Fish reproduction is a topic that is highly varied. How fish mate depends entirely on what type of fish are involved. If you are interested in how fish mate for the purposes of getting your own fish to breed, please be aware that it is not a beginner’s challenge. Environmental conditions, timing, nutrition, and confirmed sex of the fish involved all need to align for any chance of success. If you do not want to become entangled in this highly involved process, just learn to identify the difference between male and female and let nature take its own course.
So How Fish Mate
The majority of fish mating, no matter the method, naturally requires a male and a female fish. There are a few species of fish that do not require a partner to mate with; they are parthenogenetic, and can spontaneously reproduce on their own. Their offspring will be female, just like their technically unisex mother. These fish are not as commonly found in home aquariums.
Let’s take a look at visible gender differences between common types of household fish, and how they mate. In goldfish, the males usually have small white spots about their gills. They are also more slender, while female goldfish have larger, rounder bodies. Male goldfish also have been observed to be more active, chasing the females around. When a female goldfish is carrying eggs, you may notice that the round body looks a bit uneven or lumpy. These differences are usually easiest to spot when the fish are least a year old.
Female betta fish are smaller and not as colorful as their male counterparts, but identifying when they are ready to mate can be simple, as they develop stripes vertically along their bodies. These mating stripes are usually not as bright as the “fear stripes” anxious bettas are known to develop. Mating bettas in the home is not as common as it is with something like a goldfish, since bettas are fighting fish that require separation. Bettas raised together may not be as aggressive toward one another, but if you have a male and female that live separately, proceed to the mating process with caution.
A lot of fish mate when the female lays eggs, which are then fertilized by the male. This sounds almost accidental, or impersonal, but some male fish make bubble nests for the female to lay her eggs in. After that, a number of things can happen, depending on the temperament and species of the fish. The fertilized eggs may remain in their bubble nest, or be hidden in vegetation by the mother. If vegetation is scarce or unhealthy, the eggs may just be secured to a weighty object or a corner. The eggs, in rarer cases, may be buried by the mother. Some fish are mouthbrooders, which means the eggs will be carried in the mouth of the male or female until hatching. Fish known to do this include types of catfish, cichlids, and even some bettas.
Unfortunately or not, fish may eat the fertilized eggs before they have the opportunity to hatch. This has been observed both domestically and in the wild, so while it’s not always an issue with your home aquarium, do some research on the most favorable environmental factors for mating fish. It may be totally normal for a male guarding the eggs to eat a few while on watch, while others may observe either the mother, father, or other fish in the tank eating the entire nest of eggs. Some aquarium owners will separate the eggs and mother into a “breeding tank”, to increase the chances of egg survival.
Still other fish utilize the live-bearing method of reproduction. This is commonly seen in tropical fish in home aquariums. The eggs remain inside of the mother, where they are fertilized by a male fish. The live babies exit the mother upon hatching. This new school of baby fish, no matter how they hatch, is called a ‘fry’.
The hatching time after fish mate varies with species, and can take a few days or a few weeks. Some live-bearing fish are known to carry their new crew around for a month. Assuming the eggs have survived, and are now free-swimming little fish, they should be separated from the adult fish, if they are in a domestic aquarium environment. Filial cannibalism, which involves the parents eating their young, is not a deviant behavior, but an ecological function that has some benefits to the environment and species. So if you intend to keep your new little fish, they should promptly be removed from their birth environment. And as stated before, planning is crucial. A lot babies in the fry may die; this is no cause for alarm, and the mortality rate makes sense when you see exactly how many little ones emerge from just one mating session. Baby fish need to eat (preferably a specialty food designed for young fry) a few times a day, and they also need a little privacy to settle into. Ample vegetation or partial coverings for the aquarium are suitable for this. As with all fish, but especially with babies, water temperature and quality should be rigorously monitored.
Outside of the home aquarium, how fish mate is a serious topic for the planet, as marine life is under threat. Environmental ills and overfishing have had a huge impact on the biodiversity of marine life, and many species of fish have become endangered or extinct. Overfishing is exactly what it sounds like- the fish cannot mate at a fast enough rate to replace what humans catch, accidentally catch, and consume. Some organizations estimate that in the next one hundred years, half of all life under the sea will have become endangered or extinct. With pollution and climate change, the oceans are increasingly becoming a hostile environment for breeding, just as one may find on a much smaller scale in the home aquarium. See if you can make a difference for fish everywhere by being mindful of your own actions, so we can remain in one another’s company for centuries to come.