The Complete Aquarium Guide - Part 4

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The Complete Aquarium Guide - Part 4

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The invertebrates, as their name indicates, have no backbone. Their body is soft, but it is protected on the outside, by a carapace in the case of the crustaceans, or by a shell in mollusks, or it is supported by an internal calcareous skeleton, as in corals

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  1. THE MAIN INVERTEBRATE GROUPS T he invertebrates, as their name indicates, have no backbone. Their body is soft, but it is protected on the outside, by a carapace in the case of the crustaceans, or by a shell in mollusks, or it is supported by an internal calcareous skeleton, as in corals. Although they are considered less evolved animals than the vertebrates - the group to which fish belong - invertebrates sometimes adapt in surprising ways to ensure their survival. The crustaceans, for example, can walk or swim to look for food or flee an enemy, while corals and anemones unfurl to capture microparticles, such as plankton, in open water, or retract to escape their predators. SPONGES COELENTERATES These animals, slightly more evolved than sponges, were also classed as vegetables for many years; even now the term animal-flowers is used to describe them. The Coelenterates comprise medusas ("jellyfish") - rarely seen in aquariums, apart from a few public ones - and the Anthozoa, which include anemones and corals, some of which are found in aquariums. Up until the 19th century, naturalists hesitated when classi- fying sponges: animal or vegetable? It must be admitted, however, that their field of research was extensive, as there are around 10,000 species of sponges. These very old animals were among the first to appear on earth or, more exactly, in the sea. Freshwater species are rare and are not found in aquariums, but some marine species can be kept in captivity. WORMS Worms are barely evolved soft-bodied animals. They are more common in aquariums as live food than as resi- dents, but are never found in fresh- water aquariums. A few specific species can be kept in captivity in sea water. They live in a tube and are often sedentary. The col- oring of worms can vary enormously, but they are usually blue or purple, flecked with white, and almost always bicolor.
  2. MOLLUSKS Their limp body is protected by a shell, which has two parts - these are the bivalves - or a single part - as in the case of :he gastropods. The bivalves half-open their shell - formed, as their name suggests, by two valves - to filter water. In this way they absorb oxygen and capture food particles, particularly vege- tal plankton. Keeping them in an aquarium does not, there- fore, pose any problems. The gastropods, related to land snails, have a spiraled shell which varies in shape, according to the species. An organ in the mouth in the form of a grater, the radula, allows them to graze micro-algae on the decor, glass sides, or plants. This cleaning function constitutes their main attraction for aquar- ists. Do not, however, expect them to gobble up all your unwanted algae, as they play a more preventive role to restrict their untimely growth. They can sometimes attack the leaves of plants or eat a surplus of the food intended for fish. Some species are carnivorous. CRUSTACEANS ECHINODERMS The crustaceans' bodies are protected by an articulated These possess a symmetry based on five, which is extremely carapace. The animal abandons its carapace when it rare in nature, as most animals have a binary symmetry, becomes too small due to body growth; this phenomenon is meaning that, if they are cut down the middle, two identi- called the molt. The crustacean is particularly vulnerable to cal parts can be observed. This is not possible with echino- attacks from predators during the formation of the new derms, because they have to be cut into five sections to carapace. The crustaceans found in aquariums belong to the obtain identical pieces. Echinoderm means spiny skin: this is decapod group, which have five pairs of walking legs, the highly appropriate in the case of sea urchins, less so in rela- first of which are used as pincers, with varying degrees of tion to the rough starfish. Generally speaking, echinoderms strength. The two pairs of antennae, highly developed in will not survive for long outside water. They are found only shrimps, play a tactile and sensory role. Crustaceans are car- in sea water. nivorous, and can feed on live or dead prey - they are not difficult to feed in an aquarium.
  3. FRESHWATER INVERTEBRATES Although freshwater invertebrates play a significant ecological role in their natural habitat, they are not popular with aquarists, and this is a great shame. They are represented by two main groups: the mollusks and the crustaceans. MOLLUSKS CRUSTACEANS Bivalves commonly known as freshwater In freshwater tanks, these are mainly repre- mussels can be found in some tropical sented by several species of shrimps, waters. Although they differ as regards their although it is occasionally possible to find a anatomy, they are in fact distant cousins of tropical crawfish, and even small crabs. As the mussels on our coasts. They live buried, crustaceans' carapaces mainly consist of or partially buried, in the sediment. They eat calcium carbonate (CaCO3), it is advisable by filtering micro-algae or vegetal plankton to keep them in hard water, and some dissolved in the water. This can be a useful crabs can even live in brackish water. Car- attribute in an aquarium, as it helps contain nivorous fish are obviously out of the ques- the proliferation of this type of algae. On tion as roommates. Small species of fish are the other hand, if there is not enough food, not normally at risk from crustaceans, but a they will eventually die - which is not weakened or sick fish may be captured and always noticeable at first, and therefore devoured. Crustaceans' role in the wild as entails a risk of pollu- environmental regulators can be repro- tion from their dead duced in captivity. bodies lingering in the Whatever species you may choose, all crus- water. Bivalves there- taceans feel more at home if they are pro- fore have a somewhat limited appeal to fish- keepers, especially as few tropical species are available in the aquarium trade. As regards the gas- tropods, some species are considered pests - physas, for instance - while others, such as the Planorbidae, Am- pullaria, and Malay- sian snails, play a positive ecological Shrimps from the Macrobrachium genus are role, above all by becoming increasingly common in freshwater feeding on unwanted aquariums. • Ampullaria sp., algae. In good conditions, they proliferate like this golden rapidly; they can be removed by hand or vided with shelters, especially during the variety, are one of by trapping them with a leaf of lettuce or molt. If they are fed properly, this process the most effective boiled spinach: if you put one of these in gastropods against will occur regularly, but the animal is vul- algae. a tank at night, the next morning it will be nerable while it is forming a new carapace. covered in snails. If a population of gas- It is during this critical period in their life- tropods disappears from an aquarium, this cycle that crustaceans usually attack each is probably a sign of imbalance. other. 166
  4. MARINE INVERTEBRATES Marine invertebrates are sometimes more difficult to keep in an aquarium: on the one hand, they are very sensitive to the quality of the water, which must be as faultless as possible, and, on the other, feeding them is complicated, particularly in the case of sponges, Coelenterates, anemones, and corals. It is also important to consider the compatibility of invertebrates, not only with each other but also with fish — as invertebrates are the favorite meal of some fish! For all these reasons, the best option is a 400-500 liters is the absolute minimum for specialist tank, which will provide a spec- a tank containing several species of inver- tacle just as fascinating as that of a fish tebrates. A maximum height of 50 cm is Mounting a tank aquarium, although those fish which can recommended to allow the light to pene- almost entirely cohabit with invertebrates represent a log- trate, as well as making it easier for the composed of ical complement to this type of aquarium. aquarist to intervene. It makes sense any- invertebrates, with a few fish added, The invertebrates which are most robust way to install as large a tank as possible, requires ample and easiest to acclimatize can reproduce in as your enthusiasm for these creatures is knowledge of captivity (especially some species of bound to grow. these animals. • anemones), but success in this area requires a solid background in marine aquariums on the part of the hobbyist. Nevertheless, some marine aquarists hesitate to cross the threshold from fish to invertebrates, on the grounds both of cost and risk. However, these days there is a craze for this type of aquarium, but you must not get carried away: it is not feasible to reconstitute a coral reef, although it is possible to achieve satisfy- ing results, both in terms of ecological equilibrium and an engrossing spectacle. GENERAL MAINTENANCE CONDITIONS The aquarium The bigger it is, the easier it is to acclimatize the invertebrates. Do not con- sider a tank of under 300 liters for a medium-sized anemone, accompanied by its clown fish. A volume of 167
  5. INVERTEBRATES LOWERING THE PH IN A Light MARINE INVERTEBRATE TANK This is extremely important, both as regards quantity and quality. Apart from The pH in a coral tank sometimes undergoes the aesthetic effect, lighting serves to slight but regular decreases. When it enhance the development of Zooxanthel- drops to under 8.3, it can be raised lae, the micro-algae which live in the ani- with sodium carbonate. Dissolve mals' tissues and contribute to their 5 g in 1 liter of water, and add equilibrium. 1 ml of this solution to each If the water is less than 50 cm deep, use liter of clean water. This pro- fluorescent tubes as day lighting, in con- cess is repeated every day junction with a blue tube. Deeper water until a pH of 8.3 is obtained. requires powerful HQI lamps, again com- There are also some ready- bined with a blue tube. The lighting must to-use solutions for this be strong (around 1 W per liter of water) purpose available in the and should be left on for about 13 hours aquarium trade. every day. UV lamps are not recom- mended for invertebrates. More detailed information on lighting can • Easy-to- be found in the chapter Equipment and use tests Accessories (page 226). make it possible to control water Water quality, which This must be stirred vigorously: use a The substrate must be perfect in pump with an outflow equal to at least Fine-grained soils are to be avoided, a size an invertebrate five times, and up to ten times, that of the of 2-5 mm being perfect. The bed must be tank. volume of the aquarium. Do not forget calcareous and comprise sand made from that the water in an invertebrate tank will corals and marine algae, which can be never be as agitated as in a natural setting. complemented by crushed oyster shells to The water must be very clear, to facilitate guarantee a moderate supply of calcium the penetration of light. It is therefore vital carbonate. to have good mechanical filtration, possi- bly in conjunction with an air pump. Invertebrates are extremely sensitive to nitrates (NO3-). A box filter is indispensable, and its vol- ume must equal at least 10% that of the aquarium. It must be pointed out, however, that tanks containing true corals, or madreporites, which form reefs can some- times work well without this type of filter. In order to facilitate the operation and reduce the burden of the filter, thus increasing its efficacy, put the protein • The substrate in marine tanks consists of coral skimmer in its first section. As a comple- elements in fairly large grains. ment to these techniques, you are strongly advised to perform partial water changes, at a rate of around 10% of the volume, once a week. It is advisable to change the water the day after the weekly feeding session, as this will help to reduce pollution. The specific gravity of the water must be around 1.024, although it can go up to 1.026. 168
  6. MARINE INVERTEBRATES ZOOXANTHELLAE These are green micro-algae which live in the skin of Anthozoa and other organisms, such as sponges or giant clams, a type of bivalve mollusk. They exchange substances with the cells of their hosts. The carbon dioxide (CO2) resulting from the metabolism of the cells - i.e. the oxidation of the foodstuffs - is collected by the Zooxanthellae. These, in their turn, absorb nitrogenous and phosphorous substances, carry out photosynthesis, and produce organic substances that enhance both their own growth and that of their host. This type of mutually beneficial association taking place inside an animal is known as endosymbiosis. The Zooxanthellae contribute, to some extent, to the feeding process of Anthozoa, which there- fore need only a very scanty external supply of nutrients: some organisms, such as the anemones, need to be fed only around once a week in an aquarium. • The green coloring of this Anthozoa indicates the presence of a significant number of Zooxanthellae: this animal must therefore be placed under fairly intense lighting. The decor Caulerpa This serves as a support for some animals. prolifera is a common alga in Create an aquascape in tiers or with steps, marine and place the species on it according to invertebrate tanks. their need for light. This is easy to do with artificial materials, and the decor can be finished off with dead coral and rocks. 169
  7. INVERTEBRATES tank is recommended. When handling invertebrates, be aware of the stinging capability of some species (such as anemones and madreporites). SPONGES Sponges enjoy shadows or darkness as they can only tolerate a small amount of light. They do not like water with a high content of nitrates or filamentous algae, which smother them. They reproduce, either sexually - rarely achieved in an aquarium - or through asexual division, with a detached piece of sponge evolving into a new specimen. A sponge is a kind of "sack" devoid of any specialized organs. Water penetrates the walls, circulates in the canals, as a result of the movements of thousands of strands protecting the cells, and leaves via the opening in the top. The water provides oxygen and the particles on which the sponge feeds, particularly the micro-algae of phytoplankton. Removing a sponge from water has fatal consequences, as air bubbles enter the canals where the water circulates and block them. The sponge, unable to elimi- • When well Vegetation nate the bubbles, eventually dies. acclimatized, the Plants release substances that have a ben- Sponges are fed in the same way as Coe- Coelenterates lenterates, with a preparation based on soon deploy their eficial effect on invertebrates, although as tentacles, which is yet we still know relatively little about the mussels, or special liquids available com- a sign of good mechanism of this process. mercially from specialist suppliers. health. Use algae of the Caulerpa genus, but do not allow them to become too dense. In addition, remain on the lookout for the COELENTERATES growth of certain filamentous algae, as The Coelenterates constitute a complex there is a danger that they might smother group (see table, page 171). They include some sponges and delicate Coelenterates. the Anthozoa, which are divided into hexacorals, where the number of tentacles Acclimatizing invertebrates is a multiple of 6, and octocorals, where As the characteristics of invertebrates' the number of tentacles is a multiple of 8. native waters are radically different from The hexacorals are divided into: those of the tank in which they will be - Actiniaria (true anemones); placed, great care must be taken with - Ceriantharia; respect to their acclimatization. The con- - Zoantharia (colonial anemones); tainer in which the new arrival has been - Corallimorpharia (discus anemones); transported must be gradually filled with - Scleractinia (madreporites or true water from its future aquarium, to enable corals). the invertebrate to slowly adapt before it These invertebrates are characterized by is carefully transferred into its new habi- tentacles attached to a foot, and the whole tat. The whole process takes about 1 hour. organism is called a polyp. Anemones and A quarantine period in an acclimatization Ceriantharia are isolated polyps, while 170
  8. MARINE INVERTEBRATES the other Anthozoa are colonial polyps, WHAT IF YOU TOUCH A COELENTERATE? connected to each other at their base, which end up by spreading out over large Some species have a greater stinging capability than others. Serious areas like certain plants. reactions, such as cramps or breathing difficulties, rarely encoun- tered among aquarists, can be provoked by certain medusas (jelly- Darts for defense fish), due to a phenomenon known as anaphylaxis: the body is sen- The bodies of Coelenterates, particularly sitized to the venom after an initial contact and becomes more vul- nerable. In the event of an accident, detach the tentacles and, above the tentacles, are covered with urticant all, do not rub your eyes. Treat the stung area immediately with (stinging) cells, equipped with a strand diluted ammonia, but it is best to consult a doctor. that is sensitive to contact with other organisms. When a Coelenterate is touched, thousands or even millions of cells open and eject a filament with a microscopic dart at the tip which injects venom; in this way, a prey is quickly par- alyzed before being eaten. Care should be taken when handling, therefore. Introducing Coelenterates to an aquarium Coelenterates must of course present all the necessary signs of good health before being introduced to an aquarium: they should be unfurled, swollen, and full of water. If they are in a bad state, they look wilted and may not be viable. Anthozoa like clear and well-lit water, as it benefits both them and the Zooxanthel- lae to which they play host. They must be placed close to the surface of the aquar- ium. The water quality is, of course, very important, and in addition the calcium
  9. INVERTEBRATES levels must be monitored with particularly tralia for almost 2,000 km. It is the biggest close attention. structure of animal origin in the world! The skeleton of corals is mainly com- This ecosystem, one of the richest and posed of calcium carbonate, which is most diverse in existence, is also fragile abundant in the natural habitat - up to and constantly subject to attack. The last 500 mg/liter - and so an aquarium that is few decades have witnessed the destruc- to be inhabited by corals must also have tion of some reefs, the coral being used to the same level. build houses, roads, and even airport run- The concentration in an aquarium can ways! Obviously, aquarists have been sometimes fall below 300 mg/liter, accused of taking part in this pillage, depending on how many organisms there which seems grossly exaggerated: the are in the tank, and in these cases calcium removal of corals from their natural habi- must be added. Several relatively simple tat for the aquarium trade does occur, but methods for raising the calcium level are it is negligible compared to other large- detailed in the box on page 173. scale extractions. Furthermore, some Certain species of species are protected by law and never fish and marine Coral reefs reach hobbyists' tanks. invertebrates The accumulation of calcareous coral Public marine aquariums can, on the con- found in trary, make a contribution to the study of aquariums come skeletons gradually forms reefs, of which from coral reefs. the most famous is the Great Barrier Reef, invertebrates. The aquarium of the stretching north-eastward from south Aus- Monaco Oceanographic Museum, for W H E N MUST CALCIUM BE ADDED? Calcium is added when the concentrated measured is less than 400 mg/liter. There are tests on the market to measure the quantity of this parameter. Remember that the mea- surement of CH, in sea water, reveals the quantity of carbonates and bicarbonates. When this is less than 7°CH (128 ppm), it can be concluded that a lack of calcium car- bonate is more than likely and steps should be taken to remedy this. 172
  10. MARINE INVERTEBRATES H O W TO SUPPLY CALCIUM TO A CORAL AQUARIUM Method 1 From the start, i.e. when you put the first water in, use com- mercial salts enriched in calcium. Then, add the same salts over the course of regular partial water changes, at the rate of 10% per week. Some commercial salts are specially designed for marine invertebrates. • Method 2 When adding Use commercial products specially prepared to increase calcium, the pH value must not calcium levels. rise above 8.5, Method 3 regular control is Place a calcareous element, such as calcareous rock, or crushed and washed oyster necessary. shells, in the filter, and this will gradually release calcium. However, this method will not give rise to any rapid or significant increase in calcium levels. Method 4 Prepare a solution of slaked lime, Ca (OH)2, available in aquarium stores, at a rate of 1.5 g/liter. Pour in 1 ml of this solution per liter of sea water. Proceed gradually, monitoring the pH constantly to ensure it does not rise above 8.5. Method 5 This is the most complicated, but also the most effective. Prepare two solutions: - one of dehydrated calcium chloride (CaCI2, 2H2O) at a rate of 15 g/liter, which will provide the calcium; - the other of sodium bicarbonate (NaHCO3), at a rate of 17 g/liter, which will pro- vide the carbonates. Then calculate the difference between a carbonate hardness of 130 ppm (7.2°CH) and the one measured in the aquarium. Multiply the result by the net volume of the tank, and divide the result by 10. This will give the amount of each solution required, in milliliters, to pour into the aquarium. Example: for a tank with a net volume of 500 liters, with a carbonate hardness of 100 ppm (5.6°CH), the result is: Amount of each solution (in ml) = 500 x (130-100) + 10 = 1,500 ml. The following table gives you the required amount of each solution (in ml) for specific cases. 173
  11. INVERTEBRATES Feeding Coelenterates By filtering the water, the Coelenterates trap small suspended particles, particu- larly the crustacean zooplankton. Collect- ing, keeping, and distributing plankton is not a task to be taken lightly, and it is best to look for other solutions. However, it must be made clear that com- mercial foods on the market provide little more than a stopgap. It is possible to use rotifers or freshly hatched brine shrimp nauplii, normally used as the main food for fish, but not everybody breeds these animals. There is another food which is available to all hob- • The leather example, is carrying out research in this byists, as it is inexpensive, easy to make, corals of the field, using a 40 m3 tank containing several and can be frozen: it is usually called mus- Sarcophyton genus sel choppy. Mussels are not only cheap will not tolerate tons of corals, which are nurtured and being dose to bred. Until recently, raising corals on this but also rich in proteins, carbohydrates, Coelenterates scale in captivity was impossible, above all mineral salts, and vitamins. Other possi- highly prone to because of their very great sensitivity to stinging. nitrates (NO3-). Scientists solved this prob- lem by allowing these nitrates to turn into nitrogen gas (N2), thanks to the anaerobic bacteria which survive at the bottom of the tank, where the oxygen levels are low. In their natural habitat, The nitrogen produced by the metabolism Coelenterates feed of these bacteria then passes into the on animal atmosphere. plankton, but these are difficult This complicated technique is beyond the to supply in an reach of most aquarists, however experi- aquarium. • enced they may be. FOOD FOR SPONGES AND COELENTERATES: A RECIPE Ingredients: - mussels or cockles; - white fish, i.e. lean and free of lipids; - shelled shrimps in cans (optional). Cook the mollusks and fish. Put the shrimps in boiling water for 1-2 minutes. Remove the mollusks' shells. Mix all the ingredients thoroughly. You can add a vitamin solution, flakes or granules of fish food, boiled spinach, or the special foods for invertebrates available commercially. If the paste is too thick after mixing, thin it with sea water. Pass the mixture through a sieve. What is left behind in the sieve can be distributed to anemones or small fish; this puree can also be frozen. Allow the puree to stand for several hours in the refrig- erator, then discard any excess water. The resulting paste can be used straightaway for feeding, or can be frozen. It is best to put the food into the aquarium at night, 1 or 2 hours before switching off the lights. Switch off the filters, pumps, and aeration for a moment. Thaw the food, if necessary, and distribute the equivalent of one tablespoon of the prepared liquid for every 200 liters of water. Deposit the food above the invertebrates with a narrow, rigid tube. The filtration and aeration systems can be switched back on a few minutes afterwards. 174
  12. MARINE INVERTEBRATES The Coelenterates can cohabit with algae - encrusting or otherwise - and even with small fish. bilities are cockles, the flesh of lean fish, introduction of certain fish is possible, or cans of shelled shrimps, which are pro- even desirable, but there are cases of clas- duced in large quantities in Asia, cost lit- sic incompatibilities (see table, page 178). tle, and are readily available. Specially designed artificial decor can be The other problem is establishing a feed- colonized quickly, depending on the ing schedule. It must be remembered that organisms' rate of growth and reproduc- the majority of organisms being fed play tion. This can sometimes make it difficult host to Zooxanthellae, which often satisfy for even a practiced eye to spot the dif- a significant proportion of their dietary ference between artificial and natural needs, and so a weekly feed is more than decor in an aquarium which has been in sufficient. Do not forget that the best time operation for several months. for this is the night before a water change, to reduce the risk of pollution. The larger anemones feed on adult brine WORMS shrimps, small pieces of mussel, fish, or Some species belonging to the Annelida, a shrimps or a mixture of these. group that includes the sea worms used as bait in fishing, live in a tube which they Compatibility between Coelenterates build themselves: these are known as Urticant (stinging) Coelenterates must be kept apart from the more delicate species: a safety margin of 10-15 cm is often rec- ommended. The madreporites and anemones are among the most urticant, and they must not be put alongside a In an invertebrate tank leather coral from the Sarcophyton genus, the development for example. Other alternatives for a Coe- of algae must be lenterates tank are algae - whether restrained, so that encrusting or not - supported by live they do not smother the rocks, or even caulerpae. Their develop- Coelenterates (left, ment must be controlled so that they do a Cerianthus). not end up smothering the Anthozoa. The 175
  13. INVERTEBRATES cowries, well known to collectors of shells, can be kept in captivity. Some fish may nibble the "mantle", the part of the animal's body used outside the shell. Of course, in the event of any danger the animal retreats into its shell. Hobbyists enchanted by the beauty of this shell can put a specimen in a tank containing small Pacific fish (Gobiids, Blenniids, Grammids. Pseudochromis, for example). In the bivalve group there is the famous giant clam, which can sometimes grow up to a length of 1 m in the wild, where it feeds on vegetal plankton. Some smaller species can be acclimatized in an aquarium. However, these animals are only recommended for • This cowry has experienced hobbyists. withdrawn its sedentary Annelida. The brightly colored mantle into its branchial plume which sticks out of it traps shell. oxygen, as well as the organisms which CRUSTACEANS make up zooplankton. At the sign of any It is easy to keep a few species in a danger, or if the tank or its support are marine aquarium, to take advantage of knocked, this branchial plume retreats into their bright colors. These invertebrates are its tube. The feeding of Annelida in cap- carnivorous: in an aquarium they should tivity is identical to that of Coelenterates. be fed on mussels, fish, or white meat. When you buy one, make sure that the branchial plume is func- tioning correctly and its tube is intact. It is best to buy a worm fixed to a piece of rock. MOLLUSKS Few mollusks are found in Shrimps play an aquariums, and they are not ecological role by feeding on fishes' often available commercially. leftovers. Among the gastropods, the • Hermit crabs are highly striking invertebrates which run around the aquarium in all directions to look for their food. They withdraw into their shell when frightened. Shrimps These rarely swim and prefer to get about by walking on the decor. If they are dis- turbed they abruptly recoil by tucking up their abdomen. Several specimens can live together, but it is vital to keep them away from carnivorous fish. 176
  14. MARINE INVERTEBRATES food or a sucker. The latter allows sea urchins to develop on rigid supports or the glass sides of the tank. Starfish These are not recom- mended for a marine invertebrate tank, as they attack other species, such as sponges. Starfish are in fact either carnivo- rous, gripping their • Enomotoplus sp., the lobster crab, related to the prey with their long langoustine, is an attractive and placid resident. arms that emerge from a central disc, or Crabs microphages, in The small abdomen is tucked under the which case they feed lower part of the body. Their pincers are on small organisms particularly well developed. The larger on the bed. specimens, which can be aggressive, must The ophiuroids, sometimes called brittle- Some species not be put into marine aquariums, as they stars and closely related to starfish, have of sea urchins with can attack other invertebrates, and some- articulated arms which allow them to varying sizes of prickles can be times even fish. move around quite quickly. These arms, found in marine like those of the starfish, can regenerate aquariums. Pagurids themselves if they break off. These are better known as hermit crabs. Some tropical species can be found com- mercially, some of them bearing a small "LIVE ROCKS" anemone on the gastropod shell which These are pieces of rock or fragments of houses them. The shell is discarded when dead coral (madreporites), that are bound it becomes too small for the growing ani- together by calcareous rocks or various mal, so it is vital to provide bigger ones, pieces of debris from invertebrates. They as, unlike other crustaceans, a pagurid's abdomen is not protected by a carapace that it makes itself. ECHINODERMS Sea urchins These are not very easy species to accli- matize. It is possible to keep one small specimen at most, which will often live away from the light. They are herbivores that sift the substrate looking for algae to eat. In among the prickles it is possible to see the articulated pedicellariae, which end either in a tiny pincer for trapping "Live rocks" are covered with many small organisms (worms, Coelenterates) which would be difficult to introduce into an aquarium in any other way. • 177
  15. INVERTEBRATES are sometimes removed from their natural COMPATIBILITY BETWEEN setting and sold commercially. "Live INVERTEBRATES AND MARINE rocks" harbor various organisms: bacteria, FISH algae, sponges, small Coelenterates, and sometimes even small crustaceans, hidden Invertebrates cannot cohabit with just any in crevices. They can therefore be consid- fish, for a number of reasons. The first is ered as living pieces of decor which con- that they are liable to become prey for tribute to the equilibrium of the aquarium. carnivorous fish. Coelenterates are com- If, before sale, they have been suitably pletely incompatible with angelfish transported, cared for, and housed, then (Pomacanthids), for example. Secondly, they are worth acquiring, despite their some lively and active fish, of over 10-15 high price, as they permit the introduction cm in length, can jostle and disturb inver- of a variety of beneficial organisms into tebrates in the aquarium. the aquarium, in the most "natural" way Furthermore, the bigger and more active a possible. fish, the more it excretes nitrogenous sub- Another option is to collect these types of stances, leading to the accumulation of rock yourself, off the shores of Florida, for nitrates (NO3-), which are harmful to example. Organisms capable of surviving invertebrates. It is therefore best to avoid in a tropical tank grow there in summer, the presence of this type of fish. Too when the water temperature is higher. many fish produce the same result and the There is always a chance, however, of same degree of harm for invertebrates. introducing an undesirable organism or of Finally, there is another problem when a finding that some residents of the "live sick fish has to be treated, particularly rock" deteriorate and die, with an ensuing with substances containing metals, which risk of pollution. It is therefore best to are toxic for most invertebrates. Remem- proceed with caution and isolate the rock ber that it is always preferable to nurse a in a quarantine aquarium. fish in a hospital aquarium. 178
  16. INVERTEBRATES These days, more and more aquarists seem to be taking an interest in these animals. Ecologically speaking, invertebrates represent a natural complement to fish and plants; in visual terms, you can put on a spectacle of luminous beauty, particularly in sea water, using anemones and corals, to which can be added small fish, either lively or placid, but always brightly colored. There are also a few species of freshwater mollusks and crustaceans which are easy to keep in captivity, although they are little known and oftenoverlooked.
  17. FRESHWATER INVERTEBRATES GASTROPODS T hese are often unintentionally intro- duced into aquariums, usually via plants containing eggs or small juveniles which are difficult to spot. Gastropods lay their eggs in a small, transparent, gelati- nous mass. Ampullaria Some species of the apple snail can grow to 20 cm in the wild, but those found in an aquarium (belonging to the Ampullaria genus) do not exceed 7 cm. They eat vegetation and detritus, helping to restrict the development of algae, and like fairly hard water. Unlike many other gastropods, they are sexed and lay their eggs outside the water. Size: 6-7 cm. • Ampullaria gigas Planorbis These are water snails with a flattened shell. Their orange-red body contains plenty of red globules to establish a high oxygen concentration, as they live Planorbis sp. in environments lacking in oxygen and breathe through their lungs, sometimes rising to the water surface. They graze on both short and filamentous green algae, whose growth they help to restrict. Size: 3-4 cm. Malayan snails They breathe through their branchiae and can retreat into their tapered shell, which closes with an operculum. They relish the tiny algae which encrust the decor; if they are well fed, they proliferate quickly. They are considered less effective than the planorbis, but as they bury themselves, they contribute to the equilibrium of the aquarium by turning over and aerating the bed. If you want to get rid of them, introduce a fish from the Tetradon genus, which will appreciate these mollusks. Several Malayan snail species belonging to the Melanoides genus (such as Melanoides tuberculata), native to South-East Asia, can be unintentionally introduced into tanks along with plants. Size: 1-2 cm. Physas Their spiraled shell is markedly less elongate than that of Malayan snails and they are also slightly bigger. They do not play an important role in the control of unwanted algae. As they reproduce rapidly, it is best not to introduce them into an aquarium. Size: 1-2 cm. Melanoides sp. (Malayan snail) Physa sp. • 180
  18. CRUSTACEANS CRUSTACEANS T he word crustaceans usually brings marine species to mind, and it is often forgotten that they also live in fresh water. Less colorful than their marine cousins, they are nevertheless interesting to observe. They prefer hard water, on account of the calcium carbonate that forms their carapace. Shrimps Few species are commercially available, even though they are abundant in certain tropical regions. Several specimens can live together, if there are a sufficient number of shelters to provide hiding places in the aquarium. Atya These shrimps are found in many tropical regions in the Americas, Africa, and Asia, sometimes in brackish water. They are bottom-dwellers that feed on leftover food - both natural and artificial - and fish, and so their ecological role is quite substantial. These shrimps from the Atya genus (particularly Atya moluccensis, native to South-East Asia) are only occasionally found in the aquarium trade. They like lively, well-oxygenated water and are sociable, and so can be kept in small groups. Size: 6-7 cm. • Atya moluccensis Palaemonidae This family includes the familiar pink shrimp, as well as a large number of freshwater tropical species, such as the genus Macrobrachium (which covers some 200 species). These long- pincer shrimps are sometimes raised for restaurants: this is the case with M. rosenbergii, which grows to 25 cm, without counting its pincers. It is the smaller species that are sold in the aquarium trade, with M. lanchasteri being the most common at the moment. Native to South-East Asia, it acts as a garbage collector in a tank by eating the particles left behind by the fish. This shrimp likes filtered light and shelters for taking refuge if it is disturbed. When it is really frightened, it can jump out of the water to escape from danger. It is prone to attack the fish fry, which it easily detects with its acute sense of smell. Size: 7-8 cm. Macrobrachium sp. Crawfish There are around thirty species of crawfish in the world, distributed across the temperate and subtropical zones. Although some European species can adjust to tropical aquariums, it is advisable to let them remain in the wild as the regulations concerning their entrapment are strict. One crawfish, Procamburus darkii, the Louisiana crawfish, has been imported by a number of countries. It can cause a great deal of damage as it is fossorial and burrows in river banks. It grows quickly (starting to reproduce at the age of 7 or 8 months) and is highly adaptable, as it tolerates a wide range of temperatures and requires little oxygen. Many of the imported specimens come from South-East Asia, where there are red and blue varieties. It is omnivorous and can attack plants and fish, as well as other crustaceans. It is therefore best to keep a single specimen, even if the aquarium is very big and endowed with hiding places. Size: 15 cm. • Procamburus clarkii 181
  19. MARINE INVERTEBRATES SPONGES T he form and color of sponges are extremely diverse: balls, mats, or tubes, in red, orange, yel- low, brown, or gray. They attach themselves to a sup- port (rocks, but also dead coral or mollusk shells) and shy away from the light. Sponges seem to proliferate spontaneously in marine tanks, as they can be intro- duced, in sizes invisible to the naked eye, along with other invertebrates, live rocks, or in water. Both the com- mon and scientific names are little known and it is difficult to ascertain with any exactitude which species are found in the aquarium trade in the absence of detailed research. • Red Sea sponge COELENTERATES T hese are the favorites among aquarists that specialize in inver- tebrates, although their availability - and their price - can vary enormously. Furthermore, there is sometimes confusion over their names: some species may not even have one as they have yet to be systematically studied and described! Hexacorals This group covers the majority of the Coelenterates found in marine aquariums, particularly anemones and corals. Do not forget that most of them need strong light, as they contain Zooxanthellae, and that they can be fed on small morsels of animal origin. The aquar- ist must take care when handling some species, as their capacity to sting can be considerable. The great majority of these animals are imported from the Indian or Pacific Oceans, but they are only spo- Anthozoa sometimes provide a refuge for radically available in the aquarium trade. shrimps, protecting them from their predators. Sea anemones (Actinia) These live on the substrate, attached by their single foot, which acts as a sucker, but they can move around and find the place that suits them best (sometimes the tank's front pane). Some rare species live in the sand and can retreat into it. They are fairly robust in an aquarium if in water that is well lit and aerated (some anemones have Zooxanthellae). A large living space must therefore be planned for them, as other Anthozoa do not appreciate their tentacles; moreover, they sometimes excrete filaments of mucus that can pollute the water. Only clownfish can accustom themselves to contact with their tentacles. Anemones eat small pieces of mussel, shrimp, fish, or a choppy made from these ingredients. Sexual reproduction is a possibility, and some anemones are livebearers; asexual multiplication can take place via budding, which will go on to produce a young anemone. When buying anemones, make sure that they are puffed out and unfurled, as these are signs of good health. Heteractis (formerly Radianthus) This has a large number of tentacles, which are quite long (up to 10 cm) and somewhat rigid. Species of this genus can achieve a diameter of several dozen centimeters, and they are appreciated by several species of clownfish. Diameter: 30-40 cm. Heteractis magnifica 182
  20. COELENTERATES Stichodactyla (formerly Stoichactus) In its natural habitat a species of the Stichodactyla reaches lengths of 1 m. The tentacles are arranged in dense ranks, particularly round the edge of the anemone. Diameter: 20-50 cm. Entacmaea This genus was created a few years ago to cover some species from the old Radianthus genus (the remainder being included in the Heteractis genus). Aiptasia The glass anemones are often introduced to an aquarium along with rocks or water. They are livebearers that can quickly colonize a tank, to the detriment of other Anthozoa. However, they do have advantages in an aquarium with butterfly fish (Chaetodontid family), as they constitute these fishes' staple diet. Diameter: 5-10 cm. • Stichodactyla mertensii • Entacmaea quadricolor sheltering the clownfish Amphiphon bicinctus. Ceriantharia These resemble anemones, although they can be distinguished by their non-retractable tentacles. Moreover, they are not attached by a single foot but live in a self-secreted tube, whose support requires a layer of not too rough sand, 15-20 cm thick. Ceriantharia feed on finely ground mussels, fish, shrimps, or brine shrimps. Certain species can sometimes be found in the aquarium trade, although their name is often unknown or incorrect. Height: 20-30 cm. • Aiptasia sp. Parazoanthus sp. Cerianthus sp. Zoantharia (colonial anemones) These are neither anemones, as they live in colonies, nor corals, as they have no calcareous skeleton. These animals colonize rocks, mollusks' shells, and sometimes sponges, corals, and Gorgonians. They can harbor Zooxanthellae, and therefore need the appropriate light level. Parazoanthus sp. This colonial anemone consists of small polyps which can reach a height of up to 2 cm, with tentacles that do not exceed 5 mm in length. They must be placed 10 or 20 cm under the water surface in an aquarium to take maximum advantage of the light, due to the presence of Zooxanthellae. They must not be put close to stinging Anthozoa. Like many other animals in this group, their food consists of a fine choppy based on mussels. When buying this encrusting anemone, make sure that it is attached to a rock. 183
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