Serpae Tetra (Megalamphodus eques)

Getting to know the Serpae Tetra

The Serpae Tetra is a small, gregarious fish from South America and a very common tetra in the aquarium trade. Each purchase is one live fish, so the real decision is how many to order: this species belongs in a group of at least 12, in a tank with at least an 80 × 30 cm base, and it is not a safe companion for long-finned or timid fish because of its reputation for nipping fins. Get those three things right and it is an adaptable fish for a planted tank.

In the wild it comes from the Amazon, Guaporé and Paraguay River basins, where FishBase records it holding position near the surface among the stems of emerging plants, often in still water. That picture explains much of the advice below: planting that reaches up towards the surface, gentle water movement and plenty of company of its own kind.

One fish, several names

You will see this tetra under a handful of names. Seriously Fish lists jewel, red minor, blood and callistus tetra, and jewel tetra is the common name on the FishBase species summary. It is widely traded as Hyphessobrycon eques, the name many suppliers and references still use. FishBase now treats Hyphessobrycon eques as a synonym and lists the species as Megalamphodus eques in the family Acestrorhamphidae, the American tetras, which is why the scientific name in our title reads Megalamphodus eques. FishBase also notes that the species belongs to a complex of ‘blood’ tetras, and that hybrids within that complex are commonly offered in the aquarium trade.

Wild status and bred forms

FishBase lists the species as Least Concern on the IUCN Red List. Seriously Fish notes that several selectively bred ornamental strains have been developed, including metallic, long-finned, balloon and fairy-fin forms. This listing is sold under the species name alone rather than as one of those named strains, and the care on this page is written for the species.

What each purchase includes

• One fish per unit. For a group of 12, set the quantity to 12 or more.
• Two sizes: 2–3 cm and 3–4 cm. The size you select is the size supplied, not the adult size. Sizes sell out from time to time, so check the product page for the one you can order.
• Sex: Sex is guaranteed only when the selected option explicitly states male or female. This Hyphessobrycon eques listing has no sex-guaranteed option.

Key numbers

• Maximum size: 4 cm standard length, the figure FishBase and Seriously Fish both record.
• Group: at least 12 fish.
• Tank: an 80 × 30 cm base, about 72 litres, as the absolute minimum for a group.
• Aquarium water: 20–28°C, pH 5.0–7.5 and 1–15 dGH.
• Natural range: the Amazon, Guaporé and Paraguay River basins.

Who it suits

A quick check before you order

1. Is the tank mature, with a base of at least 80 × 30 cm?
2. Can you order 12 or more at once or in planned stages?
3. Does the tank already hold any long-finned or timid fish?
4. Does your tap water fall within pH 5.0–7.5 and 1–15 dGH?

A note on the photograph: Gallery images have been digitally enhanced to improve image quality. Natural colour, pattern, size and maturity can vary between live animals. Seriously Fish adds that this tetra shows better colouration in a well-furnished tank with live plants and a dark substrate, so the setting you give it affects how it looks.

How many to buy

This is a fish to buy by the dozen. FishBase describes a gregarious species, and the Seriously Fish species profile sets a clear bar: a group of at least 12 specimens should be considered the minimum requirement. Its reasoning is practical. In a larger group the fish are more likely to be distracted by each other than by their tankmates, the display looks more natural, and males show better colouration when rivals of their own kind are present.

Why 12 rather than five

The OATA care sheet for tetras and pencilfish advises groups of at least five in the home aquarium, adding that more is better, and FishBase’s aquarium note also gives groups of five or more. Both set a floor rather than a target. The Seriously Fish figure is set with this species’ fin nipping in mind, which it notes is most pronounced when too few are bought or space is limited. OATA also warns that tetras kept singly or in too small groups will often become stressed, so trimming the group is a false economy.

Life inside the group

Seriously Fish describes Serpae Tetras forming loose hierarchies, with rival males continually battling each other for female attention and for position within the group. That sparring is ordinary behaviour for the species rather than a sign that something has gone wrong, and it is one more reason to give the group room and enough numbers to spread the attention around.

Planning the order

• Species tank: Seriously Fish advises a group of 12–15 in an 80 × 30 cm tank with no other upper-water species.
• With companions: adding other compatible species requires a larger tank than that minimum.
• Timing: the filter bacteria must catch up each time fish and food increase, so bring the group into a mature tank that is not already heavily stocked, and test more often than usual in the days that follow.

Tank size and furnishing

Seriously Fish gives an 80 × 30 cm base, or equivalent, as the absolute minimum for this species, which works out at about 72 litres. FishBase’s aquarium note gives a minimum aquarium length of 60 cm, so the Seriously Fish figure is the larger of the two species-level minimums and the one to plan around. OATA’s general advice points the same way: buy as large an aquarium as you reasonably can, because more water keeps temperature and water quality steadier.

Furnishing for colour and calm

Seriously Fish notes that décor is not especially critical, but that this tetra shows better colouration in a well-furnished set-up with live plants and a dark substrate. A natural-looking arrangement might use:

• A soft, sandy substrate, ideally darker in colour; OATA’s tetra sheet also accepts aquarium gravel or sand.
• Wood roots and branches placed so that plenty of shady spots form.
• Dried leaf litter, which adds a biotope feel and grows beneficial microbes as it breaks down; the tannins and other chemicals released by decaying leaves help simulate natural conditions. Leaves can be left to break down fully or removed and replaced every few weeks.
• Live plants for cover, or plastic plants and ornaments such as plant pots and model caves if you would rather not grow them.

Leave room to swim

OATA stresses that tetras need space to swim and a gentle current for the smaller species. Taller stem plants rising towards the surface at the sides and back, with an open lane through the middle, echo the plant-stem habitat FishBase describes while leaving the group room to move together.

Filter and heater sizing

Filtration is not optional. The RSPCA’s aquarium environment guidance says no fish should be kept without a well set up and maintained filter: fish release ammonia, which is toxic, and a working biological filter grows the beneficial bacteria that turn it into nitrite, also toxic, and then into the safer nitrate. OATA makes the same point for tetras: whatever the size of the aquarium, a filter is always essential.

Sizing the filter

Seriously Fish sizes equipment for its minimum tank of about 72 litres. With a turnover of four to five times the tank volume an hour, it suggests a filter rated at 290–360 litres per hour. For a larger aquarium, multiply the volume by four and by five to find the equivalent range; a 100 litre tank, for example, points to roughly 400–500 litres per hour. Keep the outlet flow gentle, in line with OATA’s advice for smaller tetras.

Sizing the heater

To hold 20–28°C in a tank of about 72 litres, Seriously Fish estimates roughly 50–75 W of heating, assuming a room around 20°C. A colder room or a bigger tank needs more. Pair the heater with a thermometer you check daily, so a stuck thermostat is caught early.

Water values and what to aim for

Three sources describe Serpae Tetra water, and they are written for different purposes. Reading them together gives you both the safe range and a sensible target.

What to aim for

Keep the tank inside the Seriously Fish aquarium range, because that is written for this species in captivity. Within it, the ground where all three sources agree is 22–26°C and pH 6.5–7.5, and that is where we would set up a new tank. Seriously Fish notes that the vast majority of fish in the trade are bred commercially and are more adaptable than wild specimens, describing the fish sold in stores as fairly adaptable where water chemistry is concerned and happy within pH 5.0–7.5. Stability matters more than chasing an exact number.

The values that must stay at zero

• Ammonia: zero mg per litre.
• Nitrite: zero mg per litre.
• Nitrate: no more than 20 mg per litre above normal tap water levels. If your tap reads 5 mg per litre, the tank should stay at or below 25.

Checking your tap water first

Because every water change brings in tap water, test its pH and hardness before the fish arrive. Our water parameter matcher compares your readings with this fish’s ranges, and the guide to what to test in aquarium water, and why explains each value. Seriously Fish’s 1–15 dGH covers soft to moderately hard water. FishBase’s higher 10–25 dH is its record of the natural environment, so it is no reason to harden soft tap water. If your tap sits well above 15 dGH or 7.5 pH, talk to us before ordering so we can help you judge whether it will suit.

Feeding a Serpae group

In the wild, FishBase records the Serpae Tetra feeding on worms, crustaceans, insects and plants, and Seriously Fish describes it as likely omnivorous. OATA’s tetra sheet agrees that tetras are omnivorous and will take most food types. It may survive on dried food alone, Seriously Fish says, but like most fishes it does best on a varied menu.

A varied menu

• Everyday base: a good quality flake or granule, or another quality dried product.
• Live or frozen extras: bloodworm (chironomid larvae), mosquito larvae, Daphnia and Moina, all named by Seriously Fish; OATA adds small bloodworm and tubifex.
• Freeze-dried options: freeze-dried bloodworm and freeze-dried Daphnia are convenient alternatives when live or frozen food is not to hand.

Portion and timing

OATA’s rule for tetras is to feed only what they can eat within a few minutes once a day. Uneaten food breaks down and releases toxic waste, and that matters more with a group of 12 or more than with a handful of fish.

Spread the food out

FishBase notes something every Serpae keeper should know: the species is generally peaceful, but when there are too many of them crowding at feeding, they bite each other’s fins. Scatter food across the surface rather than dropping it in one spot, so the whole group can eat without jostling at a single point. If companions share the tank, make sure slower eaters get their share too.

A worked example: a 12-fish Serpae tank

Pulling the figures together, here is one way to set up a species tank for a first group. It uses the Seriously Fish minimum footprint, so treat it as the smallest sensible version rather than the ideal.

Scaling up for companions

To add other species, start from a bigger tank rather than the 80 × 30 cm minimum, since Seriously Fish says adding compatible species requires more room. The same ratios carry over: filter flow of four to five times the volume an hour, a heater sized for the room temperature, and a weekly change of a quarter of the water.

Preparing a mature tank

Tetras can be stressed by even the smallest amounts of ammonia, OATA warns, so the tank has to be ready before a group this size goes in. A new aquarium needs time for nitrifying bacteria to build up in the filter. When fish arrive before that, or too many arrive at once, the bacteria cannot cope with the extra waste; ammonia and nitrite rise to unhealthy levels, which may cause fish to become ill or die. OATA calls this ‘new tank syndrome’.

Readiness checklist

• The filter has been running and ammonia and nitrite both test at zero.
• Nitrate is detectable, a sign the bacteria are working, and sits within 20 mg per litre of your tap reading.
• The heater holds a steady temperature inside the range you have chosen.
• The tank is an appropriate size for the number of Serpae Tetras you plan to keep.

If this is your first aquarium, our guide to setting up a tropical tank in ten safe steps covers the maturing stage from the beginning.

Keeping the water clean week by week

A group of 12 tetras produces a steady stream of waste, and OATA’s routine for tetras is designed to keep it under control. Build it into the same day each week.

Protecting the filter bacteria

Never run filter media under the tap. Any chlorine or chloramine in tap water may kill the beneficial bacteria established in the media, and losing them sends the tank back towards the conditions of a new aquarium. A light rinse in the tank water removed during the change keeps most of that population in place.

When your fish are delivered

We hand-bag your fish in pure oxygen and pack them in an insulated poly box, adding a heat pack when the weather calls for it. A licensed live-animal courier carries the parcel, and we email the tracking number and your confirmed delivery date so you know when to be in. Live fish cannot be left unattended, so someone must be at the delivery address to receive the parcel, and it should be opened and inspected on the day it arrives. Our delivery and Live Arrival Guarantee policy sets out the full terms.

Step by step on delivery day

1. Start recording before the parcel is opened: a continuous unboxing video showing the sealed parcel with the outer box visible. Record every delivery this way, as the Live Arrival Guarantee needs it for any claim.
2. Carry on recording in one take while you open the box, until the fish are visible in their sealed bag.
3. Float the sealed bag in the aquarium for 20–30 minutes before releasing, so the fish acclimatise slowly.
4. Move the fish into the tank without adding the bag water; never pour the bag water into your aquarium.
5. If anything is wrong, message us the same day, ideally on WhatsApp, with the order number and your video, and we will arrange a replacement or refund.

The continuous video matters because our licensed live-animal courier may ask us for that evidence when we raise a claim.

The first week

Healthy fish have clear, bright eyes, undamaged fins, intact scales and no ulcerations or bumps. Watch the group settle over the following days, and test the water more often than usual, since a dozen new fish is a real increase in load for the filter.

Spotting problems early

Every fish varies a little, so the useful habit is noticing change. OATA suggests keeping an eye on these signs:

• Swimming: hanging at the surface, sitting on the bottom or swimming erratically.
• Colour: turning darker or paler than normal.
• Temperament: a change in the level of aggression, or hiding more than normal.
• Breathing: gill covers moving faster or slower than normal.
• Appearance: white spots or fluffy growths, or loss of fins or scales.
• Condition: an increase or decrease in body weight.
• Feeding: eating less, or losing interest in food.

Ragged fins in a Serpae tank

Because fin nipping is part of this species’ reputation, damaged fins can point to stocking as much as to water. If fins look torn, check that the group is at least 12 strong, that the tank is not crowded, that food is spread out at feeding time and that no long-finned or timid fish are being singled out, as well as testing the water.

When to get in touch

If you are concerned, test the water first, then contact us with the readings and what you have seen, and we will help you work out the next step.

Breeding behaviour

The Serpae Tetra is an egg-scattering free spawner that shows no parental care. According to Seriously Fish, adults in good condition spawn often, and in a mature aquarium a few fry may appear without any intervention; leaf litter helps here, because the microbes that grow on decaying leaves can be a valuable secondary food for fry.

How breeders raise more fry

To increase the number of young, Seriously Fish describes conditioning the adult group together, then using a smaller aquarium filled with mature water. The base is covered with a mesh coarse enough for eggs to fall through but fine enough to keep adults out; plastic ‘grass’ matting or a layer of glass marbles work too, as does filling much of the tank with a fine-leaved plant such as Taxiphyllum or with spawning mops.

Telling the sexes apart

Sexually mature females are noticeably rounder-bodied and a little larger than males, Seriously Fish notes. Sex cannot be chosen when you order, so a group of 12 or more gives the best chance of both sexes being present.

Tank mates and fin nipping

This is the section to read twice. Seriously Fish calls the Serpae Tetra notorious as an aggressive community inhabitant with a reputation for nipping the fins of tankmates, and FishBase’s aquarium note also labels it aggressive. The same sources explain when the problem is worst: Seriously Fish says it is most pronounced when too few are bought or space is limited, and FishBase notes fin biting among the fish themselves when too many crowd in at feeding. Group size, tank size and the choice of companions therefore decide whether a Serpae community works.

Companions to avoid

OATA’s tetra guidance is that larger or more boisterous tetras should not be kept with any timid or long-finned fish, as they may nip their fins. That rule fits the Serpae Tetra. Leave out long-finned fish of any kind and shy, timid species, however peaceful they are themselves. OATA also advises that small tetras should not be kept with any fish large enough to eat them, which rules out big predatory tankmates for this 4 cm fish.

What makes a good companion

Tetras mix best with species of a similar size and temperament to themselves, OATA says. For a Serpae group, that means robust, active fish of similar size with short fins, able to hold their own around a busy shoal, and comfortable in the same water.

Before adding any companion, run through these questions:

• Is it close in size to a 4 cm tetra, neither small enough to be harried nor large enough to eat one?
• Are its fins short, with no trailing or flowing finnage?
• Is it confident rather than shy or timid?
• Is it comfortable within 20–28°C and pH 5.0–7.5?
• Is the tank already bigger than the 80 × 30 cm minimum?

A companion that fails any one of these is better left out.

Space for a community

Seriously Fish’s advice is a group of 12–15 in its minimum 80 × 30 cm tank with no other upper-water species; adding other compatible species requires larger tanks. If you want a mixed display, size the aquarium up rather than squeezing companions into the minimum footprint.

When a calmer tetra is the better choice

OATA describes tetras as generally small, colourful and peaceful fish, with some exceptions, and the Serpae Tetra is one of those exceptions. If your aquarium already holds long-finned or timid fish, or you cannot give a group of 12 the room it needs, a gentler species will suit your tank better. Our full range of tetras lets you compare other shoaling fish before you decide.

Species tank or community?

A single-species tank of 12–15 Serpae Tetras is the most straightforward way to enjoy them, and it gives you the natural display and male colour that Seriously Fish links to a proper group. A community is possible in a larger tank, provided every companion passes the size, temperament and fin tests above.

Serpae questions answered

How big does a Serpae Tetra get?

FishBase and Seriously Fish both record a maximum of 4 cm standard length. The fish are supplied at 2–3 cm or 3–4 cm, which is the size at dispatch rather than the adult size.

What size aquarium do they need?

Seriously Fish gives an 80 × 30 cm base, about 72 litres, as the absolute minimum for a group of 12–15 with no other upper-water species. A community with other species needs a larger tank.

How many Serpae Tetras should I keep together?

Keep at least 12. Seriously Fish treats 12 as the minimum because a larger group is more likely to be distracted by each other than by tankmates, and OATA warns that tetras kept singly or in too small groups will often become stressed.

Is it a good fish for beginners?

It is adaptable about water, and commercially bred fish are fairly tolerant of chemistry, but it asks for planning: a mature tank, a group of at least 12 and no long-finned or timid companions.

What does the Serpae Tetra eat?

It is omnivorous. Offer a good quality flake or granule, with live or frozen foods such as bloodworm, Daphnia, Moina or mosquito larvae, and feed only what the group eats within a few minutes once a day.

What temperature and pH does it need?

For the Serpae Tetra in aquariums, Seriously Fish gives 20–28°C, pH 5.0–7.5 and 1–15 dGH. A comfortable target inside that range is 22–26°C and pH 6.5–7.5, with ammonia and nitrite at zero.

Is the Serpae Tetra aggressive, and does it nip fins?

It has a reputation for nipping the fins of tankmates, and Seriously Fish calls it notorious for this. The behaviour is most pronounced in small groups or cramped tanks, so a group of 12 or more and enough space make a clear difference.

What fish can live with it?

Choose robust fish of a similar size and temperament, as OATA advises for tetras. Avoid any timid or long-finned fish, and any fish large enough to eat a small tetra.

How does a Serpae Tetra arrive alive in the UK?

It travels hand-bagged in pure oxygen inside an insulated poly box, with a heat pack when needed, carried by a licensed live-animal courier. Someone must be in to receive it. Record a continuous unboxing video from the sealed parcel onwards, then float the bag for 20–30 minutes before releasing; that video is needed for any Live Arrival Guarantee claim.

Sources

• FishBase: Megalamphodus eques species summary (reached from Hyphessobrycon eques): accepted name, family, natural range, environment values, wild behaviour and diet, maximum length.
• Seriously Fish: Hyphessobrycon eques: aquarium size, water ranges, equipment sizing, décor, diet, behaviour, sexing and breeding.
• OATA: How to look after tetras and pencilfish: group guidance on water quality, group size, maintenance, health signs, feeding and compatibility.
• RSPCA: fish environment: filtration and the nitrogen cycle.
• Tropical Fish Co: Delivery and Live Arrival Guarantee policy, for packing, delivery and acclimatisation.