The female will normally have a more rounded belly as she prepares to give birth and look noticably fatter than the male. A swordtail is a livebearing species of fish so they do not lay eggs but give birth to baby fish known as fry who will be freeswimming from the moment of birth.
Danios are egg layers and can not get pregnant.
You wouldn't ever be able to tell this, because carp fish do not get pregnant. Pregnancy implies carrying the young internally, which carp do not do.
Pregnant fish may appear rounder or have a swollen belly. You can tell if a fish is expecting offspring by observing its enlarged abdomen and possibly seeing small, developing eggs inside.
To determine if a fish is pregnant, look for signs such as a swollen abdomen, changes in behavior like increased hiding or aggression, and a darkened gravid spot near the anal fin. Additionally, some pregnant fish may exhibit a bulging or squared-off belly shape.
I would imagine that with some fish it would be nearly impossible to tell until they give birth. However, with a thin, transparent fish, you sometimes can see a dark spot in their belly!
Goldfish of any type are all egg laying fish which means that they do not get pregnant
With a guppy you need to look at the gravid spot. This is a dark spot in the fish's belly. A large gravid spot indicates the fish is likely to be pregnant. You can tell how pregnant the fish is by how large the spot is. Sorry I have no experience with other species.
To determine if a fish is pregnant, look for signs such as a swollen abdomen, changes in behavior, and a darker gravid spot near the anal vent. Pregnant fish may also exhibit increased appetite and aggression.
Orandas, or any other type of goldfish are egg laying fish, so they do not get pregnant
Black moors are a variety of goldfish which are egg layers so they can't get pregnant.
To determine if your fish is pregnant, look for signs such as a swollen abdomen, changes in behavior like increased hiding or aggression, and a dark spot near the fish's anal vent. Additionally, you may notice the fish's scales appearing raised or separated. If you observe these signs, it is likely that your fish is pregnant.
A female guppy is pregnant for about 1-2 months, if you have a pregnant guppy i can tell that she will need to be separated from the other fish in a breeding box, you can buy breeding boxes from most stores for £3.97 ($5.97), because if she is left with other fish they will eat the babies. Some tell tale signs that she is close to delivering the babies is that she will stop eating, hang around away from the other fish and her gravid spot will be almost black. Pleased to help.