biology

San Marcos gambusia

San Marcos gambusia 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 San Marcos gambusia rather than just read about it. In short: The San Marcos gambusia (Gambusia georgei) is a likely extinct species of Gambusia from the family Poeciliidae that was found only in the San Marcos Springs of Central Texas. The fish has not been seen since 1983.

Key takeaways

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

Reference excerpt

The San Marcos gambusia (Gambusia georgei) is a likely extinct species of Gambusia from the family Poeciliidae that was found only in the San Marcos Springs of Central Texas. The fish has not been seen since 1983.

Etymology The specific name of this fish honors the American ichthyologist George S. Myers (1905–1985).

Description The San Marcos gambusia was typically less than 1.6 inches (4 cm) in length. It had a dark body with a slight blue tint, although the median fins were lemon yellow. The scales were strongly crosshatched, and the dorsal fin had a dark stripe along its edge. The species' exact diet is not known, but other poeciliids typically eat insect larvae and other small invertebrates. The fish were live bearing and were known to give birth to a few dozen young at a time.

Habitat

The San Marcos gambusia has only been identified in a 0.6-mile (1-km) stretch of the headwaters of the San Marcos River. They appeared to need clean and clear water, with little temperature variability. They apparently also preferred shallow, quiet water, along with partial shade.

Extinction As of 1969, the population was less than 1,000 individuals. The species was threatened by reduced spring flows and pollution, including sprayed herbicide along the river and introduced fish (Gambusia affinis) and plants (Colocasia esculenta). There have been no specimen sightings since 1983 and was proposed to be delisted from the Endangered Species Act in 2021. The US Fish and Wildlife Service delisted the species effective November 16, 2023.

References

External links San Marcos gambusia (Gambusia georgei) page from the Texas Parks and Wildlife Department

Illustrations

Worked examples

Example 1 — a first encounter with San Marcos gambusia

Start with the simplest possible case. Write down what San Marcos gambusia 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 San Marcos gambusia 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 San Marcos gambusia 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 San Marcos gambusia

In research: San Marcos gambusia 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 San Marcos gambusia 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: San Marcos gambusia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Endemic fauna of Texas, Extinct animals of the United States, Fish described in 1969, so understanding it makes those chapters shorter.
In everyday life: Look for San Marcos gambusia 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 San Marcos gambusia in 20 minutes

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

Frequently asked questions

What is San Marcos gambusia in simple terms?

Why does San Marcos gambusia 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 San Marcos gambusia?

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 San Marcos gambusia.