Saltwater Fish · Basslets
Chalk Bass
Serranus tortugarum
Blue-marked dwarf bass that actually shoalsBeginner
- Lifespan
- 5-8 years
- Size
- 8 cm (3 in)
- Social needs
- Singly, or a group of 3-5 added together
- Time
- Daily feeding; weekly testing/changes
- Cost
- Medium
- Diet
- Carnivore (mysis, enriched brine, marine pellets)
Overview
What is this animal?
- The Chalk Bass is one of the smallest of the true sea basses, a roughly 8 cm (3 in) Caribbean serranid with a pale lavender-tan body scattered with iridescent blue markings and a row of darker bars along its sides.
- It lives in loose aggregations over sand-and-rubble bottoms, often well below the bright shallow reef, and it ranks among the hardiest and most forgiving of all marine aquarium fish.
- It is a genuinely sensible first saltwater fish, not just a marketed one.
- Its defining trait is sociability, which is rare in small marine fish.
- Unlike the Royal Gramma, which is normally kept one to a tank, Chalk Bass can live in a loose shoal of three to five if every fish is added at the same time.
- They are simultaneous hermaphrodites, and spawning pairs famously take turns releasing batches of eggs in a behaviour biologists call egg trading, a mating system studied in this exact species.
Temperament
- Chalk Bass are peaceful toward unrelated tankmates and fully reef-safe with corals, spending the day hovering a few centimetres above the rockwork in a loose, active shoal.
- Within a group there is brief sparring while a pecking order forms, after which squabbles are rare so long as the tank is 210L (55 gallons) or larger and the whole group went in together.
- Kept singly they are equally content and become bold, ever-visible residents.
- The one caveat is that bass mouth, which can engulf very small tankmates such as sexy shrimp, other tiny ornamental shrimp, and the smallest nano gobies.
- Full-sized cleaner shrimp and normal-sized fish are ignored.
- Add the whole group in one go, keep singletons in the smaller tanks, and never assume a second Chalk Bass can be slipped in with an established one months later.
A good fit for
- First-time marine keepers wanting a near-bulletproof fish
- Anyone wanting a rare shoaling saltwater fish for open water
- Peaceful fish-only and mixed reef community tanks
- Recently cycled systems that need a hardy first resident
- Keepers fascinated by the egg-trading breeding behaviour
Common mistakes to avoid
- Open-top tanks — jumping is their top cause of death
- Adding group members later instead of all at once
- Keeping a shoal of 3-5 in only a 30-gallon tank
- Tiny ornamental shrimp and nano gobies fit that bass mouth
- Overfeeding — they beg convincingly and eat fast
Enclosure
Minimum 110 litres (29 US gallons)
Fine alone or with company. Singly, or a group of 3-5 added together
- A single Chalk Bass needs a cycled aquarium of at least 110L (30 gallons), and a shoal of three to five needs 210L (55 gallons) or more so the group has room to spread out.
- Build piles of live rock and rubble with plenty of crevices, because this is a rubble-slope fish that hovers in open water and bolts into gaps when startled.
- Hold temperature at 22-27°C (72-80°F), salinity at 1.023-1.026, pH at 8.1-8.4, and keep nitrate low, under 20 ppm and lower still in a mixed reef.
- A tight-fitting lid is non-negotiable, as startled Chalk Bass are determined jumpers and carpet-surfing is their single most common cause of death.
- Coming from deeper water, they do not need intense lighting and appreciate a shaded overhang or two.
- The classic keeper mistake is buying one now and adding more later, which turns the resident into a territorial bully instead of a shoalmate, so decide on group size before the first fish goes in.
Supplies
Setup
- Tank, stand and sump
- Return pump and powerheads
- Protein skimmer
- Reef lighting
- Rock and sand
- Salt mix, refractometer and test kits
- Quarantine tank
Ongoing
- Frozen mysis shrimp
- Frozen enriched brine shrimp
- Small sinking marine pellet
- Frozen chopped seafood blend
- Vitamin or HUFA soaking supplement
- Turkey baster for target-feeding near rockwork
- Small thawing cup and strainer
Safe substrate: Aragonite sand · Dry or cured live rock · Bare bottom
Care routine
Daily
- Check salinity, temperature and flow
- Check the lid
- Feed
- Head-count and look everyone over
- Top up evaporation with fresh water
Weekly
- Service the skimmer and filter socksevery 3 days
- Check each fish still has a cave
- Clean the glass
- Test the water
Monthly
- Water changeevery 2 weeks
- Calibrate the refractometer
- Check salt, RO/DI and reagents
Less often
- Deep-clean pumps and powerheadsevery 3 months
- Replace RO/DI filter mediaevery 6 months
Vet: Quarterly review with a territory check — every 3 months
Top resources for more info
Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.
YouTubers
HumbleFish & ReefSaltwater fish disease, quarantine and treatment (Humble.Fish forum)BRStvReef tank setup, fish health and quarantine series (run by a retailer)FishOfHex AquaticsBeginner saltwater guides, avoiding common mistakes and tank disasters
Sites
Go deeper
Diet
- In the wild the Chalk Bass hovers above the rubble picking off zooplankton such as copepods, so it takes prepared foods almost immediately in captivity.
- Offer frozen mysis, vitamin-enriched brine shrimp, finely chopped marine seafood, and a quality sinking marine pellet, fed once or twice daily.
- Refusal to feed is so unusual in this species that it should be treated as an early warning sign of illness.
- Remember that this is a true bass with a surprisingly large mouth for its 8 cm body.
- It will happily swallow food items that look oversized, and in a group the boldest fish will hog the feed, so scatter food across the tank so everyone eats.
- Keep portions modest, because its eagerness makes overfeeding and fouled water an easy trap.
Health
- The Chalk Bass is among the most disease-resistant marine fish in the trade and shrugs off the minor parameter wobbles that kill more delicate species in young tanks.
- That hardiness is not a licence to skip quarantine, since a new arrival can still carry marine ich or velvet into the display.
- Early trouble shows as clamped fins, hiding more than usual, rapid breathing, or that tell-tale refusal of food.
- The biggest killers of Chalk Bass are not diseases at all but jumping from an uncovered tank and slow decline from chronic bullying in a group kept too small or built up over time.
- Keep salinity and temperature stable, keep the lid on, and give each fish rubble of its own.
- A well-kept specimen should live a solid five to eight years.
Is your enclosure big enough?
Minimum volume110 litres (29 US gallons)
CompanyFine alone or with company. Singly, or a group of 3-5 added together
Is this urgent?
In a reef, stability matters more than any single target number. A parameter moving fast does more damage than a parameter sitting slightly off.
Go now
Any detectable ammonia or nitriteWater change now with matched, mixed and aerated saltwater. Stop feeding. Directly toxic, and a marine system has less margin than a freshwater one.
NowTemperature or salinity has moved sharplyCorrect slowly, over hours, not minutes. Check the heater and the top-off. The speed of the change does the damage. Correcting fast repeats the injury in the other direction.
NowRapid gilling, or a fish hanging in the flow breathing hardIncrease aeration and check temperature and salinity. Warm water holds less oxygen, and a heater failure shows up here first.
NowToday
White spots, or a fine dusting like icing sugarIdentify which parasite before treating. Most reef tanks cannot be treated in place. The two common parasites look similar and need different handling; velvet can kill a tank in days.
TodayCorals closed for more than a day, or receding tissueTest alkalinity first, and compare it against the last reading rather than a target. Unstable alkalinity is the most commonly cited coral killer, and a swing shows up in the trend, never in a single point.
TodayA new fish added without quarantine now looks unwellRemove it to a separate system today if you can. Nearly every wipeout in a reef tank traces back to a skipped quarantine.
TodayQuarantine every new animal, including corals and inverts. It is the single practice that separates a reef that lasts from a reef that restarts.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Bedding and substrate
In a marine system the rock and the sand are life support, and how you start them decides the first six months.
Safe
Aragonite sandThe standard marine substrate. Buffers pH and hosts the biology.
safeDry or cured live rockDry rock avoids importing pests but takes longer to mature. Cured rock is faster and riskier.
safeBare bottomCommon in high-flow systems. Easier to keep clean, but it removes a large part of the biological buffer.
safeWith a caveat
Deep sand bedsPowerful nutrient processing when they work and a sulphide release when they are disturbed. Choose shallow or deep deliberately, not by accident.
with a caveatUncured live rockIt will cycle the tank for you, and it will also bring in whatever was living in it.
with a caveatNever
Silica play sandDoes not buffer, and it is commonly blamed for feeding diatom blooms in a new tank.
neverAny rock or decor of unknown originMetals and phosphate leach for months and are almost impossible to trace once the tank is running.
neverThis is our general list for saltwater fish. We have not built one specific to Basslets yet.
My kit says 0.25 ppm. Is that dangerous?
A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.
Compare with other animals
The same axes for every animal, side by side — the way the guides are written makes that a fair comparison rather than two articles.
Keep going
Basslets, side by side
Same axes, same care guides — the honest way to choose between types.
See all Basslets side by side →
