Diversity of fishes

Question 1

How many species of fish exist, and what percentage of vertebrate diversity do they represent?

Answer 1

Over 30,000 species, representing 50% of vertebrate diversity.

Question 2

How does fish biomass in the mesopelagic oceanic waters compare globally?

Answer 2

Dominated by Cyclothone species, it accounts for 1–10 billion tonnes.

Question 3

How does fishing contribute to global food security and livelihoods?

Answer 3

It provides 1/3 of human protein consumption and supports livelihoods for 60 million people directly, with greater impact in secondary industries.

Question 4

Why is the fish sector particularly important for women in the global south?

Answer 4

It provides employment, income, and independence, especially in secondary sectors.

Question 5

Why is the term ‘fish’ considered paraphyletic?

Answer 5

it includes a common ancestor and some, but not all, of its descendants
It excludes tetrapod vertebrates, which evolved from fish ancestors, making it paraphyletic.

Question 6

What are the general characteristics of fish?

Answer 6

• Aquatic

Oxygen obtained via gills
Ectothermic (mostly)
Limbs in the form of fins

Question 7

Provide examples of exceptions to typical fish characteristics.

Answer 7

• Mudskippers and lungfish can survive out of water.

Some tunas and sharks are relatively endothermic.
Eels have reduced fins.

Question 8

Name the four major fish groups and their species counts.

Answer 8

• Jawless fishes (Agnathans): <100 species

Cartilaginous fishes (Chondrichthyes): ~1,200 species

Ray-finned fishes (Actinopterygii): >30,000 species

Lobe-finned fishes (Sarcopterygii): 8 species

Question 9

What is the significance of Nelson’s Fishes of the World?

Answer 9

It is a well-regarded resource for fish taxonomy and systematics.

Question 10

What was the contribution of Bentacur et al. (2017) to fish phylogeny?

Answer 10

They proposed a molecular data-based hypothesis of fish evolution and relationships.

Question 11

What are the key evolutionary traits of vertebrates?

Answer 11

Vertebrates possess a notochord, V-shaped myomeres, and teeth.

Question 12

What evolutionary traits define gnathostomes?

Answer 12

Gnathostomes have distinct jaws.

Question 13

How are Osteichthyes distinct in their skeletal structure?

Answer 13

They possess an ossified skeleton, including Sarcopterygii and ray-finned fishes.

Question 14

What is the evolutionary significance of hagfish and conodonts?

Answer 14

Hagfish have unusual features similar to extinct conodonts, which are placed within vertebrates by some experts.

Question 15

What are the key characteristics of Chondrichthyes?

Answer 15

• Cartilaginous skeleton

Jaws with serially replaced teeth from dermal denticles

Males with external pelvic fin claspers

Electroreceptive sensory organs (Ampullae of Lorenzini)

Question 16

Why is electroreception important for Chondrichthyes?

Answer 16

It detects muscle contractions of prey in water where electrical signals travel farther than light.

Question 17

What limits our understanding of Chondrichthyes evolution?

Answer 17

Fossils mostly consist of teeth and fin spines, making detailed analysis difficult.

Question 18

How can you determine the sex of a Chondrichthyan?

Answer 18

Males have external claspers near the pelvic fins for fertilization.

Question 19

What are the two main reproductive styles in Chondrichthyans?

Answer 19

• Oviparity: Laying eggs in keratinous casings (e.g., ‘mermaid’s purse’).

Viviparity: Live birth with forms like yolk sac viviparity, oophagy, and placental viviparity.

Question 20

Describe oophagy and placental viviparity in Chondrichthyes.

Answer 20

• Oophagy: Embryos consume unfertilized eggs for sustenance.

Placental viviparity: Yolk sacs develop into umbilical cords for nutrient exchange with the mother.

Question 21

How diverse are ray-finned fishes (Actinopterygii)?

Answer 21

They have over 34,000 species, accounting for 53% of all living vertebrates.

Question 22

What morphological constraints have influenced ray-finned fish evolution?

Answer 22

Their hyperdiversity evolved under specific constraints unique to this group.

Question 23

Why do scientists differ in their approaches to fish evolution?

Answer 23

Fossil records often conflict with molecular and modern taxa-based hypotheses.

Question 24

What challenges arise from the fossil record of Chondrichthyes?

Answer 24

The reliance on teeth and fin spines limits comprehensive understanding of their biology.

Question 25

How are skates, rays, and sharks evolutionarily related?

Answer 25

Skates and rays are closely related to sharks within the Chondrichthyes group.