Carinotetraodon lorteti

Carinotetraodon: from the Latin carina, meaning 'keel', and the generic name Tetraodon, within which members have formerly been included.

lorteti: presumably named for French zoologist Louis Charles Émile Lortet (1836-1909).

Known from the lower Mekong basin in Thailand, Vietnam, and Cambodia, the Chao Phraya watershed in central Thailand, and may occur in smaller river systems between.

Type locality is 'Thu-dâu-môt, Vietnam'.

Inhabits slow-moving to standing water in shady forest streams, minor tributaries, and floodplains. Aquatic or dense riparian vegetation often grows densely in such environments, while the substrate may be covered in fallen leaves and branches.

An aquarium with dimensions of 60 ∗ 30 ∗ 30 cm24 ∗ 12 ∗ 12 in or equivalent should be the smallest considered.

This species requires a well-decorated aquarium with driftwood roots or branches plus plenty of aquatic plants, of which floating varieties can be used to provide additional shade. The addition of dried leaf litter further emphasises the natural feel and as well as offering cover brings with it development of microbe colonies which can provide a valuable early food source for fry.

Any flow from the filter should not be strong, and regular small water changes are recommended since this species is sensitive to deteriorating conditions.

Tetraodontids lack true teeth, the jawbone itself being modified into four fused toothlike structures. These grow continuously at a surprising rate, so offer regular meals of shelled invertebrates such as snails, small crab legs, cockles, etc., in order to maintain them at a reasonable length. There is some evidence to suggest that aufwuchs form a significant proportion of the natural diet, therefore it may be worth permitting or even encouraging algal growth on hard items of décor.

Additional foods can include chopped shellfish, small earthworms, and live or frozen chironomid larvae (bloodworm), Artemia, etc. Dried products should not form the principal component of the diet, although pelleted formats with a very hard consistency may prove useful.

Unsuitable for the general community aquarium and best maintained alone due to its tendency to bite the fins of tankmates, especially in smaller aquaria.

It is territorially aggressive but a group can be kept together provided the aquarium is arranged correctly (see 'Maintenance') and sufficient space is available.

Adult males possess well-developed dorsal and ventral keels on the body, which are erected during threat displays and courtship. In addition, males possess a uniformly-coloured body and caudal-fin, while females display a reticulated colour pattern on the body and caudal-fin.

This species has been bred in aquaria. Courtship is initiated by the male and characterised by an intensified colour pattern plus displays involving the dorsal and ventral crests. Semi-adhesive eggs are deposited among aquatic vegetation (fine-leaved mosses such as Taxiphyllum are particularly suitable) close to the substrate.

Post-spawning the male assumes sole responsibility for guarding the brood, with the eggs typically hatching in 60-72 hours. The fry initially possess a yolk sac which is fully absorbed within a couple of days, at which point they become free-swimming and should initially be offered infusoria-grade foods on account of their small size.

C. lorteti is included in a group often referred to as 'red-eyed puffers', which currently contains four recognised species distributed in Indochina and the Greater Sunda Islands. It can be distinguished from C. borneensis, C. irrubesco, and C. salivator, the remaining members of this group, by the following combination of characters: 12-13 dorsal-fin rays; 14 pectoral-fin rays; 11-12 anal-fin rays; 11 caudal-fin rays; eyes not bulging above the head; in males dorsal-fin reddish, black spot on dorsal-fin base present, pectoral-fin base hyaline, anal-fin reddish with black spot at base, caudal-fin greyish proximally and black with white edge distally, throat unmarked, no bars on body; in females ventral surface unmarked or with faint spots, 4-5 bars on caudal-fin.

Carinotetraodon is distinguished from other genera within the family Tetraodontidae by the presence of distinctive dorsal and ventral keels in males, plus distinct sexual dimorphism in terms of both morphology and colour pattern. Tetraodontidae is the most speciose group among Tetraodontiformes and its members mostly inhabit coastal waters in South America, Central Africa, and Southeast Asia. It is the only tetraodontiform family in which a number of members exclusively inhabit freshwater, and genetic evidence suggests that the timing of these invasions differed, occurring around 0–10 million years ago (MA) in South America, 17–38 MA in Central Africa and 48–78 MA in Southeast Asia.

Tetraodontids are commonly referred to as ‘puffers’ due to the ability of many species to inflate their body to an enormous size when stressed or threatened. This is achieved by drawing water into a specialised ventral diverticulum of the stomach, although air can also be used if the fish is removed from the water. As a result of these morphological adaptations puffers swim via a unique combination of pectoral and median fin undulations referred to as ‘diodontiform’ swimming. They are also able to produce sounds by grinding the jaw/pharyngeal teeth or vibrating the swim bladder. Puffers are secondary freshwater fishes, with the majority of members exclusively inhabiting marine environments.

Other defining characters of tetraodontids include a tough skin usually covered with small spines, a beak-like dental plate divided by a median suture, a reduced gill opening anterior to the pectoral-fin base, no pelvic fins or spinous fin rays, typically short-based dorsal and anal fins, and no ribs.

Puffer flesh is toxic and can cause clinical poisoning and human mortality, although it is regarded as a delicacy in certain countries. The predominant toxin, usually either tetrodotoxin or saxitoxin, is dependant on species, geographic area, and time of year. The toxins are not produced by the fishes themselves, but by bacteria living in symbiotic association, or they are acquired via the food chain.