The Warmouth is a robust, highly predatory North American sunfish. Characterized by its cavernous mouth and dark, mottled brown coloration, it closely resembles a Rock Bass. It is highly aggressive and territorial, requiring a spacious tank. It will rapidly consume any tank mate small enough to fit in its large mouth and thrives in heavily structured aquariums mimicking slow-moving, weed-choked waters.
Warmouth At a Glance
Warmouth Tank Requirements
Will Warmouth fit in your tank?
Care guides tell you what Warmouth needs, the next question is whether your tank can safely provide it. Test Warmouth against your tank size, maintenance needs, and the fish you already keep before you buy.
Warmouth Water Parameters
Warmouth Temperament & Compatibility
Warmouth Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Adult / Standard
The fully grown adult Warmouth. Requires a large aquarium with heavy filtration and plenty of hiding spots (driftwood and plants) to establish a territory. Best kept strictly alone or with similarly sized, robust native fish in very large aquariums (400L+).
Same care requirements as the base species
Also known as: Adult, Full Grown
Juvenile (Grow-out)
Young Warmouth sold at smaller sizes. They grow very quickly and are extremely predatory even at a few inches long. A smaller grow-out tank can be used temporarily, but a rapid upgrade to a large tank is mandatory.
Differs in 5 traits from base species
Also known as: Baby Warmouth, Fry, Juvenile
Warmouth Care Guide Summary
The Warmouth, scientifically known as Lepomis gulosus, belongs to the Other family group. Adults reach a maximum size of approximately 25 cm and have a compressed body shape with a moderate growth rate. Classified as aggressive, this species primarily occupies the mid-level and bottom zones of the aquarium and produces a high level of biological waste.
To thrive, the Warmouth requires a freshwater only aquarium with a minimum volume of 280 litres and a tank length of at least 120 cm. Water temperature should be maintained between 10°C and 28°C, with a pH range of 6.5–8.5 and a general hardness of 5–20 dGH. A low water flow is preferred.
Due to its specialist needs, the Warmouth is best suited for fishkeepers who can provide a carefully planned setup. This species is available in 2 varieties: Adult / Standard and Juvenile (Grow-out). Each may differ slightly in size, temperament, or care needs, so it is worth checking the specific requirements of the variety you plan to keep.
Warmouth Habitat Setup
When setting up an aquarium for the Warmouth, a low water flow best suits their natural preferences. Because this species occupies the mid-level and bottom zones, the aquarium layout should prioritise open swimming space in the centre of the tank for free movement and sufficient floor space with hiding spots among rocks, wood, or dense planting. Useful additions include driftwood, which can serve as both a hiding place and a dietary supplement, leaf litter or blackwater tannins to replicate their natural soft-water habitat, and dense planting to provide cover, break sightlines, and reduce stress.
Warmouth Compatibility Notes
Classified as aggressive, the Warmouth is best housed alone, as they do not tolerate others of their kind in confined spaces. When choosing tankmates, any fish small enough to fit in its mouth will likely be eaten, ornamental shrimp are not safe companions, territorial behaviour may cause issues if hiding spots or floor space are limited, and their energetic swimming style may stress more sedentary or timid species. Selecting tankmates that favour different water layers from the mid-level and bottom zones can help reduce competition and territorial overlap.
Who Warmouth Is Actually For
Warmouth is best for a fishkeeper who expects a species with attitude and plans the tank around that behavior and can provide someone who understands its individual space requirements. It makes the most sense for a hobbyist who will actually build around its needs, especially plants.
The most common mistake is buying Warmouth for looks first and only later discovering how its adult size, behavior, or bioload changes the whole tank plan. Another frequent problem is forcing it into an over-busy community when it would do better with more room or more deliberate tankmate choices.
Warmouth Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Warmouth.
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
180 Gallon Standard
350 Liter (120cm Deep)
Show 1 more tank size
Warmouth Feeding & Diet Considerations
The Warmouth is a predatory species that will readily consume small fish, so nano or bite-sized tankmates should be avoided and will hunt and eat ornamental shrimp, making it unsuitable for shrimp-focused setups.
Frequently Asked Questions About Warmouth
How big does Warmouth get?
Warmouth (Lepomis gulosus) typically reaches a maximum adult size of approximately 25 cm. They have a compressed body shape and a moderate growth rate.
What tank size does Warmouth need?
A minimum aquarium volume of 280 litres and a tank length of at least 120 cm are recommended for Warmouth. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Warmouth need?
Warmouth thrives in freshwater only conditions with a temperature range of 10–28°C, a pH between 6.5 and 8.5, and a general hardness of 5–20 dGH. A low water flow is preferred.
Is Warmouth peaceful or aggressive?
Warmouth is classified as aggressive with an aggression score of 8 out of 10. Careful tankmate selection is essential to avoid conflict.
Can Warmouth live with others of its kind?
No. Only one Warmouth should be kept per tank. Keeping multiples in the same aquarium typically results in aggression and stress.
Is Warmouth safe with shrimp?
No. Warmouth is known to eat ornamental shrimp and is not recommended for shrimp tanks. Even larger shrimp species like Amano Shrimp may be at risk.
Does Warmouth have any special tank requirements?
Yes. Warmouth benefits from plants - densely covered, driftwood (digestion/hiding), and leaf litter/blackwater in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Useful setup supplies
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- May 11, 2026
- Last updated
- May 11, 2026
- Issues or corrections?
- Contact the editorial team
Plants That Suit Warmouth
These plants pair well with Warmouth based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Beckett's Water Trumpet
Cryptocoryne beckettii
Broad-leaved Crypt
Cryptocoryne pontederiifolia
Crypt Wendtii
Cryptocoryne wendtii
Cryptocoryne Lutea
Cryptocoryne walkeri var. lutea
Dwarf Crypt
Cryptocoryne parva
Dwarf Water Lily
Nymphaea stellata
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