Aquaria/Lemon tetras
Lemon tetras have been popular aquarium fish since the 1930s.
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 interspered with open swimming areas where the fish 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 cichlids, 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.
The lemon tetra does well with water chemistry of soft (hardness less than 8°H) 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 eight years, though six years is a more typical figure.
Reproduction
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Lemon tetras exhibit an interesting behaviour pattern in the aquarium, replicated by several other characin species, in which males will adopt 'landmarks' within the aquarium and use these as places from which to display as maturity approaches. Displays are principally performed between rival males, which position themselves in a slightly head-up posture, unpaired fins held erect to appear as large and as imposing as possible, and swim forwards with 'flicking' movements of the body. If two rival males approach closely, they will then begin to make passes at each other, which to the causal observer look like attacks: this is an entirely ritualised behaviour, best referred to as 'jousting', where the males make darting movements toward each other but pull away at the last moment. No damage is incurred by either contestant in these events, and evenly matched males that are at a similar level in the social hierarchy will continue such behaviour for 30 minutes or more at a time. This behaviour serves not only to establish the social rankings of the males, but also as an indicator of reproductive fitness to the watching females.
A breeding aquarium for the lemon tetra thus requires good quality filtration and aeration, fine-leaved plants, and an 'egg trap' present to prevent large-scale losses because of the aforementioned parental instincts. Temperature should be slowly raised over a period of a few days to 28°C, the pair conditioned with copious quantities of live foods if possible, and the aquarium should be sited so as to receive illumination by morning sunshine, as this is a well-documented spawning stimulus for the lemon tetra. Parent fishes should be removed from the breeding aquarium and returned to the main aquarium once spawning is complete. Sometimes, best results are obtained by using two males with one female.
Development
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Fertile lemon tetra eggs take about 72 hours to hatch at 28°C. The fry spend a further 24 to 48 hours absorbing the yolk sac, when they become free-swimming. At this stage, the fry should be fed with infusoria or a special egglayer fry food, and frequent partial water changes (around 10% of the aquarium volume every 24 to 48 hours) initiated. After 7 days, the fry should be ready to feed upon newly hatched brine shrimp. The fry appear to be almost transparent at first, with the exception of the eyes, and do not begin to develop the 'lozenge' shape of the adult body until the differentiation of the finfold into the unpaired fins is complete (around 4–6 weeks). Once this process is complete, the fish are ready to take sifted Daphnia. Maintenance temperature for the fry should be carefully and slowly reduced to around 25°C once the fish are recognisable miniature versions of the adults. The first signs of black colouration on the unpaired fins may take a further two weeks or more, and the fish must be at least 12 weeks old to fully represent miniature versions of the parents. Even at this stage, the black colouration of the unpaired fins will be incompletely developed, and until sexual maturity is achieved (approximately 8 to 9 months after hatching), the black border on the anal fin may not be a reliable gender differentiation characteristic.