Dwarf Indian Puffer

The maximum documented size is 3.5 cm (1.4 in) total length (TL), with individuals typically reaching less than 2.5 cm (0.98 in) TL, making dwarf pufferfish one of the smallest pufferfish in the world. Both sexes are primarily greenish-yellow, with dark green to brown-black iridescent patches on the flanks and dorsal surface. Patterns and colouration vary considerably between individuals. Their pectoral fins are short, fan-shaped, and described as "slightly emarginate", that is to say, slightly indented at the tip. The dorsal and anal fins are situated opposite each other toward the posterior of the fish, both short and round, while the caudal fin is larger than the other fins and truncate, in that it terminates in a more-or-less vertical edge. Their bodies are round and oblong. As with other members of the genus, sexual dimorphism is apparent in mature fish, with males being more brightly coloured than females and having a yellow ventral surface. Males can also have a dark stripe down the centre of their pale belly and iridescent, blue "eye wrinkle" patterns that females do not have. Females are more rounded, tend to be larger than males, and may have more small spots between their larger dark markings. Their abdomens are white, and they may have a yellow patch on their throat.

Natural defenses. …

Although closely related to marine pufferfish, they are not found in salt water, and reports to the contrary are based on misidentification. Dwarf pufferfish are one of only 27 known species of Tetraodontidae adapted to freshwater. They are a potamodromous species, meaning they migrate within freshwater river systems, and are endemic to rivers, lakes, and estuaries in Kerala and southern Karnataka in the Western Ghats of Peninsular India. They can be found in waters with a pH of 7.5–8.3 and temperatures of 22–28 °C (72–82 °F). Inhabiting heavily vegetated waters with beds of gravel and rock or clay loam with silt and sand, the species is reported from 13 rivers in Kerala, lakes such as Vembanad, the Nilambur harbours, and Kallar Stream, part of the Neyyar Wildlife Sanctuary. They have been reported as rare in Bharathapuzha and the Nilgiri Biosphere Reserve. The species was also found in inundated brickyards in Puthukkad, as well as ditches, ponds, irrigation channels, and artificial tanks or abandoned water bodies in paddy fields. Their presence in small, isolated water bodies is likely due to unintentional dispersal by waterfowl.

Conservation status. Several researchers have considered the species endangered, though with no rationale provided. …

Dwarf pufferfish are euryphagous carnivores in that they consume a wide variety of animals. Dwarf pufferfish favour insect larvae but will rely on crustaceans and annelids as alternate feed when the availability of preferable prey decreases. Their diet in the wild mainly consists of small animals such as water fleas, rotifers, copepods, and seed shrimp, and aquatic larvae such as those of Odonata, Hemiptera, mayflies, and flies, with some amounts of plant matter, largely diatoms and green algae. Sand and detritus, presumably ingested by mistake when feeding on small, bottom-dwelling animals, have also been found in their gut.

In captivity, dwarf pufferfish benefit from a varied diet and will eat small freshwater snails, shrimps, as well as foods like frozen mussel meat or other frozen shellfish. They will also readily eat live foods such as red and white mosquito larvae and other small animals they would predate in the wild. Dwarf pufferfish are commonly associated with plants in the genus Cabomba, and the presence of these plants has been shown to reduce mortality among captive specimens. Dwarf pufferfish are a slow-swimming, demersal (bottom-dwelling) species. …