Lemon Tetra - Reproduction

Reproduction

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 serves as an indicator of reproductive fitness to the watching females.

In the wild, the lemon tetra is a communally spawning fish. Tens of thousands of pairs will spawn together, and choose thickets of fine-leaved aquatic plants as the repository for their fertilised eggs. This behaviour has several ramifications for captive reproduction, as will be duly noted.

When ripe females are receptive, males will court them, after a chase sequence through aquatic foliage in which several males may pursue an individual female, breaking off to pursue a different female as the opportunity arises, resulting in the aquarium in mad dashes hither and thither. Eventually, close observation will see a male court a female in some secluded area of aquatic foliage. The courting gesture of the male consists of a quivering motion, with a head-down posture, and the 'flicking' of the unpaired fins in such a manner as to generate flashes of yellow colouration in the visual field of the female. These flashes will be readily visible to the observing aquarist. If the female is ready to spawn, then the pair will migrate to fine-leaved aquatic plants such as Cabomba or Java Moss, whereupon the pair will adopt a side by side position. The release of eggs and sperm is signalled by a quivering motion upon the part of both fishes, followed by an 'explosive' parting of the couple accompanied by the appearance of a cloud of eggs. The eggs are non-adhesive, and fall through the foliage, coming to rest either in thicker foliage at the base of the plants, or on the substrate.

One of the problems presented to the aquarist by this species is that of egg-eating. In the wild, as has already been noted, tens of thousands of pairs spawn simultaneously, and in order to reduce the competition for their own offspring, a pair will turn around and eat some of the eggs being produced by neighbouring spawning pairs. The same instinct, needless to say, manifests itself in the aquarium, but in an aquarium setting, the only eggs present are usually those of the single spawning pair. Consequently some of the pair's own eggs will be devoured. Special measures to reduce losses through this behaviour are therefore required if the aquarist is interested in obtaining as large a yield of fry as possible. Special 'egg traps' have been devised for the purpose - these may consist of evenly spaced glass rods in a frame, a layer of glass marbles on the aquarium bottom, or some other such device. The purpose of all these designs is the same - to allow eggs to fall through small gaps into a space where they will be beyond the reach of the adults, who are unable to pass through the same gaps. However, the speed of movement of the adult fishes is such that even with an 'egg trap' in place, a small percentage of eggs will still be eaten.

A large adult female in prime condition may produce as many as 300 eggs.

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.