The most common term for a mass of fish eggs is “roe,” used widely in both culinary and general contexts. Roe describes the fully developed, unfertilized eggs found within the ovaries of a female fish. More specific terms exist depending on the egg’s biological state, commercial preparation, or the reproductive act itself. Understanding these distinctions clarifies the different stages and uses of fish eggs.
The Scientific Terminology: Ova and Milt
Biologically, the female fish egg is known as an ovum (plural: ova), which is the unfertilized gamete cell. The ovum forms through a process called oogenesis, developing a yolky interior to provide nutrients for the future embryo. The mature ovum is typically surrounded by a hard shell or envelope, known as the chorion or zona radiata, which protects it in the aquatic environment.
Fertilization is accomplished by the male gamete, contained within a milky fluid called milt. Milt is the reproductive fluid from male fish, containing spermatozoa, or sperm cells. When ova and milt combine, usually after being released into the water, the resulting fertilized egg is called a zygote. The sperm must enter the ovum through a tiny channel in the egg shell called the micropyle.
Roe vs. Spawning: Defining the Mass and the Act
The distinction between roe and spawning separates the physical mass of eggs from the behavior of releasing them. Roe refers to the mature, unfertilized egg mass, including the ovarian tissue that encases the eggs, while they are still inside the female fish. For example, a female cod or herring is “full of roe” when her ovaries are ripe and ready for reproduction.
Spawning is the behavioral act where the fish releases its gametes—both ova and milt—into the water. This is the most common form of reproduction for bony fish. The female deposits her eggs, and the male simultaneously or subsequently releases his milt to achieve external fertilization. This process is often called “broadcast spawning,” where eggs and sperm are released into the open water.
The term spawn can also be used as a noun referring to the collective mass of eggs and sperm that have been released. Commercial fisheries often target fish “ripe” with roe just before spawning, as the fully developed egg mass is a valuable food product. Spawning can be a migratory event, such as salmon swimming upriver to deposit their eggs on the gravel substrate.
Culinary and Commercial Designations
In the food industry, fish eggs are known by many names, depending on the species and processing method. The designation caviar traditionally refers only to the processed, salted roe of the Sturgeon species (e.g., Beluga or Ossetra). True caviar is defined by its origin and the salt-curing method used for preservation.
Many other fish eggs have specific commercial names, particularly in Japanese cuisine. These names distinguish the roe based on species origin, size, color, and preparation:
- Ikura is large, reddish-orange salmon roe, known for its distinct flavor and glistening appearance.
- Tobiko refers to the smaller, crunchy roe of the flying fish. It is often dyed green with wasabi or black with squid ink.
- Masago is the even smaller roe from the Capelin, a type of smelt.
- Masago has a subdued flavor and its minute size gives it a sandy texture.