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Brackish Livestock Selection

by Neale Monks

Choosing brackish water fishes involves all the same considerations as choosing freshwater or marine fishes, plus one additional factor: salinity. Broadly speaking, brackish water fishes divide up into species that are essentially freshwater fish with some tolerance of salt, marine fish that tolerate reduced salinity, and truly euryhaline fishes that are happy across a wide range of salinities. An example of a salt-tolerant freshwater fish is the common krib, Pelvicachromis pulcher. It is ideally kept in freshwater, but will also do well in slightly brackish water. On the other hand, it cannot be kept in moderately or strongly brackish water. Many marine fishes enter brackish water to spawn and consequently mangroves and estuaries are often called the "nurseries of the sea" by marine biologists. The dog-faced puffer Arothron hispidus is an example of a marine fish that spawns in brackish water and juveniles are very common in estuaries. Many marine fishes will also make forays into brackish water to feed, taking advantage of the relative abundance of food in estuarine habitats. Finally, there are those fishes that are able to quickly adapt to changes in salinity and are able to move freely between freshwater habitats and the sea. Of the species kept by aquarists, the common scat Scatophagus argus is the best known example, and in the wild it spends its entire life in coastal waters making periodic forays into rivers and sometimes being found dozens of miles inland, well into the freshwater zone.

Although less often discussed, brackish waters are teeming with invertebrates as well, ranging from insects and insect larvae through to large molluscs and crustaceans. Crabs, hermit crabs, shrimps, oysters, clams, mussels, and marine snails of various types are all classic brackish water invertebrates, although insects, particularly mosquitoes, are also very important parts of many brackish water invertebrate faunas. In fact, mid to high salinity brackish waters often contain much the same variety and density of invertebrates as marine waters, with a few notable differences; for whatever reason, echinoderms, anemones, corals, barnacles, and cephalopods are rarely seen in brackish waters. For this reason, the aquarist trying to create an authentic brackish water habitat should certainly consider adding some oyster or mussel shells to his aquarium, but bleached corals and barnacle shells would be much less appropriate except perhaps as pulverised rubble on the substrate.

Planting the brackish water aquarium is problematical because apart from mangroves, higher plants are not really a key feature of most brackish water habitats. By the time a river reaches the sea, it is usually heavy with sediment, and few plants thrive in such murky water. Mangroves grow above the waterline of course, so they aren't bothered by this, and in fact the sediment gets trapped around their roots and forms an excellent, nutrient-rich substrate. Along the edges of the estuary where the water is shallow, plants may be found, but large algae, particularly brown algae, are much more characteristic. Brown algae generally do not do well in aquaria, and are best replicated using plastic alternatives. Among the plants that inhabit brackish waters, a few are traded commercially, most notable Java ferns, Java moss, Bacopa monnieri, Crinum calamistratum and Crinum pedunculatum, Cryptocoryne ciliata, Lilaeopsis brasiliensis, and Samolus valerandi. These will happily take a specific gravity of around 1.005 if acclimated carefully, and some species will accept significantly higher salinities after adaptation. At lower salinities (SG 1.003 or less), most hard water tolerant plants will do acceptably well if other factors such as lighting and nutrients are good, including Amazon swords, Hygrophila spp., and Vallisneria spp.

The small, low-salinity brackish water aquarium

For the aquarist with limited space, a low salinity aquarium, planted or otherwise, is a worthwhile option. A typical low salinity brackish water environment would be a coastal stream thick with plants, where the influence of the sea is only very slight. There are many small brackish water fishes, in particular gobies, livebearers, killifish, glassfish, halfbeaks, pufferfish, and dwarf cichlids that would work well in an aquarium based around this environment. Some of these will do well even in tanks as small as 10 gallons. A low salinity aquarium should be maintained at SG 1.003-1.005, the exact salinity depending on which fish and plants being kept.

Colourful or interesting species for the small (10-30 gallon) low salinity aquarium include:

Common name	Latin name	Comments
Guppy	Poecilia reticulata	Doesn't need salt, but has a high salt tolerance.
Endler guppy	Poecilia wingei	Doesn't need salt, but has a high salt tolerance.
Dwarf mosquitofish	Heterandria formosa	Very small, lively fish best mixed with other small species, such as gobies.
Common mosquitofish	Gambusia affinis	Aggressive, very hardy, but for a single species aquarium only.
Fancy mollies	Poecilia hybrids	All do very well in brackish water, but need tanks 20 gallons or bigger.
Banded lampeye	Aplocheilichthys spilauchen	Very peaceful little fish, ideal for use with gobies in a planted aquarium.
Florida flagfish	Jordanella floridae	Mildly aggressive towards its own kind; an excellent algae-eater, needs greens in its diet.
Wrestling halfbeaks	Dermogenys spp.	Males fight among themselves; relatively easy to keep and breed by halfbeak standards.
African pipefish	Microphis "smithi"	Difficult; needs lots of live food; best in a single-species aquarium with lots of plants.
Orange chromides	Etroplus maculatus	Territorial when breeding, but otherwise unproblematic and very attractive.
Kribensis	Pelvicachromis pulcher	Optimal breeding conditions are at pH 7.0, but otherwise thrives in brackish water.
Butterfly-goby waspfish	Neovespicula depressifrons	Very grouper-like (including ability to swallow smaller tankmates); otherwise easy to keep.
Asian freshwater flatfish	Brachirus spp.	Nocturnal, feed on bloodworms and other small animals; easily starve in busy tanks.
Bumblebee goby	Brachygobius spp.	Beautiful, active, territorial little fishes; superb in planted aquaria.
Rhinohorn goby	Redigobius balteatus	Similar to bumblebee gobies in terms of care, but less often seen.
Spaghetti eel	Moringua raitaborua	A scaled-down moray eel; feeds on worms and insect larvae; nocturnal; likes to burrow.
Peacock spiny eel	Macrognathus siamensis	Needs sand for digging; sociable; nocturnal; quickly escapes from uncovered aquaria.
Glassfish	Parambassis ranga	Lively, like to chase one another, so keep in groups! Prefers live/frozen foods, rarely eats flake.
Figure-8 puffer	Tetraodon biocellatus	Very entertaining; best kept alone or in groups (10-15 gallons per pufferfish).
Red-nose shrimp	Caridina gracilirostris	Does better in brackish water than fresh; easy to keep.
Amano shrimp	Caridina multidentata	A freshwater species that will do well at a low salinity.
Olive nerite	Vitta usnea	Does much better in brackish water than fresh; excellent algae eater.
Colombian ramshorn	Marisa cornuarietis	Tolerates brackish water, but doesn't need salt; destroys plants.
Malayan livebearing snail	Melanoides tuberculata	Does very well in brackish water; excellent for keeping sand clean; eats some algae.

A medium-sized, moderately brackish water aquarium

In an aquarium around 30-55 gallons in size it becomes possible to keep some of the more interesting oddball brackish water fishes. Many of these are euryhaline species that can adapt to a range of salinities, but a moderate salinity between 1.005-1.010 would work well for most of the species listed below. Moderately brackish water habitats tend to lack aquatic plants except mangroves, and so the aquarist would find decorating the tank with sand, rocks, wood, and shells much more true to life (as well as easier to do). Adding peat granulate to the filter (or blackwater extract to the water) is a great way to create the dark water conditions most of these fish enjoy, but keep a close eye on the pH, as this should be maintained around 7.5 to 8.0.

Colourful or interesting species for a medium-szied, medium salinity aquarium include:

Common name	Latin name	Comments
Fancy mollies	Poecilia hybrids	Lively and colourful, but don't keep with aggressive or predatory tankmates
Sailfin molly	Poecilia latipinna	Best kept in large schools, as the males can be aggressive.
Giant sailfin molly	Poecilia velifera	Rarely seen, larger version of the sailfin molly.
River halfbeaks	Zenarchopterus spp.	Large size (~6") demands a wide, broad tank, depth immaterial; nervous, keep with gentle tankmates.
Four-eyed fish	Anableps spp.	Not easy to keep, but fascinating fish for the single-species aquarium.
False anableps	Rhinomugil corsula	An Asian mullet; nervous, schooling fish, but hardy and not too big (~6" in aquaria).
Grunting toadfish	Allenobatrachus grunniens	Up to 12"; pretty inactive; predatory but otherwise peaceful.
Hogchoker sole	Trinectes maculatus	Typically 6" or so; nocturnal; prefers live foods, especially worms.
Oriental sole	Brachirus orientalis	Up to 8"; nocturnal; hardy; eats most live and frozen foods.
Mudskippers	Periophthalmus spp.	Most are 3-6"; territorial; hardy; need land and humid air; only use water for "dipping".
Violet goby	Gobioides spp.	Around 10-15"; territorial; need sand for digging; filter feeders, also need some algae.
Clay goby	Dormitator lebretonis	Midwater goby; territorial; omnivorous; will eat small tankmates.
Knight goby	Stigmatogobius sadanundio	Midwater goby; territorial; predatory; will eat small tankmates.
Sleeper goby	Eleotris spp.	Around 6"; territorial; predatory; will eat small tankmates.
Crazy fish	Butis butis	Around 6"; territorial; predatory; will eat small tankmates.
Moray eel	Gymnothorax tile	Up to 2', so keep in a 40-55 gallon tank; predatory, best kept in groups, in a single-species tank.
Green spotted puffer	Tetraodon nigroviridis	Around 5-6"; territorial, best kept alone.
Topaz puffer	Tetraodon fluviatilis	Around 5-6"; territorial, best kept alone.
Freshwater archer	Toxotes microlepis	Prefers SG 1.005 or less, but small size (4-5") makes it an attractive subject for home aquaria.
Papuan scat	Selenotoca papuensis	Rarely traded, but small size (around 4") makes it a highly attractive species.
Orange mono	Monodactylus kottelati	Sometimes mixed with common monos; much smaller than other monos (less than 4").
Olive nerite	Vitta usnea	Other nerites work well too, e.g., Puperita pupa and Neritina virginea.
Red-claw crab	Sesarma bidens	Amphibious, need similar aquarium to mudskippers.
Fiddler crabs	Uca spp.	Amphibious, need similar aquarium to mudskippers.

A large, high salinity brackish water aquarium

Aquarists with 100-200 gallon tanks at their disposal have some excellent species to choose from, including many of the more spectacular and attractive brackish water fish. In a high salinity aquarium a protein skimmer will work well. For all these fish, a high pH and hardness is important, so adding a calcareous substrate in the aquarium as well as using calcareous rocks for decoration can be very helpful. Many of these fishes are predatory, or at least opportunistic, so mix species of similar size. Catfish and archerfish in particular are easily underestimated as piscivores! Some of these are schooling fish, in which case keep in groups of six or more for best effect. Blue-legged hermit crabs are excellent scavengers, while nerite snails are superb algae eaters, some species even eating diatoms and blue-green algae. Pufferfish will, of course, eat both hermits and nerites given the chance.

Colourful or interesting species for a big, high salinity salinity aquarium include:

Common name	Latin name	Comments
Sailfin molly	Poecilia latipinna	Best kept in large schools, as the males can be aggressive.
Giant sailfin molly	Poecilia velifera	Rarely seen, larger version of the sailfin molly.
River halfbeaks	Zenarchopterus spp.	Large size (~6") demands a wide, broad tank, depth immaterial; nervous, keep with gentle tankmates.
Grunting toadfish	Allenobatrachus grunniens	Up to 12"; pretty inactive; predatory but otherwise peaceful.
Hogchoker sole	Trinectes maculatus	Typically 6" or so; nocturnal; prefers live foods, especially worms.
Oriental sole	Brachirus orientalis	Up to 8"; nocturnal; hardy; eats most live and frozen foods.
Spotted sleeper	Dormitator maculatus	Big (12") goby; territorial; easily tamed; omnivorous; will eat small tankmates.
Estuarine bagrid	Mystus gulio	Around 12"; schooling fish; peaceful but predatory.
Eel catfish	Plotosus lineatus	Around 12"; territorial when mature, schooling when young. Venomous: handle with care.
Shark catfish	Hexanematichthys seemanni	Around 10-12" in aquaria; very peaceful schooling fish, but predatory; beautiful!
Moray eel	Gymnothorax tile	Up to 2', so keep in a 40-55 gallon tank; predatory, best kept in groups, in a single-species tank.
Black-chin tilapia	Sarotherodon melanotheron	Territorial; omnivorous; paternal mouthbrooder.
Maya cichlid	Cichlasoma urophthalmus	Territorial; big; an attractive euryhaline cichlid.
Green chromide	Etroplus suratensis	Schooling vegetarian; prefers moderate SG, no higher than 1.012.
Dog-face puffer	Arothron hispidus	Keep at SG 1.012 or more; very hardy, and relatively peaceful (for a puffer).
Topaz puffer	Tetraodon fluviatilis	Around 5-6"; territorial, best kept alone.
Green spotted puffer	Tetraodon nigroviridis	Around 5-6"; territorial, best kept alone.
Targetfish	Terapon jarbua	Peaceful schooling fish when mature, but juveniles territorial; up to 6" in captivity.
Common archer	Toxotes jaculatrix	Big, around 6-8" in aquaria, but 10"+ in the wild. Territorial, often squabbles with conspecifics.
Common scat	Scatophagus argus	Big, messy, but loveable fish. Peaceful and easy to keep, but watch water quality.
Common mono	Monodactylus argenteus	Reach 4-6" in aquaria; needs lots of swimming space; best kept in groups of 6 or more.
Olive nerite	Vitta usnea	Other nerites work well too, e.g., Puperita pupa and Neritina virginea.
Blue-legged hermit	Clibanarius tricolor	Hardy, easy to keep algae eater; SG 1.010 upwards. Good with monos, scats, etc.
Mangrove horseshoe	Carcinoscorpius rotundicauda	Difficult to keep; needs sandy substrate, lots of fine food, plenty of space.

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