Diversity of fishes Flashcards
How many species of fish exist, and what percentage of vertebrate diversity do they represent?
Over 30,000 species, representing 50% of vertebrate diversity.
How does fish biomass in the mesopelagic oceanic waters compare globally?
Dominated by Cyclothone species, it accounts for 1–10 billion tonnes.
How does fishing contribute to global food security and livelihoods?
It provides 1/3 of human protein consumption and supports livelihoods for 60 million people directly, with greater impact in secondary industries.
Why is the fish sector particularly important for women in the global south?
It provides employment, income, and independence, especially in secondary sectors.
Why is the term ‘fish’ considered paraphyletic?
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.
What are the general characteristics of fish?
- Aquatic
Oxygen obtained via gills
Ectothermic (mostly)
Limbs in the form of fins
Provide examples of exceptions to typical fish characteristics.
- Mudskippers and lungfish can survive out of water.
Some tunas and sharks are relatively endothermic.
Eels have reduced fins.
Name the four major fish groups and their species counts.
- Jawless fishes (Agnathans): <100 species
Cartilaginous fishes (Chondrichthyes): ~1,200 species
Ray-finned fishes (Actinopterygii): >30,000 species
Lobe-finned fishes (Sarcopterygii): 8 species
What is the significance of Nelson’s Fishes of the World?
It is a well-regarded resource for fish taxonomy and systematics.
What was the contribution of Bentacur et al. (2017) to fish phylogeny?
They proposed a molecular data-based hypothesis of fish evolution and relationships.
What are the key evolutionary traits of vertebrates?
Vertebrates possess a notochord, V-shaped myomeres, and teeth.
What evolutionary traits define gnathostomes?
Gnathostomes have distinct jaws.
How are Osteichthyes distinct in their skeletal structure?
They possess an ossified skeleton, including Sarcopterygii and ray-finned fishes.
What is the evolutionary significance of hagfish and conodonts?
Hagfish have unusual features similar to extinct conodonts, which are placed within vertebrates by some experts.
What are the key characteristics of Chondrichthyes?
- Cartilaginous skeleton
Jaws with serially replaced teeth from dermal denticles
Males with external pelvic fin claspers
Electroreceptive sensory organs (Ampullae of Lorenzini)
Why is electroreception important for Chondrichthyes?
It detects muscle contractions of prey in water where electrical signals travel farther than light.
What limits our understanding of Chondrichthyes evolution?
Fossils mostly consist of teeth and fin spines, making detailed analysis difficult.
How can you determine the sex of a Chondrichthyan?
Males have external claspers near the pelvic fins for fertilization.
What are the two main reproductive styles in Chondrichthyans?
- Oviparity: Laying eggs in keratinous casings (e.g., ‘mermaid’s purse’).
Viviparity: Live birth with forms like yolk sac viviparity, oophagy, and placental viviparity.
Describe oophagy and placental viviparity in Chondrichthyes.
- Oophagy: Embryos consume unfertilized eggs for sustenance.
Placental viviparity: Yolk sacs develop into umbilical cords for nutrient exchange with the mother.
How diverse are ray-finned fishes (Actinopterygii)?
They have over 34,000 species, accounting for 53% of all living vertebrates.
What morphological constraints have influenced ray-finned fish evolution?
Their hyperdiversity evolved under specific constraints unique to this group.
Why do scientists differ in their approaches to fish evolution?
Fossil records often conflict with molecular and modern taxa-based hypotheses.
What challenges arise from the fossil record of Chondrichthyes?
The reliance on teeth and fin spines limits comprehensive understanding of their biology.
