The Fishes The Fishes Three types of fishes

The Fishes

The Fishes • Three types of fishes – Jawless fish (Class AGNATHA) – Cartilaginous fish (Class CHONDRICHTHYES) – Bony fish (Class OSTEICHTHYES)

Jawless Fish o Jaws are absent o Paired fins are generally absent o Early species had heavy bony scales and plates in their skin

Jawless Fish v In most cases the skeleton is cartilaginous. The embryonic notochord persists in the adult. v Seven or more paired gill pouches are present. v Hagfish sheds slime layer

Jawless Fish Ø A light-sensitive pineal eye is present. Ø The digestive system lacks a stomach. Ø External fertilization; both ovaries and testes present in individual but gonads of only one sex functional in hagfishes, no larval stage; separate sexes and a long larval stage in lampreys.

Lamprey Dissection • • • External Mouth Head & Pharynx Heart Gonads

Cartilaginous Fish • Cartilaginous fishes are jawed fish with: – paired fins – paired nares – scales – a heart with its chambers in series – skeletons made of cartilage rather than bone

Cartilaginous Fish • Chondrichthyes also lack ribs, so if they leave water, the larger species' own body weight would crush their internal organs long before they would suffocate.

Cartilaginous Fish • Their tough skin is covered with dermal teeth called placoid scales making it feel like sandpaper.

Cartilaginous Fish • Do not have bone marrow – red blood cells are produced in the spleen and the epigonal organ

Cartilaginous Fish • Breathe through 5 -7 gills, depending on the species. – Pelagic (surface) species must keep swimming to keep oxygenated water moving through their gills – Demersal (deep water) species can actively pump water in through their spiracles and out through their gills.

Cartilaginous Fish • Reproduce through internal fertilization. – Some sharks have live birth

Cartilaginous Fish • Divided into two subclasses: – Elasmobranchii (sharks, rays and skates) – Holocephali (chimaeras, sometimes called ghost sharks)

Sharks, Rays, Skates

Chimaeras

Bony Fish • A group of fish that have bone, as opposed to cartilaginous, skeletons. • The vast majority of fish are Osteichthyes – 45 orders – 435 families – 28, 000 species

Bony Fish • All bony fish possess gills. – some species can respire through their skin, intestines, and/or stomach • Primitively ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water.

Bony Fish • Bony fish typically have swim bladders, which helps the body create a neutral balance between sinking and floating.

Bony Fish • They also are able to see in color, unlike most other fish. • Bony fish have no placoid scales. Mucus glands coat the body. Most have smooth and overlapping scales.

Bony Fish • Some bony fish are hermaphrodites, and a number of species exhibit parthenogenesis. • Fertilization is usually external, but can be internal. • Development is usually oviparous (egglaying) but can be ovoviviparous, or viviparous.

Bony Fish • Although there is usually no parental care after birth, before birth parents may scatter, hide, guard or brood eggs – with sea horses being notable in that the males undergo a form of "pregnancy", brooding eggs deposited in a ventral pouch by a female. http: //www. youtube. com/watch? v=Ea. OHLQy_bj. U

Bony Fish • Two types of bony fish – Ray-Finned – have rays in their fins – Lobe-Finned – have thick chunky fins