Part 2: Three Riparium Biotope Ideas - Blackwater Swamps

This post is the second in a series on creating biotope aquarium displays with riparium plants. The first article, Part 1: Southern United States, Mexico & Central America, offered tips on combining Ruellia Tall Bluebell, Asclepias Mexican Milkweed and other riparium plants with cichlids and livebearers.

Part 2: Blackwater Riparium Biotopes

The Biotope: rather than a specific geographic region, this biotope is suggested as a specific kind of aquatic habitat found in some tropical areas, the blackwater swamp. This term is the most familiar aquarium hobby discussions of the animals and plants that live in such places, although scientific descriptions usually use the similar term, peat swamp forest

Extensive tropical blackwater swamps can be found in two broad geographic regions: 1. Southeast Asia, especially the large islands of Borneo, Sulawesi and Sumatra 2. Lowland Tropical South America. There are a few other places, such as West Africa, where some blackwater swamps occur.

Blackwater swamps are characterized by unique water chemistry and biodiversity. Having developed in areas with clean sand, the water of blackwater swamps has low (acidic) pH and it is very low in minerals and nutrients. Many of the trees and other plants in blackwater swamps have thick, leathery foliage that is resistant to herbivory by insects and other animals, as well as attack by fungi and bacteria. When these decay-resistant leaves fall to the water, they tend to decompose little, instead sinking to the bottom where they accumulate over many years as thick layers of peat. The tannic acids that leach from the dead leaves stain the water a rich, coppery-brown color, while also making the water even more acidic. This is similar to the way that Sphagnum spp. mosses contribute to the formation of acid bogs in northern temperate areas. 

Blackwater Riparium in 11.4-gallon Glass Aquarium

The fishes and plants of blackwater swamps have special adaptations for these challenging conditions. While the wetland-adapted trees and other plants growing above the water can grow in low-nutrient, acidic conditions, the underwater habitat is especially difficult for plants. The tannin-stained water blocks the penetration of most photosynthetically useful light and dissolved nutrients are very scarce. Underwater plants are uncommon in blackwater swamps.

Hardscape & Substrate: an appealing aspect of blackwater swamp biotope aquariums is the ease with which an attractive layout can be developed with just a few materials. A thin layer of white pool filter sand in combination with sunken hardwood leaves will create a convincing blackwater swamp pool bottom. The leaves will contribute natural tannins to stain the water, while also creating hides for small fish. The leathery leaves of subtropical live oak (Quercus) and evergreen Magnolia trees are the most popular choices for this use. While these species do not occur in the blackwater swamps of Southeast Asia and South America, their leaves with simple oval shapes resemble many tropical species. The toothed and lobed leaves of temperate oak trees are somewhat less realistic, but will also work well as blackwater swamp sunken foliage. A single manzanita stump or similar sunken aquarium driftwood can complete the blackwater swamp layout and provide additional fish habitat structure.

These features and their surrounding of tannin-stained water create a beautiful contrast in combination with bright green riparium foliage.

Other kinds of dried plant parts, such as palm fronds, seed pods and nut shells, provide additional opportunities to enrich the blackwater biotope aquarium with authentic natural features. Tannin Aquatics lists a diverse offering of aquatic botanicals, including the striking seed pod of Cariniana legalis (below) along with instructions for their use.

Livestock: hundreds of species of aquarium-suitable fish live in wild blackwater swamps. Some of these are rather adaptable and might also be found in other aquatic habitats, while others, such as Parasphromenus spp. licorice gouramis, are blackwater swamp specialists. This section provides a quick overview of the main groups of blackwater-associated fish species kept in aquariums. 

Among blackwater swamp fish of Southeast Asia, various tropical cyprinids (Boraras spp., Rasbora spp., Trigonostigma spp. & others), loaches and species Betta can be good aquarium inhabitants. I wrote an article published in the May/June 2016 issue of AMAZONAS Magazine on developing a riparium biotope for a group of Betta schalleri, a species from Banka, Indonesia.

In the blackwater swamps of South America, various characins (Parachaeirodon spp., Hemmigrammus spp. and others) are the most common small schooling fish. Cichlids are represented by some Apistogramma spp., angelfish, discus and others. The fascinating small catfish species of these areas (Corydoras spp., Lorricaridae and others) includes many other excellent aquarium choices.

Riparium plants: a convincing blackwater swamp riparium biotope can be created with a combination of suitable plants that originate from the respective areas, along with a few other riparium “stand-ins”, plants that originate from other areas, but recreate the general appearance of the habitats.

It might be difficult to find the exact plant species that grow in the blackwater swamps of Southeast Asia because few of these are common in the horticultural trade. I was able to find a characteristic palm from the swamps of Borneo, Licuala paludosa, offered for sale by a nursery in Hawaii and it grew very well in the 56-gallon riparium housing the group of B. schalleri. This setup also used Pandanus pygmaeus, an unusual plant that I was able to find for sale in an online auction. The pandans (Pandanus spp.) are fascinating tropical plants with graceful arching foliage and striking stilt roots. While P. pygymaeus originates from Madagascar, it worked well in my setup as a representative for the several pandan species that grow in the blackwater swamps of Southeast Asia. There are a few swamp aroids (Schismatoglottis spp. and others) that occur in this area that might also be found with some research and diligent shopping.

Two easy-to-find and easy-to-grow plants stand out as choices for a South America blackwater biotope; Spathiphyllum spp. peace lilies and some Echinodorus spp. swordplants. While these might require some compromises—it can be difficult to find the exact species that grow in a given area—the common selections in the gardening trade will represent these South American plants that grow in blackwater swamps and other habitats in and near the water. Peace lilies are popular houseplants and among the easiest of riparium plants to grow. I have tried several different swordplants in ripariums and I have observed the best results with Echinodorus cordifolius and its white-variegated cultivar, E. cordifolius ‘Tropica Marble Queen’; and E. grandiflorus. Many Echinodorus can transition for growth as underwater (immersed) or above water (emersed) foliage. It is easiest to establish riparium swordplants by planting specimens grown in the emersed state, as many commercial aquarium Echinodorus are.

While they do not occur naturally in the region, with their dark green leaves and rather generic tropical plant texture, Spathiphyllum might also be considered as stand-in foliage for a Southeast Asia riparium biotope. As additional stand-in possibilities, Dwarf Cyperus Umbrella Sedge and Acorus Japanese Sweetflag are two more plants that do not occur naturally in the backwater swamps of Southeast Asia or South America, but can work well to recreate grassy blackwater swamp shoreline vegetation.