Curiosity about how to tell if your goldfish is pregnant usually comes from observing that a fish has suddenly grown big or looks like it has gotten plump very quickly. Curiosity and concern would be proper reactions, since fish usually eat up fish eggs, including their own, and that might not be what you want for your pets. So it’s important to recognize the signs of a goldfish that’s ready to lay eggs, or spawn, and be prepared for it. You will learn what signs to look for here.
Technically, goldfish don’t get pregnant—that is, carrying offspring inside the body and giving birth to live young. Goldfish lay eggs. The male fish then fertilizes the eggs after the eggs come out. Therefore, a female goldfish does not need a male to lay eggs, but without a male to fertilize them, the eggs will not hatch. A fish’s preparedness for laying eggs is determined by several factors: its gender, its age, the season, and the water temperature. Knowing all these will help you determine if your goldfish is ready to lay eggs.
Find out if your goldfish is female. The best way to know is to ask when you purchase the fish. You would be lucky if you bought a fish that was already carrying eggs inside it, but it’s not likely if the pet shop owner is looking to breed more fish to sell. If you forgot to ask, however, or if the goldfish was given to you, you may observe the features of the fish to know if it’s female. Females typically have plumper bodies. When seen from above, females have fuller bellies and males have more slender middles. The pectoral fins of females (the fins just behind the gills) are shorter and rounder, too. To be sure, you can compare your fish with photos in books or online, or bring it to a pet shop owner or a vet. It’s harder to determine the age of a goldfish, but you can tell a mature fish from a young one by consulting books or the Internet, or asking someone knowledgeable. Goldfish are ready to breed at one to two years old. If your fish is female and around this age, then it is probably ripe for breeding.
Goldfish breed around the summer, after a cold winter season, in clean and toxin-free water with a temperature of about 68° F. If these conditions are right, and your goldfish is exhibiting the other symptoms, then chances are, it is carrying eggs.
Other signs that a goldfish may be ready to spawn: they are not as active as before; they may seem slower or may be having difficulty moving around. Not all goldfish do this, but some do, when the eggs in their bellies weigh them down. It may also start refusing food; if it used to have a good appetite and suddenly doesn’t like to eat, then it may be that it will spawn soon. A goldfish that’s about to spawn will likely “nest”—that is, stay close to, explore, and hide among vegetation or places of shelter in its bowl or aquarium; this is its instinct kicking in to find good hatching places for its eggs. Their bodies will appear larger and plumper especially around the abdomen, and their colors may look brighter.
Knowing these signs and paying attention to your fish will ensure that your goldfish breeds successfully. If you want the fish to multiply, you will need to provide the necessary care for them for optimum survival conditions. In the meantime, the signs given here will tip you off, so you will know how to tell if your goldfish is pregnant, and proceed from there.