Breathing: most fishes breathe by drawing water over 5 pairs of gills, located in chambers, covered by a protective bony flap called the operculum . Water is drawn into the mouth, though the pharynx, and out between the gills by movement of the operculum and contraction of muscles surrounding the gill chambers.
Movement: Fishes control their buoyancy with an air sac known as a swim bladder. Movements of gases from the blood to the swim bladder increases buoyancy and the animal rises, transfer of gas back to the blood makes the animal sink.
Reproduction: the details vary extensively. Most species are oviparous, reproducing by external fertilization after the female sheds the large number of small eggs. Birthing and internal fertilization characterize other species.
Adaptations: Glands in the skin secrete a slimy mucus over the skin to reduce drag during swimming
Cartilaginous = the skeleton of the species in the clade is composed predominantly of cartilage , often impregnated with calcium. Also termed- elasmobranches = flexible endoskeleton.
More than 750 species
Major group consist of sharks, rays and skates ; second of ratfishes and chimaeras.
Have bilateral symmetry as most Chordates
All information about the phylum (Chordata-vertebrates) of the clade is the same as for Osteichthyes.
Info for the Chondrichthyes (cartilaginous fishes)
Characteristics of the clade:
Cartilaginous skeleton (derived characteristic)
Respiration through gills
May lay eggs or give birth
Acute senses, include lateral lines
Life of the Chondrichthyes (mainly sharks here)
Movement: Sharks are swift swimmers; cannot maneuver vey well. Although a shark gains buoyancy by storing a large amount of oil in its liver, the animal is still more dense than water and if it stops swimming, it sinks. Continual swimming ensures the water flows into the shark’s mouth and out through the gills , where gas exchange occurs (because sharks do not have lungs)
Feeding: Largest sharks and rays consume plankton. Most sharks are carnivores = swallow their prey whole with several rows of teeth and powerful jaws. Within a shark intestine is a spiral valve, a corkscrew-shaped ridge that increases the surface area =>makes longer the passage of food through the digestive tract.
Adaptations : acute senses; sharp vision, but are color blind, have a pair of regions in the skin of their head that can detect el. Fields produced by muscle contractions of nearby animals.
Reproduction: Sharks have a unique form of reproduction- internal fertilization . The male transfers the sperm into the reproductive tract of the female using its claspers on its pelvic fins. Depending on the species of shark, it can either be:
- oviparous (the eggs hatch outside the mother’s body)
- ovoviviparous (the fertilized egg is retained in the oviduct)
- viviparous (the young develops in the uterus and nourished by the mother prior to birth).
More than 100 million metric tons of bony fishes are harvested every year for human consumption
Bony fishes are also used to feed livestock, make fertilizer, and produce fish oil and production of metallic paints, leather, glue, and medicines
Sharks can and do attack humans, although the risk of dying from a shark bite is about 1 percent of the risk of being killed by lightning. Only about one to two dozen deaths by shark attack occur annually.
In contrast, an estimated 30,000 human illnesses occur each year when people eat poisonous fish.