOT place the female in brackish water! While I found out that adults survive quite high salinities, the eggs fail to hatch if the water is brackish – I lost two batches this way.

REARING THE LARVAE

The newly hatched young are whitish and exceedingly small, approximately 1.8 mm long. The larvae are planktonic, positively phototactic, and hatch as early Mysid stage larvae. For the first weeks they swim in a curious vertical, head-down, position, after which they adopt a more horizontal swimming position.

In nature, adult Amano-shrimp live in mountain streams and the larvae are washed out into the sea where they feed on marine plankton and grow. After metamorphosis they migrate back up into the streams. We must mimic this cycle in order to breed the shrimp. Therefore the larvae have to be transferred to salt water as soon as possible, at the latest at the 8th day after hatching, because after that they become unable to live in fresh water. There is no need to gradually increase salinity, the larvae have no problem being unceremoniously dumped straight into salt water. To make the salt water, I would suggest using either filtered natural seawater, or a quality commercial salt mix intended for coral reef aquaria, e.g. Instant Ocean, which should be aerated vigorously prior to use.

THE ISSUE OF SALINITY

There is some controversy surrounding what the optimal salinity is for the developing larvae. Hayashi & Hamano report total failure to survive in salinities up to and including 8.5 ppt; optimal survival at 17 ppt (80% survival rate); and suboptimal survival (11%) at salinities up to 35 ppt (full marine salinity). This is quite different from what I found, with zero survival at salinities lower than 25 ppt, suboptimal survival at 25 ppt (3 larvae, out of at least 200, survived for four weeks without metamorphosing at which point the attempt was aborted), and high survival at 30-35 ppt (an estimated 80% reaching postlarval stage). Other people who’ve experimented with salinities have come to the same conclusion: any salinity below 30 ppt or over 35 ppt will result in heavy mysid-stage larval losses!

However, after metamorphosis the postlarval shrimp no longer tolerate full-strength seawater and should be moved to fresh water. Alternatively losses might be avoided by lowering salinity to 17 ppt when the first larvae start to metamorphose.

I’ve used an airstone with reduced flow for circulation. There may be problems with flotation of larvae if aeration is too vigorous.

FEEDING THE LARVAE

The larvae require fine-particulate food for the first weeks, after which they are capable of accepting larger food particles. Judging by published reports, the larvae can subsist on pretty much any food small enough – successful rearing have been reported using e.g. fine-crushed Spirulina-flake, and dry yeast.

I fed mine about 5 times per day, initially with small amounts of brewers yeast, Baby Star II (50-100 microns microencapsulated feed for egg-laying freshwater fish), and after a week also Golden Pearls (microencapsulated food for marine invertebrate larvae, 50-100microns). There was also quite a lot of diatom algae growing in the tank, you can see it as brownish “dust” in the photos, and I’ve since learned that diatoms is an important food for shrimp larvae.

Seriously, I think access to diatoms is absolutely necessary. Hayashi & Hamano report that larvae did not begin to feed until the fourth day (first ecdysis), after which they successfully raised their larvae on a diet of “adhesive diatoms, Cymbella and Navicula, or a grated artificial diet, mixed with a small amount of rice bran”, and note that the larvae were capable of foraging on the tank walls and bottom. Hayashi & Hamano failed to raise larvae on a diet of just rice bran, or a diet of Chlorella phytoplankton + rotifers.

Diatoms. You need them. Remember I told you so.

Once they could eat it the golden pearls was a good feed – the larvae eagerly accept it, grow fast, and the strong color of the feed makes it easy to see that the larvae are eating (the guts turn brownish red, and eventually the whole larva turns orange).

The larvae will both catch food drifting in the water, and browse on surfaces.

I tried feeding the shrimp freshly hatched Artemia, but although I could see them catch & eat some artemia, most of the artemias quickly grew too big for the shrimp to eat, and actually started reproducing in the rearing tank. As the Artemia are clearly competing with the larvae for food, I’d advice against feeding Artemia to Amano-larvae.

GROWTH

My shrimp larvae started metamorphosing to postlarvae at day 30 to 60. The settled postlarvae are about 8 mm long. My experiences suggest they are capable of being transferred to fresh or brackish water immediately after metamorphosis, and will die within a few days if left in full marine salinity.

THE END

The larvae do not metamorphose into adult form all at the same time. It will take several weeks until the last has metamorphosed.  An interesting observation: Whenever I change water in the aquarium, the postlarvae start swimming around like crazy, and continue doing so for a few hours. Presumably the water change triggers their migratory instincts.

At day 127 after hatching, the largest of my shrimp were about as big as the smallest Amanos one see in shops, i.e. about 25 mm, and ready to sell. With heavier feeding, and a larger grow-out tank, the shrimp would have reached marketable size faster.

Links

An amazingly good page with information on the keeping and breeding of this shrimp: http://caridina.japonica.online.fr/

Another very good report on a successful breeding: http://maitrebull.free.fr/aqua/caridinajaponica.htm

References:

Hayashi, K-I. and T. Hamano. 1984. The complete larval development of Caridina japonica De Man (Decapoda, Caridea, Atyidae) reared in the laboratory. Zoological Science 1:571–589. CSA

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