Hello!

​Last week’s post looked at animals in an organic aquarium: when to add them, how many to add, how succession unfolds, and why it is safer to wait than to rush.

This week follows on from that discussion and highlights some of my favourite fish to use in an organic aquarium.

In most cases a soil-based aquarium will be a densely planted environment with little or no mechanical water circulation. For this reason, the fish that do best are those that come from slow-moving waters with dense vegetation. Ideally, they will also contribute very little waste relative to their size (to stop their waste from overwhelming the tank's natural filtration).

Below are five freshwater fish that naturally suit this approach's constraints:

Honey Gourami (Trichogaster chuna)​
A single honey gourami can work well as a calm centrepiece fish in a small planted aquarium. They originate from slow-moving, plant-rich waters and tend to hover and wander rather than aggressively dart around the place. I love this species and they have so much personality. (Middle illustration)

Chili Rasbora (Boraras brigittae)​
One of the smallest commonly kept aquarium fish. In the wild, they inhabit shallow, still waters rich in leaf litter. Their low activity level and minimal bioload make them particularly well suited to organic systems. Despite their tiny size, their vibrant colour contrasts the natural greens of a planted tank really nicely. The perfect match. (Top left illustration)

Celestial Pearl Danio (Danio margaritatus)​
Despite being a danio, this species does really well in structure/cover. They are comfortable in tanks with dense planting and broken sightlines, where they exhibit natural foraging behaviour. And they look like mini wild trout so that is big win. (Top right illustration)

White Cloud Mountain Minnow (Tanichthys albonubes)​
A too often overlooked species dismissed as 'beginner fish'. White Clouds are an adaptable species that tolerate a wide temperature range. Their modest waste output and steady behaviour make them a reliable option in lightly stocked, planted aquariums. In my experience, their colouration blossoms in a planted aquarium, so don't be deterred if they look muted in the shop! (Bottom left illustration)

Pygmy Corydoras (Corydoras pygmaeus)​
Unlike larger corydoras, pygmys explore the water column rather than constantly hoovering the substrate. They are social, gentle, and contribute little waste. Pygmy corys have two traits that will make you fall in love with them: firstly, they'll occasionally stop and hover like little hummingbirds in the middle of your aquarium; and secondly, they will use leaves as hammocks to take a rest every now and again. So if you weren't convinced by looking at them, surely that'll do it! (Bottom right illustration)

If you had to pick one common thread here it would be size. Fish that remain small place fewer demands on the system as a whole.

Next week’s email will step back from theory (catch up on theory here!) and focus on building the aquarium itself, from substrate to planting to balance. So if you're not subscribed already, make sure to enter your details below!

Happy fishkeeping,

Oli