The Mantis Shrimp

Mantis shrimps are not the shrimps normally chosen by a marine aquarist to live in their display aquarium, and for good reason. They are very efficient predators. Aquarists are much happier with cleaner shrimps etc.

Sometimes a mantis shrimp gets into the display aquarium, perhaps with live rock, or the rock attached to a coral. The shrimp is noticed as it scurries into its hide hole and the best way of removing it is to lift out the entire rock if that is practical.

If not practical the normal way is to attempt to catch it using a narrow necked bottle of suitable size - clear glass ones are the best. The bottle should be of the type where the neck is more narrow than the bottle itself, the glass opening out from the neck to the body.

Ensure that the bottle is absolutely clean inside and out. Then, place some food in the bottle, but not too much. Flake isn’t of use, but a small piece of fish such as sold for aquarium use or the like will do. Then lower the bottle into the aquarium allowing it to slowly fill with seawater. Leave it standing more or less upright if possible, with the top rim close to the rock where the shrimp lives, again if possible. Don’t leave the food in the bottle in the aquarium long enough for it to rot - remove the bottle and renew the food.

The idea is that the shrimp will detect the food and track it down. Having found it, the shrimp cannot get out of the bottle again because it is too smooth.

Alternatively the aquarist could try using a commercial device designed to catch livestock, though the aquarist could end up with a caught fish.

The capture method will need patience and a number of attempts may be required before there is success.

As said, the easiest and quickest way is to remove the shrimp complete with its rock.

Once caught what can be done? Put it in the sump is one possibility, where it can become interesting in its own right. If there isn’t a sump available, perhaps pass it to an aquarist who has one, or take it to the local retailer.

If they can be interesting in a sump, why are they not welcome in a reef? As said, they are efficient predators and can take fish and crustaceans as prey. This isn’t going to please the aquarist.

Where does the name mantis shrimp come from? It is derived from the land based praying mantis as it is thought there is some similarity in the way that insect sits and waits for and then captures prey. There are two attack methods used by mantis shrimps, spearing and clubbing.

The spearing mantis will usually attack fish and other shrimp. If these come within reach the forward legs flash forward and the victim is speared on the spines.

The smashing mantis will normally hunt hermit crabs, ‘normal’ crabs, snails and other shrimp. Once in range it will club the victim so hard that it is stunned. Three or so hits with the club will normally cause the victim’s armour to crack. It is interesting to note that scientists have measured the power of the club in action, and have found it to be only a little less powerful than the impact of a .22 bullet!*

There are around 300 species of mantis shrimp of various sizes, and all of them are predators.* If prey is not available (for example they have been moved to a sump) they will take mysis shrimp, krill, and small de-frozen fish and the like.

The shrimps can be just 5cm (circa 2″) in length up to a whopping 40cm (circa 15¾”).* I wouldn’t like my finger near one of the latter! Most seen in aquaria are of course small types.

So if a mantis is spotted in the aquarium it needs to come out.

If a sump is available, or another small tank, keeping a mantis is interesting and different. They are efficient predators, and can be fed quite easily. All they need is a rock or two to call home.

(* Reference: Marine Atlas. Hans A Baensch & Helmut Debelius)

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Tags: cleaner-shrimp, Invertebrates, marine-aquarium, pistol shrimp, reef-tank, shrimps

The Pistol Shrimp

Shrimps are very well known to the marine aquarist. Perhaps the most well known are the cleaner shrimps, which are so interesting and ‘friendly’ - they climb around on the aquarist’s submerged hand without a care, though they’re actually looking for a morsel to eat. The hand must look like a very strange fish, but then there are some very strange looking fish in the wild, just look at frogfish as an example.

The mantis shrimp is less well known and much less welcome. This shrimp is a predator but doesn’t deserve to be relegated to the ‘must avoid’ list really, as in a selected environment, such as a sump, they are interesting and easy to keep.

There is another shrimp that could be called the ‘sudden shock’ shrimp. There’s the aquarist sitting watching TV when the sound of an aquarium glass pane breaking sets him/her bolt upright! Careful checking of the condition of the glass reveals nothing wrong, and there won’t be as the crack sound was generated by a pistol shrimp.

Pistol shrimps are widespread and can be found in large numbers on the wild reef - they are the most common family of shrimp on the reef.* They have varying colouration according to type and can be attractive. They eat detritus and/or hunt smaller shrimp or very small fish. They prefer isolated lives and are likely to shy away from bright lights. The aquarist is more likely to hear one during the aquarium lights-out period when it is hunting.

Certain pistol shrimp are fairly well known, these are the ones that live in a symbiotic relationship with certain goby fish. As far as I know the following has not been proven, but the pistol shrimp is thought to have very poor eyesight - when they are digging and maintaining their caves they are in constant danger of predation. The goby fish sits in front of the shrimp and in physical contact with it, and at the approach of danger the goby warns the shrimp and they both enter the cave. The advantage to the shrimp is obvious, and the goby fish obtains security as well.

The majority of pistol shrimps live without any relationship in what might be considered a normal shrimp lifestyle.

The pistol shrimp is so called because it can generate a sound that can be likened to a pistol shot. It is easily heard outside the aquarium, and as mentioned there has been many an aquarist who has assumed they have a glass aquarium problem.

This sound is generated by one of the shrimp’s claws. This claw is much larger than the other and has powerful muscles which cause it to snap together which in turn produces a strong jet of water. Nature’s reason for this is to create a shock - the shrimp cracks the claw within striking distance of prey and the prey is stunned. The prey is then easily caught.

The pistol shrimp does not form a threat in the reef aquarium that a mantis shrimp does. The pistol shrimp would in fact be in danger from the mantis.

Many years ago I had an aquarium in the wall, designed as a living picture. It was successful and I derived a great deal of pleasure from it. I clearly remember the first time I heard a ‘crack’, I had no idea what it was, and examined the glass where of course nothing was found wrong. Research showed me that it was in fact a pistol shrimp. I heard him (her?) many times, but try as I might, night or day, I never ever got a glimpse of the creature. I didn’t make any attempt to catch it as no harm was being done. Obviously prey of some kind was being caught, but the populations of tiny life in the rocks didn’t seem to diminish.

So if there is a sudden startling ‘crack’ it doesn’t necessarily mean that water is escaping through a new leak in the aquarium glass. It could just be a pistol shrimp obtaining a meal.

(*Ref: Marine Atlas. Helmut Debelius & Hans A Baensch)

Here is an interesting video which was located on You Tube. It’s very good so I recommend you watch it.

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Tags: aquarium, Invertebrates, mantis shrimp, reef-tank, saltwater-aquarium, shrimps