Dwarf pufferfish

Dwarf pufferfish are a potamodromous species[7][8] endemic to rivers, lakes, and estuaries in Kerala and southern Karnataka in the Western Ghats of Peninsular India.[1][9] It is reported from 13 rivers in Kerala, inhabiting heavily vegetated waters,[3] including Pamba River,[2] Chalakudy River,[10] Periyar, Kechery,[11] Muvattupuzha,[12], Vembanad, Meenachil River, and Cherthala,[13] and reported as rare in Bharathapuzha[14] and the Nilgiri Biosphere Reserve.[15] The species was also reported from inundated brickyards in Puthukkad,[11] as well as ditches, ponds, irrigation channels, and artifical tanks or abandoned water bodies in paddy fields. The large range of their distribution and their appearances in small, secluded bodies of water is likely mediated in part by piscivorous birds unintentionally dispersing individuals.[16]

Several researchers have considered the species to be endangered,[17][18][10] though with no rationale provided. The dwarf pufferfish is officially classified as vulnerable on the IUCN Red List due to declining populations because of damming, indiscriminate deforestation for agriculture, pollution from waste water, and, primarily, overharvesting for the aquarium trade.[1][3] In 2010, some researchers estimated that the population would decline by 30–40% from 2005 to 2015,[1][17] while others estimated it had already declined by the same amount between 2005 and 2010.[19]

A juvenile dwarf pufferfish in an aquarium

Both sexes are primarily greenish-yellow with dark green to black iridescent patches on the flanks and dorsal surface, and light yellow or white and typically without patches on the ventral surface. Patterns and colouration varies considerably between individuals. Their pectoral fins are short, slightly emarginate, and fan-shaped. 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 and truncate.[2] As with other members of the genus, sexual dimorphism is apparent in mature fish, with males being more brightly coloured than females.[5] Males can also have a dark stripe down the center of their pale belly and iridescent "eye wrinkle" patterns that females do not have. Females are more rounded, tend to be a bit larger than males, and may or may not show more smallish spots between their larger dark markings.

Sexing of juveniles is impossible because these fish "choose" their sex as they mature. Once one pufferfish begins becoming a male he excretes hormones to prevent the other puffers from becoming male. However, if two fish start to mature into males at the same time one will become the dominant male. There is also a dorsal crest, but it lacks special colouration when not erect. Both crests are displayed during courtship while the male circles the female. They also will have more yellow colouration.

Dwarf pufferfish are a slow-swimming,[16] demersal species.[7][8] Their diet in the wild mainly consists of small animals such as cladocera, rotifers, copepods and insects. Sand and detritus, presumably ingested by mistake when feeding on small, bottom-dwelling animals, has also been found in the gut of dwarf pufferfish.

Though many freshwater pufferfish accumulate saxitoxin in their skin due to their consumption of specific cyanobacteria present on or in their food sources, there is little or no reliable evidence to suggest dwarf pufferfish also contains this neurotoxin.[20]

Ramshorn snails are commonly used to feed dwarf pufferfish.

In captivity, the dwarf pufferfish will eat small snails such as ramshorn snails, bladder snails, and Malaysian trumpet snails, as well as some frozen foods like bloodworms, and brine shrimp, which can also be fed live. Pufferfish like to have a varied diet and it's important to feed different foods when keeping dwarf puffer fish in captivity. Other members of the genus feed on zooplankton and various benthic crustaceans and molluscs.[21] Food items of specimens maintained in aquaria appears to be similar.[5] 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.[3]

Unlike many other pufferfish species that are primarily solitary, dwarf pufferfish are found in large shoals, occasionally consisting of hundreds of individuals, mainly during summer months (January to May) and very rarely during the rainy season.[11] Due to their shoaling nature, aquarium hobbyists have found the fish will exhibit aggression between conspecifics when kept in groups of fewer than six individuals, or when there is more than one male for every two females.

When first described in 1941, K. Nair noted that dwarf pufferfish were a favourite of children, who would catch and use the fish as playthings.[2] They are regarded as "frog tadpoles" by local fisherman[11] and otherwise given little regard. They are of no interest to fisheries[25], are not a food fish, and are only valued as ornamental fish in aquaria.[26][1]

Wikimedia Commons has media related to Carinotetraodon travancoricus.

• Pufferfish Enthusiasts Worldwide Dwarf Pufferfish Care Sheet
• Care information for Dwarf Puffers kept in the home Aquarium