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Aquatic Invertebrates in the Freshwater Aquarium
By Andrew Pollock
Shrimp are decapods or 10 limbed crustaceans along with crayfish, cherax crabs and others. Historically only really crayfish were kept, in the last 10-15 years shrimp and other crustaceans have become increasingly popular in home aquaria. This article will try to give an overview on owning, keeping and breeding of the dwarf freshwater shrimp, fan handed shrimp and longarmed shrimp as well as the dwarf crayfish. Although not precise the term "shrimp" will be primarily used to cover all of these. Because of the wide number of decapods being covered generalisations will occur and more specific details should be sought once a choice of inhabitant has been choosen.
The different types of Decapods covered include:
1. The algae eaters mainly from the neocardina and cardinia species: these are collectively referred to as the dwarf shrimp.
2. Long-armed or macrobrachium which are opportunistic hunters and so have different requirements as far as tank mates and raising of young
3. The fan shrimp or atya, atyoides and atyoida species which can be quite large and are generally peaceful, should generally be housed in groups. They are named after the specialised adaptations to their first appendages which have developed to sieve the water and fan particles toward there mouths. they need good circulation and suspended bacteria/microorganisms to feed on often near a filter return or perched on some ornament
4. Dwarf crayfish (need to check legality of english keeping) which are as they say smaller peaceful version of their larger cousins. Most of this group come from the Cambarellus group. Procambarus crayfish are much larger.
Inhabitants: A species-only tank is best, unfortunately many new keepers wish to have them as part of a community often because we have only one tank and want as much variety and interest as possible. The shrimp suffer and often hide from the fish in this type of situation, depriving us of the most enjoyment and depriving the shrimp of the most suitable habitat. With the long armed shrimp being predators and often consuming protein, other fish, shrimps and even snails will be taken at times dependant on the particular species. Again a species only tank is therefore best for separate reasons with these. The dwarf crayfish although generally peaceful, can even be harmful to each other with males to male aggression being more likely and again is most suited to a species only tank. There will always be reports of successfully keeping varied combinations of shrimp, crayfish, fish, etc. and it is not for me to say that these combinations will not work in individual situations. It is important just bear in mind the basic guidelines and decide what is more important to you which is hopefully your inhabitants health and welfare.
Water requirements: For the majority of shrimp a neutral and medium hardness water is generally suitable. Some species of shrimp do have preference's for slightly acidic or moderately alkaline waters though a range of 6.5 to 7.5 pH and hardness levels around 10 gH are adequate starting points in most case's. Once deciding on a specific species it would be advisable to research further it's exact water requirements. You can easily check the species requirements for shrimp and crayfish by visiting each respective species information page. Check out the Shrimp Species Page and Crayfish Species Page for a list of all species.
When changing water it is important to try and match the new water with the old water in respect to temperature and hardness or tds readings. I find this more important with shrimp than with fish. Most important in water is ensuring that chlorine, chloramine and heavy metals are removed with dechlorinators prior to adding to the tank. With their increased sensitivity to heavy metals shrimp are more susceptible to leached ions from hot water systems in which water contact with copper pipes is longer. It is highly recommended not to use any hot tap water when performing water changes. If the water from the tap is too cold please read the article Changing Water in the Winter for detailed information on how to overcome the difficulty with changing water when the tap is too cold.
Tank Floor Space: Is probably more important than actual tank volume and shrimp can be kept in very small containers successfully. Just remember it is easier to keep water parameters stable in larger tanks and i wouldn't advise anything smaller than 25 litres (6.5 gallons). Hiding places should be provided either with foliage, rockwork or ornaments. This is particularly important in the dwarf crayfish species as they can be quite vulnerable whilst molting.
Filters: Basic air driven sponges are generally the most suitable methods of filtration for shrimp only tanks. if you have a larger tank and want a more powerful pump then an intake sponge is going to be needed. In order to stop shrimp being sucked into the filter you will need to protect the filter intake. Certainly the shrimp will happily climb on the intake and look safe but they can and will find a way into the filter intself. I will often find shrimp alive in the filter when cleaning a canister filter that does not have a sponge pre-filter on the intake. When more circulation is needed because of higher plant levels, or for providing current to the fan handed shrimp, then larger powerheads or canister pumps are required and yet again sponges are important with these. You must to protect the intakes in order to prevent your shrimp from being chopped apart.
Temperature Requirements: Around 20 celsius (68F) is generally achievable in most homes without heating of the tank. Your local geography and enviroment obviously have a huge bearing on this. If your water falls below 20c then it maybe better to have a heater in the tank (i have had shrimp survive over winter outdoors but that is not recommended). Equally for those in warmer climates chillers or fan cooling is often required. Fluctuations in temperature of the tank, if slight, may actually be beneficial to survival and longevity of the shrimp. You can easily check the species requirements for shrimp and crayfish by visiting each respective species information page. Check out the Shrimp Species Page and Crayfish Species Page for a list of all species.
Lids: Some shrimp will climb and can survive short periods out of water especially if unhappy with their enviroment, water quality or tank mates. It is highly recommended that lids are used on tanks to stop accidental losses to dessication, or drying out, on the floor. Equally, attempts to leave a tank should alert the keeper to an issue within the shrimps enviroment that is less than ideal.
Aquatic Plants: Simple aquatic plants are probably best suited to these tanks. Low maintenance and ease of growth allows the shrimp to still find algae and other biofilms on which to graze. High maintenance algae free fertilised tanks are a much more difficult area in which to successfully maintain shrimp, high plant growth will compete with biofilm and algae production and reduce natural shrimp food sources. There is some thought that fertilisers can be toxic to shrimp at higher levels notably copper. Carbon dioxide addition to planted tanks is another contentious issue as far as shrimp health. My experiences have been that i can keep shrimp alive in tanks with carbon dioxide injected and as yet i have not seen breeding activity, equally when carbon dioxide levels elevate shrimp activity seems to slow. My preffered shrimp setups include moderate light no water column fertilisation (enriched substrates are ok) and no carbon dioxide additons.
Compatible Tankmates for Shrimp: There are some compatible tankmates for shrimp. Some other species of shrimp, fish with specialised feeding mouths i.e. otocinclus cory's and ancistrus or other small plecs and some of the specialised surface feeding fish. Any larger fish will frighten shrimp whether predating or not. Obviously depending on what you initially want and size of tank, choices may vary from many varieties of dwarf shrimp with the biggest concern being cross breeding of the various species to breeding tanks of dwarf crayfish in which only females maybe held with the male introduced for short breeding periods. Please read the article Will These Shrimp Interbreed for more information on possible interbreeding and hybridization.
Most aquarium shrimp strains are chosen for there high coloration. This is an exaggerated trait that reduces the shrimps camouflage abilities and tends to make them more interesting to most fish. I can not stress enough the importance of not keeping fish and shrimp together. Basically any fish that can fit a shrimp in it's mouth will most likely eat a shrimp. Once fish associate the shrimp with food they will quickly hunt down all shrimp in a tank, the exceptions previously listed are not inclined to do this and exceptions exist to almost any rule. Please read the article Safe Tankmates for Shrimp for more information on potential tankmates.
If you intend to breed shrimp then no fish is best as baby shrimp are so small that they will inevitably be eaten by even the most mild mannered of fish. Just think baby brine shrimp are one of the most popular foods for fish breeders. Even shrimp will consume dead and sick cohabitants , small dwarf crayfish have been recorded to predate dwarf shrimp and it goes without saying that the longarmed shrimp will predate or pick off small sick and sleeping fish and shrimps.
Dwarf shrimp often can be sexed by body shape(females have extended what are the shell pieces (pleura) called on the tail region for assisting in carriage of egg's, males are slimmer and prehaps less coloured. Males will often have longer antennae- more pronounced on the second smaller pair of antennae. Though in certain species this is not so easy and the most correct biological way is to actually look for the genital openings beneath the shrimps the female opening is located on the 6th body segement whilst the males is between the 6th and 8th (not much use ina 2-3cm shrimp i know).
In macrobrachium the size of the clawed first appendage is usally the easiest way to tell male from female with males having the larger claws, commonly there is a signifcant body size difference in fully grown specimens as well.
Fan handed shrimp tend to have larger first walking leg's in male shrimp and the extension of the carapace or pleura ventrally to assist in egg carriage.
In the dwarf crayfish external genital differences are visible beneath the tail where the first pleopod shows specialised adaptions.
Of interest is the recording of partial hermaphroditic changes in most decapods and certainly the farmed interest in single sex (males grow faster and thought to be economically more profitale) rearing via androgenic hormone manipulation.
Two different ways all shrimp produce egg's in the ovaries which can often be seen developing through the shell on the back and just behind the head, at moulting these egg's. If mating has occurred the unfertilized eggs pass down and through the genital opening (where sperm has been deposited at mating) to be fertilised and held on the swimmerrettes or pleopods under the tail of the female.
Most dwarf shrimp take about 3-4 weeks for these egg's to hatch, if you see a shrimp carrying egg's under the tail they are almost always fertilised.
1. Some shrimp produce fully developed miniature versions of adult shrimp
2. Others produce a planktonic life stage (zoea) which is free floating and swimming. This planktonic breeding cycle requires an increase in salinity and smaller suspended particulate foods to develop to the juvenile stage.
There is currently very limited detail on invertebrate disease. With the increasing popularity of shrimp in aquaria this may change.
At present most research has been focussed on food producing species, which are not covered in this article, such as the larger decapods prawns, crayfish, yabbies, lobsters (some detailed articles on disease in farmed shrimp can be found at the food and sgriculture organisation of the United Nations web site: www.fao.org )
Good water quality and correct environment are obviously important in maintaining the health of your shrimp, as with fish many illness are attributable to failure to provide appropriate conditions. Certain medicinal products are known toxic to invertebrates , copper, acriflavine, organophosphates. Whilst others are suitably safe ie formalin, malachite green, and many antibacterials
At present i have only experienced 2 disease scenario's: Ffungusing of egg's whist being carried and sometimes secondary infection of the shrimps shell. This in my experience has been cleared when the shrimp shed without any specific treatment. Another I have experienced is a general opaque or translucency developing in shrimps body. I am unsure whether this is just a failure of osmotic controls and a non specific pre death change that is seen in more than one particular illness or an actual specific disease. I would be inclined to guess the former
Shell Disease in Crayfish: These can be regenerated at the next moult though it will take a few moults to regain full size. In farmed crustacean a shell disease is commonly noticed , this is primarily a secondary bacterial infection in damaged carapace area's. Much akin to fin rot in fish, many different bacteria have been implicated. Improved husbandry and water quality should control this and cure is often seen after a moult. Crayfish plaque caused by a fungus 'aphanomyces' infecting the soft non calcified body parts perhaps similar to what i have encountered in shrimp. Porcelain disease of Australian crayfish due to a microsporean infection, thelonia, there is no known treatment for this at present other than removal of affected individuals. A small flatworm, temnocephalan, usually none pathogenic and can be cleared by saline baths. An encysted worm larva , where the crustaceans are thought to be an intermediate host is also recorded. Again from farmed lobster species a protozoan parasite is known to cause sudden deaths, paramoeba, it attacks the nervous system leading to paralysis and death usually within a 24 hr period - aka limp lobster syndrome. Aaeroccocus a gram positive bacteria can cause reddening of the ventral abdomen, mortality is higher at high temperatures, at present i can fins no recorded antibacterial treatment success's