Basically, there are different spawning methods for different species of fish and it can be grouped to either internal fertilization or external fertilization. Let us discuss some of the common examples here and what are the differences between those two.
Internal generally means “inside” whereby spawning activity will lead to sperm from the male injected into the female for fertilization to take place. Livebearers such as swordtails, guppies are few of the examples. The fry are born free swimmers (as shown in above image) and the developing embryos can either receive the nutrition directly from their mother or having their own egg sacs. Once released, the fry will naturally develop the survival instinct to search for a place to hide (as means to protect themselves from predatory fish and also from their own parents). They are generally larger as compared to fry from egg-layers but are slower in terms of growth and development. However, they are easier to cultivate and usually taking care of fish fry from livebearer is a good learning experience for fish hobbyist interested in breeding for home aquarium.
External fertilization is basically the opposite, as eggs will be deposited in the natural surrounding either by scattering or depositing. Egg scatterers generally release the eggs in random manner and the eggs are self-adhesive and will stick to the surface in which it first comes into contact with as it was being released. After laying the eggs, the parents won’t look after them and some are even notorious in eating their own eggs as well. A fine example of fish classified in this group is goldfish. For more thorough understanding, you can also take a look on labyrinth fish such as how the kissing gourami breeds.
A different pattern can be seen on egg depositors whereby the eggs are released on substrates which can be either enclosure, pit or cave and the parents generally don’t eat their own eggs while some even provide good care of the developing fry. Examples of this type of fish are certain species of Cichlids and Discus.
There is also another behavior of fish known as mouth brooders in which it can be either internal or external fertilization. For internal fertilization, sperm will actually be released by the male into the mouth of the female fish and once the eggs hatch, the fry will remain in the mother’s mouth as it develops. For external fertilization, females will lay eggs on a surface and are then taken by the male into its mouth. The father will keep them there inside the mouth until the fry hatch and will protect the young until certain stage of development. Arowana is a fine example of external fertilization exhibited using the mouth brooding method for spawning.
Related fish keeping topics:
» Community Aquarium Fish Species
» Setup your own Aquarium
» Dealing with Fish Disease
» Factors that Trigger Fish Spawning