Marine Betta
Calloplesiops altivelis
A stunning spotted comet that mimics an eel; peaceful but eats small shrimp.
| Difficulty | Intermediate |
| Min. Tank Size | 300 L |
| Temperature | 24.0–27.0 °C |
| pH Range | 8.1–8.4 |
| Max Size | 20.0 cm |
| Lifespan | 5-10 years |
| Diet | Carnivore |
| Temperament | Peaceful |
Overview
The Marine Betta (Calloplesiops altivelis) is a stunning spotted comet that mimics an eel; peaceful but eats small shrimp. It is a popular choice among Australian aquarists, reaching around 20 cm and living roughly 5-10 years when properly cared for.
This complete guide covers how to keep the Marine Betta successfully - tank size and setup, water parameters, the best foods (including recommended brands), suitable tank mates, breeding, sexing and the health issues to watch for. It is rated Intermediate to care for.
Natural Habitat & Origin
This is a saltwater species from tropical coral reefs. It requires a stable, mature marine aquarium with correct salinity (around 1.024-1.026), excellent filtration and pristine water.
Matching the temperature, water chemistry and cover a species evolved with is the simplest route to keeping it healthy and seeing its natural behaviour and colour.
Tank Size & Aquarium Setup
Provide a minimum of 300 litres for the Marine Betta. Give it a large footprint with sight-breaks and cover to reduce territorial aggression.
Marine fish need a mature saltwater tank with plenty of live rock for grazing, shelter and natural filtration, plus a protein skimmer, good flow and rock-stable salinity. Mix a quality reef salt with RO/RODI water - never use plain tap water.
Always add fish only to a fully cycled, mature tank with stable biological filtration. Match filtration generously to the fish's size and waste output.
Water Parameters
Keep the Marine Betta in a stable marine system at 24-27 °C, pH 8.1-8.4, and a salinity of about 1.024-1.026 specific gravity (35 ppt), measured with a refractometer.
Ammonia and nitrite must read zero, with nitrate low (below 10 ppm, or below 5 for a reef). Keep salinity, temperature and pH rock-steady - marine fish are far less tolerant of swings than freshwater fish - and top up evaporation with fresh RO/RODI water, not saltwater.
Diet & Feeding
The Marine Betta is a carnivore and needs a protein-rich, meaty diet.
In Australia, good options include Hikari Marine and Dymax frozen marine foods such as mysis and brine shrimp (note the mandarin dragonet needs a mature tank full of live copepods). Feed small amounts once or twice a day (only what is cleared in a minute or two), vary the diet for the best colour and health, and avoid overfeeding, which is the leading cause of poor water quality.
Temperament & Tank Mates
The Marine Betta is peaceful and community-friendly. It mixes well with other calm species that share its temperature (24-27 °C) and pH (8.1-8.4) needs, are too large to be eaten and not large enough to eat it.
Breeding
The Marine Betta is rarely or not bred in the home aquarium; most stock is commercially farmed or wild-collected, and home breeding is considered very difficult.
Even if you are not planning to breed it, recognising this behaviour helps you understand what you are seeing and respond well - for example by adding cover for fry or giving a guarding pair extra space.
How to Tell Males from Females
Sexing depends on the species; some change sex, others show size or colour differences only when paired.
Common Health Problems
Marine fish are prone to marine ich (Cryptocaryon) and velvet; quarantine new arrivals and keep salinity and water quality rock-stable. Quarantine new arrivals for 2-4 weeks and watch daily for early signs such as loss of appetite, unusual hiding, clamped fins or laboured breathing - caught early, most issues are very treatable.
Prevention beats cure: keep water pristine, avoid overstocking and overfeeding, quarantine new arrivals, and act at the first sign of trouble.
Is the Marine Betta Right for You?
The Marine Betta suits keepers with some experience and a stable, mature, appropriately sized tank, as long as you can provide at least 300 litres, water at 24-27 °C and pH 8.1-8.4, the right diet and suitable tank mates.
Meet those needs and the Marine Betta will reward you for around 5-10 years. Use our free aquarium calculators to plan your setup, and explore our other fish, plant and disease guides to build a thriving aquarium.
