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.