Need a definition? That’s what you’ll find in Dictiotuna, the Planet Tuna glossary. And if you look up a word and it isn’t there, don’t hesitate to ask us what it means in the Ask a Scientist section. We’ll tell you and we’ll add it to Dictiotuna.


Human parasitic infection caused by worms of the Anisakis genus that are present in raw or undercooked fish or cephalopods. It affects the gastro-intestinal tract and can cause allergic reactions. If you want to find out how to avoid it, read our articles and watch our videos.


A parasitic nematode worm which, in the course of its life cycle, is hosted by fish or squid until it finally reproduces inside a marine mammal. If we eat infected fish, we can have intestinal disorders and allergic reactions (anisakiasis). Read the article and watch the video here. Red the article and watch the video here 


Invertebrate marine animals belonging to the Cephalopoda class of mollusks. Octopuses, squid, and cuttlefish are examples of cephalopods. They are an important part of the diet of many marine predators, including tuna.


The density of the water in the ocean isn’t always the same. It varies according to its temperature and salinity. Ocean water is usually denser when it’s colder and saltier. Every year, in the summer, two masses of water with different densities converge around the Balearic Islands in the Mediterranean Sea.


The set of all fossils discovered to date. The oldest are indications of bacterial life in rocks over three billion years old, whereas the most recent ones have only been around for a few thousand years. Scientists study the fossil record to know how life on Earth evolved.


Anatomical structures made of bone or cartilage that support the gills of a fish.


The organ that produces male or female sex cells.


Animals that tend to gather in groups. Tunas show this behavior when they migrate. The word “gregarious” comes from the Latin gregarius, which means belonging to a flock.


The process by which the young of various animals emerge from an egg. Among fish, it occurs when the larva breaks the chorion, the membrane surrounding the egg. In the case of tuna, the head is the first part of the larva to emerge from the egg.


Small, shrimp-like crustaceans. They are part of the diet of many species of fishes, birds, and marine mammals. They undertake long daily migrations, rising during the night from the deep waters to the surface, where phytoplankton –the single-cell algae they feed on– are most abundant. Sometimes they form groups that look like huge stains when seen from the air. Krill can be intermediate hosts for Anisakis.


Early stage in the life of an animal in which it is very different from what it will become as an adult. In the case of fish, larvae cover the transitional stage from the egg to the juvenile. When tuna larvae hatch, they are only 3-4 millimeters long. During this stage, their mortality rate is very high, because the larvae are very sensitive to environmental variables and to the amount of predators and available food.


In biology, the life cycle is the set of processes and changes an organism undergoes beginning in one stage, such as reproduction, and closing the cycle when it reaches that same stage in its development. Tuna start their lives as eggs, hatch into larvae, become juveniles, and, when they reach adulthood, are able to breed and lay eggs, starting the cycle all over again.


Nematodes are cylindrical, usually small worms found both on land and in water. They are much more common than we tend to assume: in one square meter of sea floor, there can be thousands of individuals. About 20,000 species of nematodes have been described, but there are likely to be many more which have not yet been studied. Their lifestyles vary enormously. Some, like Anisakis, are parasites.


An early version of a backbone. In tunas, the notochord can be seen during the larval stage, before the backbone is fully developed.


An organism that lives off and harms another living being. During a certain period, the parasite and the host live together. Anisakis is a parasite that can live in several different animals before it reaches its definitive host.


Fish that spend most of their life cycle in the area of the ocean (or lake) water that is neither near the bottom nor near the coast. This classification is determined by the habitat in which different species live (a pelagic habitat, in this case) and covers everything from small pelagic species, like sardines or anchovies, to large pelagic species such as tunas.


Large group of fish, usually of the same species, traveling together.


Spanish government-run organization focused on oceanographic research. One of its centers is the Balearic Oceanographic Center, located in Mallorca.


An expert who classifies organisms into systematic, hierarchical categories, organizing them according to their species, genus, family, order, class, phylum or division, kingdom, and domain. For example, the Atlantic bluefin tuna is classified as the species Thunnus thynnus, genus Thunnus, family Scombridae, order Perciforme, class Actinopterygii, phylum Chordata, kingdom Animalia.


The yolk sac is a membranous sac which, in the case of fish larvae, contains the energy store that will feed them during the first hours or days of their lives, until they can start eating external food. In bird eggs, we call it the yolk.