Excerpted from: Puffed up with pride; New and unusual pufferfish species for the discerning aquarist by Neale Monks
The dwarf puffers, genus Carinotetraodon 

This genus of pufferfish includes a number of small, strictly freshwater pufferfish from South and South East Asia. Apart from their size, the most characteristic feature of this genus is pronounced sexual dimorphism: the makes are usually much more brightly coloured and invariably posses erectile ridges along the belly and back. In fact, the scientific name of the genus, Carinotetraodon, comes from these structures, karina meaning ‘keel’ in Greek. When males are displaying to females, or threatening one another, they raise these keels, presumably to make themselves look more imposing. Both sexes can puff themselves up in the normal manner when alarmed, just like other pufferfish. 

Although Carinotetraodon spp. are territorial and snappy towards one another, like most other pufferfish, their small size makes it possible for multiple specimens to be accommodated in a sufficiently large aquarium. Under such circumstances, males and females will eventually pair off, and following some fairly rough courtship behaviour they will spawn, often in a thick mass of Java moss. The male will then drive off the female and guard the eggs until they hatch, which normally takes about three days. Once the fry are free swimming, after another couple of days, they will accept tiny lived foods, such as microworms, and after a week or two they can be weaned onto newly hatched brine shrimp and small Daphnia. 

There are three species of Carinotetraodon regularly traded, of which the most common is probably Carinotetraodon travancoricus, an Indian species often simply called the dwarf puffer. It is indeed a tiny fish, barely 2 cm long when mature, and a densely planted 40-litre (10 gallon) aquarium will comfortably house a single make and three females without much risk of aggression between them. Unfortunately, males and females are very similar when young; so sexing the fish in your retailer’s tanks is difficult. However, once mature, sexing them is quite easy: while both fish have a dark band along the ventral surface, the male’s is much darker. Males may have stronger overall colouration as well, particularly when spawning, but this is an unreliable indicator because there is so much variation in the colouration of these fish anyway. Besides variation between specimens, individual fish can also change their colours depending on their mood. 

Carinotetraodon travancoricus are confirmed fin-nippers, and keeping them with tankmates such as small tetras or barbs is a bit of a gamble. On the other hand, they generally get along well with dwarf suckermouth catfish (Otocinclus spp.) and freshwater shrimps (Caridina spp.). As far as feeding goes, these fish are very adaptable, and will take all kinds of live and frozen foods, including small snails, bloodworms, clean Tubifex worms, and Daphnia. Brine shrimp are a good treat and willingly taken, but their nutritional value is low so they shouldn’t be used as a staple. One nice thing about Carinotetraodon travancoricus is that it is predominantly day-active, and is in fact remarkably outgoing given its size. It is also very tolerant of water chemistry, doing equally well in both slightly soft and acidic conditions and moderately hard and alkaline ones. As with all pufferfish though, it does not appreciate rapid changes in pH and hardness, and is very intolerant of nitrite and ammonium. Provided they are kept in a well-filtered, mature aquarium, these are lovely fish, and excellent oddballs for the aquarist with only limited space. 

Less commonly encountered is the red-eye puffer, Carinotetraodon lorteti. Found throughout much of South East Asia it has been known to the hobby for decades, often being traded under an old name, Carinotetraodon somphongsi. Though well know, its availability has been patchy, almost certainly because its high level of aggression and persistent fin nipping make it impossible to keep in a community tank.  In terms of basic requirements, this species is comparable to the dwarf puffer in most respects, though being a larger fish it does need a bigger aquarium. A matched pair may be housed in a 40-litre (10 gallon) aquarium. Males are easily distinguished from females by their colours; males are basically brown with mustard yellow stripes across the head and back. The belly is cream-coloured belly except for a reddish stripe across the keel running from just behind the mouth to the base of the anal fin. The tail fin is greenish-blue and fringed with a thin white band. Females are attractive but in a different way, sporting a mottled pattern of light and dark brown above and off-white below. Both sexes sport red irises, from which comes their common name. 

The least widely seen of the three popular Carinotetraodon species is the red-tail puffer, Carinotetraodon irrubesco. It is sometimes muddled up with the red-eye puffer, and females of the two species are virtually identical, the only obvious difference being that female Carinotetraodon irrubesco bear thin brown stripes on the belly that female Carinotetraodon lorteti lack. Male Carinotetraodon irrubesco can be immediately recognised by their red tails, but they also have red dorsal fins and the lighter bands on the dorsal surface are tan coloured rather than yellow. While it is a toss-up which of the two species is the more attractive, Carinotetraodon irrubesco definitely has the advantage as far as personality goes. It is relatively peaceful and can be kept with a variety of other fish, provided slow moving species with long fins are avoided. My own species seem to get along well with cardinal tetras, gobies, Otocinclus, and juvenile halfbeaks. 

Two additional species of Carinotetraodon are traded very occasionally, the Borneo red-eye puffer, Carinotetraodon borneensis, and the banded red-eye puffer, Carinotetraodon salivator. Male Borneo red-eyes are similar to C. lorteti but the with greenish-yellow banding instead of bright yellow and they also have a distinctive blue tail. Female Borneo red-eye puffers are essentially identical to female C. lorteti, though the colour banding on the back may be a trifle more yellowy. Banded (or striped) red-eye puffers are easy to recognise because of the vertical banding on the head and body. These bands vary in intensity, being most obvious on spawning males, but even on quiescent males should be apparent. Female striped red-eye puffers look a lot like female Carinotetraodon irrubesco. Unfortunately, males of these two species are extremely aggressive, both towards females and other fishes in the aquarium. Aquarists intent on spawning these fish, should they be lucky enough to obtain them, will almost certainly need to condition the female apart from the male, and only introduce the male when she is carrying eggs. Even then, there are no guarantees that they will spawn, and separating the fish if things turn nasty will be essential.