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Discussion Starter · #1 · (Edited)
by Marc Elieson

Fin Organism Yellow Fish Adaptation

Most African Cichlids are what's called "maternal mouthbrooders." Mouthbrooders are highly advanced from an evolutionary standpoint. They have developed a method for protecting their young at the most vulnerable time of their development. Mouthbrooders brood their eggs in their mouths!

Once a male has fertilized the eggs, the female will pick them up, and incubate them in her mouth for a period of 21 to 36 days, depending upon the species and temperature of the water. While "holding" the eggs, the mother does not eat, which can be very taxing on her, especially if she and the male are still in the same tank, as he will chase her, trying to mate with her yet again. I have observed, however, that during the last week of incubation, the mother will pick at small pieces of flake most likely to feed to her fry. Once the yolk sac has disappeared and the fry are free-swimming, she will release them.

Most male Cichlids (and even some females) have "egg spots" on their anal fin. In this photo of a male Ps. Zebra (to the right), nine egg spots can be seen clearly. I have seen males with anywhere from 1 to 12 egg spots. Some will even have more on the posterior tip of their dorsal fin as well. These egg spots seem to serve a useful purpose in getting females to spawn, or in the indirect fertilization of her eggs. More on this below.

Water Fin Fish Electric blue Ray-finned fish

They are called egg spots because, to the female, they appear to be eggs. They are the same size as eggs (in my estimation) and the same color. Furthermore, as the male does his shimmying dance, the spots will wave.

Organism Fish Water Fin Rectangle

The movement of these spots on the male's fin induces her to either lay her eggs, or if she has already picked up her laid eggs, the movement will cause her to think that she has left some behind. She will then open her mouth and reach for them. At this point, the male will release his sperm into the water, fertilizing the eggs on the gravel, or in her mouth if she has already picked them up.

The male will repeat this process dozens of times, and seems to only stop because the female loses interest. It seems logical to me that after a few dozen fertilizations, the female would be confident that they've been successfully fertilized by that point. Now whether the male actually releases sperm each time he does his dance and she shows interest, I don't know. Probably not.

Nature Organism Fish Adaptation Rectangle

Interestingly enough, females will spit out eggs during their incubation period if they were not fertilized. If you watch your pregnant female closely throughout her holding period, you will notice that the load she carries in her mouth decreases after a few days. You may even be lucky enough (or rather unlucky) to see her discard them. Once she spits them, they probably won't be around for long if she has any tankmates. Recently, however, I found an unhatched egg among a group of fry that I stripped from a wild Protomelas taeinolatus, but this is a rarity in my experience.

Several studies performed by Eva Hert have shown that egg spots are not absolutely necessary for fertilization but that females prefer, and more stimulated by, males that have them. In fact, she determined that egg spots have the effect of priming females to produce more eggs!

Nature Organism Fin Fish Adaptation

In her first study, Hert showed that females of Haplochromis elegans prefer males with egg spots. She divided a group of males into two, the experimental males from whom she erased the anal fin spots (by touching the skin briefly with a metal that had been dipped in super-cold liquid nitrogen) and the control males whose spots remained intact. Females found the males with egg spots more attractive than those lacking them.

In a subsequent experiment, she showed that males who possessed more egg spots primed females to produce more eggs. Females placed with males showing egg spots produced twice as many eggs as females placed with males lacking them! She later did this experiment with Ast. elegans and achieved the same results.
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