Lecture 12: Fishes

• Chondricthyes are cartilaginous fish
• Sharks have no swim bladders, a heterocercal tail, denticles, 5-7 gill slits, and have multiple rows of teeth
• Skates and rays have enlarged pectoral fins, 5 ventral gill slits, a spiracle, and molar teeth

  Some have venomous spine and produce electric discharge
• Manta rays feed on plankton and live in the open water
• Skates have no tail spine and are oviparous
• Rays have a tail spine and are ovovivoparous
• Skates live in temperate climate zones
• Rays live in tropical climate zones
• Chimaeras differ from other cartilaginous fish in that they have an upper jaw attached to a braincase, lack a spiracle, and have one gill slit covered with an operculum
• Bony fish are more diverse in form and habitat than cartilaginous fish
• Osteichthyes include:

  Sarcopterygii (lobe-finned fishes; Coelacanth)

  Actinopterygii (ray-finned fishes; Sturgeon)

  Neopterygii
• Actinopterygii anatomy:

  Swim bladder, fin rays and bony skeleton, bony scales embedded in skin, operculum, median and paired fins, homocercal tail
• Coloration in fishes through chromatophores/iridophores and countershading
• Locomotion in fishes:

  Red muscle used for slow, long sustained swimming

  White muscle used for fast, short bursts of energy
• Fish respiration through a countercurrent system

  The outflowing water has a tension lower than the blood leaving the gill
• Gill pumps are where water is pumped over gills by a dual pumping system, which provides predominantly unidirectional flow of water over the gill surface
• Ram ventilation is the generation of a respiratory current by swimming with the mouth open so water flows over the gills
• Osmoregulation

  Sharks, skates, rays, and coelacanths are isosmotic

  Marine ray-finned fishes are hypoosmotic (lose water/gain salts at gills)
• Dynamic lift production from fins and body for buoyancy
• Sharks and rays do not have swim bladders but have large livers filled with oil for bouyancy
• The swim bladder has two parts: physostome and physoclist
• The physostome is the connection between the swim bladder and the esophagus
• The Physoclist has no connection between the swim bladder and esophagus
• Most fish focus images on the retina by moving a rigid spherical lens forwards and backwards
• Rod cells in the retina used for low light intensity

  Cone cells used for high light intensity and color sensitivity
• Mechanoreceptors used for motion (vibration) detection

  Superficial neuromasts used to detect strong current stimuli (velocity)

  Canal neuromasts used to detect finer scale stimuli (acceleration)
• Mechanoreceptors as part of sound detection