Transcript:

Today on Animal Fact Files we’re discussing tunas. For the purposes of this video the word “tuna” will be used in reference to the tuna tribe which consists of approximately 15 living species. Tunas as a group are found worldwide, but certain species have preferences on where they live. For example, some prefer tropical waters like yellowfins while others stay in more temperate waters such as albacore. Some tuna species migrate to spawn like bigeyes and bluefins; these spawn seasonally. Conversely, skipjacks, especially those living towards the equator, mate year round.

In size tunas can reach up to 10 feet in length, though there are smaller species who barely manage 3 feet long. The big species, like the Atlantic bluefin, are likely the most well known as they can fetch prices over a million US dollars for a single fish, however these make up just a tiny portion of tuna fisheries. I mean, they are endangered so it’s not like they have the populations to make up anything more than a percent or two. The tuna species which make up more than 80% of fisheries include skipjacks, yellowfins, bigeyes, and albacores and they are the types you’ll find in cans. Basically what we mean to say is that the tuna in sushi and the tuna in cans aren’t necessarily the same species.

Tunas form schools of thousands of members. This works as a safety in numbers tactic to protect against predators. Besides humans, tuna predators include other large fish like sharks, sea birds, marine mammals like dolphins and even whales when it comes to tuna larvae. Tuna larvae hatch after eggs are released and fertilized externally in warm, surface waters. Apart from the largest species like bluefin who take longer to reach adult sizes, tuna reach sexual maturity around two to five years of age. Depending on the species, these fish live five to more than twenty years in the wild!

Tuna larvae feed on plankton while juveniles and adults eat other fish, cephalopods, and crustaceans. They can dive deep for prey, even into cold waters. This is because tuna have the extraordinary ability to regulate their body temperatures. Most fish are not able to produce their own heat and must rely solely on their environment for warmth. Like a reptile, if they get too cold, they’ll be unable to move. Fish are also quite sensitive to temperature changes. Too drastic a change can send them into shock. But tunas don’t suffer this. A tuna can swim from 75 degree water to 48 degree (24 to 9) water while diving over the course of just a minute. Most other fish wouldn’t be able to tolerate the shock, but because tuna can create their own heat, they survive. In fact, tuna are able to get so hot when really working their muscles that some have cooked themselves while fighting against fishing line - which is called “burn” in the angling world.

Like the billfish they’re closely related to, tuna are excellent swimmers. Their pectoral gills neatly fit into a grove on their sides to give them a streamlined body shape that cuts through the water. A tuna’s gill surface area is much larger than most other fish, and they are thus able to obtain more oxygen from the water while swimming. These fish also have red muscle which allows them to sustain fast speeds over a long course of time. Tuna are ram ventilators which means they can’t stop swimming or they’ll suffocate. This is similar to some, but not all sharks.

For more facts on tunas, check out the links in the description. Thank you to hallo for today’s request! Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files!