We have previously gone over the problem of Angelfish eating their eggs while spawning, or shortly thereafter. We will now go over fertility. Next we will go over what happens once the eggs hatch, but before the fry are free swimming. Fertility is an issue with Angelfish and will vary drastically between different pairs. Some pairs will be totally infertile; other pairs will be infertile at first and then will become fertile. On pairs that are fertile, the percentage of fertile eggs will range from just a few to, best case scenario, about 90% fertility. The amount of fry produced can vary from just a few to a couple of thousand. There are three main causes of infertility in Angelfish. The first one is mechanical and is caused by the male not doing his job and fertilizing the eggs. The second and third are biological and are due to either the eggs or sperm being genetically or chemically infertile. When Angelfish lay eggs, the male should follow the female on a fertilizing run as soon as she does an egg laying run. Some males only make the run after every two or three egg laying runs. It is my experience that these males tend to have a lower fertility rate. Some males will not fertilize at all. These tend to be the males that also are most aggressive on eating the eggs. There is very little you can do to change these males. Some Angelfish are infertile due to water chemistry. To optimize fertility, water temps should be kept constant between 84 and 88 degrees. Ph should be kept constant at 6.5. Heavy filtration, if possible, is a big plus. I try and avoid doing water changes at this time. The hatch rate is the best when the water is soft. Fluctuation in any of the water conditions while the eggs are developing will result in infertility. So once you put them in the hatch tank, DO NOT change any water conditions. Angelfish that are genetically infertile will never be fertile. Please note that keeping water temperatures above 96 degrees for over a week will usually result in the permanent infertility of Angelfish. Some Breeders have been known to purposefully sterilize the Angelfish they sell to keep others from being able to breed the strains they have developed. We would never do this.