The dwarf pufferfish (Carinotetraodon travancoricus), also known as the Malabar pufferfish (leading to easy confusion with the related C. imitator), pea pufferfish or pygmy pufferfish, is a small, freshwater pufferfish endemic to Kerala and southern Karnataka in Southwest India. It is threatened by overfishing for the aquarium trade, and by habitat loss.
The maximum documented size is 3.5 cm (1.4 in), making it one of the smallest pufferfish in the world. Although closely related to marine pufferfish, they are not found in salt water, and reports to the contrary are based on misidentification.
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.
Both sexes are primarily yellow with dark green to black iridescent patches on the flanks and dorsal surface, but as with other members of the genus, sexual dimorphism is apparent in mature fish, with males being more brightly coloured than females. 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.
The diet of dwarf pufferfish 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. In captivity the dwarf puffer will eat small snails such as ramshorn snails, bladder snails, and Malaysian trumpet snails (MTS) as well as some frozen foods like bloodworms, and brine shrimp, which can also be fed live. Puffers 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. Food items of specimens maintained in aquaria appears to be similar. 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.
Social or Solitary?
Unlike many pufferfish species that are solitary and fiercely territorial, some hobbyists proposes that the dwarf pufferfish is very social and occurs in shoals in the wild. The hobbyists propose that they should never be kept alone or in group sizes consisting of less than 6 individuals . with females outnumbering males 2:1 When kept in groups consisting of at least six in the correct male to female ratio, they are much more confident, have a better feeding response, are more social and less aggressive to each other. Solitary C.travancoricus are likely to become shy, nervous and emaciated owing to a decreased appetite. They should never be kept in captivity in groups of less than six individuals. Aggression between conspecifics is common in groups consisting of less than six individuals. A group of six should be housed in a 60-litre tank as a minimum, giving each fish 10 litres of water each.
However, other hobbyists has also observed that the dwarf puffers only shoal when they feel insecure even in groups of less than six fishes, i.e. moving to a new tank, having the aquascape changed. When they feel secure enough they will resort to their territorial self like other puffers.
Nevertheless, it is important to keep them in heavily planted tanks with sufficient hiding places. They will be as confident and be as active as being kept in a shoal of at least six but under insecure setups.
Captive breeding of pufferfish is somewhat difficult, and capture for the pet trade threatens the species in the wild. Dwarf pufferfish eggs are fertilized externally. In the aquarium, dwarf pufferfish are often plant-spawners, laying eggs in plants (including java moss in aquariums) or on the substrate hidden within plants. Eggs have been seen to hatch after five days at 27 °C (81 °F), with fry initially being fed on infusoria, then brine shrimp when they are a week old, and finally regular-sized food. Dwarf pufferfish do not guard their eggs or fry, and breeders do not keep the adults and the fry together.
Dwarf pufferfish have become quite popular as aquarium fish thanks to their attractive colours, small size, and relative ease of maintenance. The dwarf puffer is also one of the few aquarium fish to regularly eat small live snails, so it is used in controlling snail populations. This popularity is a major threat to the species, as it is often wild-caught.