It is extremely difficult to tell the difference between male and female goldfish when the fry are less than a year old; however the females are likely to be bigger than their brothers of the same age. This page is to serve as an aid in helping you determine your fishes sex as stated by Dr. Yoschichi Matsui, Professor of Fish Culture, Kinki University, Japan, 1972.

The sex of the mature fish may be determined by the shape and appearance of the anal opening. (A) and (B) show the female in profile and underview, respectively; (C) and (D) show the male. The female's profile is more rounded and, when she is ripe, tends to protrude.

As fish approach their spawning time, it is relatively easy to distinguish the males from the females, although in some of the more highly developed types of fishes, the only sure way to differentiate the sexes is to note which fish lay eggs. As the eggs mature and develop in the female, a thickening can be noted in her ventral region.

At about the same time, the male will start to develop small white tubercles on his gill plates and on the leading rays of his fins, particularly the first ray of the pectoral fin. Excessive growth of tissue on the gill plates of some varieties can make detection of the tubercles difficult, but they can usually be noted on the pectoral fin. To the practiced eye, the anal opening serves to distinguish the sexes (diagram above). The male opening is small and oval, while the female one is larger, projects a little more and is circular in shape. These differences too are most apparent as spawning time approaches, since the female opening will be larger and more distended when the eggs are ripe.

When the male is ready for spawning, milt may be pushed out of the ventral opening by running a finger lightly along the sides of the fish. However, when the male is ripe, his tubercles will plainly indicate his sex, and it is not necessary to handle the fish to prove it. Once spawning is completed, the tubercles may vanish on the male because of decreased sex hormone secretion. As the next spawning time approaches, new tubercles will be seen to appear but on a weaker scale.

There is a great deal of pleasure in raising goldfish which have been spawned by others, but it does not compare with the satisfaction of seeing your fish hatch out of the eggs and watching the developing fry, always with the hope that among them there may be that one beautifully perfect specimen.

Goldfish kept outdoors will spawn readily when the spring comes, but if the eggs are not given the proper attention, very few young fish will be raised. On the other hand, if the eggs and young fish are cared for properly, thousands of goldfish can be raised from one spawning. While it is much easier to induce goldfish to spawn outdoors, with a little care and careful planning, goldfish will spawn in indoor aquariums as well.

Conditioning Your Goldfish

As spring approaches, it is important that our potential parent fish be in the best possible condition for spawning. Not only will healthy, well-nourished fish spawn more readily, but the quality of their eggs will be better. Well-conditioned parents product more eggs, a higher percentage of them will be fertile and the fry hatching out will be stronger. As the spawning season approaches, most of the nutriments taken in by the fish go into building up the eggs of the females and the milt of the males. Therefore, pay special attention to feeding parent fish in the early spring. A good supply of live food, such as chopped earthworms, bloodworms, etc., is helpful although not absolutely essential. In addition to its nutritive values, live food accelerates the production of sex cells.

Courtship

In the spring, when the water temperature has risen to just below 60 degrees F or into the high sixties, you will notice that the goldfish start to group together while swimming about. Small goldfish will follow fish two or three times their size and rub against the larger fish. Soon some of the more active males will single out a female and drive her vigorously through the water. As the actual spawning days draw closer, this driving becomes more prolonged and intense. These are the usual signs which precede the actual spawning, but the more exotic types of fish may not go through these preliminaries, so be warned, if breeding the latter, that there will not necessarily be any preliminary indications.

Spawning commences early in the morning, usually as the first light reaches the tank, and continues to about noon. As the spawning female throws her eggs, other goldfish not in on the spawning drive may follow her about and eat all the eggs they can find. Indeed, once the spawning fishes have completed their activity, they will often turn around and eat the eggs themselves. With such cannibalistic inclinations, a young fish must be fortunate indeed to survive to maturity.

Spawning Nests

Nets on which the goldfish will spawn can be made up of bunches of fine-leaved water plants such as Anacharis, Cabomba or Myriophyllum tied together. Water hyacinths are probably the spawning medium most commonly used by the hobbyist. They have the advantage of floating naturally while eggs deposited on their trailing roots are easily seen. It is not necessary to use living plants for fish nests. Clumps of dried willow roots or bunches of Spanish Moss are good substitutes. Nylon mops and nettings, which can be cloated by tying them to a piece of wood or cork, are also suitable. You can also buy knitting yard and wrap it about 60 times around an average hardback book. Slip it off and tie one end with a strand of yarn and cut the other end with scissors. This makes a tassle that can be hung or floated in the tank. These are very easy to make and very inexpensive.

Spawning

Goldfish begin spawning when the water reaches about 68 degrees F, but often the fish will not start to spawn until the fish nests are provided. Rubbing against the nests stimulates the desire to spawn. When everything is ready, we put the breeders in the spawning tank along with the nests, the morning before we wish the spawning to take place. If all goes well, the fish will be depositing eggs on the nests the next morning. The eggs are adhesive and will stick to just about anything. They are about 1.5 mm in diamter, the size of a pinhead, but as they take on water, they increase in size. After two or three hours, the eggs are water-hardened and if kept at 50 to 55 degrees they can be transported safely for long distances.

Hatching and Caring for Fry

Sometimes it is more convenient, once spawning is completed, to remove the adult fish. A greater number of eggs will hatch using this method, since it is never possible for the spawning nests to catch all of the eggs, because some may fall to the bottom while others adhere to the fixtures and glass of the tank. Usually, however, transferring the nests to a hatching tank is more practical.