The lemon tetra (Hyphessobrycon pulchripinnis) is a species of tropical freshwater fish which originates from South America, belonging to the family Characidae. It is a small tetra growing to 2 inches in length.
The lemon tetra is one of the deeper-bodied tetras, contrasting with slender, torpedo-shaped relations such as the cardinal tetra and the rummy nosed tetra, whose approximate body shape when seen from the side is that of a lozenge,(often referred to as a diamond, is a form of rhombus). The basic body color of an adult specimen is a translucent yellow, with a pearlescent lustre emanating from the scales in particularly fine specimens. The dorsal and anal fin of the fish are marked with black and yellow: specifically, the anal fin is hyaline (glass-like appearance), with a black outer margin, the anterior three or four rays being an intense, acrylic lemon-yellow in hue, while the dorsal fin is principally black with a yellow central patch. The tail fin is mostly hyaline but in fine specimens (particularly alpha males) acquires a gunmetal-blue lustre. The pectoral fins are hyaline whilst the pelvic fins are translucent yellow, becoming more solidly and opaquely yellow with black posterior edges in fine specimens (again, alpha males are particularly notable in this regard). The eye is a notable feature of this fish, the upper half of the iris being an intense red, in some specimens almost gemstone-ruby in appearance. The colour of this part of the iris is an indicator of the health of the fish: if this red colouration fades, or worse still turns grey, then this is an indicator of serious disease in the fish. In common with many characins, the lemon tetra possesses an adipose fin. This fin may acquire a black border, particularly in males, though this is not a reliable characteristic. Black areas of colouration on adult fishes frequently acquire a glossy sheen, enhancing the beauty of the fish.
Determining the gender of the fish is achieved in adult specimens by examining the black outer border of the anal fin. In female specimens, this consists of a fine black line, appearing almost as if drawn onto the fin with a fine pencil. In male specimens, particularly alpha males, the border is conspicuously wider, and in breeding alpha males, can cover up to a third of the total area of the anal fin. This is the only reliable means of differentiating gender in this species – while males frequently have taller and more pointed dorsal fins, some females also possess tall, pointed dorsal fins, and thus this characteristic is not reliable. Ripe females are fuller bodied, particularly when viewed from directly above, as the body cavity expands to accommodate the eggs forming within the female’s reproductive tract.
Juvenile fishes are usually translucent with only a hint of the colour of the adult. Additionally, the gender characteristics in juvenile fishes are not fully formed, so differentiating juveniles into male and female individuals is extremely difficult.
The lemon tetra inhabits clear waters with a modest to moderate current flow, remaining in shallower waters in close proximity to stands of aquatic plants. The water chemistry is slightly acidic, and the waters are relatively mineral-deficient. Lemon tetras congregate in their chosen waters in large shoals, numbering several thousand individuals, where the black and yellow colouration becomes disruptive from the standpoint of predatory fish species attempting to track an individual fish. The fishes are capable of moving at speed when required, and in a shoal the fishes will, when danger threatens, weave in and out of each other, adding to the visual confusion for a predator. The species preferentially occupies the middle and mid-lower water levels in the wild.
Lemon tetras fare best in a planted aquarium, where they should be kept as schooling fishes, allowing them to replicate their wild behaviour as closely as possible. A minimum of six individuals should be kept in an aquarium, though if space allows, a larger number is preferable, as the species exhibits a marked preference for grouping together in large shoals of its own kind where possible. In a planted aquarium, the Lemon Tetra displays more vivid colouration – juvenile specimens in bare dealer aquaria usually appear ‘washed out’ in appearance and do not show the full splendour of which this species is capable. The aquarium for this species should be furnished with plant thickets interspersed with open swimming areas where the fishes can display to each other. Suitable companions in an aquarium include other tetra species, small barbs, small danios, small rasboras, Corydoras and Otocinclus catfishes, and in aquaria where space allows, certain species of dwarf cichlid such as the smaller Apistogramma species. Tankmates should be chosen to be peaceful, not too large, and a more natural display results if the companion fishes chosen are other South American species. An aquarium containing large shoals of lemon and cardinal tetras makes a particularly stunning display, the blue and red of the Cardinals contrasting with the brilliant yellow and black of the lemons.
While the preference of the lemon tetra with respect to water chemistry lies within the realm of soft (hardness less than 8° dH) and acidic (pH around 6.6) parameters, the species is notably hardy, and will accommodate itself to a wide range of conditions, the pH range for the fish being from 6.0 to 7.4. Temperature range for the species is 21 °C to 28 °C, though the species is capable of withstanding water temperatures up to 32 °C for considerable periods of time if the water is well oxygenated. Aeration and good quality filtration should be provided for this fish (and indeed for all aquarium fishes) though the fish is sufficiently hardy to cope with aquarium equipment failures provided these are attended to upon discovery.
Extremes of high pH (8.0 or higher) and hardness should be avoided, as these will subject the Lemon Tetra to potentially life-threatening stress.
Feeding the lemon tetra poses few problems for the aquarist, as the fish readily and eagerly devours all fish foods offered to it. For prime conditioning (especially if captive reproduction is to be attempted) live foods such as Daphnia should be offered. The lemon tetra is particularly fond of live bloodworms (these are the aquatic larvae of Chironomus midges) and will attack this particular food item with a relish that has to be witnessed to be fully appreciated! Prepared foods such as flakes, freeze dried Tubifex worms and similar fare are also devoured avidly.
The lifespan of the lemon tetra in the aquarium can be as much as 8 years, though 6 years is a more typical figure.