Grasscutter Catfish (Schilbe intermedius)

Choose a Grasscutter Catfish for a big open-water shoal

The Grasscutter Catfish (Schilbe intermedius) is an African catfish of the family Schilbeidae, and it lives nothing like the bottom-hugging catfish most fishkeepers know. It is a silvery, flat-sided fish that swims in open water in loose shoals, becomes most active after dark and, in the wild, eats a great many smaller fish. FishBase records a maximum of 50 cm standard length (SL, measured without the tail fin) but notes that it rarely grows beyond 30 cm SL, and ScotCat's care sheet plans for about 30 cm. Treat the Grasscutter Catfish as a large, active predator for a long aquarium and a group of its own kind.

Grasscutter is a trade name. In reference works the species is the silver catfish (FishBase) or the butterfish (ScotCat). We could not find a reliable source for where the grasscutter name comes from, so we do not repeat the stories told about it online. The species name intermedius means intermediate: ScotCat explains that it was described as intermediate between Schilbe uranoscopus and another schilbid then placed in the same genus.

Its range is one of the widest of any African catfish. FishBase lists Senegal, Gambia and many West African basins including the Niger and Volta, the Nile and Lake Victoria basins, the Congo, the Zambezi (including Lake Kariba), East African rivers and southern systems such as the Limpopo, Incomati and Pongola. It prefers large rivers and lakes, rarely enters small rivers, lives mainly in shallow open water and rises towards the surface at night. FishBase gives its IUCN Red List status as Least Concern (assessed 2019) and notes that it is caught as a food fish across its range.

Recognise it by the anal fin and flank bands

ScotCat also pictures an albino form, and notes that Schilbe marmoratus looks similar but is smaller, lighter brown and marbled, with the same dark shoulder patch. Browse the rest of our African catfish, or the full catfish and plecos range.

Tell it apart from our Striped Schilbe (Schilbe mystus)

We also sell the Striped Schilbe Catfish (Schilbe mystus), and customers often ask whether the two are the same fish. FishBase treats them as two separate, valid species, and the confusion comes from a change of name rather than from the fish themselves.

Until 1990 the fish now called S. intermedius was itself known as Schilbe mystus. That year a study of the original specimen of Silurus mystus, the fish on which the name was founded, showed that it belonged to the species then called Schilbe niloticus. The older name takes priority, so S. mystus now means the former S. niloticus, and the widespread species previously known as S. mystus became S. intermedius. ScotCat still lists S. mystus among the synonyms of S. intermedius, which reflects the older usage, and the aquarium trade still uses both names.

Compare the two species side by side

The quickest check in the tank is the adipose fin, the small fleshy fin on the back between the dorsal fin and the tail. A fully developed adipose fin points to S. mystus in the FishBase sense; no adipose fin, or only a tiny one, fits S. intermedius, although some Central and East African Grasscutters do have one. Both are shoaling, open-water predators of a similar size, so the care on this page suits either.

Two more names cause mix-ups. Our Silver Catfish (Chrysichthys nigrodigitatus) shares an English name with this fish in FishBase but is a different, bottom-living catfish from another family. Our African Glass Catfish (Pareutropius debauwi) belongs to the same family as the Grasscutter but is far smaller, and an adult Grasscutter would eat it, so they are relatives, not tank mates.

Know exactly what you receive

• One live Grasscutter Catfish per purchase, supplied as a young fish in the standard size available. It is not yet fully grown and needs room to reach adult size.
• Sex is not selected. ScotCat notes that females grow larger than males, with typical lengths of 20–21 cm SL for females and 14–15 cm SL for males, so a group usually shows a range of sizes as it matures.
• Our photographs are illustrations. Markings and colour vary between fish and change with age, so use the identification features above to check your fish.

Plan a group of four or more

ScotCat recommends keeping four or more and notes that the species does better with its own kind, and FishBase describes it as often shoaling in the wild. A single fish loses the company it relies on. One purchase is one fish, so choose a quantity of four or more and make sure the aquarium can hold the whole group at adult size. Read our delivery and Live Arrival Guarantee terms before you order.

Plan an aquarium of 150 cm or longer

ScotCat advises a large, well-filtered aquarium from 150 cm (5 ft) long upwards for a group. Length matters most, because this is an open-water swimmer that cruises up and down rather than resting on the floor. OATA's guidance on very large fish adds two points that apply here: choose a tank that can house the fish at full size from the start, and remember that many large species grow quickly, so a tank that suits a juvenile may not last. For the biggest species OATA notes that volumes often run to more than 500 litres.

Our tank volume calculator converts your tank's measurements into litres, and the stocking calculator helps you check the whole adult population before you buy.

Use a three-step space check

1. Measure the length: confirm at least 150 cm, with enough width for a shoal to turn.
2. Count the whole adult group: four or more Grasscutters plus every companion, all at adult size.
3. Plan for adult bodies: use about 30 cm per Grasscutter, and remember that FishBase records larger wild fish.

Leave open water and frame it with plants and wood

ScotCat describes the layout this fish wants: wide open spaces, long grass-like plants and a few pieces of bogwood around the margins. That leaves the centre of the tank free for the shoal to swim, while the planted edges give it somewhere to retreat. OATA recommends sand or fine gravel for catfish because of their sensitive barbels, and a fish-proof cover for large fish, which can be jumpy, especially in new surroundings.

Divide the footprint by function

Keep décor to the edges rather than in the swimming lane, and place heaters and filter intakes where a fast-moving fish cannot collide with them or wedge itself behind them.

Match the water values

Published water values for this species are few. ScotCat gives 22–25°C in its data box and 23–26°C in its care notes, with a pH of 6.5–7.2; FishBase gives none. OATA's general catfish guidance fills in hardness. The table shows each source and a range that satisfies them.

UK tap water varies from soft to very hard depending on where you live, so test yours before you plan. Treat every change of water with a conditioner that removes chlorine and chloramine, as OATA advises. Our water matcher compares your readings with these ranges, and our water chemistry guide explains pH and hardness in plain terms.

Separate habitat values from waste readings

These limits come from OATA. A shoal of fish that each reach about 30 cm produces a great deal of waste, so test every week and after every addition of fish.

Filter for a shoal of large predators

ScotCat stresses a well-filtered aquarium, and OATA's very-large-fish guidance explains why: big fish produce large amounts of solid waste, and several large aquarium filters or a pond filter may be needed to keep up. Check filters for blockages and rinse the media lightly in water removed from the tank, never under the tap, so the beneficial bacteria survive. Our guide to aquarium filtration explains the options, and our nitrogen cycle guide explains why a new tank must mature before large fish arrive.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite, nitrate, pH and hardness at least once a week.
2. Change about 25% of the water at least once a week, as OATA recommends.
3. Treat the new water with tap-water conditioner and bring it to tank temperature.
4. Siphon solid waste from the sand.
5. Rinse filter media only in the old tank water and check intakes for blockages.
6. Count the shoal at feeding time and note any fish that hangs back.

Feed a meaty diet in measured meals

In the wild the Grasscutter eats almost anything it can catch. FishBase lists fish of all ages, aquatic and land insects, molluscs, freshwater prawns and other crustaceans, algae and other bottom and open-water organisms, with plant matter and eggs also recorded, and says it is mainly a fish-eater between 13 and 34 cm total length. It is described as a nocturnal surface feeder. In the aquarium, ScotCat says it accepts most standard foods, so there is no need to feed live fish.

OATA's guidance for large fish suggests appropriately sized pellets, with larger frozen foods such as mussel, shrimp or lancefish for carnivores. From our range, frozen Mysis, small frozen krill and Tropical Krill Gran granules make a good rotation. Feed once a day, and only what the fish finish within a few minutes, so that leftovers do not foul the water.

Build one measured meal

• Time it for the evening: FishBase describes the species as nocturnal, so a feed as the light fades suits its rhythm.
• Use food that stays in the water column: slowly sinking granules and thawed frozen food reach a surface and mid-water feeder.
• Watch for a few minutes: make sure every fish in the group gets a share, not just the boldest.
• Remove leftovers: siphon out anything still uneaten after a few minutes.
• Rotate foods: alternate granules with frozen Mysis and krill through the week.

Introduce the group to a mature aquarium

Before the fish arrive, make sure ammonia and nitrite read zero and that the temperature and pH sit within the ranges above. OATA's floating-bag method suits these fish: switch off the aquarium lights, float the sealed bag for 10 minutes to equalise the temperature, add small amounts of tank water over up to 20 minutes, then release the fish, leaving as much bag water behind as possible. Our guide to acclimatising new fish walks through each step.

Introduce the whole group together so the shoal forms straight away. Catfish carry spines on their pectoral fins and just behind the gills, so OATA advises handling them with care and double-bagging them for transport; a fish that tangles in a net is better lifted out in a container.

Use a first-week checkpoint plan

OATA advises monitoring water quality closely during the first week, because a new group adds a sudden load to the filter.

Read normal Grasscutter behaviour

Expect a group that holds together in mid-water, cruising the open lane and turning as one. FishBase describes the species as nocturnal and notes that it rises towards the surface at night, so the group is often livelier after the lights go out than in the middle of the day.

Pair each behaviour with a response

Choose tank mates too big to swallow

ScotCat warns that tank mates must not be too small, as they may be eaten at night, and advises fish of the same size or larger. OATA's large-fish guidance gives the same rule: avoid mixing with much smaller fish. The safest plan is a group of Grasscutters as the main open-water shoal, with robust fish that are already too large to fit in an adult's mouth.

From our range, robust catfish such as the Featherfin Synodontis and other Synodontis catfish, the Senegal Bichir on the floor and the Tinfoil Barb in open water are candidates for a big aquarium, provided sizes are matched when you add them. Check every combination in our tank mates tool.

Screen every companion the same way

Handle the spines and watch its health

OATA lists the warning signs that something is wrong in a catfish aquarium. Check them at every feed, and when you see one, test the water before doing anything else.

Pair each sign with an action

FishBase records a maximum observed lifespan of almost 10 years, so a well-kept group is a long commitment. OATA adds a rule for every aquarium fish: never release an unwanted fish or plant into the wild.

Know the breeding and sexing notes

ScotCat reports that the species has not been bred in aquariums. In the wild FishBase describes spawning throughout the year with one peak: during the rainy season fish migrate upriver in fairly compact shoals to spawn in flooded pools, and the eggs are left unguarded. Females grow larger than males, which is the most practical way to tell the sexes in a mature group.

Answer Grasscutter Catfish buying questions

What is a Grasscutter Catfish?

Grasscutter Catfish is a trade name for Schilbe intermedius, a silvery, open-water African catfish from the family Schilbeidae. FishBase calls it the silver catfish and ScotCat the butterfish. It lives in shoals, feeds mostly at night and eats smaller fish.

Is it the same fish as the Striped Schilbe (Schilbe mystus)?

Not according to FishBase, which keeps them as two separate species. The Grasscutter was itself called Schilbe mystus until 1990, when that name was moved to the species formerly called Schilbe niloticus. The true S. mystus has a fully developed adipose fin, while the Grasscutter usually has none or only a small one. Their care is very similar.

How big does a Grasscutter Catfish get?

Plan for about 30 cm. FishBase records a maximum of 50 cm standard length but says it rarely grows beyond 30 cm, and ScotCat gives about 30 cm. Females grow larger than males.

How many Grasscutter Catfish should I keep?

Four or more. ScotCat recommends a group of at least four and says the species does better with its own kind. One purchase is one fish, so choose a quantity of four or more.

What size tank does a Grasscutter Catfish need?

ScotCat recommends a large, well-filtered aquarium from 150 cm long upwards, with wide open swimming space, long grass-like plants and a few pieces of bogwood around the edges.

Will a Grasscutter Catfish eat my small fish?

Yes. FishBase describes it as voracious and predatory and mainly a fish-eater once it reaches about 13 cm, and ScotCat warns that small tank mates may be eaten at night. Keep it only with fish too large to swallow.

What water does a Grasscutter Catfish need?

ScotCat gives 22–25°C in its data box and 23–26°C in its care notes, with a pH of 6.5–7.2. Aim for 23–25°C and pH 6.5–7.2, with zero ammonia and nitrite and nitrate no more than 20 mg/l above your tap water.

What should I feed a Grasscutter Catfish?

Meaty foods: good granules or pellets alongside frozen Mysis, krill and similar foods, once a day and only what the group finishes within a few minutes. ScotCat says it accepts most standard aquarium foods, so live fish are not needed.

Consult the care references

• ScotCat: Schilbe intermedius — common name, synonyms (including S. mystus), distribution, size, description and markings, sexing, breeding, tank size, layout, water values, diet and compatibility.
• FishBase: Schilbe intermedius (silver catfish) — maximum size, lifespan, range, habitat, behaviour, wild diet, reproduction, adipose-fin and anal-fin features, the 1990 name change and IUCN status.
• FishBase: Schilbe mystus (African butter catfish) — the separate species now carrying the name S. mystus: adipose fin, anal-fin rays, size and range.
• OATA: How to look after catfish — UK guidance on catfish water values, waste limits, substrate, maintenance, feeding, acclimatisation, handling and health signs.
• OATA: How to look after very large (tankbuster) fish — planning for adult size, filtration, feeding large fish, lids, compatibility with smaller fish and never releasing fish.
• Tropical Fish Co delivery policy — current dispatch and Live Arrival Guarantee terms.