Betta Dreams A field guide
Issue I · Vol. 01 · A field guide to Betta splendens

From Mekong
paddy to the
aquarium cup.

One species, seventy wild relatives, a hundred and fifty years of Thai selective breeding, and a pet trade that still sells the result in half a litre of stagnant water. Care, disease, breeding, genetics, wild species, history. Every claim cited.

Begin with Care The wild bettas
Sections
Six.
Articles
79 published
Species covered
70+
Citation index
410 sources
A wild-type Betta splendens male with translucent fins photographed at a Thai breeder's facility.
Betta splendens
Specimen no. 001 · Holding cup, Bangkok
New: First captive breeding of B. hendra, Sebangau peat — 2026 Updated: Fin-rot differential diagnosis protocol — Apr 2026 IUCN re-listing: B. mahachaiensis moves to Endangered Now in archive: 24 wild-species profiles, with peat-swamp ecology Long read: Marble & the jumping gene — 11 min New: First captive breeding of B. hendra, Sebangau peat — 2026 Updated: Fin-rot differential diagnosis protocol — Apr 2026 IUCN re-listing: B. mahachaiensis moves to Endangered Now in archive: 24 wild-species profiles, with peat-swamp ecology Long read: Marble & the jumping gene — 11 min
Editor's note · 2026

Betta splendens is a labyrinth fish, an anabantoid that breathes atmospheric air through a folded, highly vascularised organ in the head. It evolved in the shallow, oxygen-poor, seasonally flooded rice paddies and ditches of the lower Mekong basin, where water temperatures swing from 22°C at dawn to 34°C by late afternoon and dissolved oxygen drops to values that would kill most aquarium fish before lunch.

The wild type is a drab, mottled olive-brown. The scarlet halfmoons, the copper dragons, the marble kois — every form the pet trade sells is a hundred and fifty years of Thai selective breeding stacked on top of that single dun-coloured ancestor. We try to write about both: the animal in the cup, and the animal in the paddy. Start with the Siam-to-splendens history for the Rama III fighting-fish lineage, or the wild-species guide for the seventy-plus relatives still living in Borneo, Sumatra, the Malay peninsula, and southern Thailand.

Four guides, one genus.

57articles across the four
No. I Anabantoidei · Osphronemidae A male halfmoon betta in full flare, photographed against a black backdrop.

Care

Tanks, water chemistry, food, cycling, tank mates, lifespan. The beginner core at the depth hobbyists actually need.

22 articles
No. II Pathology & treatment Reference photograph of a healthy halfmoon betta — the visual baseline against which symptoms are read.

Disease

Fin rot, ich, velvet, columnaris, dropsy, mycobacteriosis. Veterinary references, dosing in grams per gallon, no guesswork.

16 articles
No. III Reproduction & rearing A male betta tending a foam bubble nest at the surface.

Breeding

Pair selection, conditioning, spawning, fry rearing, culling ethics. The craft audience, covered without sugarcoating the hard parts.

8 articles
No. IV Genus Betta · 70+ spp. Betta imbellis, the peaceful betta of peninsular Malaysia.

Wild species

Betta macrostoma, channoides, hendra, the Krabi endemics. IUCN status, peat-swamp ecology, and the cultural history most sites skip.

11 articles
Flooded rice paddies in Phrao district, northern Thailand — the wild habitat of Betta splendens.
Phrao district, northern Thailand. Shallow, warm, seasonally flooded, densely vegetated. Photo: Takeaway / Wikimedia, CC BY-SA 3.0.
Chapter I · The myth

They do not live in puddles.

The single most repeated lie in the betta hobby is that wild bettas live in teacup-sized puddles, which pet retailers use to justify selling them in half-litre cups. The 2022 Aceh Betta diversity survey documented wild B. splendens in connected stretches of water up to thirty metres long, with flowing exchange to larger drainage networks, dense submerged plant cover, and an actual food web.

During the dry season a paddy section shrinks. During the monsoon it reconnects to a river. The fish do not experience life in five hundred millilitres of stagnant water. The hobby built a welfare disaster on a misreading of dry-season photography. Read the long version.

30mMaximum stretch length recorded, Aceh 2022
22–34°CDaily temperature swing in habitat
0.5LMedian pet-store retail volume
19LIBC minimum captive volume
A halfmoon plakat male in full flare, showing the 180-degree caudal spread.
A halfmoon plakat in full flare. Forty years of selective breeding on top of the older Thai plakat fighting line. Photo: Ar-betta / Wikimedia, CC BY-SA 4.0.
Chapter II · The colour

Fifteen tail types, four pigment layers, one transposable element.

Modern betta colour is the net effect of four pigment layers stacked in the skin: black melanophores, red erythrophores, yellow xanthophores, and iridescent blue-green iridophores built from crystalline purine platelets. The 2020 chromosome-level genome assembly resolved twenty-one linkage groups and mapped the major colour loci. The marble gene turned out to be a transposable element in Kit Ligand A, which is why marble bettas shift pattern across their lifetime.

Tail form is a separate axis. Halfmoon, crowntail, double-tail, plakat, delta, rosetail, and another nine named variants each derive from different dominant or recessive alleles, often with welfare trade-offs the hobby does not advertise. Read the marble-gene piece for the jumping-gene mechanism in detail.

A male betta tending a foam bubble nest he has constructed at the surface.
Male beneath his nest, conditioning complete. Photo: ErgoSum88 / Wikimedia, public domain.
Chapter III · The craft

Breeding is eighty percent what you do in the two weeks before the pair meets.

Conditioning, pair selection, and a correctly prepared spawning tank determine whether a spawn produces two hundred healthy fry or an attacked female and a dead male. Thai village jarring, Western open-tank, and sealed foam-lid methods all work, but each assumes specific upstream decisions. The breeding guide lays out the protocols article by article, and the genetics guide backstops the colour and form decisions.

A genus of seventy-plus species,
ordered by description year.

From the splendens complex of the Mekong to the peat-swamp giants of Pahang. The first 36 described, IUCN status included. The full working register lives at the species page.

36/70+shown here · 2026
No. 001 B. splendens Mekong basin VU
No. 002 B. imbellis Peninsular Malaysia LC
No. 003 B. smaragdina NE Thailand LC
No. 004 B. mahachaiensis Samut Sakhon EN
No. 005 B. macrostoma Brunei VU
No. 006 B. channoides Mahakam, Borneo LC
No. 007 B. albimarginata East Kalimantan LC
No. 008 B. coccina Sumatra peat swamps VU
No. 009 B. persephone Johor, Malaysia CR
No. 010 B. hendra Sebangau, Borneo CR
No. 011 B. brownorum Sarawak EN
No. 012 B. burdigala Bangka Island EN
No. 013 B. ibanorum Sarawak VU
No. 014 B. akarensis Borneo blackwater VU
No. 015 B. picta Java LC
No. 016 B. unimaculata Borneo, lowland LC
No. 017 B. patoti East Kalimantan VU
No. 018 B. pugnax Penang, Malaysia LC
No. 019 B. taeniata Borneo LC
No. 020 B. waseri Pahang, Malaysia EN
No. 021 B. hipposideros Selangor peat EN
No. 022 B. tomi Singapore (extinct) CR
No. 023 B. siamorientalis E Cambodia / S Vietnam LC
No. 024 B. apollon Surat Thani VU
No. 025 B. dennisyongi N Sumatra EN
No. 026 B. livida Selangor peat EN
No. 027 B. uberis C Kalimantan VU
No. 028 B. miniopinna Bintan, Indonesia EN
No. 029 B. anabatoides Borneo lowland LC
No. 030 B. edithae Borneo, Sumatra LC
No. 031 B. simplex Krabi province VU
No. 032 B. prima S Cambodia LC
No. 033 B. stigmosa Terengganu VU
No. 034 B. pi Pahang peat EN
No. 035 B. pulchra S Thailand peat VU
No. 036 B. krataios C Sumatra VU

Open the full species register →

Recently published.

Jul 20 26

Betta Fish Medications: What to Keep on Hand Before You Need Them

Six medications cover 90% of betta disease situations. What each treats, what to buy, what to avoid, and how to store them. Buy before you need them.

Buyers Guide
Jul 19 26

Betta simplex: The Mouthbrooding Betta of Krabi's Limestone Streams

Betta simplex: Near Threatened mouthbrooder from Krabi Province, Thailand. Limestone stream habitat threatened by tourism development. Profile and care.

Wild Species
Jul 18 26

Giant Betta Fish: Genetics, Care, and What Makes Them Different

Giant bettas reach 12 cm or more. Betta splendens selected for size, not a separate species. Recessive size genetics, care differences, and welfare trade-offs.

Genetics
Jul 17 26

Best Water Test Kits for Betta Tanks: What to Buy and Skip

The API Freshwater Master Test Kit is the standard. Why liquid reagent tests beat strips, what other tests are worth having, and why you need to test at all.

Buyers Guide
Jul 16 26

How to Cycle a Betta Tank: Fishless, Fish-In, 6-Week Timeline

How to cycle a new betta tank. Fishless with pure ammonia is the fastest method. What to test, when the cycle is complete, and how to speed it up safely.

Care
Jul 15 26

Betta Fish Water Parameters: The Complete Reference Table

Every water parameter a betta keeper tracks: temperature, pH, GH, KH, ammonia, nitrite, nitrate. Ideal ranges, acceptable ranges, and what happens outside them.

Care

Every article, newest first →

The dispatch

One letter when something worth reading lands.

No daily slop, no SEO product round-ups. Roughly one essay or guide a fortnight, plus a short note when the wild-species register gets an addition.

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