Fish ecology

Question 1

What limits a fish’s diet?

Answer 1

A fish’s diet is limited by what it can fit into its mouth, with bigger prey offering higher energy efficiency and quality.

Question 2

What are the two main features of marine food webs?

Answer 2

Size-structured food webs: Trophic level increases with body size.

Predator:Prey Mass Ratios (PPMR): Predators are 100–10,000 times larger than their prey.

Question 3

How do marine food webs differ from terrestrial food webs in trophic structure?

Answer 3

Marine species pass through multiple trophic levels as they grow, unlike terrestrial animals, which often stay at consistent levels.

Question 4

What is trophic transfer efficiency?

Answer 4

It is the percentage of energy transferred between trophic levels, typically around 10%.

Question 5

How does primary production differ between terrestrial and marine systems?

Answer 5

• Terrestrial: Dominated by large vascular plants, carbon-rich, stable energy sources.

Marine: Dominated by transient unicellular phytoplankton, requiring consumers to efficiently utilize short-lived carbon stores.

Question 6

Why do fish larvae feed at lower trophic levels?

Answer 6

Lower levels have concentrated carbon and higher transfer efficiencies, maximizing phytoplankton-fixed carbon into fish tissues.

Question 7

What are the three main methods for studying fish diets?

Answer 7

Stomach content analysis.

Stable isotope analysis.

Environmental DNA (eDNA).

Question 8

What are the advantages and disadvantages of stomach content analysis?

Answer 8

Advantages: Direct observation of ingested species.

Disadvantages: Costly, limited to recent feeding history, and can require lethal sampling.

Question 9

How does eDNA improve fish diet analysis?

Answer 9

It rapidly identifies taxa using DNA traces, particularly useful for small or soft-bodied prey difficult to identify in traditional stomach analyses.

Question 10

How do thrust and drag influence fish movement in water?

Answer 10

Neutral buoyancy reduces gravity’s influence, so movement is primarily determined by overcoming frictional (viscous) and inertial drag.

Question 11

What is Reynold’s number, and why is it important?

Answer 11

It describes the transition from laminar to turbulent flow. Small fish (low Reynold’s numbers) experience higher frictional drag, making swimming energetically costly.

Question 12

Why is rapid growth advantageous for small larval fish?

Answer 12

Reduces predation risk.

Decreases energetic cost of swimming.

Allows access to habitats with fewer predators and higher oxygen levels.

Question 13

Why do larval fish often inhabit surface waters?

Answer 13

Surface waters have higher oxygen, fewer predators, and abundant food during specific times.

Question 14

What is ontogenetic migration?

Answer 14

Directed movement during specific life stages to optimize survival and growth, such as larvae moving to surface waters or adults migrating for spawning.

Question 15

Define migration in the context of fish movement.

Answer 15

Persistent, straightened-out movement driven by the fish’s locomotion, often inhibiting station-keeping behaviors temporarily.

Question 16

What are examples of migration types in fish?

Answer 16

Adopted migration: Learning from experienced individuals.

Differential migration: Linked to demographic traits like age or size.

Homing: Returning to a previous location (e.g., natal homing).

Irruptive migration: Rapid expansion in range and abundance.

Ontogenetic migration: Life stage-based movement.

Partial migration: Coexistence of migratory and resident individuals.

Philopatry: Multi-generational return to breeding sites, leading to reproductive isolation.

Question 17

What is connectivity in migration?

Answer 17

The linkages between different areas caused by fish movement, including nutrient transfer, genetic exchange, and resilience to local disturbances.

Question 18

What challenges do small fish face as larvae?

Answer 18

High predation risk.

High oxygen demand due to mass-specific metabolic rate.

High energetic cost of swimming.

Question 19

Why do adult fish often migrate to spawn?

Answer 19

To lay eggs in habitats favorable for larval survival, such as areas with abundant food or currents transporting larvae to ideal habitats.

Question 20

How does the relationship between fish size and Reynold’s number affect migration?

Answer 20

Larger fish experience lower swimming costs as inertial drag dominates, whereas smaller fish face higher frictional drag.

Question 21

Why is it misleading to assign a single trophic level to a fish species?

Answer 21

Fish grow significantly in size throughout their life, passing through multiple trophic levels as predator-prey mass ratios change.

Question 22

Why is primary production more transient in marine ecosystems compared to terrestrial ones?

Answer 22

Marine primary production relies on phytoplankton blooms, which are short-lived and require consumers to efficiently use dispersed carbon stores.

Question 23

What is the implication of higher transfer efficiency at lower trophic levels in marine systems?

Answer 23

Small larval fish benefit by feeding on concentrated carbon stores at lower trophic levels, maximizing energy conversion into biomass.

Question 24

What limitation does eDNA face in diet analysis?

Answer 24

It depends on the availability of primers and can misidentify species due to ingestion of non-prey particles like settling detritus.

Question 25

Why are stable isotope analyses important for studying fish diets?

Answer 25

They provide long-term dietary data, reflecting feeding habits over weeks or months, rather than just recent meals.

Question 26

Why do small fish prefer shallow and surface waters?

Answer 26

These areas offer higher oxygen availability, fewer predators, and abundant food resources during specific periods.

Question 27

How does connectivity enhance ecological resilience?

Answer 27

By linking populations and habitats, connectivity increases genetic diversity and nutrient transfer while mitigating local disturbances.

Question 28

What are some examples of migration types in fish?

Answer 28

Homing: Salmon returning to natal streams to spawn.
Ontogenetic migration: Larval fish moving to surface waters and adults migrating to spawn.
Partial migration: Coexistence of migratory and resident forms in species like striped bass.

Question 29

Why do fish larvae experience high mortality?

Answer 29

Their small size makes them vulnerable to predators and increases their energy demands for swimming and oxygen consumption.

Question 30

What is the primary advantage of ontogenetic migration for fish?

Answer 30

It allows individuals to exploit optimal habitats at different life stages, enhancing survival and growth rates.