science

Marine hatchetfish

Marine hatchetfish is a science 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 Marine hatchetfish rather than just read about it. In short: Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic ray-finned fish of the stomiiform subfamily Sternoptychinae. They should not be confused with the freshwater hatchetfishes, which are not particularly closely related Teleostei in the characiform family Gasteropelecidae.

Key takeaways

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

Reference excerpt

Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic ray-finned fish of the stomiiform subfamily Sternoptychinae. They should not be confused with the freshwater hatchetfishes, which are not particularly closely related Teleostei in the characiform family Gasteropelecidae. The scientific name means "Sternoptyx-subfamily", from Sternoptyx (the type genus) + the standard animal family suffix "-inae". It ultimately derives from Ancient Greek stérnon (στέρνον, "breast") + ptýx (πτύξ, "a fold/crease") + Latin forma ("external form"), the Greek part in reference to the thorax shape of marine hatchetfishes.

Description and ecology

Found in tropical, subtropical and temperate waters of the Atlantic, Pacific and Indian Oceans, marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to the c.12 cm (4.7 in)-long giant hatchetfish (Argyropelecus gigas). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophores. The latter allow them to use counter-illumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at a few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep. The body is deep and laterally extremely compressed, somewhat resembling a hatchet (with the thorax being the "blade" and the caudal peduncle being the "handle"). The genus Polyipnus is rounded, the other two – in particular Sternoptyx – decidedly angular if seen from the side. Their pelvis is rotated to a vertical position. The mouth is located at the tip of the snout and directed almost straight downwards. Their scales are silvery, delicate and easily abraded. In some species, such as the highlight hatchetfish (Sternoptyx pseudobscura), large sections of the body at the base of the anal fin and/or caudal fin are transparent. They have perpendicular spines and blade-like pterygiophores in front of the dorsal fin. The anal fin has 11–19 rays and in some species is divided in two parts; almost all have an adipose fin. Their large, sometimes tube-shaped eyes can collect the faintest of light and focus well on objects both close and far. They are directed somewhat upwards, most conspicuously in the genus Argyropelecus. This allows them to discern the silhouettes of prey moving overhead against the slightly brighter upper waters.

Genera There are three genera in this subfamily, with some 40 species altogether:

Argyropelecus – silver hatchetfishes (7 species) Polyipnus (32 species) Sternoptyx (4 species) Four fossil genera are also known:

Eosternoptyx (middle-late Eocene of Iran) Polyipnoides (middle Eocene of Georgia) Horbatshia (Oligocene of the Carpathians) Discosternon (Miocene of Italy)

Footnotes

Illustrations

Worked examples

Example 1 — a first encounter with Marine hatchetfish

Start with the simplest possible case. Write down what Marine hatchetfish claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Marine hatchetfish 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 Marine hatchetfish 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 Marine hatchetfish

In research: Marine hatchetfish appears in science 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 Marine hatchetfish 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: Marine hatchetfish is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bioluminescent fish, Deep sea fish, Sternoptychidae, so understanding it makes those chapters shorter.
In everyday life: Look for Marine hatchetfish 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 Marine hatchetfish in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Marine hatchetfish 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 Marine hatchetfish out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Marine hatchetfish in simple terms?

Why does Marine hatchetfish matter?

Because it connects several science 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 Marine hatchetfish?

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 Marine hatchetfish.