biology

Skipjack tuna

Skipjack tuna is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Skipjack tuna rather than just read about it. In short: The skipjack tuna (Katsuwonus pelamis) is a perciform fish in the tuna family, Scombridae, and is the only member of the genus Katsuwonus. It is a cosmopolitan pelagic fish found in tropical and warm-temperate waters.

Key takeaways

Skipjack tuna belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Skipjack tuna to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Skipjack tuna from memory before moving on to harder problems.

Reference excerpt

The skipjack tuna (Katsuwonus pelamis) is a perciform fish in the tuna family, Scombridae, and is the only member of the genus Katsuwonus. It is a cosmopolitan pelagic fish found in tropical and warm-temperate waters. Skipjack tuna can grow up to 1.1 m (3 ft 7 in) in length, and is a very important species for fisheries.

Description

It is a streamlined, fast-swimming pelagic fish common in tropical waters throughout the world, where it inhabits surface waters in large shoals (up to 50,000 fish, often in combination with other scombridaes), feeding on fish, crustaceans, cephalopods, and mollusks. It is an important prey species for sharks and large pelagic fishes and is often used as live bait when fishing for marlin. It has no scales, except on the lateral line, and circling around the body behind the head forming a large, thick band called a "corselet". Like other tuna, it lacks a swim bladder, and must keep swimming to stay buoyant. It commonly reaches fork lengths up to 80 cm (2 ft 7 in) and a mass of 8–10 kg (18–22 lb). Its maximum fork length is 108 cm (3 ft 7 in), and its maximum mass is 34.5 kg (76 lb). Determining the age of skipjack tuna is difficult, and estimates of its potential lifespan range between 8 and 12 years. Skipjack tuna has the highest percentage of skeletal muscle devoted to locomotion of all animals, at 68% of the animal's total body mass. Skipjack tuna are highly sensitive to environmental conditions and changes. Climate change effects are significant in marine ecosystems, and ecological factors may change fish distribution and catchability.

Behaviour Skipjack tuna are batch spawners. Spawning occurs year-round in equatorial waters, but it gets more seasonal further away from the equator. Fork length at first spawning is about 45 cm (18 in). It is also known for its potent smell.

Taxonomy The genus name Katsuwonus comes from the Japanese name for the fish, katsuo (鰹/かつお).

Fisheries

It is an important commercial and game fish, usually caught using purse seine nets, and is sold fresh, frozen, canned, dried, salted, and smoked. In 2018, landings of 3.2 million tonnes (3.5 million short tons) were reported, the third highest of any marine capture fishery (after Peruvian anchoveta and Alaska pollock). Countries recording large amounts of skipjack catches include the Maldives, France, Spain, Malaysia, Sri Lanka, and Indonesia. Skipjack is the most fecund of the main commercial tunas, and its population is considered sustainable against its current consumption. Its fishing is still controversial due to the methodology, with rod and reel or fishery options being promoted as ecologically preferable. Purse seine methods are considered unsustainable by some authorities due to excess bycatch, although bycatch is said to be much reduced if fish aggregation devices are not used. These considerations have led to the availability of canned skipjack marked with the fishing method used to catch it. As much as 95% of skipjack tuna catches may be used as canned tuna. Skipjack is considered to have "moderate" mercury contamination. As a result, pregnant women are advised against eating large quantities. In addition, skipjack's livers were tested globally for tributyltin (TBT) contamination. TBT is an organotin compound introduced into marine ecosystems through antifouling paint used on ship hulls and has been determined to be very toxic. About 90% of skipjack tested positive for contamination, especially in Southeast Asia, where regulations of TBT use are less rigorous than in Europe or the US.

As food

Japan Skipjack tuna or katsuo (鰹/かつお) is used extensively in Japanese cuisine. It is eaten raw in sushi and sashimi, as well as slightly seared in katsuo tataki. It is also smoked and dried to make katsuobushi, and the shavings are commonly used to make dashi (soup stock). Katsuobushi flakes are also used as seasoning, such as in onigiri (rice balls) or on top of tofu. The raw viscera of skipjack tuna is salted and fermented to make shutō, a type of shiokara. The fish's fat content changes during migrations along the Japanese islands. When they migrate north in summer, they are called hatsugatsuo ("first katsuo") or noborigatsuo ("ascending katsuo"), and have a lesser amount of fat. When they migrate south in autumn, they are called modorigatsuo ("returning katsuo") or kudarigatsuo ("descending katsuo"), and have a high level of fat.

Other places In Indonesian cuisine, skipjack tuna is known as cakalang. The most popular Indonesian dish made from skipjack tuna is cakalang fufu from Minahasa. It is a cured and smoked skipjack tuna dish, made by cooking the fish after clipping it to a bamboo frame. Skipjack known as kalhubilamas in Maldives is integral to Maldivian cuisine. Skipjack tuna is an important fish in the native cuisine of Hawaii (where it is known as aku) and throughout the Pacific islands. Hawaiians prefer to eat aku either raw as a sashimi or poke or seared in Japanese tataki style. The trade in pickled skipjack tuna is a driving force behind the commercial fishery of this species in Spain.

Notes

References

Sources Pacific skipjack tuna NOAA FishWatch. Retrieved 5 November 2012. Western Atlantic skipjack tuna NOAA FishWatch. Retrieved 5 November 2012.

External links Media related to Katsuwonus pelamis at Wikimedia Commons Photos of Skipjack tuna in the Sealife Collection

Illustrations

Worked examples

Example 1 — a first encounter with Skipjack tuna

Start with the simplest possible case. Write down what Skipjack tuna claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Skipjack tuna before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Skipjack tuna ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Skipjack tuna

In research: Skipjack tuna appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Skipjack tuna in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Skipjack tuna is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal taxa named by Carl Linnaeus, Commercial fish, Cosmopolitan fish, so understanding it makes those chapters shorter.
In everyday life: Look for Skipjack tuna outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Skipjack tuna in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Skipjack tuna means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Skipjack tuna out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Skipjack tuna in simple terms?

Why does Skipjack tuna matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Skipjack tuna?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Skipjack tuna.