Brackish Water Pufferfish (family Tetraodontidae)

As far as the brackish water aquarist is concerned, pufferfish divide up into three camps: freshwater species that sometimes inhabit slightly brackish water; marine species that periodically enter brackish water; and species that spend more or less all their lives in brackish water.

Primarily freshwater pufferfish that occasionally found in brackish water are listed below; these can be expected to tolerate slightly brackish conditions in aquaria, at least SG 1.003, and perhaps as high as 1.005.

• South American pufferfish Colomesus asellus
• Sea frog pufferfish Tetraodon cutcutia
• Target pufferfish Tetraodon leiurus
• Fahaka or Nile pufferfish Tetraodon lineatus
• Giant African pufferfish Tetraodon mbu
• Football pufferfish Tetraodon pustulatus

Numerous marine pufferfish enter brackish water to breed or feed, and in some cases estuaries may be important habitats for juvenile fish in particular. The following are some of the species that can do well in mid to high salinity brackish water systems for extended periods; maintaining saltwater puffers in brackish water conditions is further discussed in the Marine Pufferfish part of this FAQ.

• Stars-and-stripes pufferfish Arothron hispidus
• Immaculate pufferfish Arothron immaculatus
• Reticulated pufferfish Arothron reticulatus
• Starry pufferfish Arothron stellatus
• Milk spotted pufferfish Chelonodon patoca
• Gold spot pufferfish Chelonodon sp. Gold Spot
• Parrot pufferfish Colomesus psittacus
• Peacock pufferfish Takifugu ocellatus
• Japense pufferfish Takifugu rubripes

The following species are true brackish water species. While there has been much debate about their preferred conditions in the wild, under aquarium conditions they invariably do better in brackish water, rather than freshwater, conditions.

• Figure-8 puffer, Tetraodon biocellatus
• Green spotted puffer, Tetraodon nigroviridis
• Ceylon puffer, Tetraodon fluviatilis

Taxonomy: Will the real Green Spotted Puffer please stand up!

It’s worth mentioning that Tetraodon nigroviridis and Tetraodon fluviatilis were both treated as a single species the ‘green spotted puffer’ and referred to as Tetraodon fluviatilis in the past. Some books still maintain this approach and many retailers will sell both species as green spotted puffers. In strictly scientific terms, identifying the two species with 100% reliability is impossible on morphology alone: colouration varies, and individuals of one species can have colour markings like those of the other species. To correctly identifyTetraodon nigroviridis, Tetraodon fluviatilis and the (at least one) not-yet-identified look-alike species requires analysis of their DNA, something beyond most hobbyists!

Water chemistry

All pufferfish need good, clean water. In the case of brackish water species the aquarist must also ensure that the water is hard, alkaline and sufficiently saline.

require clean water, regular water changes, plenty of swimming space, and preferably soft sand for digging. None are ideal community fish and most are best kept alone, one to a tank. In terms of diet, unshelled crustaceans and molluscs are preferred, selected according to the pufferfish being maintained. Pond snails, clams, krill, shrimps, and crayfish are all useful foods. Soft foods, like mussel meat and bloodworms are enjoyed, but these do not wear down the pufferfish’s teeth. Like rodents, puffers have teeth that grow constantly, and without abrasion, become too long for the puffer to feed properly. They can be clipped manually using cuticle cutters, but it is best to simply prevent this happening by offering suitably "crunchy" foods.

Pufferfish quickly learn how to beg for food and rapidly train their owners to give them food whenever the pufferfish wants it (which is pretty much always). Resist this lesson! Small pufferfish only need to be fed once a day, and larger fish not even that often. The exception may be Takifugu ocellatus, a fish that may need to be fed more regularly than this (see below). Overfeeding pufferfish causes a variety of problems, the chief of which is reducing water quality. Pufferfish are sensitive to dirty water, and must be kept in mature tanks with good filtration, and weekly water changes of at least 25% are essential.

	=	=	=
	Tetraodon biocellatus	Tetraodon fluviatilis	Tetraodon nigroviridis
	Figure-8 pufferfish	Ceylon, topaz or green spotted pufferfish	Green spotted pufferfish
	Note the two circular markings on each flank, one below the dorsal fin, the other close to the base of the tail fin.	Most, but not all, specimens have saddle-like markings that cross the back.	Upper surface colour is bright green when young, darkening with age. Most specimens are covered with small black spots, but these are irregular blotches on the Sabah form.

The figure-8 puffer is a small (6-8 cm) species distinguished by its pattern of yellow squiggles on a dark green body. It has a clear white belly. Across the back, the yellow squiggles often join to form loops, typically one large loop on the head and another joined on to it and lying over the back. Together, these loops form the "figure-8" of this species' name. In addition, there are usually a pair of yellow circles on either side of the body, one below thr dorsal fin and another on the base of the tail. Figure-8 puffers are aggressive towards one another and sometimes other fish, so keeping them in groups or mixing them with tankmates is far from safe. That said, in a suitably large tank multiple specimens can get along; around 50 litres per fish is required. Bumblebee gobies are one species that seem to get on well with these fish (as well as having similar requirements) but a lot depends on the temperament of the particular pufferfish. Figure-8 puffers need a low to moderate salinity; specific gravities between 1.003-10 work well. Older books recommend these fish be kept in freshwater, based on observations of these fish in the wild, but for whatever reason, in aquaria they do consistently better when kept in brackish water. Kept well, these fish will live for over 10 years.

The green spotted puffer is a fairly large (around 15 cm) pufferfish with a brilliant green body covered in small black spots. Juveniles are sociable and fairly peaceful, but as the fish mature they become more territorial and somewhat predatory; given around 120 litres per fish, it is possible to keep multiple specimens in the same tank, but otherwise they should be kept alone. Some success has been had keeping them with robust brackish water fish such as monos and scats, but many specimens become inveterate fin-nippers, so the best approach is to keep these fish on their own. A fairly high salinity is needed for these fish, with SG 1.005-1.012 being required over the long term. They can also be kept in full-strength seawater.

The Ceylon puffer, sometimes called the topaz puffer or (arguably erroneously) the green spotted puffer is very similar to the green spotted puffer as far as requirements go, though tends to be a bit more aggressive and fin-nippy. It is of similar size as well, but is different in colouration. Instead of a uniform pattern of small black spots, it has a pattern of large dark blotches. Across the back there are usually transverse green bands separating a few saddle-like markings. Its colouration is particularly brilliant when young, but older fish often have a rather muddier cast.