By Hannah Nielsen
The beautiful tetra with a feisty streak
You've seen a photo of a serpae tetra and fallen for that blood-red body — and now every guide either gushes about the colour and skips the catch, or buries the warning three scrolls down where you'll never read it. The catch is this: serpae tetras nip fins. They are, by reputation, one of the worst community fin-nippers in the hobby [4]. Sold that fact up front, you can plan around it. Sold a peaceful-community fairy tale, you end up with a betta whose fins look like they've been through a shredder.
I'm Hannah — I write the schooling-fish guides here and I've spent more hours than I'd admit photographing tetra shoals, which means watching exactly how they behave when the group size is wrong. This guide is the honest version: what the serpae tetra actually is, why it nips, the one trick that fixes it, and which tank mates to keep well clear of. It's the answer I'd give a customer who emails asking "are serpae tetras aggressive, and can I keep them with my angelfish?" — short version, no, not with the angelfish.
Serpae tetras (Hyphessobrycon eques) in one of our holding tanks. Note the black comma-shaped mark behind the gills and the black-edged fins — the field marks that separate a true serpae from the look-alike phantom tetras. Photo: Tropical Fish Co.
The serpae goes by a small pile of names, which is half the confusion around it. You'll see it sold as serpae tetra, red minor tetra, jewel tetra or blood tetra, and labelled scientifically as Hyphessobrycon eques, Hyphessobrycon callistus, Hyphessobrycon serpae or even Megalamphodus eques. They're all the same fish, or near enough — the "blood" tetras are a tight knot of closely related species and trade hybrids that even ichthyologists argue over. The modern name is Hyphessobrycon eques.
Five facts about serpae tetras most UK guides miss
- The genus name is a recent reshuffle. The serpae sat in the genus Megalamphodus for decades — FishBase still files it that way [1]. A 1997 systematic study folded Megalamphodus into Hyphessobrycon and defined the so-called "rosy tetra clade" the serpae belongs to [3]. That's why you'll see four different Latin names on the same fish.
- The fin-nipping is a numbers problem, not a temper problem. Serpae tetras form loose hierarchies and squabble constantly for rank. Kept in too-small groups they run out of rivals and redirect the aggression at tank mates — the behaviour "tends to be most pronounced when insufficient numbers are purchased or space is limited" [2].
- They nibble plants, unlike their phantom-tetra look-alikes. Serpae are often confused with red phantom tetras, but one tell-tale difference is that serpae will nip soft plant tips while phantoms leave them alone [6]. Tough-leaved plants — anubias, java fern, cryptocoryne — shrug it off.
- They tolerate harder water than almost any other "Amazon" tetra. FishBase records them across hardness up to 25 dH [1], which means they thrive in the hard, alkaline tap water that covers most of the UK south-east — Thames Water runs 250–320 mg/L CaCO₃ [5]. No reverse-osmosis kit required.
- They outlive the popular nano tetras. A well-kept serpae reaches around five years, against two to three for neon tetras. Their hardiness and wider parameter tolerance buy them that extra longevity — provided they're in a proper group and not stressed by isolation.
How serpae tetras compare to the calmer tetras
The honest question most buyers have is "is the serpae too aggressive for my tank?" — so here's where it sits against the two most popular peaceful tetras and another robust schooler. The columns that matter most are temperament and fin-nipping risk.
| Attribute | Serpae Tetra | Neon Tetra | Cardinal Tetra | Black Neon Tetra |
|---|---|---|---|---|
| Scientific name | H. eques | P. innesi | C. axelrodi | H. herbertaxelrodi |
| Adult size | 4 cm | 4 cm | 5 cm | 4 cm |
| Temperament | Semi-aggressive | Peaceful | Peaceful | Peaceful, robust |
| Fin-nipping risk | High (manage with group size) | Low | Low | Low–moderate |
| Best tank mates | Robust, fast or bottom-dwellers | Calm community | Calm soft-water community | Calm community |
| Long-finned mates OK? | No | Yes | Yes | Usually |
| Minimum group | 8 (12 ideal) | 8 | 8 | 8 |
| Minimum tank | 60 L | 40 L | 60 L | 60 L |
| UK hard water OK? | Yes | Maybe | No (prefers soft) | Yes |
| Lifespan | 5 years | 2–3 years | 5–8 years | 5 years |
If your community already contains delicate or long-finned fish, pick a peaceful tetra from the right-hand columns. If you want bold colour in hard water and you can commit to a real group with robust tank mates, the serpae is hard to beat — just go in with eyes open.
Group size, fin-nipping, and the tank mates to avoid
This is the section that earns the page, so let me be precise.
Group size is the lever. Serpae tetras live in a permanent low-level pecking order. In a group of eight or more they spend their energy on each other — chasing, displaying, jostling for position — and your other fish get ignored. In a group of six they run out of internal targets and start aiming outward. Eight is the practical floor; Seriously Fish puts the genuine minimum at twelve [2]. There is no upper limit that causes problems — bigger is always calmer.
Tank mates to avoid — be strict about this:
- Bettas — trailing fins, slow movers. A guaranteed shredding.
- Angelfish — long flowing fins; also, mature angels may turn on the serpae. A lose-lose pairing.
- Fancy guppies — long tails are an irresistible target, and guppies are too slow to escape.
- Slow fancy gouramis and any long-finned variant — same problem.
The rule of thumb from Practical Fishkeeping is blunt and correct: keep serpae "in large numbers and with no long-finned fish, and the problem will go away" [4].
The most common way I see this go wrong: someone buys "a few" serpae — usually six because that's the number stuck in everyone's head for tetras — adds them to a community with a betta or an angelfish, and within a fortnight there are nipped fins and a stressed centrepiece fish. The fish aren't faulty. The group is too small and the tank mates are wrong. Buy eight to twelve, skip the long-finned fish, and the same serpae become a well-behaved, jewel-bright shoal.
What they CAN live with are robust fish that either move fast or live in a different layer of the tank — which is exactly where the next section comes in.
Tank mates that genuinely work — robust, not long-finned
The safest companions for serpae tetras are sturdy fish that aren't trailing fins around in the serpae's mid-water zone. Bottom-dwellers and inverts are the standouts because they simply aren't in the firing line, and other robust schoolers work once your serpae group is large enough to keep them occupied [2].
- Corydoras catfish — armoured, peaceful bottom-dwellers that live below the serpae entirely. Panda and pygmy corydoras are perfect scale-matched substrate companions.
- Amano and cherry shrimp — adult shrimp are robust enough to coexist in a well-planted tank; they work the substrate and biofilm, out of the serpae's path. (Shrimplets will be eaten — treat that as population control, not a problem.)
- Nerite snails — completely ignored by serpae, and the best algae-grazers we sell. A genuinely zero-conflict addition.
- Black neon tetras — a notably more robust neon than the standard; a sturdier mid-water schooler than fragile cardinals, and a sensible same-layer companion when your serpae group is twelve-strong.
- Harlequin rasboras — fast, sturdy and active enough to stay out of trouble; their copper-and-black colour also sets off the serpae red nicely.
Want the broader robust-community shortlist? Our tetra hub lists everything schooling and in stock, and the tropical fish for sale hub widens it to the full robust community range.
A serpae tetra at full colour. The black edging on the anal fin and the dark shoulder mark are the field marks to look for — faded, washed-out red usually means a stressed or under-grouped fish. Photo: Tropical Fish Co.
The robust mid-water schoolers below are the same-layer companions worth considering once your serpae group is properly sized — sturdier than the fragile nano tetras, and active enough to keep out of trouble.
When your serpae tetras arrive — our UK delivery protocol
Serpae tetras are hardy shippers — their wide water-chemistry tolerance means they handle the small pH and hardness shifts of a bag-to-tank move better than a sensitive cardinal would. A roughly 30-minute drip is the sweet spot: enough to equalise gently, not so long that the fish sit in cooling, fouling bag water.
- Receive in a quiet, dimly-lit room and check the box temperature. Open the bags carefully.
- Float the sealed bags for 15 minutes to equalise temperature.
- Drip-acclimate for about 30 minutes at one to two drops per second [7]. Serpae don't need the long 45-minute drip a cardinal does.
- Net the fish into the tank — never pour the bag water in.
- Lights off for two hours so the new arrivals settle without being spotlit.
- No feeding for 24 hours, then start with small amounts.
With most fish we'd suggest staggering new arrivals — with serpae it's the opposite. Add your entire shoal together rather than a few at a time. A half-sized group of four or five, even temporarily, is exactly the situation that triggers fin-nipping, and any existing fish become the target while you wait for the rest. Buy the full group and acclimate it in one go.
Every live order ships with our live-arrival guarantee: if any fish are DOA, photograph the unopened bag within two hours of delivery and we'll refund or replace.
Ready for more?
Comparing schools before you commit? The cardinal tetra guide covers the calmer, soft-water alternative, and the ember tetra guide is the nano-tank schooler for tanks too small for a boisterous serpae group.
For the deeper husbandry detail, the neon tetra care guide and the harlequin rasbora care guide both cover robust schooling partners that can share a serpae community.
Shopping by type? Our tetra hub has every schooling tetra in stock this week, and the tropical fish for sale hub is the full live-stock list.
