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Q46 (IAS/2021) Environment & Ecology › Ecology & Ecosystem Basics › Animal adaptations Official Key

Which one of the following is a filter feeder?

Result
Your answer: —  ·  Correct: C
Explanation

The correct answer is Option 3: Oyster.

Filter feeders are a sub-group of suspension-feeding animals that strain suspended matter and food particles from water by passing it through a specialized filtering structure. Oysters are classic examples of bivalve mollusks that use their gills to capture microscopic algae (phytoplankton) and organic detritus from the surrounding water column. A single oyster can filter up to 50 gallons of water per day, playing a vital role in maintaining water clarity and ecosystem health.

In contrast, the other options utilize different feeding mechanisms:

  • Catfish: Primarily bottom feeders or opportunistic predators that use barbels to locate food.
  • Octopus: Active predators that hunt and capture prey using tentacles and a sharp beak.
  • Pelican: Carnivorous birds that use their large throat pouches to scoop up fish, rather than straining microscopic particles.

Therefore, based on the physiological mechanism of feeding, the Oyster is the only true filter feeder among the choices provided.

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PROVENANCE & STUDY PATTERN
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Q. Which one of the following is a filter feeder? [A] Catfish [B] Octopus [C] Oyster [D] Pelican
At a glance
Origin: Mostly Current Affairs Fairness: Low / Borderline fairness Books / CA: 0/10 · 2.5/10
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This is a 'Functional Ecology' question disguised as a species quiz. It tests your understanding of Ecosystem Services (water purification) rather than just taxonomy. While standard books mention 'bottom feeders' (Catfish), the answer relies on knowing that Oysters are nature's water pumps—a fact often cited in pollution and mariculture chapters.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is catfish a filter feeder?
Origin: Weak / unclear Fairness: Borderline / guessy
Indirect textbook clues
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Lake ecosystem > p. 26
Strength: 5/5
“Such fsh (catfsh) are called as 'bottom feeders'. Energy moves through the lake ecosystem from the sunlight that penetrates the water surface to the plants. From the plants, the energy is transferred to herbivorous animals and carnivores. Animals excrete waste products, which settle on the bottom of the lake, which is decomposed by the microorganisms that live in the mud of the lake. In this process, plants use carbon from CO2 for their growth and in the process release oxygen. Tis oxygen is then used by aquatic animals, which flter water through their respiratory system. In India, most of lakes lie in the Himalayas and the Satluj-Ganga-Brahmaputra Plains.”
Why relevant

Explicitly labels catfish as 'bottom feeders', a feeding category that typically consumes benthic material and detritus rather than filtering plankton from the water column.

How to extend

A student could use this rule to contrast 'bottom feeder' diets with known filter-feeding mechanisms and ask whether catfish species commonly show filter-feeding anatomy/behaviour.

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Animal Life in a marine ecosystem > p. 32
Strength: 4/5
“Te marine zooplanktons are generally larger in size than the phytoplankton and are more diverse in form, ranging from one celled animals to young jelly-fsh. Although the distribution and numbers of zooplankton depend on the available phytoplankton, they are not directly dependent on light, and can exist to all depths, probably deriving food from detrital material which sink down. Apart from zooplankton, the only other direct plant feeders are some of the bottom-living (demersal) fauna of shallow seas. In deeper waters, the zooplankton forms virtually the only link between the primary producers and other forms of marine life. Zooplankton is fed on directly by many surface water (pelagic) fsh, including mackerel, sardines and herring in cooler waters, and basking shark and tunny in warmer waters.”
Why relevant

Describes zooplankton as the link between primary producers and many pelagic fish that feed directly on plankton (examples: mackerel, sardines, herring), illustrating what kinds of fishes are typical plankton/ filter feeders.

How to extend

Compare anatomical/behavioral traits of those pelagic plankton feeders with catfish to judge whether catfish are likely to be filter feeders.

Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > 2. Fish Farming > p. 90
Strength: 3/5
“Fish farming is the principal form of aquaculture, while other methods may fall under mariculture. It involves raising fish commercially in tanks or enclosures, usually for food. Fish species raised by fish farms include salmon, catfish, tilapia, cod, carp, trout, and others. Increasing demands on wild fisheries by commercial fishing operations have caused widespread overfishing. Fish farming offers an alternative solution to the increasing market demand for fish and fish protein.”
Why relevant

Lists catfish among many commercially farmed species, implying catfish is a broad group with varied ecology and importance in aquaculture.

How to extend

Use this to consider species diversity within 'catfish'—a student could check whether some farmed catfish species are raised on particulate diets (suggesting non-filter feeding) or on plankton-based diets.

Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 14: Marine Organisms > l.4.4.1. Functions > p. 209
Strength: 3/5
“• Sea grass beds physically help • to reduce wave and current energy, • to filter suspended sediments from the water and • to stabilise bottom sediments to control erosion. • z. Provides habitat for marine invertebrates and fishes. • 3. Seagrass beds are widespread in lagoon & in such areas, the population of fish and migratory birds also higher due to the availability of food and shelter. • 4. Sea grasses on reef flats and near estuaries are also nutrient sinks, buffering or filtering nutrient and chemical inputs to the marine environment.”
Why relevant

Explains environmental 'filter' functions (seagrass beds filtering sediments/nutrients), offering a clear notion of what 'filtering' means in aquatic contexts.

How to extend

Apply this concept of filtering (removing suspended particles/nutrients) to animal feeding modes and ask whether catfish morphology/behaviour matches that function.

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Statement analysis

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Statement analysis

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