Percula Clownfish - Reproduction

Reproduction

Since these fish live in a warm water environment they can reproduce all year long. Each group of fish consists of a breeding pair and 0–4 non-breeders. Within each group there is a size-based hierarchy: the female is largest, the breeding male is second largest, and the male non-breeders get progressively smaller as the hierarchy descends. They exhibit protandry, meaning each fish is born male, but will only change to female if the sole breeding female dies. If the female dies, the breeding male changes sex, becomes the breeding female and the largest non-breeder becomes the breeding male. The spawning process is correlated with the lunar cycle. At night time the moon maintains a higher level of alertness in the A. percula and this increases the interaction with the males and females. Before spawning, the male attracts the female via courting behaviour. These courting actions include extending their fins, biting the female and chasing her. The males also swim rapidly in an upward and downward motion to attract the females. The nest site is also important for the survival of the eggs. Depending on the size of the female spawn about 400–1500 eggs per cycle. The expected tenure of breeding females is approximately 12 years and is relatively long for a fish of its size, but is characteristic of other reef fish.

It has been unclear why the non-breeders continue to associate with these groups. Unlike non-reproductives in some animal groups, they cannot obtain occasional breeding opportunities, because their gonads are non-functional. They cannot be regarded as helpers at the nest, since it has been found their presence does not increase the reproductive success of the breeders. Recent research (Buston, 2004) suggests that they are simply queuing for the territory occupied by the breeders, i.e. the anemone; non-breeders living in association with breeders have a better chance of eventually securing a territory than a non-resident. The probability of a fish ascending in rank in this queue is equal to that of the individual outliving at least one of its dominants because an individual will ascend in rank if any one of its dominants dies, and not simply when its immediate dominant dies.

The development of the fish from juvenile to adult is dependent on the system of hierarchy, and can be described as density-dependent. There is aggression involved in these small families although usually not between the male and the females. The aggression usually exists between the males. The largest male will suppress the development of the next smallest male and the cycle continues until the smallest fish is evicted from the host anemone. Within each anemone, the regulation of the species is controlled by the female, since the amount of space for fish in her anemone is directly proportional to her size (which eventually reaches a maximum), so she ultimately controls the size of the other fish. Amphiprion percula are very competitive fish and this causes the smaller fish to have a stunted growth. There is the potential for a fish to ascend in rank by contesting its dominant. This depends on the relative body sizes of the two fish, and is very unlikely to happen since A. Percula maintain well-defined size differences between adjacent individuals in rank. However in an aquarium, this fish is peaceful, and it can live in an aquarium environment well.

The fish lay their eggs in a safe spot close to the anemone from where they are easily protected, and the parents can retreat to the safety of the anemone if danger threatens. Anemonefish usually lay their nests in the evening after a few days of carefully cleaning and examining the chosen site. Preferred egg sites are flat or slightly curved rocks or some other item the fish have dragged near their nest for the purpose. (In captivity, clay pots and saucers are an attractive choice.) First the female deposits some eggs with her ovipositor (a whitish tube descending from her belly), making a wiggling pass over the surface, then the male follows behind her fertilizing the eggs. After many passes, the nest is complete and will hatch in 6–8 days shortly after sunset, usually on a very dark night. In the meantime, the male is very protective of the nest and ceaselessly fans the eggs to provide proper oxygen circulation, and checks them for any bad eggs, which he eats before they can rot and damage more eggs. Females may or may not help the male tend the nest. At hatching, the larvae burst free and swim up toward the moonlight and the open ocean to ride the currents and eat plankton for about a week, before the still tiny metamorphosed clowns return to the reef and look for an anemone to settle into. Eventually the cycle repeats.