My Dwarf Gourami are fighting. How do I tell their sex and stop it?

If they are less than a year old, it is difficult to reliably determine sex. Males will be more streamlined than females and, during breeding season, will develop white "dots" (tubercles) on the gill covers. Their vents will also be smaller and more oval shaped. Females will have larger, deeper bodies (for carrying eggs) and their vents will be rounder and more pronounced.

Unfortunately, aggression between species of fish is not uncommon. I am not sure if this is a new finding, or if anything has changed in the dynamic in your school of fish (any new introductions or any deaths of fish), but this often can then change how the rest of the fish interact with one another. You can try to give the platy places to hide and escape from the guppy, or you can end up dividing the tank. If you do not want to add dividers, you can also separate the guppy into another tank as well. I hope that gives you a place to start, and good luck!

If the Betta is not acting aggresively, there is no need to remove him. Guppies, especially males, will fight with one another but it usually isn't serious. Providing plenty of cover for them to hide may be all you need. If the fighting persists, remove the aggressive guppy to his own tank.

The black fish is a Black Moor Goldfish. The white fish is a kissing gourami. It is commonly called a "kissing fish". This species of Gourami can be very territorial. What it is doing is bullying the Moor and trying to chase it away. You may need to remove one or the other. Gouramis are best kept in pairs or small groups. Consider also removing some of the plastic plants as they may injure the Moor's eyes.

GloFish are schooling fish. They do best in groups of 6 or more. If you have just a few, they may be stressed which can cause aggression. Check the water parameters since an imbalance in chemistry can cause stress as well. You can use a home test kit (one with liquid drops, not test strips) or submit a sample to you local pet store or aquarist. Most will perform water testing for free or for a nominal fee. Ideal parameters measure 0 ppm (parts per million) ammonia and nitrites with nitrates at 40ppm or less. pH of the water should be between 6 and 8. They are cool water fish, so aim for a water temp between 65 F and 75 F. Hopefully, this will help. The other option you have is to remove the aggressor. You can request a consultation to discuss the situation and set up in greater detail or if you have further questions or concerns.

Juveniles smaller than about 4 inches are difficult to sex. Once they reach that size or larger, it is quite simple.Female sliders are larger, have shorter front claws and thinner. smaller tails than males. Males can be territorial and could "argue" if the tank is not of sufficient size. Ideally, you want to allow about 10 gallons per inch of turtle. Sliders can get big (12 inches fully grown), so be sure you have the space and budget for a large tank.

Separate out the aggressive one. It could be nipping due to hunger, stress or aggression. Consider hand feeding to avoid accidental bites as well as dividing them into two tanks to provide more space. As they mature, they will require a significantly larger space. This number of turtles ideally will need a tank in the hundreds of gallons range or a small pond. A general guideline is 10 gallons per inch of turtle. Sexing turtles is easier when they are mature. Without knowing the species, it can be difficult, but in general, females are larger than males. Males have a shorter, thicker tail in comparison and usually have longer front claws. A female will have a flat plastron whereas the male will have a slight concavity. Males have a v-notch at the rear of the carapace to accommodate the tail when mating. Lastly, you can check the cloaca, or vent. Females will have a rounder vent closer to the body whilst males will have more of a slit farther down under the tail. All these differences are best seen when comparing two turtles or a proven pair.