Figure Eight Puffer Care Guide

Introduction

Dichotomyctere ocellatus, the figure eight puffer, is a small, strikingly patterned pufferfish from Southeast Asia named for the figure-eight shaped markings on their yellow-green and dark green body. Unlike many puffer species, figure eight puffers are a brackish water fish: they come from tidal estuaries and mangrove areas where freshwater meets salt, and they thrive in low to moderate salinity.

Native to coastal rivers and estuaries of Southeast Asia, including Thailand, Malaysia, Indonesia, Cambodia, and the Philippines, figure eight puffers are sold in the freshwater section of most fish stores but actually require added aquarium salt to remain healthy long-term. Keeping them in purely freshwater shortens their lifespan.

They are intelligent, personable, and beautiful fish with the same characteristic curiosity and eye-movement that makes all pufferfish so engaging. Their care requirements, including a brackish environment, snail diet for dental health, and species-appropriate tank mate limitations, make them a specialty fish for dedicated keepers.

Basic Overview

Common Misconceptions

"Figure eight puffers are freshwater fish." They are brackish water fish. While they survive short-term in freshwater, long-term freshwater keeping causes declining health, repeated infections, and shortened lifespan. A specific gravity of 1.005–1.008 is needed.

"They can be kept in a community tank." Figure eight puffers are nippy and may attack other fish, particularly those with trailing fins. They do best in a species-specific tank or very carefully chosen brackish community with robust, similar-temperament fish.

"Any food is fine." Like all pufferfish, their ever-growing beak-like teeth need hard-shelled food to wear them down. Snails are essential. Without hard-shelled prey, teeth overgrow and eventually prevent feeding.

"Marine salt and aquarium salt are interchangeable." Marine salt (reef salt mix) is the correct choice for brackish fish. Plain aquarium salt lacks the calcium, magnesium, and other minerals that make brackish water chemically appropriate for these species.

Recommended Setup

• 30+ gallon tank for one figure eight puffer
• Sand or crushed coral substrate
• Brackish water: specific gravity 1.005–1.008 using marine salt mix
• Hardy brackish-tolerant plants: Java fern, anubias, Vallisneria (tolerate low salinity)
• Caves and hiding spots: rocks, driftwood, PVC pipe
• Moderate filtration with gentle to moderate flow
• A snail culture running in a separate container for a constant food supply

Diet

Figure eight puffers need hard-shelled prey to prevent dental overgrowth. Dental health is the most critical aspect of their diet:

• Snails (bladder snails, ramshorn snails, Malaysian trumpet snails; their primary and most important food)
• Frozen bloodworms (a favorite; feed regularly)
• Frozen brine shrimp and mysis shrimp
• Clams on the half shell (excellent for dental wear and enrichment)
• Frozen krill and small shrimp pieces

Feed once daily. Maintain a live snail culture to provide a continuous supply of the hard-shelled food essential for their dental health. Check teeth monthly: if the beak is misaligned or overgrown, veterinary trimming may be necessary. A puffer that cannot eat due to overgrown teeth will starve even in a well-stocked tank.

Personality

Figure eight puffers are among the most personable and interactive fish in the freshwater and brackish hobby. They recognize their keeper instantly and approach the glass eagerly at feeding time, tracking movement with their independently rotating eyes in a way that seems almost intelligent.

They are curious investigators that examine every new object in their tank, often hovering motionless and staring at something new before deciding whether to investigate or ignore it. Their ability to express what appears to be genuine curiosity and individual preference makes them compelling pets.

As with all puffers, individual personalities vary: some are bold and gregarious; others are cautious and territorial. Learning your individual puffer's behavior patterns is part of the joy of keeping them.

Setting Up Brackish Water

Brackish water is created by adding marine salt mix to freshwater until the specific gravity reaches the target range. Use a hydrometer or refractometer (refractometers are more accurate) to measure salinity. A specific gravity of 1.005–1.008 is appropriate for figure eight puffers.

For a 30-gallon tank at 1.005, you will need approximately 100–130 grams of marine salt mix per 30 gallons. Mix salt into fresh water before adding to the tank; never add salt crystals directly to a tank with fish.

Water changes must use pre-salted water matched to the current tank salinity. As water evaporates, salinity rises, so top off evaporation with plain fresh water, not salted water. Only use salted water for actual water changes.

Water Parameters

Figure eight puffers need brackish water that approximates their native tidal estuary environment:

• Specific Gravity: 1.005–1.008 (use marine salt mix)
• pH: 7.5–8.4
• Hardness (gH): 10–20 dGH (moderate to hard)
• Temperature: 74–82°F
• Ammonia and Nitrite: 0 ppm
• Nitrate: below 20 ppm

Here are some top tips to deal with unwanted parameters:

• Use a refractometer, not a swing-arm hydrometer, for accurate salinity measurement. Swing-arm hooydometers are less accurate and the difference matters for brackish fish health.
• Weekly 25–30% water changes with matched-salinity water maintain excellent conditions. Avoid large sudden salinity changes, which stress the fish.
• A mature, well-cycled filter is essential. The beneficial bacteria in a brackish tank are the same as in freshwater; cycling the tank before adding fish is equally important.
• Crushed coral substrate both looks natural and helps maintain the alkaline pH that brackish fish require.