Manipulating Conditions to Induce Breeding
Many if not most aquatic animals are brought into breeding condition by environmental changes that occur within their habitats. In some cases, the change involved may be quite subtle, such as a short-term drop in temperature. In other cases, dramatic events such as the changing of a season may be necessary to induce breeding.
It is nearly impossible to describe the range of factors that influence the reproductive strategies of the world's aquatic animals. What is known is that many require delicate manipulations of certain conditions if they are to breed in captivity. As has been mentioned, corals over huge sections of the Great Barrier Reef in Australia reproduce simultaneously, somehow brought into condition by as yet little understood factors. What is apparent, however, is that the complex system of environmental cues is involved.
In some areas of the world, falling water levels induced by drought concentrate food animals, resulting in a bonanza for predatory creatures that, under these conditions, are brought rapidly into breeding condition. Over large tracts of the Amazon River basin, seasonal floods allow fish and invertebrates to enter forests that are normally above the river's water level. There they feed ravenously upon fruits, plants, and animals that are otherwise unavailable to them. This glut of seasonally available nutrients likely stimulates reproduction in some species.
In cases like those previously mentioned and countless others, complex chemical changes to the water are also no doubt taking place. As water levels drop, salts and minerals become concentrated, causing the pH and specific gravity to change. Similarly, floods might dilute these elements while introducing others that were missing previously.
In seeking to learn more about captive reproduction and other aspects of aquarium keeping, be sure to consult older books and publications. In the days before advanced life-support systems were readily available, aquarists generally paid great attention to the daily lives and habits of their pets. Sadly, such vital information is often bypassed today.
Perhaps the most common reproductive cue is temperature change. Temperate species often require a “cooling down” period if they are to reproduce successfully. Along with this period of reduced temperatures, these species generally must experience a change in day length. Manipulation of light cycles in the aquarium is often an important aspect of husbandry.