Subtitle: A taxonomic quest for the most diverse freshwater aquarium possible.
Note 1: The title is a little misleading. It’s not meant to imply the creation of a reef-like environment, but rather the presence of reef-like diversity.
Note 2: You can skip the introduction and head past the first asterisk (to the second area) for the main bones of the post. The intro is just a bit of background about me and my standing in the hobby. The second area details the progress of my search; skip to the second asterisk (third area) for the detailed results. At the third asterisk (fourth area) you’ll find my conclusion: a summary of my findings and an application of this data to the theoretical stock list of my desired tank.
Note 3: This is not academic and so I haven’t included references (I was counting on any reader interested in the sources to look up the information themselves based on the taxonomic names written about here). If you were hoping for sources, I’m sorry I couldn’t have been of greater help. Also, do forgive the occasional run-on sentences, as I found it hard to avoid some of them when writing down my thoughts.
Hello to everyone on here! This is my first post, and I'd like to take the time to say that I am not a professional or an expert on any of these matters. A couple of short-term tanks aside, I don't even have much direct experience with aquarium-keeping at all (blame it on college life and limited funds). That being said, I've been an aquarium aficionado since I was a little kid (and an "armchair biologist" for at least as long), and have been serious about keeping them since then. With few funds or resources at hand, I've spent my years learning as much as I could about the different facets of aquarium-keeping and planning my ideal "Perfect Tanks" so that I could execute them properly when the time comes. This post is the result of one line of inquiry across the years.
One of the things I've always liked about saltwater aquariums is the great diversity of life you can contain within them. Initially, I had always preferred freshwater because it seemed easier (and cheaper) to maintain, and I enjoyed the idea of breeding the fauna in my tanks to maintain stable populations that I wouldn't have to keep purchasing (this obviously only applies to some species under certain circumstances). But being a fan of diversity, I often wondered why a freshwater aquarium couldn't be at least half as diverse as a saltwater one. With that germ of an idea, I set out on an amateur taxonomic analysis to see just how many groups are represented in freshwater, and how many of them would be viable in captivity.
Starting out with the animals, I searched each phylum to see which ones had freshwater representatives. Right off the bat I wanted to rule out parasites and obligate amphibious species on the spot. They must be able to live without access to land (ruling out many "aquatic" vertebrates and invertebrates), and they must be free-living. Other criteria slowly became clear to me on the way: they must be small enough to be kept by the average hobbyist (no River Dolphins, please), they must be capable of reproducing in freshwater in captivity (ruling out some species of mollusks and arthropods), and (because of my goal for diversity) they must be non-predatory on their fellow tank-mates (unless the predator is not voracious, and the prey is a prolific breeder); additionally, they must be able to survive indefinitely (at least to the end of their lifespan, after reproduction) under typical (non-special) aquarium conditions (this rules out most sessile invertebrates, which have particular needs regarding feeding and water quality); they must also share a tolerance for similar water parameters (preferably tropical; this is actually the trickiest, as many of these species - and their preferred water chemistry and temperature tolerance - are poorly known); finally, they must also be plant-safe.
Having started with the animal kingdom, I ended up checking out the remaining eukaryote kingdoms as well, and even the prokaryotes, with more criteria developing to cover the additional bases that these groups provided. It should be noted that when I couldn't find freshwater representatives in a given group, I often searched (via Google) to see if any would turn up. I was occasionally rewarded with a freshwater species in a seemingly all-marine group, but most of the groups turned out to be irrelevant to me. The echinoderms, my favorite all-marine group, even had a good excuse, because their water-vascular system wouldn't work in freshwater.
As my search expanded, I started noticing a sharp practical division amongst all the groups I was researching: many of them had no aesthetic value (beyond, possibly, that of a curiosity), and many actually had negative consequences for a freshwater tank (these would eventually be ruled out); nonetheless, even amongst those species with no good looks, there were some of them that had practical value, manifesting itself as a cleanup crew that fulfilled detritivorous duties. The result of my search is (I hope) the most expansive list ever compiled of freshwater species that are viable in a community aquarium setting. Many of these species are poorly researched (especially in the context of aquarium keeping) and can only be provisionally included until they are experimentally kept by someone that can conclusively prove or disprove their captive viability. As my research was highly basic and partly theoretical, it remains to be seen whether it has any practical value to the aquarium hobby. So without further ado, the results of my search for the "Freshwater Reef"...
The prokaryote group have almost nothing to offer from the aesthetic standpoint (unless you're a hardcore microbiologist), and their use is entirely practical: namely, those bacteria that fulfill a role in the Nitrogen Cycle, as well as those that form part of the Aufwuch community that some invertebrates (such as Dwarf Shrimp) depend on. The ball-forming members of the genus Nostoc might be of aesthetic interest, but they may be finicky in the average aquarium, requiring nutrients in certain proportions that mere fish waste might not easily provide.
Planktonic microalgae are only useful as feeders for some species (usually in a separate breeder tank); when out of control, they cause the Pea Soup effect in the tank. Fungus-like protists (and true Fungi) are decomposers that I wouldn't willingly inoculate into a tank (some of them are even pathogenic). Benthic microalgae, and protozoa, would form part of the Aufwuchs and Micro Cleanup Crew; I wouldn't willingly inoculate microalgae in a tank (it usually arrives by itself anyway, and can be an eyesore) but the protozoa are fun to look at under a microscope, and their added diversity might be beneficial to a tank community. The most important groups are the (mostly paraphyletic) classics: Amoeboids, Flagellates and Ciliates. Choanoflagellates are also interesting, but it remains to be seen whether they could play a role in an aquarium, or if they'd even be viable in it.
I won't be discussing Embryophyte plants in great detail as there is already plenty of information available on them. But, to recap, aquarium-worthy species can be found in the following groups: Marchantiophyta (Liverworts), Bryophyta (Mosses), Lycopodiophyta (Quillwort - Isoetes), Pteridophyta (Ferns) and Magnoliophyta (Flowering Plants). For reefkeepers with Mangroves in their refugium, Bald and Pond Cypress (Taxodium distichum, T. ascendens) should serve as an adequate freshwater counterpart.
Freshwater Macroalgae are poorly studied, but potentially aquarium-worthy/non-pest species include: Vaucheria (a Xanthophyte), Phaeophyte Brown Algae (Heribaudiella fluviatilis, Sphacelaria fluviatilis, Bodanella sp. and Pleurocladia sp.), Branched Red Algae (Batrachospermum sp.), Crustose Red Algae (Hildenbrandia rivularis), Nitella (a non-stony Charophyte) and, most famously, Marimo (a ball-forming Green Algae).
And now, for the main course:
There are a few species of freshwater Sponges (Spongilla lacustris comes to mind) but they require smaller-than-average filter-feeder food and a highly oligotrophic environment. Upon introducing fish to a tank stocked with sponges, the sponges tend to waste away over a few week period (due to the eutrophication from the fish waste). Therefore, their interest to the casual aquarist is little to none.
I don't fully know how tolerant Bryozoans and Entoprocts are to eutrophication, but isolated individuals are sometimes found as hitch-hikers in aquaria. They are filter feeders. Regardless of their viability in freshwater aquaria, their practical value is likely none (except, possibly, for filtering the water?) and their aesthetic value is moderately low.
Cnidarians should be avoided by those who like an intact Micro Cleanup Crew (their main prey). Freshwater Jellyfish (Craspedacusta sp.) can be reared in appropriately furnished (non-planted) tanks, but they are impractical for a typical planted tank. Hydra are extremely easy to care for, but they've been known to eat young ornamental shrimps (and they may even cause harm to adults); they're usually considered a nuisance.
Rotifers, Gastrotrichs (Lepidodermella), Free-living Nematodes and Tardigrades (Hypsibius) are all so small as to form part of the Micro Cleanup crew (with the protozoa), and they're all harmless. The added diversity is likely beneficial, but there's not much more to it than that. Microscope eye candy.
Flatworms can form part of the larger cleanup crew, but they've been known to harm young shrimp, and most people consider them an eyesore; not really worth it in my opinion. Freshwater Nemertean worms are predatory, and have little to no aesthetic value. Freshwater leeches are either bloodsuckers or predators, also lacking in aesthetics. Freshwater polychaetes are uncommon, but useful as members of the larger Cleanup Crew; they include some species of Bristleworms, Stylaria and Aeolosoma. Fanworms in freshwater are represented exclusively by the genus Manayunkia; they are filter-feeders of unknown viability in a freshwater tank, and they lack most of the aesthetic appeal of their saltwater counterparts; nonetheless, they may pique the interest of oddball lovers (they piqued mine). Oligochaetes are just as useful as the polychaetes, and are represented in-part by Blackworms, Tubifex, Dero and aquatic “Earthworms”.
Freshwater Bivalves are represented by many species, but Mussels are to be avoided as their larvae are parasitic on fish gills. Golden Clams (Corbicula sp.) are sometimes kept successfully under certain circumstances, but in most planted tanks they usually starve to death and foul the water; they are not good candidates for a typical community tank. Sphaeriid Clams seem to be small enough that their dietary needs are easily met in the aquarium (although the only explicit example I’ve seen cites them as the ONLY filtration in a fishless invert tank, so your mileage may vary) and they also reproduce readily; your mileage may vary on aesthetic appeal (which also depends on whether they bury themselves), but they may entice the oddball lover, and they are likely good candidates for a planted tank.
Freshwater gastropods are a diverse bunch. Pond Snails (Lymnaeids and Physids) are usually considered a nuisance and have few redeeming qualities. Acroloxus lacustris can be part of the Micro Cleanup Crew. Ramshorns and Thiariids (Melanoides, Tarebia, Thiara) have proponents and detractors (consider me a fan); Thiariids can be useful Cleanup Crew members, but care must be taken to prevent population explosions as they can easily overrun a tank. P. bridgesii Apple Snails are Plant-safe, but they tend to produce a lot of waste. Other Apple Snails and the Giant Ramshorn tend to make short work of a planted tank. Japanese Trapdoor Snails, Brotia pagodula and some species of Tylomelania are plant-safe; other species of Tylomelania have been known to feed on some species of plants. Nerites are common in freshwater, but the only one that will breed in captivity is Theodoxus fluviatilis. Finally, there are at least two genera of freshwater slugs: Acochlidium and Strubellia (they aren’t nudibranchs, just slugs); their viability in captivity is unknown.
Water Mites (Hydrachna, Limnochares) are parasitic and predatory, depending on their life stage; they can be kept in a community tank far easier than any other parasite or predator (with minimal losses), but I don’t think they’re worth it (too small, little aesthetic value, no practical value). Both the Diving Bell Spider and most aquatic Insects are predatory, and should be avoided. Corixid Water Boatmen are fully aquatic at all life stages (though they breathe air and can leave the water), most are non-predatory, and they’re easily cared for; a worthy addition to the oddball tank (Micronecta is a Daphnia-sized genus that may be useful as part of the Cleanup Crew); they are likely to be easy to breed in captivity. Water Springtails can live atop floating vegetation (or emersed stems and leaves) and can provide a nice snack for fish (no telling how long a population will last in a tank, though, unless there’s a lot of emersed cover).
Carcinoscorpius rotundicauda is a brackishwater species of Horseshoe Crab, but all evidence points to it being able to live (and even breed) indefinitely in freshwater. That being said, it is likely to prey on many tank inhabitants, and if it doesn’t eat the plants, it will definitely bulldoze them to the substrate. I’d avoid it.
Crustaceans are the most diverse group of freshwater inverts. Branchiopods can be added provisionally to the community tank, but Triops can be predatory on some invertebrates, Fairy Shrimp might not adapt well to a planted tank, and Water Fleas (except perhaps Simocephalus) do not form viable breeding populations in a planted community tank; additionally, all species (save the Water Fleas) require desiccation of the eggs in order to hatch when remoistened (meaning they’d require separate breeding quarters in order to resupply the tank after their short lifespan). Copepods can be added to the Micro Cleanup Crew, but some species might be predatory on young invertebrates (the smallest young, that is). Ostracods are valuable Micro Cleanup Crew members, feeding on waste and feeding fish in turn; I wouldn’t dream of a tank without them (though in an overfed tank, some would consider them an eyesore). Bathynellaceans are (for all practical purposes) stygobites, and they might not do well in aquaria; their relatives, the Anaspidacean Shrimp, are native to cool waters and probably wouldn’t survive in a tropical aquarium.
Isopods (Asellus sp.), and Amphipods (Gammarus sp., Hyalella sp.) can also be added to the cleanup crew, but care must be taken to avoid population explosions as they can disturb smaller invertebrates and consume live plants when there’s not enough food. Freshwater Tanaids (Sinelobus stanfordi) are poorly known, but should be easy to care for and easily bred in captivity; the precise role they’d play in the aquarium remains to be seen, but they have high oddball value, and might (speculation on my part) play cleanup duties well. Mysids (Hemimysis anomala) have high oddball value, but might be seen as prey by some fish (perhaps even small fish); that being said, they can easily establish a breeding colony and live indefinitely in a planted tank (care must be taken to avoid a population explosion or a lack of food as they can become cannibalistic).
True Prawns (Dendrobranchiata) are represented in freshwater only by the Sergestidae family (Acetes paraguayensis, etc.); they can apparently complete their lifecycle in freshwater, though it’s unknown how easy they are to raise and how plant or community friendly they are. Caridean Shrimp are well known, but only lightly represented in the aquarium hobby; good (and breedable) community species include: Atyid Shrimp (Neocaridina davidi, N. palmata, Caridina cantonensis – some are more sensitive than others –, C. cf. babaulti ‘Green’, C. sp. ‘Malaya’, C. parvidentata, C. sulawesi, etc.), and Palaemonid Shrimp (Palaemonetes ivonicus, Desmocaris trispinosa). Fan Shrimp are interesting, but (with the possible exception of a taiwanese species) they aren’t breedable in freshwater. Palaemonetes paludosus is a little tricky to breed, and has been known to be aggressive/predatory under some circumstances. Macrobrachiums are very interesting (especially their behavior) and some can be bred in captivity, but they’re usually not community-safe (Borneo Red-claws are an exception as they are non-aggressive – except for the fact that they occasionally prey on small snails every once in a while; luckily, most snails breed readily). Alpheus cyanoteles is the only Pistol shrimp that can breed in freshwater (and they don’t seem to be finicky about water parameters), but they’re territorial, and potentially predatory on small inverts; Potamalpheops can also live in freshwater (and some sources say they can even breed in it), but their offspring are sensitive and almost impossible to raise in captivity.
Cambarellus crayfish are one of the few crayfish that are both plant-safe and community-safe; C. shufeldtii is known to be one of the most peaceful, least territorial and easiest to breed. Anomuran crabs are only represented by the Aeglidae (from South America; Freshwater Squat Lobster / Squat Crayfish / Páncora) and Clibanarius fonticola (from Vanuatu). Aeglids adapt very well to captivity and are easy to breed, but are very susceptible to high temperatures, and thus unsuitable for tropical tanks (it remains to be seen whether the northernmost species – such as A. franca – are capable of tolerating heat); it is my opinion that if such a feat could be achieved, a suitable Aegla species should be selectively bred for higher temperature tolerance. Clibanarius fonticola is the only species of Hermit Crab in the world that lives exclusively in freshwater, but it is unknown whether it is capable of breeding in captivity or if it would adapt to aquarium conditions; they use the shell of the Horned Nerite (Clithon corona).
Brachyuran Crabs have been notoriously difficult to integrate into a community aquarium as different species present different problems. Red-claws and Fiddlers are amphibious brackishwater crabs that die off in fully aquatic freshwater aquaria; they’re almost impossible to breed in captivity. Vampire Crabs (Geosesarma sp.) are peaceful, fully freshwater and can breed in captivity, but they’re also amphibious, with a preference for land (it remains to be seen whether a breeding population could thrive long-term with only a floating plant platform, but this seems unlikely). Panther Crabs (Parathelphusa pantherina) are fully aquatic, fully freshwater and capable of breeding in captivity, but they’re somewhat territorial and predatory, limiting their use. Thai Micro Crabs (Limnopilos naiyanetri) and Dwarf Mud Crabs (Rhithropanopeus harrisii; a usually brackish species that can live indefinitely and breed successfully in freshwater) are peaceful, fully aquatic and fully freshwater, but despite being freshwater breeders in nature, they seem almost incapable of breeding in captivity (the larvae are sensitive).
Only two types of crab seem suitable for the planted community tank, being peaceful, fully freshwater, fully aquatic and breedable in captivity. They are: Amarinus lacustris, from Australia (given its geographical origin, it might prefer cooler waters; more research is needed) and Trichodactylus sp. (T. borrellianus, etc.) from South America.
Entire books have been written on the subject of freshwater aquarium fish, so I won’t be dealing with them here in any detail. Just make sure to choose invert-safe species. The only special mention I’ll make (for their taxonomic significance) is for the Chondrichthyans: namely, Freshwater Stingrays, Saw Sharks and River Sharks (Glyphis), none of which are good candidates for a planted community aquarium (especially one that emphasizes inverts).
Fully aquatic amphibians are few and far between, but they include Rubber Eels (Typhlonectes sp., a Caecilian, not invert-safe), multiple species of salamanders [of which only 3 fully aquatic species might tolerate high temperatures and possibly play well with Inverts: the Southern Dwarf Siren (Pseudobranchus axanthus), the San Marcos Salamander (Eurycea nana) and some subspecies of the Eastern Newt (Notophthalmus viridescens)] and the African Dwarf Frog (invert-safe, according to reports).
The only fully aquatic freshwater reptiles are some Trionychoid Turtles (Carettochelys comes to mind), but they aren’t community-safe, and they won’t breed (lay eggs) in the water. There are no entirely aquatic birds, and all fully aquatic freshwater mammals are way too large for home aquaria (Manatee, Finless Porpoise, River Dolphins); plus, they’re probably illegal (and, if you’ll humor me, Manatees aren’t plant-safe and Cetaceans aren’t community-safe, hehe).
Those are the results of my search. Initially I tried to be expansive, but after completing the initial list, I realized I had to be pragmatic and practical when marking a species as suitable; the different criteria helped me narrow the list considerably until I got what you see here (a list of viable species with some explanations for the unviable ones).
A summarized view of suitable and experimental community species:
* Flora: Cycle Bacteria, Nostoc, Aufwuchs, Macroalga, Plants (Liverworts, Mosses, Quillwort, Ferns, Flowering Plants).
* Micro Cleanup Crew: Protozoa, Rotifers, Lepidodermella, Nematodes, Acroloxus, Hypsibius, Ostracods, Copepods, Simocephalus.
* Cleanup Crew: Polychaetes, Oligochaetes, Thiariid Snails, Micronecta, Asellus, Gammarus.
* Oddballs and Experimentals: Fanworm (Manayunkia speciosa), Sphaeriid Clams (Pisidium, Sphaerium), Slugs (Achochlidium, Strubellia), Corixid Water Boatman, Mysid (Hemimysis anomala), True Prawn (Acetes paraguayensis), Taiwanese Bamboo Shrimp (Species unknown, but different from commonly sold Bamboo Shrimp), Pistol Shrimp (Alpheus cyanoteles), Squat Crayfish (Aegla sp.), Hermit Crab (Clibanarius fonticola), San Marcos Salamander (Eurycea nana).
* The Essentials: at least 1 type of Snail (Ramshorns, Thiariids, P. bridgesii Apple Snail, Japanese Trapdoor Snail, Brotia pagodula, Tylomelania zemis, Theodoxus fluviatilis), at least 3 types of Crustaceans [at least 1 type of Shrimp (Neocaridina sp., Caridina sp., Palaemonetes ivonicus, Desmocaris trispinosa, Macrobrachium sp. ‘Borneo Red-claw’), at least 1 type of Crayfish (Cambarellus shufeldtii), at least 1 type of Crab (Amarinus lacustris, Trichodactylus borrellianus], at least 2 types of invert-safe fish (Benthic and Mid-water Swimmer) and at least 1 type of Amphibian (Southern Dwarf Siren, Neotenic or Eftless Eastern Newt, African Dwarf Frog).
* Note: Only the Plants and those in the “Essentials” section are actually essential for my premise, though I like the added diversity that the other categories would provide if included in an aquarium.
A very basic example of a community aquarium stocklist with (mostly) commonly available “essential” species: Plants, P. bridgesii Apple Snails, Cherry Shrimp, Cajun Dwarf Crayfish, A. lacustris Crab, Dwarf Otocinclus Catfish, Endler’s Livebearer and African Dwarf Frog.
A carefully calculated application of Ockham’s Razor (with some subjective criteria to suit my needs) helped me select the species that I wanted to attempt myself (it’s gonna be a while before I can, though), going for a mix of aesthetics, practicality and diversity. When planning my own tank, I chose to emphasize the diversity of animals instead of plants because plants mostly form part of the physical environment, while animals are the more dynamic element; I limited my criteria for the plants as “having at least 1 or more members of each group to the best aesthetic effect”. I wanted species that looked good, fulfilled a practical function or didn’t get in the way (while not looking bad); I also went for maximum diversity, so if a given species prevented the presence of two or more others (or a more desirable one that differed more than it, taxonomically), it had to go; I wanted to be able to breed my species, so breedability became a criteria. The remaining criteria are all just common sense, choosing species for maximum compatibility and minimal conflict.
Alas, after all my searching I still couldn’t produce something as diverse as a reef tank. But I still managed to lay the groundwork for the most diverse freshwater aquarium I could possibly make, and that’s what I really wanted all along. So I’ll just leave this post here and hope that it’ll be of use to you guys. Feel free to copy, summarize or modify this information in whole or in part for any need you might have (provided all modifications retain or increase accuracy). Happy tanking!
Last edited by SmokeyBlue; 11-17-2013 at 05:16 AM.
Reason: Format; Typos; Corrections